Chlamydial infections
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 and 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
polymerase chain reaction (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 ELISA for the diagnosis of avian chlamydial infection.
NEXT: C. psittaci
typing
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