an epidemiological study of listeriosis in dairy cattle

Bacterial culture is widely used for the diagnosis of Listeriosis along with other
tests. Several selective and non-selective culture media have been developed for
detecting L. monocytogenes in food (Curtis and others 1995) and these have been used
for isolating L. monocytogenes from clinical specimens (Gray and others 1948, Gray
and Killinger 1966, Eld and others 1993). However, the value of bacteriological culture
is disputable, because isolation of L. monocytogenes from clinical specimens does not
necessarily reflect disease due to the fact that successful isolation from brain and faeces
of healthy animals have been reported (Gronstol 1980b, Husu 1990).
Histopathologic examination of organs, especially brains, of Listeria infected
cases is currently the most reliable method for diagnosis of listeric encephalitis.
Immunocytochemical techniques (peroxidase-antiperoxidase) using polyclonal
sera (Domingo and others 1986, Marco and others 1988, Johnson and others 1995) have
been used and compared with bacterial culture methods in the veterinary field. Johnson
and others (1995) have reported the superiority of this technique over bacterial culture
but the use of polyclonal anti-sera must be regarded with caution because of cross-
reaction with other Gram positive organisms (Low and Donachie 1997). McLauchlin
and colleagues (1989) have used this technique using monoclonal sera in diagnosis of
listeriosis in people, but this is not used in the veterinary field. An immunofluoroscent
test using polyclonal anti-sera has also been used for diagnosis (Eveland 1963) but this
test faces the same problems associated with polyclonal anti - sera.
Serological tests are the only tools that can be used to detect L. monocytogenes
infection or traces of infection in live animals. Complement fixation, agglutination,
haemagglutination and precipitation tests (Gray and Killinger 1966) have been used but
lack the predictive value needed for diagnostic use. These tests employ either crude
cells or somatic (O) and flagellar (H) antigen. These antigens have been proved to cross
react with other Gram positive bacteria such as streptococci, staphylococci and
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