an epidemiological study of listeriosis in dairy cattle

pasteurisation contamination can occur at the processing plants or retailers (Kozak and
others 1996, Fenlon and others 1996) and outbreaks of Listeriosis due to a such
contamination have been reported (Linnan and other 1988, Dalton and others 1997).
These findings reflect the fact that L. monocytogenes is an environmental
organism with a broad distribution. People are exposed mainly through the oral route
and bacteria are possibly ingested at low dosages daily. The Figure 1. 3. shows the
current understanding of potential ways of transmission for Listeriosis in people.
d) Carrier status: L. monocytogenes is thought to be a normal inhabitant of the
intestinal tract of people. The proportion of human carriers varies from 0.5% to 91.7%
(Ralovich 1987). At any one time, between 5% to 10% of normal healthy population
excrete L. monocytogenes in their faeces (Farber and Paterkins 1991).
Faeces Insects
harvesting, handling
processing
Sewage environment
Animals Water Vegetables People
Plants silage, feed meat, milk, eggs
Soil (cross contamination)
Figure 1. 3. Potential pathways of L. monocytogenes transmission to people (after
Beuchat, 1996)
e) Infectious dose: The number of L. monocytogenes required to cause illness depends
on many factors, the most important appears to be the host’s susceptibility and
genetically determined and phenotypically expressed properties of the pathogen. The
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