Avian chlamydiosis is a disease of pet birds, poultry, and wild birds caused by Chlamydophilia psittaci (formerly Chlamydia psittaci). In psittacine birds (parrots, parakeets, cockatoos, macaws, etc) and humans, avian chlamydiosis is also referred to as psittacosis. In other avian species, it is sometimes called ornithosis.
C. psittaci is an obligate intracellular organism that is endemic worldwide. The organism is well adapted to avian hosts and rarely causes clinical signs of pathologic lesions. Clinical disease is usually the result of exposure to new strains, poor husbandry, overcrowding, poor nutrition, or concurrent disease. Therefore, chlamydiosis is a common and important disease in pet bird medicine and in flock medicine.
Chlamydophila has a biphasic life cycle and exists as elementary and reticulate bodies. Elementary bodies are infectious, non-replicating particles that exist outside the body. Reticulate bodies, metabolically active particles that replicate by binary fission, form from elementary bodies that have entered epithelial cells. Rapid growth of the chlamydial organisms in the infected cells causes formation of multiple micro-colonies or intracytoplasmic inclusion bodies. Reticulate bodies then condense into elementary bodies, which may be released after cell lysis. Released elementary bodies may infect other host cells or may be released into the environment. Elementary bodies were found in feather dust, feces, urine, saliva and ocular, nasal and respiratory secretions. New hosts are commonly infected when elementary bodies are aerosolized and ingested or inhaled. Nestling birds may be infected during feeding, and vertical transmission has been documented. Manifestation of chlamydiosis in birds is variable, ranging from asymptomatic to sudden death. Asymptomatic infections are common and birds may shed the organism for several months without exhibiting clinical disease. Persistent infections in carrier birds may be latent for years before a stressful episode leads to the emergence of clinical signs and shedding of the organism. Most acute outbreaks and deaths are in young birds exposed to high doses of a virulent strain.
When clinical signs occur in birds, they include yellow-to-greenish or watery gray droppings, weight loss, dehydration, lethargy, and ruffled feathers. Keratoconjunctivitis, rhinitis, sinusitis, dyspnea and, occasionally, CNS signs may also be seen. None of the aforementioned signs are pathognomonic, making a diagnosis of chlamydiosis somewhat difficult.
To aid the clinician in diagnosis, various diagnostic tests are available, each with their own benefits and drawbacks. It is important to remember that samples for testing should be taken prior to initiating therapy with antichlamydial antibiotics (tetracyclines, macrolides, fluoroquinolones, and chloramphenicol). These drugs may interfere with diagnostic tests by reducing antibody production, antigen shedding, and Chlamydophila viability.
A definitive diagnosis of Chlamydophila psittaci in the avian patient is usually obtained by isolation and identification of the organism in culture or by demonstrating a four-fold rise in antibody titer to chlamydial group antigens. Because organisms are intermittently shed, the best opportunity for isolation and identification in a live patient is serial fecal samples or combined choanal/cloacal culture collected for 3 to 5 consecutive days and pooled in transport media supplied by the Avian Section of the ADDL. For postmortem diagnosis, a portion of the following tissues (approximately 1 gram each) should be collected aseptically for bacterial culture, packaged individually, and refrigerated: lung, liver, spleen, kidney and intestine. Alternatively, a dead bird may be submitted for necropsy by wetting the carcass with soapy water, wrapping it in wet paper, and placing it in a plastic bag. It is best to keep the sample refrigerated until submitted. Only freeze the dead bird if it cannot be submitted to the ADDL within 48 hours after death.
Serologic testing for chlamydiosis can be used for diagnostic evaluation in ill birds or for screening purposes. It does not detect carriers. The two serologic assays currently being used are complement fixation (CF) and elementary body agglutination (EBA). CF detects anti-Chlamydophila IgG, while EBA detects anti-Chlamydophila IgM. Recently infected birds are expected to be EBA positive initially and then, approximately one week later, to be CF positive. Reportedly, CF titers remain detectable as long as an infection persists. After birds are treated, EBA and CF titers usually become negative, although reports exist of CF titers remaining elevated in appropriately treated birds. Although serologic testing for chlamydiosis is not performed at the ADDL, serum samples may be submitted and will be forwarded to an appropriate laboratory by ADDL personnel.
ELISA testing may also aid in the diagnosis of chlamydiosis. As with isolation and identification testing, however, ELISA may be unreliable due to intermittent shedding of the organism. For ELISA testing, a choanal and/or cloacal swab should be submitted to the ADDL.
Other diagnostics that are infrequently used include PCR and tests to detect ribosomal RNA (rRNA) and/or ompA gene from the family Chlamydiaceae. PCR can be performed on blood samples or from a choanal/cloacal swab. Although very sensitive, PCR is not very specific, and a positive result may only indicate environmental exposure and not true infection. Tests for rRNA or ompA will show the presence of replicating C. psittaci organisms and is not currently widely available.
When examining or collecting samples from a bird that potentially has chlamydiosis, every precaution should be taken to avoid self-infection. Psittacosis is a zoonotic and highly contagious disease. All persons in contact with infected birds, including staff and clients, should be informed about the nature of the disease. Consider wearing protective clothing, gloves, and a respirator if indicated. When performing necropsies, wet the carcass with detergent and water and work under a biologic safety cabinet (or equivalent).
Confirmed diagnoses should be reported to appropriate local and state health officials.
Please call the ADDL with any questions regarding sample collection or diagnostic testing.
-by Sarah Janke, Class of 2004
-edited by Tom Bryan, Avian Diagnostician
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