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Chlamydiosis, a disease caused by the intracellular bacterium Chlamydia psittaci, is commonly seem in wild and pet birds. Between 1982 and 1991, 1,344 cases of human chlamydiosis were reported to the Center for Disease Control. Of those cases where the source of infection was known, 70% were due to exposure to pet caged birds (Satalowich, et. al.,JAVMA 1993). Veterinarians should be aware of the zoonotic potential of this disease.

The infectious particles of Chlamydia psittaci, called elementary bodies, are shed in feather dust,feces, and lacrimal and nasal secretions.       Elementary   bodies   are approximately 0.3 um in size and survive for long periods outside the body. If aerosolized elementary bodies are inhaled or ingested, they will attach to and penetrate host cells. Once inside the cell, elementary bodies transform into non-infectious reticulate bodies that grow and divide by binary fission.  Often micro-colonies will  form  and  can be  seen microscopically as cellular inclusions, called LCL(Levinthal-Cole-Lillie) bodies.   As the reticulate bodies mature, they transform into the infectious elementary bodies which are released when the cell is lysed.

Clinical signs in birds range from inapparent infections to severe disease and death. Young birds are most susceptible and often appear sick, while adult birds tend only to show clinical disease after periods of stress. Latent infections are possible with clinically normal birds shedding the organism.

The clinical signs caused by Chlamydia psittaci depend on the age, condition, and species of the bird combined with the dose, strain,  and virulence  of the  bacteria. Respiratory and/or gastrointestinal signs are common along with ocular and nasal discharge, conjunctivitis, sinusitis, dyspnea, greenish diarrhea, and emaciation.     Occasionally neurological signs are seen: tremors, seizures, torticollis,        and/or        opisthotonus. Hepatosplenomegaly may be observed on radiographs.   Clinical pathology data may reveal a leukocytosis and elevated liver enzymes.

The gross lesions of chlamydiosis vary and are nonspecific. Hepatomegaly, splenomegaly, and  pneumonia  are  common  findings. Fibrinous   air   sacculitis,   serofibrinouspericarditis, and fibrinous peritonitis may be prominent. Histopathologic lesions are also nonspecific, unless the causative agent is seen. LCL bodies, which stain with Giemsa, Castaneda and Machiavello  stains,  are pathognomonic if seen. Impression smears of liver, spleen, or air sac can be stained to observe LCL bodies. If LCL bodies are present, the diagnosis can be made; but, further diagnostics are necessary if LCL bodies are not observed.

Two diagnostic serology tests are currently available.   A Chlamydia-b\ocking antibody ELISA(BELISA) identifies serum antibodies to the Chlamydia organism.   The antibodies deleted by this method are independent of the bird's shedding status; however, the assay only detects the patient's exposure to the organism, not necessarily a current infection.   False negative test results are frequent in acute infections.    An antigen ELISA test for Chlamydia trachomatis of humans is used to detect Chlamydia psittaci in birds.  Cloacalswabs can be analyzed by this test.  False negatives are possible in samples that contain low numbers of elementary bodies and in samples from birds with latent infections or irregular shedding. False positives are possible if high numbers of cross-reacting bacteria, such as Staphylococcusaureus, are present.

Culture of the organism is the only direct means of identifying Chlamydiapsittaci. Cloacal or fecal specimens can be submitted for culture. Since shedding may be inconsistent, a serial collection for three-five consecutive days is recommended. Culture must be done in a cell line and may take one-two weeks before results are seen.   Post mortem specimens suitable for culture include the liver and the spleen.

All confirmed or suspected cases of chlamydiosis should be reported to the local and/or state health departments. Professionals in these departments will oversee further work-up and treatment. Any person who has been in contact with infected birds should be warned of the zoonotic potential and take appropriate precautions.


Gerlach,H. Chlamydia. In: Hamson and Hamson, Clinical avian medicine and surgery,W.B.Saunders Company, Philadelphia, 1986: 457-463.

Satalowich, FT; Barrett,L; Sinclair, C; Smith, KA; Williams, LP."Compendium of chlamydiosis (psittacosis) control, 1994.National Association of Public Health Veterinarians Inc".Journal of the American Veterinary Medical Association.1993,203: 12,1673-1680.

Timoney,JF;Gillespie,JH; Scott, FW; Barlough,JE. Hagan and Bruner's Microbiology and Infectious Diseases of Domestic Animals, 8th edition. Comstock Publishing Associates, Ithaca, 1988.

Van Buuren,CE;Dorrestein,GM; Van Dijk, JE. "Chlamydia psittaci infections in birds:a review on the pathogenesis and histopathological features". Veterinary Quarterly 1994, 16: 1, 38-41.

- TrinaDuncan, April 1995

- edited by Robert Porter


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