Chlamydophila pecorum: Laboratory diagnosis
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 in culture,
it may again revert to a more obvious cytopathic infection
(Philips and Clarkson, 1995).
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).
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 possibility for the development of improved diagnostic tests (Everett et al.,
1999; Magnino et al., 2000).
NEXT: C.
pecorum: Typing
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