Epidemiology Disease of goats, sheep, humans, and occasionally cattle. Transmission congenital or by ingestion or contact with infected placenta, vaginal discharge, or milk
Clinical findings Abortion storms, abortions often in last 2 months of pregnancy. Weak-born lambs. Important zoonotic disease in humans
Clinical pathology Culture of organism. Serological tests and skin hypersensitivity testing for herd diagnosis
Diagnostic confirmation Only by isolation of the organism
Control Slaughter eradication. Vaccination with Rev. 1 vaccine. Rev. 1 vaccine will produce abortion in pregnant animals
Brucella melitensis causes brucellosis in goats and sheep and is capable of infecting most species of domestic animal. There are three biovars of the organism that have differing geographical distribution but no difference in pathogenicity or animal species affected. There is a close relationship to other members of the genus.1
The distribution of B. melitensis is more restricted than that of B. abortus and its primary area of occurrence is in the Mediterranean region, including southern Europe. Infection is also present in west and central Asia, Mexico and countries in Central and South America, and in Africa. Northern Europe is free of infection, except for periodic incursions from the south, as are Canada, the USA, south-east Asia, Australia, and New Zealand.
Goats and sheep are highly susceptible. Susceptibility in sheep varies with the breed, with Maltese sheep showing considerable resistance. The organism is capable of causing disease in cattle and has been isolated from pigs. The prevalence of infection varies between countries and regions but in many countries prevalence has declined in the past decade in association with mandatory vaccination policies.2
The source of infection is the infected carrier animal. Introduction to a naive herd or flock occurs with the introduction of an infected animal and persistence results from sheep or goats that are prolonged excreters. Excretion is from the reproductive tract and in milk.
Infected does and ewes, whether they abort or birth normally, discharge large numbers of brucellas in their uterine exudates and placenta. The organism can be present in uterine discharge for at least 2 months following parturition in infected goats.3 The vaginal exudate of infected virgin or open animals may also contain the bacteria but transmission between animals is most likely from the massive exposure that only an infected placenta can provide.
The majority of goats infected during pregnancy will excrete the organism in milk in the subsequent lactation and many will excrete it in all future lactations.3 In sheep the period of excretion of the organism from the uterus and in milk is usually less than in goats but the organism can be present in milk throughout lactation.4 The duration of excretion in cattle is not known.
Routes of infection for both adults and young are via ingestion, by nasal or conjunctival infection, and through skin abrasions, with infected placenta and uterine discharge as a major source.
Infection of the fetus during pregnancy does not necessarily result in abortion: infected kids and lambs may be born alive but weak or they may be quite viable. In some cases the infection persists in a latent form until sexual maturity, when pregnant animals may abort the first pregnancy.4 However, others, if weaned early from their dams and from the infected environment, become free from the infection as adults.3
Latent infection can also be acquired from the ingestion of infected colostrum and milk; this is a major route of transmission and perpetuation of infection in a herd or flock.4
The organism is reasonably resistant to environmental influences and under suitable conditions can survive for over 1 year in the environment. B. melitensis is susceptible to disinfectants in common use at recommended concentrations.
In goats and sheep the infection of a naive herd or flock will produce an abortion storm, following which most animals are infected but immune; further abortions are usually limited to introduced or young animals. Because of the limited periods of excretion in sheep the disease tends to be self-limiting in small flocks that have few new introductions. It can be a continuing problem in large flocks because of massive environmental contamination of areas used for pregnant and lambing ewes.3 In some areas the prevalence of brucellosis associated with B. melitensis is linked to the practice of animal movement to summer and mountain pastures where there is commingling of sheep and goats from a variety of sources on the same pasture.5
Spread in beef cattle is slow, presumedly because they do not abort. Spread in dairy herds can be more extensive,6 possibly via milking procedures.
Brucellosis has major veterinary and human importance in affected countries. Costs include production loss associated with infection in animals, the considerable cost of preventive programs, and human disease.2 There is further loss from restriction in international trade in animals and their products.
The occurrence of B. melitensis in the sheep and goat population of countries that have eradicated B. abortus poses a threat for the continuing problem of brucellosis in cattle herds.
B. melitensis is the most invasive and pathogenic for humans of the three classical species of the genus, and is the cause of ‘Malta’ or ‘Mediterranean’ fever in humans, an extremely debilitating disease. It is an important zoonosis in areas of the world where B. melitensis is enzootic in goats and sheep. The disease in humans is severe and long-lasting and often occurs in communities with limited access to antimicrobial therapy. Control and eradication of the infection in animal populations has high priority in all countries.
Large numbers of organisms are excreted at and following parturition, providing a source of infection for humans managing the herd or flock and also for people in the immediate vicinity from aerosol infection with contaminated dust. The risk of infection is high in cultures that cohabit with their animals or when weak, infected newborn animals are brought into the house for warmth and intensive care. Milking of sheep and goats is usually manual, often with poor sanitation and milking-time hygiene. Raw milk and cheese products from infected goats, sheep, or cattle also provide a risk and were the mechanism for the occurrence of Malta fever that initiated the definition of the disease.
Abattoir workers, shearers, and people preparing goat and sheep skins are also at risk. The risk for veterinarians is primarily with dystocial problems in infected animals and herds but is also present in the examination of any animal that is subclinically infected. There is also the risk of accidental self-inoculation during vaccination against the disease.
Vaccination of small ruminants with B. melitensis Rev. 1 vaccine is a primary method in controlling the human disease. In Greece a 15-year period of vaccination was associated with a drop in the incidence of human brucellosis but when this program was stopped the prevalence of abortions in animals and the incidence if brucellosis in humans increased dramatically, only to be controlled by the reinstitution of vaccination of animals as an emergency mass vaccination program.7 However, while the Rev. 1 vaccine is attenuated when compared with field strains, it retains some virulence and incorrect selection from the seed stock can result in vaccines with considerable virulence for both vaccinated animals and in-contact humans.
In view if its pathogenicity to humans and animals, B. melitensis requires major consideration as an agent of bioterrorism and agroterrorism. It is believed that fewer than 10 cfu are capable of infecting humans and infection can occur from aerosol infection. This would require mass therapy of human populations and destruction of animal populations, with associated problems.8
The organism is a facultative intracellular parasite. As in other forms of brucellosis, the pathogenesis depends upon localization in lymph nodes, udder, and uterus after an initial bacteremia. In goats, this bacteremia may be sufficiently severe to produce a systemic reaction, and blood culture may remain positive for a month. Localization in the placenta leads to the development of placentitis, with subsequent abortion. After abortion, uterine infection persists for up to 5 months and the mammary gland and associated lymph nodes may remain infected for years.3,4 Spontaneous recovery may occur, particularly in goats that become infected while not pregnant. In sheep the development of the disease is very similar to that in goats. In cattle, B. melitensis has a similar pathogenesis and produces a persistent infection in the mammary gland and the supramammary lymph node, with obvious significance for public health.6
Abortion during late pregnancy is the most obvious sign in goats and sheep, but as in other species there may be a ‘storm’ of abortions when the disease is introduced, followed by a period of flock resistance during which abortions do not occur. Abortion is most common in the last 2 months of pregnancy. The excretion of the organism in milk is not accompanied by obvious signs of mastitis. Infection in males may be followed by orchitis, which is frequently unilateral.
In experimental infections, a systemic reaction occurs, with fever, depression, loss of weight, and sometimes diarrhea. These signs may also occur in acute, natural outbreaks in goats and may be accompanied by mastitis, lameness, and hygroma; however, they are uncommon in the natural disease and their occurrence in the experimental disease reflects a massive challenge dose.3 Osteoarthritis, synovitis, and nervous signs may occur in sheep.
In pigs the disease is indistinguishable clinically from brucellosis associated with B. suis.
In many instances, B. melitensis infection reaches a high incidence in a group of animals without signs of obvious illness and its presence may be first indicated by the occurrence of disease in humans infected from the herd or flock. This is so in cattle where the infection is subclinical and does not produce abortion, but the organism is shed in milk.
Positive blood culture soon after the infection occurs, or isolation of the organism from the aborted fetus, vaginal mucus, or milk, are the common laboratory procedures used in diagnosis. The organism is moderately acid-fast and staining smears from the placenta and fetus with a modified Ziehl–Neelsen method may give a tentative diagnosis; however this does not distinguish this infection from B. ovis or the agent of enzootic abortion, and culture is required.
The organism can be detected by PCR in the abomasal fluid of aborted fetuses and, compared with culture, PCR has a sensitivity and specificity of 97.4% and 100%, respectively.9 PCR can also be used to detect the organism in semen.10
The conventional serological tests for the diagnosis of B. melitensis – agglutination, CFT, and the rose Bengal or card test – use the same antigens as are used for the diagnosis of B. abortus infections.
The rose Bengal test and CFT are the prescribed tests for international trade. In most laboratories these tests, in unvaccinated animals, are 100% specific and have high sensitivity. However the sensitivity is not sufficiently high to allow completely accurate detection of infection in an individual animal.11,12 They can be used for the detection of infected herds for slaughter eradication of the disease but have significant limitations when used for selective culling of positive animals within an infected herd.
Conventional serological tests will not differentiate infection with different species of Brucella nor will they differentiate infection associated with Y. enterocolitica type O:9. Other tests that have been developed include ELISA tests, radial immunodiffusion, and counterimmunoelectrophoresis; the sensitivity and specificity of these appears to vary between laboratories.12-15 An ELISA test using purified antigen is described as being able to differentiate the seropositivity of B. melitensis from that of B. ovis.16
The rose Bengal test has excellent specificity and high sensitivity,11,15 is easy to perform, and is suitable for herd and flock testing.3
For the testing of infection status of individual animals, the rose Bengal test and the CFT have the highest sensitivity in most studies. A combination of tests and tests carried out on several occasions may increase the accuracy of detection of infected animals.17 If only one test is possible, the CFT is recommended but it suffers from the requirement for a sophisticated laboratory, which is not always available in affected areas.3
Brucella-free animals are serologically positive for long periods following vaccination, with a difference in persistence with different serological tests. The period of seropositivity is shorter in animals vaccinated conjunctivally.12,13,15
Tests are also conducted on milk. They include the milk ring test, the whey CFTs, whey Coombs or antiglobulin test, whey agglutination tests, and an ELISA.3,18 They have no apparent advantage over serological tests and in many cases are less sensitive and are unsuitable as screening tests using flock or herd pooled milk samples. An ELISA test using crude polysaccharide from B. melitensis biovar 1 as antigen has a better sensitivity and may be of greater value as a screening test, although there are limited field data.19
An intradermal allergic test using 50 mg of brucellin INRA can be used for diagnosis. The injection sites in goats are the neck or caudal fold and in sheep the lower eyelid. Reactions are read in 48 hours. The test has high specificity in flocks that are free of infection and are not vaccinated. However, it has little advantage over conventional serological tests in infected herds and Rev.-1-vaccinated animals can react for years.3,15,20 It has particular value in identifying animals that are false-positive reactors due to antibody to cross-reacting bacterial antigens. It can differentiate infections with Y. enterocolitica, but cannot differentiate B. ovis infections in sheep. Anergy occurs between 6 and 24 days after injection.15 Vaccinated sheep retain an allergic state for at least 2 years.3
There are no lesions that are characteristic of this form of brucellosis. The causative organism can often be isolated from all tissues but the spleen, lymph nodes, and udder are the most common sites for attempted isolation in chronic infection.
• Bacteriology – adults: spleen, lymph node, udder, testicle, epididymis; fetus: lung, spleen, placenta (CULT – has special growth requirements, CYTO – Stamp’s or Kosters’ stain on placental smear); fetus: PCR detection in fetal abomasal fluid
Note the zoonotic potential of this organism when handling carcasses or submitting specimens.
Treatment is unlikely to be undertaken in animals and is also unlikely to be economically or therapeutically effective. A cure rate of 65% and 100%, respectively, is reported following the daily intraperitoneal administration of 500 mg and 1000 mg of tetracycline to naturally infected goats for a period of 6 weeks.21 A dose of 1000 mg of long-acting tetracycline given every 3 days for a period of 6 weeks achieved a cure rate of 75%.
Control measures must include hygiene at kidding or lambing and the disposal of infected or reactor animals. Separate pens for kidding does that can be cleaned and disinfected, early weaning of kids from their does and their environment, and vaccination are recommended. In endemic areas all placentas and dead fetuses should be buried as a routine practice.
Where a group is infected for the first time it may be most economic to dispose of the entire herd or flock. Test and slaughter procedures are prolonged because of the inaccuracy of the tests.
Many countries that have this disease have statutory control measures. The disease can be eradicated and Cyprus has recently achieved this.22 B. melitensis also can be eradicated, with difficulty, from dairy cattle.5 However, vaccination may be the only practical method of control in areas where there is a high prevalence of the disease, extensive management systems, communal grazing and a low socioeconomic level.23,24
The universally recommended vaccine is Elberg’s Rev. 1, which is effective in both sheep and goats.2,24,25 Rev. 1 vaccine is a live, attenuated B. melitensis strain derived from a virulent B. melitensis isolate. It stimulates protection against infection with B. melitensis in sheep and goats and also protects rams against infection with B. ovis. However, this is at the expense of a persistent serological response. Further, although this vaccine is attenuated when compared with field strains it retains some virulence and incorrect selection from the seed stock can result in vaccines with considerable virulence for both vaccinated animals and in-contact humans.26,27
Vaccination with Rev. 1 produces a bacteremia that is cleared by 14 weeks in goats and a shorter time in sheep. Vaccination of animals 3–8 months of age confers a high degree of immunity that lasts for more than 4 years in goats.4,28 and 2.5 years in sheep.25 The initial recommendations for use were vaccination of replacement animals with the expectation that herd/flock immunity would develop over the years; however, this has proved ineffective in some regions and whole-flock/herd vaccination is now recommended in certain countries.23
Vaccination of pregnant goats and sheep, especially in the second and third month of pregnancy, will result in abortion and the excretion of the living B. melitensis vaccine organism in the vaginal discharge and the milk. The vaccine should not be used in pregnant animals or for 1 month prior to breeding. Vaccination of lactating animals may be followed by a temporary period of excretion of the organism in the milk.3,18 Neither reduced dose vaccination nor conjunctival vaccination significantly reduces the risk of vaccine-induced abortions in pregnant animals,23 although reduced-dose Rev. 1 vaccination has been shown to provide protection for at least 5 years in endemically infected areas.29
Conjunctival vaccination does decrease the period of seropositivity following vaccination.17,1 Vaccine efficacy and safety can vary with the manufacturer.17,19 National policies promoting widespread vaccination of sheep and goats with Rev. 1 vaccine have resulted in a significant reduction in the prevalence of small ruminant brucellosis and in the incidence rates of human brucellosis.7,25,30 However, Rev. 1 vaccine is also pathogenic to humans and its excretion and persistence in milk following vaccination can result in human infection.27
The general approach in endemically infected countries is to institute a whole-flock vaccination scheme followed by a young-stock vaccination scheme until the prevalence of the disease is reduced, at which time test and slaughter can be implemented to eradicate the disease. This ignores the risk of adverse disease in the vaccinated animals and the risk for human infection from the vaccine strain. There is an urgent need for a nonvirulent vaccine that induces seropositivity that can be differentiated from the seropositivity resulting from natural infection.27
To circumvent the problem of persistent serological response, attempts are being made to develop defined rough mutant vaccine strains that would be more effective against B. melitensis. Various studies have examined cell-free native and recombinant proteins as candidate protective antigens, with or without adjuvants. Limited success has been obtained with these, or with DNA vaccines encoding known protective antigens, in experimental models.26,27
A formalin-killed adjuvant vaccine, called 53H38 vaccine, has been used but it confers less immunity than Rev. 1 and causes local reactions and a prolonged allergic and serological response.23 The rough mutant vaccine, RB51, is not of value in sheep or goats.31
B. abortus strain 19 has been used for vaccination and appears to give protection that is as good as that achieved with the attenuated B. melitensis vaccine.
A B. suis strain 2 vaccine has been used in China for some years. It can be administered in the drinking water and is used in areas where the terrain does not allow the regular handling of animals. In a comparative study of S2 vaccine and Rev. 1 vaccine, S2-vaccinated pregnant ewes had less protection than Rev.-1-vaccinated ewes when challenged with B. melitensis, and an equivalent degree of protection to the nonvaccinated controls.20
Initial studies on the pathogenicity and immunogenicity of gene-deleted mutant B. melitensis Rev. 1 live vaccines in mice suggest that they might be an effective alternate to the standard vaccines used in small ruminants. Serological testing would allow the differentiation of infection. The use of these vaccines would allow the serological differentiation of seropositive vaccinated sheep from infected sheep; however, these vaccines have not yet been tested in small ruminants.32
Verger JM, Plommet M. Brucella melitensis. In: Current Topics in Veterinary Medicine and Animal Science. Dordrecht: Martinus Nijhoff; 1985:270.
Young EJ, Corbel MJ. Brucellosis: clinical and laboratory aspects. Boca Raton, FL: CRC Press, 1989;184.
Alton GG. Brucella melitensis. In: Nielsen K, Duncan JR, editors. Animal brucellosis. Boca Raton, FL: CRC Press, 1990.
Elberg S. Rev 1 Brucella melitensis vaccine. Part III 1981–1995. Vet Bull. 1996;66:1193-1200.
Blasco JM. A review of the use of B. melitensis Rev 1 vaccine in adult sheep and goats. Prev Vet Med. 1997;31:275-283.
Nielsen K. Diagnosis of brucellosis by serology. Vet Microbiol. 2002;90:447-459.
Schurig GG, Sriranganathan N, Corbel MJ. Brucellosis vaccines: past, present and future. Vet Microbiol. 2002;90:479-496.
Blasco JM. Caprine and ovine brucellosis. In Manual of diagnostic tests and vaccines for terrestrial animals. Paris: Office International des Epizoöties; 2004. Ch 2.4.2.
1 Moreno E, et al. Vet Microbiol. 2002;90:209.
2 Elberg S. Vet Bull. 1996;66:1193.
3 Alton GG. Nielsen K, Duncan JR, editors. Animal brucellosis. Boca Raton, FL: CRC Press. 1990:379.
4 Grillo MJ, et al. Vet Rec. 1997;140:602.
5 Verger JM, et al. Ann Réch Vét. 1989;20:93.
6 Dafni I, et al. Israel J Vet Med. 1991;46:13.
7 Minas A, et al. Prev Vet Med. 2004;64:41.
8 Rubenstein E, Levi I. Curr Infect Dis Rep. 2004;4:28.
9 Leyla G, et al. Vet Microbiol. 2003;93:53.
10 Amin AS, et al. Vet Microbiol. 2001;92:65.
11 MacMillan AP. World Anim Rev. 1997;89:57.
12 Jimenez de Baques MP, et al. Vet Microbiol. 1992;30:233.
13 Dias Aparicio E, et al. J Clin Microbiol. 1994;32:1159.
14 Delgado S, et al. J Vet Diagn Invest. 1995;7:206.
15 Blasco JM, et al. J Clin Microbiol. 1994;32:1835.
16 Placket P, et al. Vet Microbiol. 1989;20:339.
17 Mahajan NK, Kulshreshtha RC. Trop Anim Health Prod. 1991;23:11.
18 Biancifiori F, et al. Compend Immunol Microbiol Infect Dis. 1996;19:17.
19 Chand P, et al. Vet Rec. 2004;155:639.
20 Ebadi A, Zowghi E. Aust Vet J. 1983;139:456.
21 Radwan I, et al. Trop Anim Health Prod. 1989;21:211.
22 Polydorou I, et al. Israel J Vet Sci. 1990;45:215.
23 Blasco JM. Prev Vet Med. 1997;31:275.
24 Kolar J. Prev Vet Med. 1984;2:215.
25 Elberg SS. Vet Bull. 1981;51:67.
26 Schurig GG, et al. Vet Microbiol. 2002;90:479.
27 Bardenstein S, et al. J Clin Microbiol. 2002;40:1475.
28 Verger JM, et al. Vaccine. 1995;13:191.
29 Diaz-Aparicio E, et al. Trop Anim Health Prod. 2004;36:117.
30 Al Khalaf SAS. Trop Anim Health Prod. 1992;24:45.
Diseases associated with Moraxella, Histophilus, and Haemophilus species
Etiology Moraxella bovis is the primary infectious agent. Pili and hemolysin are the main virulence factors. Solar radiation, flies, and dust are contributing factors
Epidemiology Cattle of all ages are susceptible. Source is carrier cattle, with transmission by mediate contagion and by flies. More common in summer months. Usually multiple cases in a herd
Clinical findings Conjunctivitis, lacrimation, blepharospasm, photophobia, central corneal opacity
Diagnostic confirmation Culture
Treatment Self-limiting disease. Topical antibiotics, subconjunctival penicillin, parenteral oxytetracyclines. Protection of eye from sunlight
Hemolytic Moraxella bovis is the primary infectious agent concerned, although other organisms can exacerbate the severity of the disease.1 Experimental infections in calves and studies on corneal tissue culture show a great variation in virulence between strains.2 Beta-hemolysin, pili, leukotoxin, and proteases are virulence factors.3 M. bovis has serologically distinct shared and variable pilus epitopes, and strains can be distinguished by their pilus antigens into seven distinct serogroups.4,5 There are two distinct types of pilus, I and Q (formerly α and β). Q pili mediate bacterial adhesion to the cornea and the establishment of infection6 by preventing removal of the organism by the continual flushing effect of ocular secretions and the mechanical action of blinking. Beta-hemolysin is cytotoxic and produces corneal damage.7 In some outbreaks of pinkeye more than one serotype can be isolated from affected eyes.5
Whereas M. bovis initiates the disease, other agents can be responsible for some of the severe keratitis that occurs. Rickettsia, Chlamydia, Neisseria, Mycoplasma, and Acholeplasma spp. and viruses have been identified as common participants.1 Infectious bovine rhinotracheitis virus causes ocular disease in its own right but it may also be involved with M. bovis in causing the more severe disease. Clinical disease in experimentally induced infectious bovine keratoconjunctivitis has been shown to be more severe when the calves are concurrently given a modified live infectious bovine rhinotracheitis virus vaccine.8
Conjunctival infection with Mycoplasma bovoculi has been found to enhance the colonization of M. bovis9 and it is possible that other organisms can act in a similar way. Branhamella ovis causes a severe conjunctivitis in sheep and goats and is also recorded from outbreaks of keratoconjunctivitis in cattle in Israel;10,11 it may be a cause of vaccine breakdown in other countries.
Because the naturally occurring disease is usually much more severe than that produced experimentally, factors other than infectious agents have been examined. Solar radiation, flies, and dust have been shown to have an enhancing effect.1 Cultural characteristics of the organisms isolated from the conjunctiva can change with the level of solar ultraviolet radiation.12
The disease occurs in most countries of the world and, although it can occur in all seasons, is most common in summer and autumn. The prevalence and severity of the disease vary greatly from year to year, and it may reach epizootic proportions in feedlots and in cattle running at pasture. Only cattle are affected, the young being most susceptible, but in a susceptible population, cattle of all ages are likely to be affected. There is no mortality, and cases in which there is permanent blindness or loss of an eye are rare. However, the morbidity rate can be as high as 80%, with the peak infection rate at weeks 3–4 of the outbreak. Severe outbreaks can be experienced in winter, especially if the cattle are confined in close quarters such as barns or intensive feedlots.
Cattle are the reservoir and the organism is carried on the conjunctiva and also in the nares and vagina of cattle. Persistence of the disease from year to year is by means of infected animals, which can act as carriers for periods exceeding 1 year.13 Receptors for I-pili may be found on tissues other than the cornea and facilitate colonization of noncorneal tissue and inapparent infection,6 and the organism can switch from expression of one pilus type to the other.5
The disease is most common in summer and autumn and reaches epizootic proportions when flies and dust are abundant and grass is long; transmission is thought to be by means of these agents contaminated by the ocular and nasal discharges of infected cattle. Under experimental conditions, transmission is unusual in the absence of flies14 and occurs generally in their presence.15 The face fly (Musca autumnalis) and Asian face fly (Musca bezzii), because of feeding preference for the area around the eyes, are important vectors. Musca autumnalis is known to remain infected for periods of up to 3 days. M. bovis can be isolated from the crops of Musca autumnalis that have fed on the eyes of infected cattle.16
It is commonly observed that there is a much higher prevalence of the disease in Bos taurus cattle as distinct from Bos indicus cattle,17 and the severity and proportion of bilateral infections is much greater in B. taurus cattle than in crossbreeds. Charolais and Chianina cows may be less susceptible than Hereford cattle.18 In British-bred cattle there is also a relationship between rate and severity of infection and the degree of eyelid pigmentation, eyes with complete pigmentation being less affected. This effect of pigmentation on susceptibility may be the basis of an apparent inherited resistance of some families of Hereford cattle.19 The exposure of the eye to ultraviolet light may increase susceptibility to the disease and the severity of signs resulting from it.
Previous infection appears to confer a significant immunity that lasts through to the next season, when further reinfection, usually with minimal clinical disease, confers further immunity. Lacrimal secretions contain antibody, and antibody directed against the pilus antigens of M. bovis will prevent adherence of the organism to the cornea. In experimental infections, significant protection against challenge can be achieved by prior vaccination with pilus antigens of the homologous strain.20-22
However, there is antigenic diversity in pili from different strains of M. bovis and vaccines composed of pili from one strain only confer protection to challenge with organisms of the same serogroup.20 Further, M. bovis in the eye can switch their pilus antigenicity in response to antibody presence and render monovalent vaccines ineffective.22 A polyvalent vaccine might provide protection but polyvalent vaccines are less immunogenic than monovalent vaccines because of antigenic competition.22
Experimental reproduction is usually preceded by irradiation of the eye with ultraviolet light prior to inoculation. Under these conditions, inoculation with Q-piliated M. bovis produces a relatively high frequency of infection and keratoconjunctivitis, I-piliated organisms produce a lower frequency, and nonpiliated organisms do not produce infection.6
Infectious keratoconjunctivitis is a prominent disease in surveys of the predominant diseases in cattle.23 Loss of milk production or body condition may be caused by the discomfort, failure to feed, and temporary blindness. The conditions under which calves are reared can affect the importance of the disease. In veal calves, the disease may have no measurable effect on growth24 but in calves running at pasture it can result in a significant reduction of weaning weight. Occasionally, animals become completely blind and those at pasture may die of starvation.
Attachment of M. bovis to the corneal epithelium is mediated by the presence of pilus antigens, and Q-piliated organisms are more infectious than I-piliated strains.5,6
Microscopic corneal erosions are present within 12 hours of infection and occur at this time in the absence of a significant inflammatory response, indicating that the initial production of the corneal ulceration is due to the direct cytotoxic activity of the organism.3 This is followed by focal loss of corneal epithelium, degeneration of keratocytes, and invasion of the corneal stroma with fibrillar destruction. An inflammatory reaction occurs several days postinfection and results in enlargement of the corneal ulcers with deeper stromal involvement, corneal edema, and corneal neovascularization. The lesions are localized in the eye and there is no systemic infection.
An incubation period of 2–3 days is usual, although longer intervals, up to 3 weeks, have been observed after experimental introduction of the bacteria. Injection of the corneal vessels and edema of the conjunctiva are the early signs and are accompanied by a copious watery lacrimation, blepharospasm, photophobia and, in some cases, a slight to moderate fever with fall in milk yield and depression of appetite.
In 1–2 days, a small opacity appears in the center of the cornea and this may become elevated and ulcerated during the next 2 days, although spontaneous recovery at this stage is quite common. With progressive disease the opacity becomes quite extensive and at the peak of the inflammation, about 6 days after signs first appear, it may cover the entire cornea. The color of the opacity varies from white to deep yellow. As the acute inflammation subsides, the ocular discharge becomes purulent and the opacity begins to shrink, complete recovery occurring after a total course of 3–5 weeks.
One or both eyes may be affected. The degree of ulceration in the early stages can be readily determined by the infusion of a 2% fluorescein solution into the conjunctival sac, the ulcerated area retaining the stain.
About 2% of eyes have complete residual opacity but most heal completely with a small, white scar persisting in some. In severe cases the cornea becomes conical in shape, there is marked vascularization of the cornea, and ulceration at the tip of the swelling leads to under-running of the cornea with bright yellow pus surrounded by a zone of erythema. These eyes may rupture and result in complete blindness.
A proportion of cases develop minimal clinical lesions and heal spontaneously, and the severity of clinical disease can also vary between outbreaks.
The organism can be identified by culture or fluorescent antibody. The hemolytic form of the bacterium is noticeably more pathogenic than the nonhemolytic form. Serum agglutinins (1:80 to 1:640) are present 2–3 weeks after clinical signs commence, and a modified gel diffusion precipitin test is capable of detecting M. bovis antibodies. An ELISA test is also used for antibody detection in experimental studies; however, neither agglutinating antibody nor antibody detected by ELISA correlates well with individual animal resistance to infection.20 There is little indication for serological examinations in clinical practice. Necropsy examinations are not usually necessary.
• Traumatic conjunctivitis is usually easily differentiated because of the presence of foreign matter in the eye or evidence of a physical injury
• Pasteurella multocida (capsular type A) has been isolated from the eyes of housed heifers that experienced outbreaks of severe keratitis with severe loss of corneal stroma within 72 hours of onset
• Mycoplasma bovis has been isolated from the eyes of steers with an outbreak of severe conjunctivitis with corneal opacity and ulceration, disease being followed by serological conversion in affected animals.25 Involvement of the eyelids with marked swelling was prominent. Conjunctivitis is prominent in other mycoplasmal infections that produce keratoconjunctivitis26
• Listeria monocytogenes iritis
• Infectious bovine rhinotracheitis
• Chlamydial keratoconjunctivitis presents with identical clinical findings but has a protracted course despite treatment and a higher morbidity.27 Chlamydiophila DNA can be detected by PCR in conjunctival swabs. This disease is a possible zoonosis
Bovine infectious keratoconjunctivitis is frequently a self-limiting disease. Recovery commonly occurs without treatment, although early treatment will reduce the incidence of scarring of the eyes. Antibacterial treatment is commonly used and mass treatment of the herd as opposed to just affected individuals may halt the occurrence of further cases.28 The route of administration is often determined by ease of repeated access to the animals, and cost.
Early, acute cases respond to treatment with ophthalmic ointments and solutions containing antibiotics but they need to be instilled in the conjunctival sacs at frequent intervals, which may be impractical under field conditions. The organism is sensitive to most antibiotics and sulfonamides but is resistant to erythromycin, lincomycin, and tylosin. The administration of an oil-based formulation containing 375 mg of benzathine cloxacillin has been found to be effective in therapy in controlled trials.28-30 Two doses, 72 hours apart, are recommended.
Subconjunctival therapy with antibiotic is effective, and when corneal vascularization is extensive the injection of a mixture of corticosteroid and antibiotic under the bulbar conjunctiva is recommended to promote healing. Often one injection is sufficient, but it may be necessary to repeat it daily for a few days in advanced cases. Recovery may require 3–4 weeks and daily examination of the eye should be made to detect any complication that may occur. Another technique for prolonging the maintenance of high levels of antibiotic in the conjunctival sac is the use of collagen inserts impregnated with an antibiotic.
Subconjunctival procaine penicillin (3–6 × 105 IU) given through the skin of the upper eyelid or under the bulbar conjunctiva gives prolonged therapeutic concentrations in conjunctival secretions31 and is commonly used in therapy, alone or in combination with subconjunctival dexamethasone. Injection of the penicillin through the skin of the upper eyelid rather than through the conjunctiva confers a significantly longer presence of penicillin in the conjunctival fluids.32 Therapy must be administered under the bulbar conjunctiva and is ineffective if given in the superior palpebral conjunctiva.33,34 A controlled trial found that subconjunctival penicillin was effective in treatment but recurrence was higher than with treatment with parenteral oxytetracyline34 and mass treatment of calves with subconjunctival penicillin does not eliminate infection.35
Parenteral therapy with sulfadimidine at the normal dose rate of 100 mg/kg BW is an effective parenteral treatment, and a single treatment with long-acting oxytetracycline (20 mg/kg intramuscularly) has shown efficacy in controlled field trials.36 Parenteral treatment with two doses of long-acting oxytetracycline (20 mg/kg) 72 hours apart, coupled with oral administration of oxytetracycline at 2 g/250 kg BW for 10 days, is credited with markedly reducing the herd incidence of the disease.28,34 Recent studies comparing other antimicrobials with oxytetracycline suggest that recovery rates are faster following therapy with florfenicol or tilmicosin.37,38
Severe cases should be placed in a dark shelter out of direct sunlight. If housing is not possible, eye flap patches are available and effective. They are glued on above the eye and can be flipped up for medication of the eye.
When corneal ulceration has occurred recovery is always protracted. The use of topical ophthalmic anesthetics combined with atropine administration may be indicated to minimize ciliary spasm and pain. Severe cases may require that the third eyelid be temporarily sutured across the globe of the eye for several days to promote healing.
Eradication or prevention of the disease does not seem possible under extensive range conditions because of the method of spread, but if fly control can be fitted into the farm’s management program this should significantly reduce the infection rate. Insecticide impregnated ear tags may help in the control of the disease but do not prevent it. In many herds the best that can be done is to keep animals under close surveillance and isolate and treat any cattle that show excessive lacrimation and blepharospasm. Cattle that have had the disease should not be mixed with those that have not until after the fly season.
There has been considerable effort to develop methods of immunoprophylaxis; however the commercial bacterins, although available for over 30 years, have given inconsistent results, providing at best limited protection from subsequent infection and clinical disease. Killed, whole-cell vaccines require repeat injections, may be associated with anaphylactic reactions and have not proven effective in the field. To avoid the need for repeated injections an adjuvant vaccine has been tested, but without apparent benefit.
Vaccines containing pilus antigens, with or without cornea-degrading enzyme antigens, protect against challenge with homologous strains of M. bovis20,39,40 and some field trials report efficacy in naturally occurring outbreaks.40,41 However, others do not42,43 and the results of field studies that have shown a beneficial effect from vaccination have been criticized on the basis of bias in the selection of controls.43 It is probable that currently available vaccines do not contain the diversity of antigens required to protect against the variety of strains that occur in natural outbreaks. Autogenous vaccines are a consideration in individual herds but a recent controlled trial of an autogenous vaccine administered by subcutaneous or subconjunctival injection found no significant effect of either route or the vaccine on the incidence of disease.44
Weekly treatment of both eyes of calves, but not the cows, with a furazolidone eye spray has been shown to be a more effective prophylaxis than vaccination with a commercial bacterin in some areas.45
Total eyelid pigmentation may reduce the incidence of this disease but the recorded differences19 are unlikely to arouse enthusiasm for a genetic approach to the problem.
Cox PJ. Infectious bovine keratoconjunctivitis. Rec Prog Vet Annu. 1984:75-79.
George LW. Clinical infectious bovine keratoconjunctivitis. Compend Contin Educ Pract Vet. 1984;6:S712.
George LW. Antibiotic treatment of Moraxella bovis infection of cattle. J Am Vet Med Assoc. 1984;185:1206.
Punch PI, Slatter DH. A review of infectious bovine keratoconjunctivitis. Vet Bull. 1984;54:193-207.
Browm MH, Brightman AH, Fenwick BW, Rider MA. Infectious bovine keratoconjunctivitis: a review. J Vet Intern Med. 1998;12:259-266.
1 Punch PI, Slatter DH. Vet Bull. 1984;54:193.
2 Chandler RL, et al. J Comp Pathol. 1985;95:415.
3 Kagonyera GM, et al. Am J Vet Res. 1988;49:386.
4 Moore LJ, Lepper AWD. Vet Microbiol. 1991;29:75.
5 Conceicao FR, et al. Can J Vet Res. 2003;67:315.
6 Ruehle WW, et al. Am J Vet Res. 1993;54:249.
7 Beard MKMcG, Moore LJ. Vet Microbiol. 1994;42:15.
8 George LW, et al. Am J Vet Res. 1988;49:1800.
9 Rosenbusch RF. Am J Vet Res. 1983;44:1621.
10 Elad D, et al. J Vet Med B. 1988;35:431.
11 Yerahum I, et al. Israel J Vet Sci. 1991;46:142.
12 Lepper AVD, Barton IJ. Aust Vet J. 1987;64:33.
13 Iwasa M, et al. J Vet Med Sci. 1994;56:429.
14 Kopecky KE, et al. Am J Vet Res. 1986;47:622.
15 Arends JJ, et al. J Econ Entomol. 1984;77:394. 399
16 Glass HW, Gerhardt RR. J Econ Entomol. 1983;76:532.
17 Makinde AA, et al. Br Vet J. 1985;141:643.
18 Steelman CD, et al. J Agric Entomol. 1993;10:97.
19 Pugh GW, et al. Am J Vet Res. 1986;47:885.
20 Lepper AWD, et al. Vet Microbiol. 1992;32:177.
21 Lepper AWD, et al. Vet Microbiol. 1993;36:175.
22 Lepper AWD, et al. Vet Microbiol. 1995;45:129.
23 Salman MD, et al. J Am Vet Med Assoc. 1991;198:962.
24 Donovan GA, et al. Prev Vet Med. 1998;33:1.
25 Kirby FD, Nicholas RAJ. Vet Rec. 1996;22:552.
26 Naglic T, et al. Acta Vet Hung. 1996;44:21.
27 Otter A, et al. Vet Rec. 2003;152:787.
28 George LW. Cornell Vet. 1990;80:229.
29 George LW, et al. Am J Vet Res. 1989;50:1170.
30 Daigneault J, et al. Am J Vet Res. 1990;51:376. 381
31 Abeynayake P, Cooper BS. J Vet Pharmacol Ther. 1989;12:25. 31
32 Abeynayake P, Cooper BS. N Z Vet J. 1985;33:6.
33 Allen LJ, et al. J Am Vet Med Assoc. 1995;206:1200.
34 Eastman TG, et al. J Am Vet Med Assoc. 1998;212:560.
35 Sargison ND, et al. N Z Vet J. 1996;4:142.
36 Edmondson AJ, et al. Am J Vet Res. 1989;50:838.
37 Gokce HI, et al. Ir Vet J. 2002;55:573.
38 Zielinski GC, et al. Vet Ther. 2002;3:196.
39 Lepper AWD. Aust Vet J. 1988;65:310.
40 Gerber JD, et al. Vet Immunol Immunopathol. 1988;18:41.
41 Lekr C, et al. Vet Med. 1985;80:96.
42 Bateman KG, et al. Can Vet J. 1986;27:23.
43 Smith PC, et al. Am J Vet Res. 1990;51:1147.
Etiology Histophilus somni (formerly Haemophilus agni, Histophilus ovis)Epidemiology Worldwide occurrence but not a common disease. In affected flocks cases occur over several weeks to result in a significant population mortality
Clinical findings Acute disease and affected sheep commonly found dead. Septicemia, polyarthritis, and occasionally meningitis primarily in lambs 4–7 months of age
Necropsy findings Multiple hemorrhages throughout the carcass. Focal hepatic necrosis. Polyarthritis, meningoencephalitis
Histophilus somni falls within the family Pasteurellaceae. This organism, previously known as Haemophilus agni and Histophilus ovis, has been isolated from sheep with a number of different pyogenic conditions including septicemia, polyarthritis, thrombotic meningoencephalitis, general pyemia, metritis, mastitis, abortion, neonatal mortality, and epididymitis.1-5
Disease associated with H. somni in sheep has worldwide occurrence but is not common.
The most common presentation is lameness and septicemia in lambs aged 4–7 months6-9 but infection with this organism can also result in polyarthritis in lambs 1–4 weeks of age. The morbidity rate varies between outbreaks but the case fatality rate is likely to be 100% unless treatment is undertaken, and the population mortality rate can approach 10%.8 Outbreaks may last several weeks and, within a flock, cases of the disease occur sporadically but over a long period.
In some outbreaks, both in lambs and adult sheep, meningoencephalitis is the primary presentation and the clinical and pathological findings are similar to thromboembolic meningoencephalitis in cattle.3,10,11 The method of transmission is unknown but the disease does not appear to spread by pen contact nor can it be produced by oral, nasal, or conjunctival exposure to the organism. Environmental or other stress may be a predisposing factor.9
The organism colonizes the respiratory and reproductive tract mucosa and invades to produce septicemia and disseminated bacterial thrombosis, leading to a severe focal vasculitis.
Affected sheep are often found dead. Depression, high fever (42°C, 107°F), disinclination to move and collapse with movement are the obvious clinical signs and affected lambs may die within 12 hours of becoming ill. Lambs that survive more than 24 hours develop a severe arthritis with a palpable increase in joint fluid and heat in the joints. They are usually recumbent and those with meningoencephalitis show hypersalivation, convulsions and opisthotonos. The clinical course is short.
Hematology and blood chemistry are not commonly conducted because of the acute nature of the disease and the availability of carcasses for postmortem. Initially there is leukopenia and neutropenia with a neutrophilia and left shift in more prolonged cases. Total cell count is elevated in cerebrospinal fluid and joint fluid and these also can be cultured for the organism. Antibody detected by complement fixation persists for about 3 months in animals that survive.
At necropsy the most striking feature is the presence of multiple hemorrhages throughout the carcass. Focal hepatic necrosis surrounded by a zone of hemorrhage is also a constant finding. Lambs that die in the early stages of the disease show minimal joint changes but those that survive for more than 24 hours develop a fibrinopurulent arthritis. Histologically, the disease is a disseminated bacterial thrombosis leading to a severe focal vasculitis. This change is most apparent in the liver and skeletal muscles. A basilar meningitis will be present in more protracted cases.
Because of the acute nature of the clinical disease, the disease is likely to be confused with acute septicemia associated with E. coli or P. trehalosi, and with enterotoxemia. The characteristic hepatic lesions and histology serve to identify the disease, and final diagnosis depends on isolation of the organism.
Antimicrobials, such as tetracyclines, need to be given very early in the course of the disease if they are to be effective. Because of the acute nature of the disease, vaccination is likely to be the only satisfactory method of control.8 Although there is no label, vaccine immunity after a field attack seems to be solid. Mass treatment of the group of sheep at risk with long-acting tetracyclines is a possible strategy to reduce the occurrence of further cases.
1 Humphery JD, Stephens LR. Vet Bull. 1983;53:987.
2 McDowell SWJ, et al. Vet Rec. 1994;134:504.
3 Philbey AW, et al. Aust Vet J. 1991;68:387.
4 Low JC, Graham MM. Vet Rec. 1985;117:64.
5 Webb RF. Res Vet Sci. 1983;35:30.
6 Kennedy PC, et al. Am J Vet Res. 1958;19:645.
7 Lundberg MS. Can Vet J. 1986;27:501.
8 Gill J. Surveillance. 1992;192:13.
9 Kearney KP, Orr MB. N Z Vet J. 1993;41:149.
Etiology Histophilus somni (formerly Haemophilus somnus)
Epidemiology High prevalence of infection in cattle population; low incidence of disease. Occurs in North American feedlot cattle, also in the UK and some European countries. Young growing cattle and those 6–12 months of age are most commonly affected, nursing beef calves less commonly. Originally, meningoencephalitis was most common lesion but pleuropneumonia and myocarditis now common. Several virulence attributes of organism may account for different forms of disease. Organism resides in respiratory and reproductive tracts of both females and males
Signs Meningoencephalitis with fever, ataxia, joint swellings, fundic lesions, weakness, recumbency, and death in 12–24 hours. Pleuropneumonia and myocarditis with rapid death
Clinical pathology Marked changes in leukon. Demonstrate and culture organism from cerebrospinal fluid, joint fluid, pleural cavity, and myocardium
Lesions Meningoencephalitis, hemorrhagic infarcts in brain, retinal hemorrhages, pleuropneumonia, myocarditis with abscessation
• Pneumonia and pleuritis: Pneumonic pasteurellosis and pleuritis
• Myocarditis: Other causes of sudden death and congestive heart failure
• Meningoencephalitis: Listeria meningoencephalitis, polioencephalomalacia, hypovitaminosis A
Diagnostic confirmation Culture organism
Control Unreliable. Mass medication of individual animals on arrival in feedlot. Vaccination with bacterin
Histophilus somni is the cause.1,2 Earlier investigations have shown that H. somni, Haemophilus agni, and Histophilus ovis represent the same species and recent analysis of genes of strains supports the allocation of this species to a novel genus within the family Pasteurellaceae as Histophilus somni.3 H. somni causes a variety of diseases in cattle, including septicemia, thrombomeningoencephalitis, pleuropneumonia, myocarditis, reproductive failure, and in sheep mastitis, septicemia, and epididymitis.
The prevalence of infection of H. somni in the cattle population is much higher than the incidence of clinical disease. More than 50% of normal bulls, 8–10% of normal cows, and 10% of normal rams have H. somni in their reproductive tract.4 Among those that have had the disease and survived, the serological reactor rate varies from 50–100%. Some surveys found more positive reactors in beef cattle and dairy cattle from infected herds than in dairy cattle from clinically normal herds. The percentage of cattle that seroconvert may be higher in dairy herds of more than 100 cows than in smaller herds.
Infection of cattle with H. somni may cause septicemia, thrombotic meningoencephalitis, polysynovitis, pleuritis, suppurative bronchopneumonia, myocarditis, otitis media, mastitis, and reproductive tract diseases. When infection of cattle with the organism was first described in 1956, the primary form of the disease was thrombotic meningoencephalitis. Since that time, many different clinical forms of the infection have been described. Suppurative bronchopneumonia, fibrinous pleuritis, and myocarditis are now being recognized with increased frequency in feedlot cattle and are being attributed to H. somni infection.5,6 Based on necropsy examinations over a 20-year period in a Saskatchewan diagnostic laboratory, there has been an increasing percentage of cattle with pneumonia and myocarditis associated with the organism and a decreasing percentage with meningoencephalitis.5 However, because of the practical difficulties in making a specific clinical, pathological, and microbiological diagnosis in situations where the disease complex occurs, there is some uncertainty about the relative importance of the organism in causing certain diseases such as pneumonia of feedlot cattle. For example, because of the variability of the nature and extent of the lesions in bovine respiratory disease in feedlot cattle, the several factors that can influence the laboratory isolation of some bacteria from affected tissues, and the common occurrence of mixed infections, it is difficult to determine whether H. somni or M. haemolytica is the primary pathogen.
The disease occurs most commonly in feedlot cattle in North America after they have been commingled from different sources. The disease has also been recognized in the UK, Germany, Switzerland, and recently in Israel.7 The disease also occurs in nursing beef calves and young cows on pasture and in young dairy cattle, but to a much lesser extent. The organism has been found in the tonsillar tissues of American bison (Bison bison)8 and has been the cause of bronchopneumonia in bison.9
The incidence rate of the nervous form of the disease in a susceptible group of calves is low, averaging about 2%, but may be up to 10% in some outbreaks. The case fatality rate, however, is 90% if affected animals are not identified and treated early in the course of the disease.
The nervous form of the disease occurred historically most commonly in feedlot cattle from 6–12 months of age during the fall and winter months, which may be a reflection of stress associated with crowding and cold and changing weather. In Canada the nervous form occurred most commonly in cattle about 4 weeks after arrival in the feedlot, with a range of 1 week to 7 months. The nervous form has also occurred in feedlot cattle in Argentina.10
The disease complex that is encountered more commonly now is characterized by pleuritis, myocarditis, and pneumonia, and can be the most significant cause of mortality in fall-placed weaned beef calves in large commercial feedlots in western Canada.11 Death from pneumonia due to the infection occurred mainly during the first 5 weeks in the feedlot; death from myocarditis, pleuritis, thrombotic meningoencephalitis, septicemia, and euthanasia because of polysynovitis occurred mainly after the third week.11 Furthermore, this disease complex is occurring despite routine vaccination of calves on arrival in the feedlot.11 A history of respiratory tract disease preceding the outbreak is common and in some cases meningoencephalitis had occurred in the same herd in the previous year. Myocarditis due to H. somni in a 6-month-old bull calf has been described in the UK.12
H. somni also causes various forms of reproductive failure in cattle. A review of the literature on this subject is available.3 The importation of infected young rams into a flock can have a deleterious effect on the percentage of ewes that lamb.13 Purchasing replacement animals and having cattle on the same farm were risk factors for infection in the flock. The possibility of interspecies transmission between cattle and sheep requires further study.
The meningoencephalitis, pleuropneumonia, and myocarditis forms of the disease occur most commonly in feedlot calves 6–12 months of age. The disease may occur in unvaccinated cattle or cattle not vaccinated soon enough before entry into the feedlot. Most weaned beef calves placed into commercial feedlots in Canada are not vaccinated for H. somni before entry into the feedlot but rather on arrival.
In Canadian feedlots, feedlot calves that have significant H. somni serum antibody levels on arrival or that are able to increase their levels after arrival tend to have a reduced risk of bovine respiratory disease.14-16
The literature on the virulence factors of the organism has been reviewed.4 Several virulence factors have been identified, including lipo-oligosaccharide phase variation, induction of apoptosis, intraphagocytic survival, and immunoglobulin Fc binding proteins.4 H. somni is able to synthesize and secrete histamine, which may contribute to the pathogenesis of respiratory disease.17 The organism is able to survive and multiply in bovine alveolar macrophages and blood monocytes, which may be related to its ability to escape macrophage killing and disseminate in the body.18
The organism is an obligate inhabitant of mucosal surfaces and an opportunistic pathogen. It colonizes the surface of mucous membranes; in the asymptomatic carrier state the organism remains at the mucosal surface without invading cells.2 The organism is able to persist in the lungs of calves for 6–10 weeks in the presence of specific antibody and in the absence of clinical abnormalities other than sporadic coughing. Attachment may be all that is necessary to produce infertility due to endometritis or degeneration of embryos. The organism attaches in large numbers to bovine vaginal epithelial cells.2 It has the ability to invade the circulatory system, resulting in septicemia. Various strains of H. somni adhere to bovine aortic endothelial cells and the adherence is enhanced by the tumor necrosis factor.4
Some isolates of the organism are able to multiply in vivo because they are resistant to complement, and bovine leukocytes are incapable of destroying the organism in the absence of specific antibody. Certain suppressive components in H. somni have been identified that inhibit the function of polymorphonuclear leukocytes. H. somni antigen has been found in heart and lung tissues in association with chronic pneumonia due to Mycoplasma bovis and BVDV.19
The organism also has cytotoxic properties that may be related to the production of endotoxin.2 Some strains are serum resistant and others serum sensitive, which may explain the ability of certain strains to invade beyond mucous membrane surfaces. Another virulence determinant is a nonimmune binding mechanism that is present on the surface of the organism.4 This determinant may be related to the organism’s resistance to complement-mediated killing, its persistence at mucosal surfaces, its capacity to evade host effector functions in vivo and its ability to cause a range of bovine infections. Differences between pathogenic and preputial isolates have been identified.4 Similarly, there are pathogenic strains of the organism in the genital tract of apparently normal cows as well as those with inflammatory disease.4
Virulence differences also exist between H. somni strains following intratracheal challenge of bovine lungs.20 Those strains isolated from encephalitic lesions, or from the prepuce, will not produce the same degree of experimental pneumonia as those strains isolated from lung lesions. Preputial and septicemic isolates of ovine H. somni are similar to bovine H. somni in pathogenicity and in surface antigens. Ovine isolates given by intracisternal inoculation to 2–3-month-old lambs caused fatal meningoencephalitis and myelitis.
In summary, many virulence factors are involved in several steps of pathogenesis. Adherence is likely to be important in colonization, complement resistance in survival in the circulation or inflammatory sites, and cytotoxicity in evading killing by phagocytes and in initiation of vasculitis, as well as invasion through the endothelium. The host damage that occurs as a result may be further exacerbated by inflammatory mediators released by the host in response to H. somni.
The method of transmission and portal of entry are unclear. A feature of infections with this organism is its persistence at mucosal sites in both subclinical and diseased animals. The organism can be isolated from the respiratory and reproductive tracts of normal animals.3
In bulls, the organism has been isolated from semen and the preputial orifice, preputial cavity, urinary bladder, accessory sex glands, ampulla of the ductus deferens and the preputial washings of steers. Most bulls harbor the organism in the prepuce. Thus, the potential exists for venereal transmission of H. somni, for lateral spread from the genital tract and for environmental contamination by the organism.
The organism has also been isolated from the vagina, vestibular gland, cervix, uterus, and bladder of cows. The prevalence of infection in normal cows varies depending on the herd and geographical location but 10–27% can harbor the organism.3 The organism can colonize the vagina of cows without causing disease and it is thought to have a primary etiological role in vaginitis and cervicitis in cows.
The role of H. somni in diseases of the bovine reproductive tract has been reviewed.3 The organism has been isolated from the udder secretions of cattle with naturally occurring mastitis.
Urine is also a source of the organism. The young beef calf in a cow–calf herd can become infected as early as 1 month of age and become a nasal carrier of the organism without showing any signs of clinical disease. The mature cow is considered to be a major source of the organism for the calf. The method of transmission is presumed to be by contact with infective respiratory and reproductive secretions or by aerosol transmission, especially in close-contact feedlots.
The organism can survive more than 70 days when it is mixed with cerebrospinal fluid, whole blood, blood plasma, vaginal mucus, or milk and frozen at −70°C (−94°F). At 23.5°C (73.5°F) it can survive beyond 70 days when mixed with whole blood and nasal mucus. The viability of the organism in urine at all temperatures is less than 24 hours and less than 15 minutes at 20°C (68°F) and 37°C (98°F). It survives for less than 1 day in milk at room temperature or when incubated at 37°C, and should be considered as a possible cause of mastitis in cases that are negative on routine bacteriological culture.
Serum antibody tests measured by several serological tests do not correlate with susceptibility to clinical disease. Naturally acquired humoral immunity does not influence the outcome of experimental intravenous inoculation of the organism. Also, the role of naturally acquired antibodies in protecting cattle from disease is uncertain. The levels of naturally occurring serum bactericidal activity to H. somni are low or absent in calves at 4–6 months of age, when they are most susceptible to the nervous form of the disease. The levels increase with age and are high in mature cows; yearlings have intermediate levels.
Experimentally, convalescent sera from calves with experimental H. somni pneumonia protects calves against acute H. somni pneumonia.21 Marked serum exudation characterizes the early stages of experimental pneumonia, and antibody should be involved in protection. The specificity of this protection is directed primarily against surface-accessible antigens of the bacterial outer membrane. These antigens may also be useful in serological diagnosis because convalescent calves have high IgG1 and IgG2 titers to H. somni for several weeks. The measurement of serum IgG1 is a more reliable test to detect a current or recently active infection. Later, there is a sustained increase in IgG2. The role of IgG2 α antibodies in providing protection against H. somni pneumonia has been examined.22 The development of a systemic IgG2 antibody response is the basis for local immunological protection in the bovine reproductive tract.
The immune response in cattle to the major outer membrane protein during infection is weak and directed to antigenically variable determinants in a strain specific manner that may have important implications in protective immunity.23 Vaccination of 1–2-month-old calves with commercial aluminum-hydroxide-adjuvanted H. somni bacterins elicits an ELISA-detectable IgE response 14 days after injection, which may be associated with severe clinical disease associated with type I hypersensitivity.24
H. somni first establishes itself in the host by colonizing the surface of the mucous membranes. Some strains of the organism are able to invade the circulatory system and cause septicemia, with localization in many tissues and organs, causing a vasculitis. The ability of H. somni to survive in both mononuclear phagocytes and neutrophils may be important in the establishment of the chronic multisystemic infection characteristic of bovine haemophilosis.18 In the thrombotic meningoencephalitic form of the disease, the sequence of events in the genesis of the lesions may be adhesion of the organism to vascular endothelial cells. The organism lipo-oligosaccharide induces endothelial cell apoptosis, which may play a role in producing vasculitis.25 Contraction and desquamation of cells, with exposure of subendothelial collagen, thrombosis and vasculitis, is followed by ischemic necrosis of adjacent parenchyma. The common site of localization is the brain, causing a thrombomeningoencephalitis. Multifocal areas of hemorrhagic necrosis occur throughout the brain, resulting in the major clinical findings of depression, paresis, and recumbency. Localization in synovia results in polysynovitis. Fibrin thrombi occur in the small vessels and capillaries of the liver, spleen, kidney, lung, heart, and brain, which suggests that disseminated intravascular coagulation may be a feature of the pathogenesis of Haemophilus septicemia. Myocarditis has been recognized with increased frequency6,26 and is characterized by acute or chronic heart failure.
The pathogenesis of the pneumonia is not clear. Although H. somni has been isolated from cattle with bronchopneumonia and fibrinous pneumonia in pure culture and in combination with Pasteurella spp., the lungs of cattle dying with thrombomeningoencephalitis are not usually affected with a fibrinous pneumonia. The pneumonia that is attributed to the organism is characteristically subacute or chronic and it is probable that the portal of entry is via the upper respiratory tract. However, it is difficult to reproduce the disease by aerosol challenge with H. somni.20 The organism produces and secretes histamine, which may be enhanced by carbon dioxide concentrations that approximate those in the bronchial tree.17 This may explain some of the postvaccination reactions.
The microscopic lesions in the lungs of cattle with pneumonia from which H. somni is isolated consist of suppurative to necrotizing bronchiolitis, particularly in calves with subacute to chronic pneumonia. The experimental pneumonia is characterized by purulent to fibrinopurulent bronchiolitis accompanied by alveolar filling with fibrin, neutrophils, and macrophages. Laryngitis and polypoid tracheitis have also been attributed to H. somni, but the evidence for a cause and effect relationship is limited.
Hemorrhagic necrotic lesions also occur in the spinal cord, which contributes to the muscular weakness, recumbency, and paralysis encountered in some cases with or without brain lesions. Lesions in the esophagus, forestomachs, and intestines may account for the bloat and alimentary tract stasis that occurs in the experimental disease.
The septicemia usually causes a marked leukopenia, neutropenia, and degenerative left shift.
Cattle dying of experimentally induced and naturally occurring disease have high levels of agglutinating anti-H. somni antibody, but not of complement-fixing antibody. Because septicemia can occur even with high levels of serum antibody, it is hypothesized that the formation of antigen–antibody complexes may contribute to the development of the vasculitis. It is possible that previous exposure to H. somni infection is necessary for typical thrombomeningoencephalitis to occur. Inoculation of colostrum-deprived calves with H. somni causes septicemia but does not produce lesions typical of thrombomeningoencephalitis. This suggests that the disease may be an example of a type III hypersensitivity reaction or serum sickness.
The organism can cause inflammatory disease in the genital tract of cows or may merely colonize the healthy genital mucosa.3 Vaginitis, cervicitis, and endometritis have been associated with infection by H. somni. Experimentally, the organism can be embryocidal, which indicates a possible role in early embryonic mortality. Sporadic abortions have been reported following septicemia.3
The range of clinical findings associated with H. somni infection in cattle has changed remarkably in the last two decades. Historically, thrombotic meningoencephalitis was the major form of the disease. However, fewer cases of the nervous form are being diagnosed now while many more cases of other forms of the disease are becoming prevalent.6
In the typical nervous form of the disease, it is common for several animals to be affected within a few days or at one time, but single cases do occur. Some affected animals may be found dead without any premonitory signs and often this may be the first sign of disease in the group.
In the more common acute form, in which there is usually neurological involvement, cattle may be found in lateral or sternal recumbency and may or may not be able to stand. The temperature is usually increased up to 41–42°C (105.8–107.6°F) but in some cases it may be normal. Depression is common, the eyes are usually partially or fully closed and, while blindness may be present in both eyes, it is usually confined to one eye, or the eyes may be normal. Originally the disease was called the ‘sleeper syndrome’ because the eyes were partially closed. Recumbent cattle that attempt to stand may have considerable difficulty and exhibit obvious ataxia and weakness. Others that are able to stand, when attempting to walk, knuckle over on the hind fetlocks, are grossly ataxic, and usually fall after walking a short distance. In the recumbent position, opisthotonos, nystagmus, muscular tremors, hyperesthesia, and occasionally convulsions will occur, but the emphasis is on muscular weakness and paralysis rather than signs of irritation. Otitis media with concurrent meningitis may also occur.
The nervous form of the disease is rapidly fatal in 8–12 hours if not treated when signs are first noticed. Affected cattle that are treated before they become recumbent commonly recover in 6–12 hours, which is an important clinical characteristic of the disease. Once recumbent, particularly with obvious neurological involvement, they will either die in spite of treatment or remain recumbent and fail to improve or get worse over several days. Secondary complications, such as pneumonia and decubitus ulcers, usually result. The organism has been isolated from a 5-month-old ram that died suddenly with pathological evidence of septicemia.
The ocular lesions consist of foci of retinal hemorrhages and accumulations of exudate that appear like ‘cotton tufts’. While these fundic lesions are not present in all cattle affected with H. somni, they are a valuable aid to the diagnosis. The organism has been isolated from the conjunctival sacs of feedlot cattle affected with conjunctivitis.
Otitis in feedlot cattle has also been attributed to the organism. The ears are commonly drooping and affected animals appear depressed. A combination of otitis and meningitis young cattle associated with the organism has been described.27
The synovitis is characterized by distension of the joint capsules, usually the major movable joints such as the hock and stifle joints but any joint may be involved. Pain and lameness are only mild and, when treated early, the synovitis usually resolves in a few days. In a few cases there is marked lameness and a preference for recumbency associated with hemorrhages in muscle. The organism has been isolated from a calf with a urachal abscess.28
The clinical findings of the respiratory form of the disease, which has been diagnosed with increased frequency in the last decade, have not been clearly described. There are no published descriptions available of the clinical findings of pneumonia or pleuritis associated with the organism. It is unlikely that there are any distinctive clinical features. Most feedlot calves with pleuritis due to H. somni die in the pen without ever having been treated.
Epidemiological surveys of weaned beef calf mortality due to pneumonia and pleuritis associated with H. somni suggest that death from pneumonia occurred during the first 5 weeks after arrival in the feedlot.11 The median fatal disease onset for pneumonia was day 12, and for myocarditis and pleuritis, day 22. It is suggested that pneumonia and pleuritis should be suspected in feedlot cattle that have been treated unsuccessfully for bovine respiratory disease in the previous several days. Laryngitis, tracheitis, pleuritis, and pneumonia can occur alone or in combination with the acute neurological form of the disease. The laryngitis is characterized clinically by severe dyspnea, mouth-breathing, and stertor. Conjunctivitis similar to that seen in infectious bovine rhinotracheitis may occur and isolation of the organism from ocular swabs is necessary to make the definitive diagnosis. Chronic suppurative orchiepididymitis in a calf from which H. somni was isolated has been described.
In the myocardial form of the disease, affected animals may be found dead without any previous illness having been recorded or they may have been treated for respiratory disease within the previous few weeks with a variable response. If seen early in the course of the myocarditis, the most common clinical findings are a fever and depression.14 With advanced stages of myocarditis, exercise intolerance, mouth-breathing, and protrusion of the tongue occur. Affected animals may collapse and die while being moved from their home pen to the hospital pen in the feedlot. Most animals with myocarditis have a previous history of being treated for an undifferentiated fever and depression within the previous 10–14 days. When returned to their home pens, they may be found dead or in severe respiratory distress.
Chronic free-gas bloat is a not uncommon finding in naturally occurring cases and occurs frequently in the experimental disease.
In most cases there are changes in the total and differential leukocyte count. Leukopenia and neutropenia may be present in severe cases while in less severe cases a neutrophilia with a left shift is more common. In the cerebrospinal fluid, the total cell count is markedly increased and neutrophils predominate. The Pandy globulin test on cerebrospinal fluid is usually strongly positive. In the synovial fluid the total cell count is also increased and neutrophils predominate.
The organism can be cultured from blood, cerebrospinal fluid, synovial fluid, urine, brain, kidney, and liver, less commonly from pleuritic fluid and tracheal washings. The laboratory isolation of H. somni from swabs, tissues, and body fluids requires special transport media and selective culture media to insure reliable recovery. It is difficult to determine whether a positive culture of the organism from a mucosal surface indicates an etiological role or merely a carrier role. The PCR technique is a more sensitive method for detection of the organism on swabs from either the cut surface or from a bronchus than bacterial culture and immunochemistry.29
Cattle with experimental or naturally occurring disease have high levels of agglutinating anti-H. somni antibody. Recovered animals are positive to the CFT within 10 days following infection and titers begin to decline to low levels 30 days after infection. Acute and convalescent sera are required for accurate interpretation of results.
A microagglutination test is available but most cattle are positive. Naturally or experimentally infected animals have elevated IgG2 antibody titers compared to controls. However, there is no significant difference in serum IgG2 titers between culturally negative and culturally positive but asymptomatic animals. An immunoblot test can detect an immune response after experimental abortion, experimental pneumonia or vaccination with a killed vaccine. It is also able to distinguish between animals with an immune response due to disease or vaccination with the organism and those animals that are asymptomatic carriers, culture negative or infected with closely related bacteria.
The characteristic lesions of the nervous form are hemorrhagic infarcts in any part of the brain and spinal cord. These are usually multiple and vary in color from bright red to brown and in diameter from 0.5–3 cm. Cerebral meningitis may be focal or diffuse and the cerebrospinal fluid is usually cloudy and slightly yellow-tinged. Hemorrhages may also be present in the myocardium, skeletal muscles, kidneys, and the serosal surfaces of the gastrointestinal tract.
There may be petechiation and edema of the synovial membranes of joints. There is an excessive quantity of synovial fluid, which is usually cloudy and may contain fibrinous flecks. The articular cartilage is usually not affected.
Pulmonary involvement is characterized by a fibrinopurulent bronchopneumonia, although the posterior aspects of the lung may be edematous and have a rubbery consistency. Histologically there is fibrinosuppurative bronchiolitis accompanied by filling of the alveoli with fibrin, neutrophils, and macrophages. Peribronchiolar fibrosis and bronchiolitis obliterans, interlobular fibrosis and thrombosis of interlobular and pleural lymphatics develop in chronic cases. Fibrinous or serofibrinous inflammation of the peritoneum, pericardium, or pleura is found in more than 50% of cases. There may be focal ulceration and fibrinonecrotizing inflammation extending from the pharynx down into the trachea. Polypoid tracheitis has also been reported.
Histologically, vasculitis and thrombosis with or without infarctions and a cellular component composed almost entirely of neutrophils may be seen in all tissues where localization occurs, especially the heart. Myocardial abscesses may develop and are most common in the left ventricular free wall, particularly in the papillary muscles.
H. somni is easily cultured from the tissues of untreated animals but immunohistochemical techniques can be attempted to demonstrate the organisms if culture is unsuccessful.30,31
• Bacteriology – culture swabs from brain/meningeal and joint lesions; lung, spleen, heart (CULT)
• Histology – formalin-fixed brain, lung, heart, kidney, synovial membrane (LM, IHC).
Meningoencephalitis due to H. somni is characterized by sudden onset of weakness, ataxia, depression, fever, enlarged joints and rapid death within 12–24 hours. There are marked changes in the cell count of the cerebrospinal fluid and the leukogram. There is a rapid response to treatment in the early stages.
• In polioencephalomalacia, blindness, normal temperature, nystagmus, opisthotonos, and convulsions are common
• In Listeria meningoencephalitis there is unilateral facial paralysis with deviation of the head and neck and a normal or slightly increased temperature. The cerebrospinal fluid in listeriosis usually contains an increased number of mononuclear cells
• Hypovitaminosis A in young cattle 6–12 months of age is characterized by sudden onset of short-term convulsions and syncope lasting 10–30 seconds, during which they may die but from which they more commonly recover to appear normal. Exercise such as walking from pasture to the farmstead will commonly precipitate the seizures. Eyesight may be slightly impaired but the menace reflex is usually present. The differential diagnosis of diseases of the brain of cattle is summarized in Table 31.3
Pneumonia and pleuritis associated with H. somni cannot be distinguished clinically from the other common causes of pneumonia in cattle and the diagnosis is usually made at necropsy.
Myocarditis due to H. somni may cause sudden death or congestive heart failure, which will require a necropsy examination for a diagnosis.
Cattle with the nervous form of the disease must be treated with antimicrobials as soon as clinical signs are obvious. Florfenicol, an analog of thiamphenicol, at a dose of 20 mg/kg BW intramuscularly and repeated 48 hours later, is effective for the treatment of acute undifferentiated fever in feedlot calves32 and may be the antimicrobial of choice if H. somni infection is a major cause of mortality in feedlot calves. Oxytetracycline at 20 mg/kg BW intravenously daily for 3 days is effective when treatment is begun within a few hours after the onset of clinical signs. The prognosis in recumbent cattle is unfavorable but treatment for 2–4 days may be attempted. A failure to respond after 3 days of treatment usually indicates the presence of irreversible lesions. The MICs of 33 antimicrobial agents for H. somni indicated high susceptibility to penicillin G, ampicillin, colistin, and novobiocin. Oxytetracycline also revealed high activity. Once the disease has been recognized in a group, all in-contact animals should be observed closely every 6 hours for the next 7–10 days to detect new cases in the initial stages so that early treatment can be given. Mass medication of the feed and water supplies may be indicated but efficacy and benefit–cost data are not available.
The treatment of pneumonia and pleuritis due to H. somni is the same as for acute undifferentiated bovine respiratory disease.
Satisfactory control procedures are not available because the pathogenesis and epidemiology of the disease are not well understood. When an outbreak of the nervous form of the disease is encountered, the provision of constant surveillance and early treatment is probably the most economical and effective means of control.
Postarrival mass medication with long-acting oxytetracycline has been evaluated to reduce the risk of hemophilosis mortality in feedlots.33 Mass medication did not reduce the risk of hemophilosis mortality but it reduced the risks of bovine respiratory disease morbidity and mortality by 14% and 71%, respectively.33 Hemophilosis accounted for 40% of the mortality in the feedlot calves for each year over 3 years.
Vaccines have been available for use in North America but their efficacy is uncertain. One bacterin is immunogenic and will protect vaccinated cattle against the nervous form of the infection produced by intravenous and intracisternal inoculation of the organism.6 Two injections of the bacterin given subcutaneously 2–3 weeks apart are recommended. Controlled field trials indicate that the bacterin reduces the morbidity and mortality rates of nervous system disease in vaccinated cattle compared to nonvaccinated animals. However, the efficacy of the bacterin has been difficult to evaluate because the incidence of naturally occurring disease in nonvaccinated control animals is usually low and may not be significantly greater than in vaccinated animals.
The efficacy of a H. somni bacterin to reduce mortality was evaluated in auction-market-derived beef calves vaccinated immediately upon arrival at the feedlot.34 The vaccine had no significant effect on overall crude mortality but appeared to reduce the incidence rate of fatal disease during the first 2 months in the feedlot when the risk of fatal disease onset was highest. When mortalities unlikely to be associated with H. somni were removed from the analysis, the mortality rate in male calves was reduced by about 17% in the vaccinated group. The incidence rate of fatal disease was higher in female calves during the first week. A second vaccination 2 weeks after arrival did not reduce the mortality risk.
Vaccination of feedlot calves on arrival with a genetically attenuated leukotoxin of M. haemolytica combined with bacterial extracts of H. somni increased serum antibody titers to both organisms and reduced acute undifferentiated bovine respiratory disease.35 However, it is not known what proportion of the respiratory disease was due to H. somni.
Vaccinating calves twice with a killed whole-cell bacterin reduced the clinical and pathological effects of experimentally induced H. somni pneumonia. Calves vaccinated once were incompletely protected.
There is no published evidence to indicate that vaccination of feedlot calves before or after entry into the feedlot with any of the available H. somni vaccines will provide protection against the various forms of clinical disease, particularly the respiratory and myocardial types described earlier. The disease complex is occurring in feedlot calves in spite of vaccination.11 A rational vaccination program would consist of vaccinating calves at least twice, 2–4 weeks apart, with the second vaccination occurring at least 2 weeks before entry into the feedlot.
Humphrey JD, Stephens LR. Haemophilus somnus: a review. Vet Bull. 1983;53:987-1004.
Miller RB, Lein DH, McEntee KE, et al. Haemophilus somnus infection of the reproductive tract: a review. J Am Vet Med Assoc. 1983;182:1390-1392.
Little PB. Haemophilus somnus complex: pathogenesis of the septicemic thrombotic meningoencephalitis. Can Vet J. 1986;27:94-96.
Harris FW, Janzen ED. The Haemophilus somnus disease complex (hemophilosis): a review. Can Vet J. 1989;30:816-822.
Kwiecien JM, Little PB. Haemophilus somnus and reproductive disease in the cow: a review. Can Vet J. 1991;32:595-601.
Siddararamppa S, Inzana TJ. Haemophilus somnus virulence factors and resistance to host immunity. Anim Health Res Rev. 2004;5:79-93.
1 Angen O, et al. Int J Syst Evol Microbiol. 2003;53:1449.
2 Corbeil LB, et al. Donachie W, et al, editors. Haemophilus, Actinobacillus, and Pasteurella. New York: Plenum Press. 1995:93.
3 Kwiecien JM, Little PB. Aust Vet J. 1991;32:595.
4 Siddararamppa S, Inzana TJ. Anim Health Res Rev. 2004;5:79-93.
5 Orr JP. Can Vet J. 1992;33:719.
6 Harris FW, Janzen ED. Aust Vet J. 1989;30:816.
7 Grinberg A, et al. Israel J Vet Med. 1993;48:61.
8 Ward ACS, et al. Can J Vet Res. 1999;63:166.
9 Dyer NW. J Vet Diagn Invest. 2001;13:419.
10 Descarga CO, et al. Vet Rec. 2002;150:817.
11 VanDonkersgoed J, et al. Can Vet J. 1990;31:821.
12 Wessels J, et al. Vet Rec. 2004;154:608.
13 Lees VW, et al. Can J Vet Res. 1990;54:331.
14 Martin SW, et al. Can J Vet Res. 1998;62:262.
15 Booker CW, et al. Can Vet J. 1999;40:40.
16 O’Connor A, et al. Can J Vet Res. 2001;65:143.
17 Ruby KW, et al. Compend Immunol Microbiol Infect Dis. 2002;25:13.
18 Gomis SM, et al. Microb Pathog. 1998;25:227.
19 Shahriar FM, et al. Can Vet J. 2002;43:863.
20 Tegtmeier C, et al. Vet Microbiol. 2000;72:229.
21 Gogolewski RP, et al. Infect Immun. 1987;55:1403.
22 Corbeil LB, et al. Can J Vet Res. 1997;61:207.
23 Tagawa Y, et al. Vet Microbiol. 2000;71:245.
24 Ruby KW, et al. Vet Microbiol. 2000;76:373.
25 Sylte MJ, et al. Infect Immun. 2001;69:1650.
26 Guichon PT, et al. Can Vet J. 1988;29:1012.
27 Duarte ER, Hamdan JS. Prev Vet Med B. 2004;51:1.
28 Starost MF, et al. Vet Pathol. 2001;38:547.
29 Tegtmeier C, et al. Vet Microbiol. 2000;76:385.
30 Haines DM, et al. Can Vet J. 2004;45:231.
31 Haines DM, et al. Can Vet J. 2001;42:857.
32 Booker CW, et al. Can Vet J. 1997;38:555.
33 VanDonkersgoed J, et al. Can Vet J. 1994;35:573.
Epidemiology Common in pigs several weeks after weaning and up to 4 months of age. Sporadic outbreaks. Environmental stressors are risk factors
Signs Sudden onset of anorexia, dyspnea, lameness, swollen joints, fever, nervous signs, and death
Clinical pathology Culture organisms from serous membranes
Lesions Peritonitis, pleuritis, synovitis, meningitis
Diagnostic confirmation Culture organism and a variety of new techniques
Differential diagnosis Erysipelas, mycoplasmal and streptococcal arthritis, other serositis, also Actinobacillus pleuropneumoniae infection, vitamin E deficiency
Initially, the agent was thought to be Haemophilus influenzae suis, now known to be Haemophilus parasuis.1,2 Now recognized as one species, it is, however, extremely pleomorphic. There were many serovars, reported first in 19523 and many of these were incorporated into a modified classification4 of 15 major serotypes. H. parasuis, together with other Haemophilus spp. has an affinity for the mucosa5 of the oropharyngeal and upper respiratory tract.5-7 H. parasuis can be isolated from the nasal cavity,8 tonsillar area,9 and trachea.10 It may be a true commensal in the upper respiratory tract.7 Responsible for a severe polyserositis in young pigs, it may also occasionally cause an arthritis in older pigs and the individual sow. The organism, like the others with a similar name, Actinobacillus suis and Streptococcus suis, has been called one of the ‘suis-cides’ of pigs, which are responsible for considerable economic loss in high-health herds and herds that practice very early weaning.11 H. parasuis is also commonly isolated from lungs with lesions of enzootic pneumonia.12-16
Although the disease occurs worldwide, reports used to be rare and mainly from Europe. However, since the onset of separate site production, and the occurrence of porcine reproductive and respiratory syndrome, virulent forms of swine influenza and PCV2-associated diseases the disease (H. parasuis) has become one of the most common of the so-called secondary infections. It is a significant contributor to the porcine respiratory disease complex. In naive or specific-pathogen-free herds when it first occurs it may be a common cause of sudden death and cases may be numerous. It also under these circumstances affects younger animals. When the disease becomes endemic it may affect older animals with less sudden death but more chronic polyserositis. The disease has also been observed in Australia, the USA,17,18 Canada,19 and the UK. The disease accounted for less than 1% of total mortalities of pigs submitted to veterinary diagnostic laboratories over an 11-year period in Ontario.19 However, the disease was the second most common cause of mortality in test station boars. In a survey of 19 excellent specific-pathogen-free pig herds, 16 were positive and the average number of culture-positive pigs per herd was 6/10 for positive herds.19
It is probably spread by aerosol and certainly by nose-to-nose contact.
The disease occurs as sporadic outbreaks – usually in weanling to 4-month-old pigs that have been recently chilled, transported, weaned or moved to different pens. The onset is sudden, with several pigs in the group affected, and occurs within 2–7 days of the initiating stress. Occasionally, it causes arthritis in older animals, or even sow herds. The case-fatality rate is high in untreated pigs. Acute myositis in primary specific-pathogen-free sows has been associated with H. parasuis.20
Little is known of the method of transmission of the disease. The causative organisms are facultative pathogens and can be frequently isolated from pig lungs diseased from other causes, even though they are generally not present in normal lungs. It is probable that a respiratory carrier state does exist and that invasion with subsequent septicemia and polyserositis is initiated by stress situations in young pigs that have lost maternal immunity but have not yet gained active immunity. Piglets probably acquire the infection soon after birth but maternal antibody protects them from clinical disease until they are 2–4 weeks of age. Animals that are weaned early are likely to have this infection so the supposition is that most pigs acquire the infection at or immediately after birth. H. parasuis has been found in the tonsil using IHC and EM.8
There are several pathogenic serovars of H. parasuis.2,8 Serotypes 3, 6, 7, 8, 9, and 11 are considered to be avirulent, 15 more pathogenic and 1, 4, 5, 10, 12, 13, and 14 virulent.21 However this pattern cannot be considered permanent as genes can be shared and in any case up to 50% of isolations are considered nontypeable. In the USA and Canada 15.2% were classified as untypeable,2 26.2% in Germany,22 29.3% in Spain,23 and 41.9% in Australia.24 In a particular pig herd, many strains can be isolated but, in most cases, one or two strains predominate.25 In many herds the untypable outnumber the typable. Of seven reference strains examined, only serotypes 1 and 5 were pathogenic26 and the seven strains have common antigenic determinants. Within specific-pathogen-free herds, many herds have common strains; no strains are common to both conventional and specific-pathogen-free herds, which is a reflection of little or no movement of pigs between these types of herd. Specific-pathogen-free pigs are often free of this organism and are highly susceptible to the infection even at several months of age if they are mixed with conventionally raised pigs that may be infected. Outbreaks with rapid spread and high mortality have been reported in specific-pathogen-free pigs.27 It has been suggested that the causative bacteria are common in most herds and that the disease arises only when pigs from uninfected herds are introduced to a contaminated environment, especially if they have been exposed to environmental stress during transport. When infection is introduced into a previously noninfected herd the disease may act as a contagious disease until herd immunity is developed or the infection eliminated. Recently, it has been suggested that the nasal cavity strains may be nonpathogenic and form a completely different population to the pathogenic strains.25 Serotypes from nasal and tracheal cultures were shown to be similar in one study.28 They found that there was a lower level of colonization in the litters of the young sows. The genetic diversity of the strains is not well understood.29 Several serotypes may be isolated from the same herd or even from the same pig.
One of the key factors may be that maternal antibody does not last a long time and may be gone by 2–4 weeks of age but will last until 6–8 weeks if sow antibody titers are high. It is the animals that become infected after their maternal protection has waned that have resulting clinical disease. Serovar 5 is highly virulent when inoculated into specific-pathogen-free piglets 6–8 weeks of age.30 Bordetella bronchiseptica increases H. parasuis colonization of the nasal cavity.31 However, it is also said that previous infection with PRRSV has no effect on the occurrence.32 The severity of the disease increases with the increase in the dose of the organisms.33
The precise relationship between protein patterns, serovars, and virulence potential remains to be defined.34 A new technique called differential display reverse transcription PCR (RT-PCR) has been used to search for virulence factors.35 The pathogenic H. parasuis may have an outer membrane protein, fimbriae and lipopolysaccharides and a cytotoxin has yet to be described but may be a membrane neuraminidase.36 The outer membrane protein may be iron-regulated and appear to have similar outer-membrane protein profiles.37 A fibrinous meningitis, polyserositis and polyarthritis are typical. A fatal septicemia can occur spontaneously or following the intraperitoneal inoculation of pigs with H. parasuis. The intranasal inoculation of H. parasuis into cesarean-derived colostrum-deprived pigs results in a suppurative rhinitis, which may represent an initial event in the pathogenesis of the systemic infection in pigs.5 After infection with H. parasuis there is a highly significant rise in radical formation and monocyte proliferation was reduced. Neutrophils reacted inconsistently.38 In this experimental study the CD25+ marker cells were markedly reduced. Experimental infections39 showed that not all field isolates are pathogenic and it may be that route of infection and dosage are most important in determining the outcome of infections. In a new study, polyacramide gel electrophoresis (PAGE) typing of H. parasuis and virulence potential based on site were looked at together.40 PAGE group I had 83.4% of the isolates from the upper respiratory tract (these were mostly of serotype 3 or untypable) but of the PAGE group II isolates 90.7% of all the isolates were from the systemic sites (these are mostly serotypes 1, 2, 4, 5, 12, or 14). It may be that there is also a tropism for some of the sites in that some strains are only found in the brain and others in the pericardium.41 This means that the systemic sites are the best sites for the identification of pathogenic H. parasuis.
Most practitioners have the opinion that the problem is more apparent when there is predisposing viral infection, particularly PRRS, swine influenza, or PCV2. Although most practitioners would say that the prevalence of PRRS-associated H. parasuis infections have increased the natural occurrence of H. parasuis, experimental confirmation is lacking.32,42 Only PRRS consistently increased the isolation of H. parasuis from the lung.43
On the other hand, both PRRS and B. bronchiseptica increase the colonization of the upper respiratory tract by H. parasuis. There is no additive effect here. There is no doubt that the occurrence of the vasculitis plays a part in the pathogenesis.
In the naive herd and where specific-pathogen-free animals have entered commercial herds, sudden death may be the only feature. Some people are of the opinion that there may be polyserositic, arthritic, and meningitic forms.
The onset is sudden, with a fever, an unusual rapid, shallow dyspnea with noisy lung fields, an anxious expression, extension of the head, and mouth-breathing. There may be a serous nasal discharge and coughing may occur. Depression and anorexia are observed. The animals are very lame, stand on their toes, and move with a short, shuffling gait. All the joints are swollen and painful on palpation and fluid swelling of the tendon sheaths may also be clinically evident. In many animals there may be just a single joint affected and that is often the hock. A red to blue discoloration of the skin appears near death. Most cases die 2–5 days after the onset of illness. Animals that survive the acute stage of the disease may develop chronic arthritis, and some cases of intestinal obstruction caused by peritoneal adhesions occur. Meningitis occurs in some pigs, particularly when these are naive or where there is an acute onset, and is manifested by muscle tremor, paralysis and convulsions. Although Glasser’s disease can occur in pigs of any age, weanling pigs are most commonly and most seriously affected. In chronic cases, pigs may lose part of an ear as a result of ischemic necrosis. There may be also wasting piglets who fade and die.
Another type of syndrome of necrosis of the masseter muscles was described44 in which sows had swollen, cyanotic heads with H. parasuis isolated from the affected muscles. Purulent rhinitis has also been described.45,46
The disease is essentially a polyserositis and arthritis and as a result the organism is recoverable from joint fluid and pleural exudate. Material aspirated from joints may be serous, fibrinous, or purulent. It may just be a few fibrin tags that have organized from an initial fibrinous exudate. The disease can be diagnosed serologically on the presence of precipitins in the serum of recovered pigs, and complement-fixing antibody can be detected following infection. But these are not reliable methods. In an experiment where 183 specific-pathogen-free pigs were given infections, the hemoglobin concentrations and hematocrit fell.47 Leukopenia developed 1–2 days after infection, with leukocytosis later. Any changes in the cerebrospinal fluid were not related to the clinical signs. One of the common findings in H. parasuis infections is vitamin E deficiency, and this is most likely to be as a result of the toxic oxygen radical damage.
In the main, Glasser’s disease is associated with three main lesions: fibrinous polyserositis and arthritis, signs of septicemia, toxemia and in some cases no gross lesions at all.
In some cases all that is seen is a small amount of peritoneal fluid or a very thin fibrin strand (tag).
A serofibrinous or fibrinous pleuritis, pericarditis and peritonitis are usually present but the exudate is scanty in some cases. Pneumonia may also be apparent. There is inflammation and edema of the periarticular tissues and the joint cavities contain turbid fluid and flattened, discoid deposits of yellowish green fibrin. A suppurative rhinitis is also possible. A fibrinopurulent meningitis is common. In specific-pathogen-free pigs, the lesions may be minimal and only successful isolation of the organism permits the differentiation of Glasser’s disease from other causes of sudden death. The distinction may be a difficult one because of the fastidious culture requirements of H. parasuis. Eventually, all surfaces are covered with a thick mat of fibrin where the individual organs may be difficult to recognize. This eventually becomes fibrotic. The spleen and liver may be enlarged.
Histologically, acutely affected serosal surfaces are thickened by neutrophils entrapped in a matrix of fibrin. As these lesions age, fibrous adhesions may develop and lead to chronic pleuritis, arthritis and pericarditis. Such cases are often culture-negative, even when selective media are used. Most isolates are made from the lungs.
The collection of samples from animals that have been dead for several hours is not worth considering even at the best of times and certainly not when H. parasuis is suspected. An acutely affected live pig, freshly autopsied, will give much better results, especially if there is no overheating of the carcass postmortem or subsequent cooling, as the organism is temperature-sensitive. Transport media to the laboratory will also be beneficial in recovery rates. It is said that culture of the nasal swabs will be as rewarding as collecting tracheal swabs but it is likely that the larynx and below is normally sterile. What you isolate from the nasal cavity may then be a commensal population of largely nontypable species, whereas the trachea harbors the pathogenic forms. Other authors say that they are the same serotypes.28 These authors have also found that a lower level of colonization was found in the litters of young sows, and a low level of colonization at weaning probably predisposed pigs to clinical disease in the nursery, assuming the presence of a virulent serotype.
Culture swabs from serosal surfaces, including joints and meninges. It is essential to collect samples from areas that are not enclosed in fibrin. Nasal swabs are more easily collected than tracheal but may indicate a different population of H. parasuis.28 It is usually said that it is difficult to isolate from fluids48 but is easier from the lesions. It is necessary to have a fresh pig with no antibiotic therapy. It may also be necessary to use Amies transport medium to preserve H. parasuis on the way to the laboratory.49
H. parasuis is a Gram-negative rod existing as a coccobacillus to long filamentous chains. There is usually a capsule but the expression of this is influenced by culture.2 NAD or V factor is required for growth (chocolate agar or staph streak and then there is satellite growth). The availability of NAD may determine growth capabilities.50,51 After 24–48 hours the colonies are small, translucent and nonhemolytic on chocolate agar.
Formalin-fixed brain, synovial membranes, liver, lung (LM). Immunohistochemistry can be used to show the organisms in the cytoplasm of neutrophils and macrophages in the lungs and in the mononuclear cells in the subscapular and medullary sinuses of the lymph nodes.52 Immunofluorescence was observed on the bronchiolar epithelium in the alveoli and in the lung parenchyma.53
The first improvement in the diagnosis of H. parasuis occurred with the development of an oligonucleotide-specific plate hybridization assay54,55 that could be used on the nasal swabs. The assay detects fewer than 100 cfu/mL in a pure culture and gives a positive result when H. parasuis is present in the ratio of 1:103–104 in a mixed culture. The assay is more sensitive than culture for detection of H. parasuis in nasal swabs.
In-situ hybridization56 will demonstrate a patchy to multifocal distribution of H. parasuis in the lung.
A repetitive-element-based polymerase chain reaction (rep-PCR) has been developed,19,57 which is a technique that compares very favorably with traditional microbiology. The rep-PCR uses repetitive sequences within the bacterial genome to produce strain-specific fingerprints, allowing comparison and differentiation between H. parasuis strains. This enables comparison of these strains and allows the source of virulent strains to be identified.
Another new technique is ERIC-PCR,24 and this is very successful compared with conventional microbiological techniques. Identification and differentiation of H. parasuis using a species-specific PCR with subsequent DNA fingerprinting using the digestion of PCR products using Hind III endonuclease has been described.58 This PCR-RFLP (restriction fragment length polymorphism) enabled eight patterns to be determined for the untypable strains.
Recently, a technique for the computer-based analysis of H. parasuis protein fingerprints has been described that is a considerable improvement on serotyping.40 It was shown59 that there is a high genetic diversity within the serovars. The authors described at least 12 different strains within the type 4 serovar and genetic diversity in the other serotypes as well. Nontypable isolates were divided into 18 genotypes. The major advantage of this technique is that there is no need for isolation, culture, and biochemical identification of the isolates. In addition, all strains can be identified, not just those of certain serotypes.59 At the moment there is no direct demonstration of a linkage between PCR-RFLP, OMP patterns and serotyping and rep-PCR. In a recent study,60 32 strains were grouped into six serovars and 11 genotypes. This led to the hypothesis that H. parasuis strains with a similar distribution of repetitive sequences can express different antigens.
The unusual combination of arthritis, fibrinous serositis, and meningitis is sufficient to make a diagnosis of Glasser’s disease, but differentiation from the many similar disease entities apparently caused by other agents can only be confirmed by bacteriological examination.
The disease may be confused with erysipelas, mycoplasma arthritis, and streptococcal arthritis on clinical examination. Mycoplasmosis is a much milder disease and is manifested principally by the presence of a few unthrifty or lame pigs in the litter just before weaning, rather than an acute outbreak with a high mortality. Differentiation between cases of Glasser’s disease with meningitis and the other diseases of the nervous system in young pigs, especially streptococcal meningitis and Teschen disease, may not be possible without necropsy examination.
Pigs are usually ill with this disease, so parenteral treatment is required first, followed by water medication, as they do not drink as they would usually, before in-feed medication is given when they are beginning to recover.
Treatment with penicillin, trimethoprim– sulfadoxine, or oxytetracycline is effective in the early stages of the disease.61
Resistance has been reported for penicillin62 and numbers of strains are resistant to tetracyclines, erythromycin, and other aminoglycosides. Tilmicosin can be used for effective treatment63,64 as it is concentrated in the macrophages and neutrophils.65 These can migrate to the site of infection and therefore there may be higher levels of antibody in the tissue.66
Medication of the water supply for several days may also be effective.
Control is only possible if there is (1) diagnosis of infection, (2) identification of prevalent strains, (3) use of autogenous vaccines, and (4) management of new strains.67
Avoidance of undue exposure to adverse environmental conditions at weaning is recommended. Prophylactic dosing at the time of shipping or medication of feed or drinking water on arrival with the above-mentioned drugs may be of value in preventing outbreaks. Feeding a mixture of 3% sulfamonomethoxine and 1% trimethoprim at 160 and 240 ppm for 5 days and challenging with H. parasuis at 3 days prevented clinical disease and bacteria were not recovered.68
Maternal antibody does not interfere with vaccination of pigs at 1–3 weeks of age.69
A formalin-killed bacterin administered before weaning with two injections at 5 and 7 weeks of age has proved highly effective in preventing the disease.70 A formalin-killed whole-cell culture bacterin developed in Ontario is effective in protecting 4-week-old pigs against experimental challenge with the organism.71-73 A recent trial74,75 showed that vaccinating sows at 80 and 95 days of pregnancy with a commercial bacterin containing H. parasuis 2, 3, and 5 was useful in reducing pneumonic lesions and arthritic joint changes in subsequently challenged piglets. Vaccination of piglets seem to have no effect. The vaccination of the sows seemed to have no effect on the colonization of the nasal mucosa by the H. parasuis, nor on the timing.28
Autogenous vaccines against homologous strains have been shown to work69,72,73 but vaccination failures do occur.1 There may be little cross-protection between strains.2,72,76
A new serotype 5 vaccination was described70 and the subsequent challenge with serotypes 1, 12, 13, and 14 produced different responses in control pigs.
Vaccination has three important components.77 First, there is the decision of commercial or autogenous vaccination and this depends on the strains in the field and whether they are in the commercial vaccine. Second, the timing of vaccination should take into account the length of persistence of maternal antibody and the peak of piglet mortality. If this peak is at 2–3 weeks then the sows should be vaccinated. The piglets should then be vaccinated at weaning and 2 weeks later. Third, since sow and piglet vaccination together is not recommended, as the sow’s vaccination can produce maternal antibody that interferes with the piglet’s active immunity, you should make a choice of one or the other.
Recently, the technique of introducing known populations of live H. parasuis to the young piglet shortly after birth, thus allowing a slow rate of acquisition of organisms, has been advocated.33,59,78
All-in/all-out by age is absolutely essential to prevent carry-over of infection and it is likely that nose-to-nose transmission is important, so solid partitions between different litters may help.
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