Chlamydiosis

Basic Information

Definition and Infectious Agent

• Psittacosis/ornithosis is a bacterial infection of humans caused by Chlamydophila psittaci. In birds, C. psittaci infection is referred to as avian chlamydiosis. Psittacosis refers to infection in humans transmitted by parrots; ornithosis refers to infection in humans transmitted by other birds. All Chlamydophila species are potential zoonotic pathogens, although C. psittaci is the most important and the best documented.

• The family Chlamydiaceae is divided into two genera:

Genus Chlamydia (C. trachomatis, C. suis, and C. muridarium)

Genus Chlamydophila (C. abortus, C. caviae, C. felis, C. pecorum, C. pneumoniae, and C. psittaci)

• Three new Chlamydophila species were derived from the previously classified Chlamydia psittaci: Chlamydophila abortus, C. caviae, and C. felis. This reclassification is controversial. Both old and new nomenclatures are used in the current literature; however, the latter recently has gained more widespread acceptance.

• Birds

Chlamydophila (formerly Chlamydia) psittaci

• Guinea pigs

Chlamydophila caviae (formerly known as the guinea pig inclusion conjunctivitis [GPIC] strain of C. psittaci)

Synonyms

In humans: psittacosis, ornithosis, chlamydiosis, parrot fever

In animals: avian chlamydiosis, mammalian chlamydiosis, chlamydial conjunctivitis

Epidemiology

Animal Species—Hosts and/or Carriers

• C. psittaci has been identified in 460 avian species from 30 orders.

• Budgerigars and cockatiels appear overrepresented among pet birds. Poultry are also affected, and flock outbreaks can occur.

• C. caviae is specific for guinea pigs.

Modes of Transmission

• Inhalation of elementary bodies (infectious, extracellular form of organism) in contaminated bedding, dust, and dander

• Ingestion of elementary bodies in feces and nasal or ocular secretions

Clinical Presentation of Animals

• Ranges from acute and life threatening to subacute or chronic disease

• Acutely affected birds typically develop conjunctivitis and rhinitis with naso-ocular discharge, variable dyspnea, ruffled feathers, lethargy, anorexia, and biliverdin-stained urates. Diarrhea may also be seen.

• Chronic disease may be associated with wasting and chronic naso-ocular discharge.

• Guinea pigs develop unilateral or bilateral conjunctivitis.

Risk Factors

• For birds

High stocking rates

Stressors such as inclement weather, transport, or other illness

Exposure to wild birds

• For guinea pigs

Unknown; however, stress and poor husbandry may play a role.

Geography and Seasonality

C. psittaci has a worldwide distribution. Prevalence of shedding may increase in summer months.

Pathobiology

• Chlamydiae exist in two forms: an infectious but metabolically inactive elementary body that is relatively stable in the environment, and the metabolically active but noninfectious reticulate body.

• Infection is initiated when the elementary body attaches to susceptible cell membranes. The organism has a predilection for cells of the respiratory and gastrointestinal tracts, serous cavities, and reticuloendothelial system.

• Multiplication of the organism causes cell lysis; this, in conjunction with host immune response, causes the clinical signs and pathologic features of the disease.

• Common pathologic findings include air sacculitis, conjunctivitis, rhinitis, hepatosplenomegaly, perihepatitis, and military necrosis of the parenchymal organs.

Clinical Presentation of Humans

Incidence in Humans

• Typically fewer than 50 cases per year are reported in the United States. Many cases likely remain unreported.

• Prevalence is as high as 15% in caregivers at bird breeding facilities.

• Most cases occur after exposure to infected pet birds, usually cockatiels, parakeets, parrots, and macaws.

Disease Forms/Subtypes

• Flulike syndrome

• Atypical pneumonia

• Septicemia

History, Chief Complaint

C. psittaci

• Association with infected or high-risk animals

• Chief complaints of fever, malaise, headache, and hacking, typically nonproductive, cough

C. caviae

• Conjunctivitis

Physical Findings in Infected Humans

C. psittaci

• Typical: fever, malaise, myalgia, cough, pharyngeal edema, hepatomegaly, and a pink, blanching maculopapular rash

• Complicated: hepatitis, splenomegaly, hemolytic anemia, disseminated intravascular coagulation (DIC), endocarditis, myocarditis, pericarditis, and glomerulonephritis

• Neurologic complications such as hearing loss, cranial nerve palsy, cerebellar symptoms, and confusion can also occur.

C. caviae

• Conjunctivitis

Incubation Period

5 to 15 days

Diagnosis

Differential Diagnosis

C. psittaci

• Interstitial pneumonia due to:

Mycoplasma pneumoniae

Coxiella burnetii

Legionella spp.

Respiratory viruses

C. caviae

• Inclusion conjunctivitis (C. trachomatis)

• Conjunctivitis due to allergy, bacteria, or virus

Birds

• Conjunctivitis/rhinitis: Mycoplasma, Mycobacterium, Cryptosporidium spp., primary bacterial, pigeon herpesvirus, foreign bodies

• Ruffled feathers and wasting: many infectious and noninfectious diseases

Guinea Pigs

• Primary bacterial conjunctivitis, nasolacrimal duct obstruction, dacryocystitis

Initial Database

Humans

• Serologic assay; greater than fourfold increase in complement-fixation (CF) titers

• Positive ELISA or microimmunofluorescence

Birds

• Complete blood count and plasma biochemistry panel: heterophilic leukocytosis often observed with or without a monocytosis; aspartate aminotransferase (AST) and bile acids may be elevated.

• Conjunctival cytologic examination may identify elementary bodies within epithelial or inflammatory cells.

• Radiographic imaging may demonstrate air sac thickening and/or hepatosplenomegaly.

Guinea Pigs

• Conjunctival cytologic examination may identify elementary bodies within epithelial or inflammatory cells.

Advanced or Confirmatory Testing

Humans

• Bacteriologic culture was the historic gold standard; currently used less because of the fastidious nature of the organism and specialized laboratory requirements and cost

• Antigen detection techniques use conjunctival swabs or blood polymerase chain reaction (PCR).

Birds

• Antigen detection techniques such as conjunctival, blood, choanal, or cloacal PCR or chlamydial cell wall antigen ELISA may also be used.

• Serologic assays such as immunofluorescence assay (IFA), enzyme immunoassay (EIA), or ELISA; sensitivity and specificity vary by species and laboratory

• Chronic or immunologic staining methods may be performed to identify intracytoplasmic inclusions of impression smears or histopathologic preparations of clinical or necropsy specimens.

Treatment

• Long-acting (5 to 7 days) doxycycline injections are the mainstay of animal treatment.

• Doxycycline or tetracycline has been used traditionally in humans with psittacosis. Azithromycin has been gaining popularity as treatment for psittacosis in humans.

Prevention

Protective measures include the following:

• When cleaning cages or handling infected birds, caretakers should wear protective clothing, which includes gloves, eyewear, a disposable surgical cap, and an appropriately fitted respirator with N-95 or higher rating.

• When necropsies are performed on potentially infected birds, wet the carcass with detergent and water to prevent aerosolization of infectious particles, and work under a biological safety cabinet or equivalent.

• Isolate newly acquired, ill, or exposed birds from other birds in the household and from noncaregiver humans.

• Avoid purchasing or selling sick birds.

Reporting—Notifiable Disease

• Notification of U.S. federal health authorities is required.

• Notification of state health authorities varies by jurisdiction—contact local public health authorities and state department of agriculture.

Prognosis

• Good with prompt diagnosis and early treatment

• Fair to guarded with delayed diagnosis or disseminated disease

Controversy

Veterinarians may be asked to declare a bird safe for residents of nursing homes or hospitals, or for persons with compromised immunity. Active client education is required, and the veterinarian should have knowledge of screening test sensitivity and specificity.

Pearls & Considerations

Comments

Currently, at least eight serovars and nine genotypes have been described for C. psittaci, which, in the future, may prove to be of importance in the epidemiology of the disease in animals and humans

Client Education

• Avoid purchasing sick birds, especially those with signs characteristic of infection with C. psittaci.

• Use quarantine, maintain high levels of husbandry, and use personal protective equipment as indicated.

• Avoid purchasing guinea pigs with conjunctivitis:

Limit handling of affected guinea pigs.

Quarantine and wear gloves while handling infected animals.

Cross-References to other Sections

Chlamydophila psittaci, Birds

AUTHOR: SIMON R. STARKEY

EDITOR: THOMAS M. DONNELLY