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Chlamydiosis (Psittacosis, Ornithosis)

By: Dr. Branson Ritchie

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Diagnosis In-depth

Your veterinarian may use radiographs (X-rays) or changes in the types of blood cells (CBC) or enzymes found in the blood (blood chemistry) to evaluate the overall health status of a sick bird. Results of these tests may raise the index of suspicion that chlamydia may be involved in the disease process.


The most common radiographic changes associated with chlamydiosis include an enlarged liver, enlarged spleen and inflammation of the air sacs. However, all of these changes can also occur from other causes.

Complete Blood Count

The most common changes in the blood are a substantial increase in the number of white blood cells, particularly heterophils and monocytes. A decrease in the number of red blood cells (anemia) is common in birds with chronic forms of the disease.

Serum Biochemistry Profile

The most common change is an increase in liver enzyme activity. All of these blood changes can also occur from other causes. Therefore, specialized testing of swabs from the choana and feces, whole blood and/or serum, will be necessary to determine if an active chlamydial infection is present.

  • Confirming an active case of chlamydiosis is best achieved by combining tests that detect antibodies against the organism with tests that demonstrate that chlamydia, or pieces of the chlamydia organism, are present in a sample. Currently available antibody assays include complement fixation, elementary body agglutination and indirect fluorescent antibody. Tests to detect the presence of the organism in living birds include culture, ELISA and DNA probe-based assays (PCR).

  • Tests like culture and DNA probe-based assays are most valuable in birds with suggestive clinical signs, since these birds are most likely to be shedding chlamydia from the respiratory and/or gastrointestinal tract. Culture remains the gold standard for documenting the presence of chlamydia in a clinical sample. However, culture is problematic, time consuming and expensive in comparison to other tests. Samples for culture should be refrigerated but not frozen. Because the quantity of chlamydia shed by an actively infected bird appears to vary from day to day, collecting a pooled sample of excrement for 3 to 5 days may improve the sensitivity of culture. During the pooling process, the samples should be kept in a sealed container in a refrigerator that is not used to store food. If a swab for DNA probe-based testing or culture is not slimy after sampling the choana and not coated with excrement after sampling the feces, then it is a poor quality sample.

  • Tests that detect antibodies to chlamydia are best for determining if birds have previously been infected. A single positive antibody titer only indicates that a bird was infected with C. psittaci in its immunologic definable past, but it does not indicate that a bird is actively infected. Currently, antibody tests can only be used to confirm an active infection if there is a significant increase in the antibody titer in serum samples that are collected several weeks apart and tested with the same type of assay.

  • Antibody tests are of least value during the earliest phases of an infection when a bird might be clinically ill, shedding the organism, but antibody negative. Additionally, early treatment with antibiotics may alter the normal immune response and thus cause false negative or lower than expected antibody results.

  • A positive result from a DNA probe-based assay is more likely to be the result of an active infection with Chlamydia.

  • Currently, there is no test that can be used to confirm that a bird does not have chlamydia. However, a lack of detectable antibodies in serum coupled with an inability to detect the organism at a portal of exit provides supportive evidence. To find an avian veterinarian in your area that can test for chlamydia, contact the Infectious Disease Laboratory at the University of Georgia College of Veterinary Medicine (706-542-8092).

    Therapy In-depth

  • Because C. psittaci can infect humans and occasionally cause disease, many states require that confirmed cases must be reported to local health officials. The requirements for what constitutes a confirmed diagnosis vary from state to state. Once the disease has been reported, a state official may dictate the treatment protocol or may leave treatment to the discretion of your veterinarian. If given a choice, your veterinarian will use doxycycline to treat your bird for chlamydiosis. Other therapies that may be needed include fluids to correct dehydration and supportive nutrition if the bird has not eaten for several days or has lost considerable weight.

  • Depending on ease of administration, your veterinarian may suggest an injectable or oral form of doxycycline. The injectable preparation is given in the muscle once each week. The oral medication is administered several times a day. If a large number of birds must be treated, your veterinarian is likely to suggest adding doxycycline to a specially prepared mixture of rice, beans and corn. Research conducted at North Carolina State University suggests that doxycycline will reach therapeutic blood levels when added to the drinking water of some birds. Irrespective of the route of administration, your veterinarian will probably recommend that treatment continue for 45 days.

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