Updates on disease testing in birds (Proceedings)


Updates on disease testing in birds (Proceedings)

Aug 01, 2011

Bacterial diseases

Chlamydophila psittici

An excellent resource for information on the testing, treatment, zoonotic and legal implications of this disease can be found in the National Association of State Public Health Veterinarians (NASPHV) Psittacosis Compendium ( http://www.nasphv.org/)

Criteria for a confirmed case include the presence of one of the following:

     1) Isolation of organism from clinical specimen
     2) Identification of Chlamydial antigen by immunofluorescence of the bird's tissue.
     3) ≥ 4-fold change in serologic titer in 2 specimens from the bird obtained at least 2 weeks apart and assayed simultaneously at the same lab
     4) Identification of the organism within macrophages in smears of the tissue stained with Gimenez or Macchiavello stain.

Antibody tests for Chlamydophila indicate exposure to the organism with host immune response, not necessarily current infection.

Additional facts from this publication include:

     - Use of a combination of culture, antibody-detection and antigen-detection methods is recommended, particularly when only one bird is tested.
     - Although there is no epidemiologic evidence of increased disease risk to young, elderly, or immunocompromised humans, more rigorous testing should be considered for birds in contact with these individuals.
     - Consultation with an experienced avian veterinarian may help when selecting tests and interpreting results.
     - Because proper sample collection techniques and handling are critical to obtain accurate test results, clinical laboratories should be contacted for specifics on specimen submission.

Diagnostic methods for Chlamydophila include:

     1) Gross pathology – although cloudy air sacs and enlargement of the liver and spleen may be observed, no specific gross lesion is pathognomonic.
     2) Histopathology - Chromatic or immunologic staining of tissue or impression smears can be used to identify organisms in necropsy and biopsy specimens.
     3) Culture
          a. Live birds - with suggestive clinical signs of Chlamydiosis, a combined conjunctival, choanal and cloacal swab specimen or liver biopsy specimen is recommended
          b. Necropsy specimens - liver and spleen are the preferred sources for culture.
          c. If feces are chosen as a site for attempted detection of C. psittaci, serial fecal specimens should be collected for 3 to 5 consecutive days and pooled for submission as a single sample. NOTE: The diagnostic laboratory should be contacted for specific procedures required for collection and submission of specimens. The proper handling of specimens is critical for maintaining the viability of organisms for culture, and a special transport medium is required. Following collection, specimens should be refrigerated and sent to the laboratory packed in ice but not frozen.

Antibody tests

A positive serologic test result is evidence that the bird has been infected by Chlamydiaceae, but it might not indicate that the bird has an active infection. False-negative results can occur in birds that have acute infection when specimens are collected before seroconversion. Treatment with an antimicrobial agent can diminish the antibody response. However, IgG titers may persist following successful treatment. When specimens are obtained from a single bird, serologic testing is most useful when signs of disease and the history of the flock or aviary are considered and serologic results are compared with white blood cell counts and serum liver enzymes. A fourfold or greater increase in the titer of paired samples or a combination of a titer and antigen identification is needed to confirm a diagnosis of avian Chlamydiosis

          - Elementary-body agglutination (EBA) - The elementary body is the infectious form of C. psittaci. Elementary-body agglutination is commercially available and detects IgM antibodies, an indication of early infection. Titers greater than 10 in budgerigars, cockatiels, and lovebirds and titers greater than 20 in larger birds are frequently detected in cases of recent infection. However, increased titers can persist after treatment is completed.
          - Indirect Fluorescent Antibody Test (IFA) - Polyclonal secondary antibody is used to detect host antibodies (primarily IgG). Sensitivity and specificity varies with the immunoreactivity of the polyclonal antibody to various avian species. Low titers may occur because of non-specific reactivity.
          - Complement fixation (CF) - Direct CF is more sensitive than agglutination methods. False-negative results are possible in specimens from parakeets, young African gray parrots, and lovebirds. High titers can persist after treatment and complicate interpretation of subsequent tests. Modified direct CF is more sensitive than direct CF.