Investigation of a listeriosis epizootic in sheep in New York state

Martin Wiedmann From the Department of Food Science, College of Agriculture and Life Sciences (Wiedmann, Arvik, Batt); the Departments of Pathology (del Piero) and Clinical Sciences (Smith, Mohammed); and the Center for Research Animal Resources (Hurley), College of Veterinary Medicine, Cornell University, Ithaca, NY 14853; and Qualicon, a subsidiary of EI DuPont de Nemours, Wilmington, DE 19880 (Bruce, Neubauer).

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Torey Arvik From the Department of Food Science, College of Agriculture and Life Sciences (Wiedmann, Arvik, Batt); the Departments of Pathology (del Piero) and Clinical Sciences (Smith, Mohammed); and the Center for Research Animal Resources (Hurley), College of Veterinary Medicine, Cornell University, Ithaca, NY 14853; and Qualicon, a subsidiary of EI DuPont de Nemours, Wilmington, DE 19880 (Bruce, Neubauer).

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James L. Bruce From the Department of Food Science, College of Agriculture and Life Sciences (Wiedmann, Arvik, Batt); the Departments of Pathology (del Piero) and Clinical Sciences (Smith, Mohammed); and the Center for Research Animal Resources (Hurley), College of Veterinary Medicine, Cornell University, Ithaca, NY 14853; and Qualicon, a subsidiary of EI DuPont de Nemours, Wilmington, DE 19880 (Bruce, Neubauer).

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Joseph Neubauer From the Department of Food Science, College of Agriculture and Life Sciences (Wiedmann, Arvik, Batt); the Departments of Pathology (del Piero) and Clinical Sciences (Smith, Mohammed); and the Center for Research Animal Resources (Hurley), College of Veterinary Medicine, Cornell University, Ithaca, NY 14853; and Qualicon, a subsidiary of EI DuPont de Nemours, Wilmington, DE 19880 (Bruce, Neubauer).

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Fabio del Piero From the Department of Food Science, College of Agriculture and Life Sciences (Wiedmann, Arvik, Batt); the Departments of Pathology (del Piero) and Clinical Sciences (Smith, Mohammed); and the Center for Research Animal Resources (Hurley), College of Veterinary Medicine, Cornell University, Ithaca, NY 14853; and Qualicon, a subsidiary of EI DuPont de Nemours, Wilmington, DE 19880 (Bruce, Neubauer).

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Mary C. Smith From the Department of Food Science, College of Agriculture and Life Sciences (Wiedmann, Arvik, Batt); the Departments of Pathology (del Piero) and Clinical Sciences (Smith, Mohammed); and the Center for Research Animal Resources (Hurley), College of Veterinary Medicine, Cornell University, Ithaca, NY 14853; and Qualicon, a subsidiary of EI DuPont de Nemours, Wilmington, DE 19880 (Bruce, Neubauer).

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Julie Hurley From the Department of Food Science, College of Agriculture and Life Sciences (Wiedmann, Arvik, Batt); the Departments of Pathology (del Piero) and Clinical Sciences (Smith, Mohammed); and the Center for Research Animal Resources (Hurley), College of Veterinary Medicine, Cornell University, Ithaca, NY 14853; and Qualicon, a subsidiary of EI DuPont de Nemours, Wilmington, DE 19880 (Bruce, Neubauer).

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Hussni O. Mohammed From the Department of Food Science, College of Agriculture and Life Sciences (Wiedmann, Arvik, Batt); the Departments of Pathology (del Piero) and Clinical Sciences (Smith, Mohammed); and the Center for Research Animal Resources (Hurley), College of Veterinary Medicine, Cornell University, Ithaca, NY 14853; and Qualicon, a subsidiary of EI DuPont de Nemours, Wilmington, DE 19880 (Bruce, Neubauer).

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Carl A. Batt From the Department of Food Science, College of Agriculture and Life Sciences (Wiedmann, Arvik, Batt); the Departments of Pathology (del Piero) and Clinical Sciences (Smith, Mohammed); and the Center for Research Animal Resources (Hurley), College of Veterinary Medicine, Cornell University, Ithaca, NY 14853; and Qualicon, a subsidiary of EI DuPont de Nemours, Wilmington, DE 19880 (Bruce, Neubauer).

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Abstract

Objective

To investigate potential sources of an epizootic of listerial encephalitis, using molecular diagnostic and typing methods.

Sample Population

A flock of about 655 sheep.

Procedure

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 < 102 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.

Clinical Relevance

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. (Am J Vet Res 1997;58:733–737)

Abstract

Objective

To investigate potential sources of an epizootic of listerial encephalitis, using molecular diagnostic and typing methods.

Sample Population

A flock of about 655 sheep.

Procedure

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 < 102 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.

Clinical Relevance

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. (Am J Vet Res 1997;58:733–737)

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