Investigation of a listeriosis epizootic in sheep in New York state.
OBJECTIVE
To investigate potential sources of an epizootic of listerial encephalitis, using molecular diagnostic and typing methods.


METHODS
A flock of about 655 sheep.


METHODS
An epizootiologic investigation was performed. Clinical, feed, and environmental samples were tested for Listeria monocytogenes, using polymerase chain reaction and culture methods; recovered isolates were "fingerprinted," using an automated ribotyping system.


RESULTS
Listeria monocytogenes was recovered from brain specimens of 7 sheep with clinical signs of listerial encephalitis. All clinical isolates had fingerprints identical to those of isolates from farm equipment used to transport silage. Corn silage, which was not fed to the sheep, also contained L monocytogenes of the same pattern type as defined by ribotyping. Listeria monocytogenes was not isolated from the stored haylage designated for feeding the sheep (the cut-off point for isolation being < 10(2) colony-forming units/g).


CONCLUSIONS
Corn silage was implicated as the source of a listeriosis epizootic. It appears to have cross-contaminated the haylage destined for the sheep during handling with a front-end loader. Suspension of silage feeding coincided with cessation of listeriosis cases.


CONCLUSIONS
Use of advanced molecular techniques can help to identify the sources and restrict the scope of an epizootic. In epizootics, a single L monocytogenes strain can lead to infection of multiple animals, with rapid progression of the disease.
Wiedmann
M
M
Department of Food Science, College of Agriculture and Life Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
Arvik
T
T
Bruce
J L
JL
Neubauer
J
J
del Piero
F
F
Smith
M C
MC
Hurley
J
J
Mohammed
H O
HO
Batt
C A
CA
D000818:Animals; D004196:Disease Outbreaks / Q000662:veterinary; D004660:Encephalitis / Q000382:microbiology / Q000662:veterinary; D005260:Female; D008088:Listeriosis / Q000209:etiology / Q000382:microbiology / Q000662:veterinary*; D008297:Male; D009518:New York; D016133:Polymerase Chain Reaction; D012756:Sheep / Q000382:microbiology; D012757:Sheep Diseases / Q000209:etiology / Q000382:microbiology*; D012820:Silage / Q000382:microbiology