Chlamydial infection in animals

Chlamydophila pecorum

Laboratory diagnosis

Culture

C. pecorum isolates, particularly those from the intestinal tract, are frequently difficult to isolate in culture, growing initially then dying out on serial passage. Cryptic infections also occur in cell culture, whereby the organism is hard to detect by conventional methods although, following several passages, it may revert to a more obvious cytopathic infection (Philips & Clarkson, 1995).

Serology

Serological detection of C. pecorum agents using the complement fixation screening test is problematic because the organism is very common in ruminants and antibodies to it cross-react with other chlamydiae, particularly C. abortus, with which C. pecorum is often associated. Antibodies to C. pecorum and C. abortus can be distinguised using immunofluorescence (Markey et al., 1993; Griffiths et al., 1996). Jones et al., 1997 have suggested that false seropositivity in field samples for enzootic abortion may be caused by the polyarthritis / conjunctivitis subtype of C. pecorum. Additionally the C. pecorum strains associated with metritis have not yet been fully characterised, but may represent a separate biovar within C. pecorum (Jones, 1999).

Nucleic acid-based

Given the problems of antigenic cross reactions, there is a strong incentive to use DNA-based techniques, where a clear distinction can be made between C. pecorum, C. abortus and other chlamydial species. PCR and other tests have been developed for this purpose (Kaltenboeck et al., 1992; Everett et al., 1999; Magnino et al., 2000). Using this kind of approach, chlamydial strains causing endometritis in cattle in northern Italy were identified (by sequencing the gene encoding the chlamydial major outer membrane protein) as being C. pecorum (Magnino et al., 2000), a method particularly useful for moleulcar epidemiological studies of individual strains. For species identification, analyses based on the rRNA genes offer considerable possibilities for the development of improved diagnostic tests (Everett et al., 1999; Magnino et al., 2000).

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