Chlamydial infections in birds

Chlamydophila psittaci

Diagnosis

Clinical examination of an affected bird, its history and other factors may permit speculative diagnosis. However, confirmation of chlamydial infection requires laboratory investigations. Serological tests, such as the complement fixation test, are not widely used for testing avian sera. During the acute phase of infection antibody activity may not be readily detected. A latex agglutination test (Moore et al., 1991) capable of detecting IgM antibody has been used to demonstrate likely current chlamydial infection. However, many chlamydial infections in avian species are sub-acute or chronic and thus produce a more IgG-biased host response. Furthermore even after antibiotic treatment, "cured" birds may retain moderate to high antibody titres by the complement fixation test. Antibody detection tests for avian chlamydiosis are more suited to epidemiological studies than for the diagnosis of infection in individual birds VanRompay et al., 1995.

Confirmation of chlamydial infection can be obtained by isolation and/or identification of C. psittaci. Isolation of these chlamydiae from organs, faecal samples or swabs can be achieved in several tissue culture lines (such as Vero, McCoy or Buffalo Green Monkey) or in fertile chicken eggs. Treatment of samples with combinations of gentamicin® vancomycin® and nystatin® can reduce contamination by other microorganisms. However, the success of isolation depends on the maintenance of a cold chain for collected specimens. A negative culture result is not an absolute indication that a bird is not carrying a chlamydial infection, as the agent may be intermittently shed in the faeces. In cell culture, the characteristic chlamydial inclusions can be identified by a number of staining techniques including Giemsa or methylene blue stains or by immunofluorescence.

A variety of methods are available to identify chlamydiae directly without the need for tissue culture. Such methods include electron microscopy (Grimes & Clark, 1996), direct inmunofluorescence (VanRompay et al., 1994) and antigen detection tests (Thiele et al., 1992; VanRompay et al., 1994; Hewinson et al., 1997). However, with antigen detection tests problems of specificity may be encountered, particularly with avian faecal samples. A PCR test to detect chlamydial DNA in faecal samples from budgerigars has been described (Takashima et al., 1996). PCR tests may be performed routinely to detect C. psittaci DNA in avian clinical samples, including faeces and tissues, but these tests are not yet available commercially. One such in-house PCR test reported by Hewinson et al., 1991; 1997 performed as well as isolation in tissue culture and better than antigen detection EIA for the diagnosis of avian chlamydial infection.

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Topic revision: r3 - 2011-04-02 - MeWard
 
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