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an epidemiological study of listeriosis in dairy cattle

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to propagate. The latter may have been the case on the farm D because the “stra<strong>in</strong>”<br />

detected <strong>in</strong> the isolates obta<strong>in</strong>ed from milk samples was detected <strong>in</strong> 2 <strong>of</strong> 5<br />

environmental samples but only <strong>in</strong> 3 <strong>of</strong> 22 <strong>an</strong>imal isolates.<br />

The “stra<strong>in</strong>s” detected <strong>in</strong> bedd<strong>in</strong>g, water, soil <strong>an</strong>d grass were also seen <strong>in</strong> faeces<br />

<strong>an</strong>d grass <strong>an</strong>d maize silage on some farms. This is <strong>in</strong> agreement with the results <strong>of</strong> other<br />

studies (Skovgaar <strong>an</strong>d Morgen 1988, Ueno <strong>an</strong>d others 1995).<br />

This <strong>study</strong> has demonstrated that a large proportion <strong>of</strong> <strong>cattle</strong> c<strong>an</strong> become<br />

<strong>in</strong>fected <strong>an</strong>d shed L. monocytogenes <strong>in</strong> their faeces without <strong>an</strong>y apparent cl<strong>in</strong>ical<br />

symptom. L. monocytogenes was isolated from the liver <strong>of</strong> <strong>an</strong> aborted foetus on farm B<br />

but this isolate was not typed. In spite <strong>of</strong> the <strong>in</strong>conclusive <strong>an</strong>alysis <strong>of</strong> the stra<strong>in</strong>s, it also<br />

suggested that environmental contam<strong>in</strong>ation <strong>an</strong>d <strong>in</strong>fection <strong>of</strong> <strong>an</strong>imals with L.<br />

monocytogenes may have been a cont<strong>in</strong>u<strong>in</strong>g cycle as illustrated <strong>in</strong> the figure 6. 13.<br />

grass<br />

faeces<br />

grass silage<br />

soil maize silage<br />

water<br />

Milk<br />

ANIMAL<br />

bedd<strong>in</strong>g<br />

214

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