an epidemiological study of listeriosis in dairy cattle

first description, it was only 1980s that L. monocytogenes infection achieved
prominence as a food borne disease (Farber and Peterkins 1991, McLauchlin 1996).
Most cases of clinical listeriosis appears to be sporadic but epidemics have also been
reported in recent years. The annual endemic rates have been reported to be between 2
and 15 cases per million (Farber and Peterkins 1991). The current incidence of clinical
Listeriosis is about 2-3 cases per million per annum in England and Wales with case
fatality rates being between 20 and 40% (McLauchlin 1996). In England and Wales
there was a dramatic increase in the number of cases reported in people in the 1980s
which coincided with an increase in animal Listeriosis reported by Veterinary
Investigation Centre (VIC), in other human disease caused by intestinal pathogens and
use of untreated human sewage sludge and animal slurry on agricultural land
(McLauchlin 1987). A decline in the number of cases has been observed since 1990.
This may be due to improved control measures associated with developments in
isolation and typing methods or increasing public awareness.
b) Risk factors: Listeriosis in people is believed to be a disease of those whose immune
system is suppressed. However, a recent outbreak in the USA has shown that L.
monocytogenes could equally be a potential health problem for immuncompetent
individuals (Dalton and others 1997). Several predisposing factors have been identified
to be associated with the occurrence of clinical Listeriosis. Extremes of age, pregnancy,
malignancy, immunsuppression (HIV infection, organ transplantation) are the major
risk factors (Lorber 1990, Farber and Peterkins 1991, Rocourt 1996).
c) Transmission: The route of transmission of Listeriosis has long been the subject of
debate. Direct contact with infected animals has been shown to be one way of
transmission for the cutaneous form of Listeriosis. 10 cases have been reported in the
UK and 7 cases in the rest of the world (McLauchlin and Low 1994, McLauchlin 1996).
Hospital cross infections during the neonatal period have been reported on 29 occasions
38