M. Wiedmann et al., INVESTIGATION OF A LISTERIOSIS EPIZOOTIC IN SHEEP IN NEW-YORK-STATE, American journal of veterinary research, 58(7), 1997, pp. 733-737
Objective-To investigate potential sources of an epizootic of listeria
l encephalitis, using molecular diagnostic and typing methods. Sample
Population-A flock of about 655 sheep. Procedure-An epizootiologic inv
estigation was performed. Clinical, feed, and environmental samples we
re tested for Listeria monocytogenes, using polymerase chain reaction
and culture methods; recovered isolates were ''fingerprinted,'' using
an automated ribotyping system. Results-Listeria monocytogenes was rec
overed from brain specimens of 7 sheep with clinical signs of listeria
l encephalitis, All clinical isolates had fingerprints identical to th
ose of isolates from farm equipment used to transport silage. Corn sil
age, which was not fed to the sheep, also contained L monocytogenes of
the same pattern type as defined by ribotyping. Listeria monocytogene
s was not isolated from the stored haylage designated for feeding the
sheep (the cut-off point for isolation being < 10(2) colony-forming un
its/g). Conclusions-Corn silage was implicated as the source of a list
eriosis epizootic. it appears to have cross-contaminated the haylage d
estined for the sheep during handling with a front-end loader, Suspens
ion of silage feeding coincided with cessation of listeriosis cases. C
linical Relevance-Use of advanced molecular techniques can help to ide
ntify the sources and restrict the scope of an epizootic. In epizootic
s, a single L monocytogenes strain can lead to infection of multiple a
nimals, with rapid progression of the disease.