INVESTIGATION OF A LISTERIOSIS EPIZOOTIC IN SHEEP IN NEW-YORK-STATE

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.