an epidemiological study of listeriosis in dairy cattle

infectious dose for the infection in people is not known. From outbreaks and sporadic
cases it can be concluded that the dose varies from 10 2 to 3.4x10 9 with the incubation
period being between less than 24 hours and 23 days (Farber and Peterkins 1991)
f) Control: L. monocytogenes is so widespread that its elimination from our
environment is beyond our technical capacity. But some strict regulations and
management practices such as HACCP (Hazard Analysis Critical Control Points) and
hygiene in processing plants and at home, can be put in place so that L. monocytogenes
does not exceed the level of infectious dose or propagate beyond the host’s ability to
cope with it (Greenwood and others 1991, Farber and Peterkins 1991, Dalton and others
1997).
1. 13 The objectives of this study:
L. monocytogenes has received tremendous attention owing not only to
economic losses and public health concern but also to its use as a model bacterial
pathogen in studying immunology, pathogenesis, behaviour of intracellular pathogens
and their interaction with host. Economic losses due to Listeriosis and L.
monocytogenes have been estimated in some studies. Low and Renton (1985) reported
£5,130 loss due to a single outbreak of Listeriosis in a flock, similarly Nash and
colleagues (1995) estimated that the economic loss would be £6,809 in a Rambouillet
flock after an outbreak with 12% mortality. In countries such as the USA, where “zero
tolerance” policies are applied the loss due to food recall could count for billions of
dollars (Archer 1996). L. monocytogenes infections in people and its consequences are
incalculable. This and the fact that there appears to be a close relationship between
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