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United States Department of Agriculture

Agricultural Research Service

Title: A Devastating Outbreak of Malignant Catarrhal Fever in a Bison Feedlot

Authors
item Crawford, T - WSU
item Li, Hong

Submitted to: Satellite Workshop for Veterinary Herpesviruses
Publication Type: Abstract Only
Publication Acceptance Date: May 15, 2004
Publication Date: July 25, 2004
Citation: Crawford, T.B., Li, H. 2004. A devastating outbreak of malignant catarrhal fever in a bison feedlot [abstract]. Satellite Workshop for Veterinary Herpesviruses. p. 19.

Interpretive Summary: In December, 2002, a flock of sheep that contained 1.375 seven month-old lambs and 375 aged ewes was pastured for a period of 20 days on the acreage adjacent to a feedlot that contained 1,610 head of bison and approximately 4000 head of beef cattle. The sheep were grazed within 600 yards of the lot during the day, and were bedded down adjacent to the feedlot at night, at a distance of approximately 20 and 30 yards from the nearest bison and cattle, respectively. The sheep were moved away after 20 days. An additional 177 head of bison were moved into the lot 25 days after the departure of the sheep. At about this time, losses from malignant catarrhal fever (MCF) began. Diagnosis was made by detection of the DNA of the ovine strain of MCF virus (OvHV-2) in tissues by PCR, and was confirmed by histologic examination of tissue lesions. Peak losses occurred between 41 and 54 days post mean exposure time (PME), and reached a maximum of 41 head per day. Total mortality at 113 days PME, when losses had slowed to about one per day, was 806 head, or 50.1% of the 1,610 initial head of exposed bison. To reduce losses, exposed but unaffected bison were shipped to slaughter as rapidly as possible during the outbreak, thereby artificially lowering apparent mortality rates. No cases of MCF were observed among the 177 head of bison that arrived in the lot after departure of the sheep. Ten of the involved lambs were randomly sampled and examined by PCR, and all were positive for OvHV-2. Of the several thousand head of beef cattle in the lot during the outbreak, only a single case of MCF was identified. This outbreak illustrates the devastating impact the MCF virus can have on bison under the proper exposure conditions, the high threat posed by adolescent lambs to susceptible species, the significantly greater susceptibility of bison than beef cattle to MCF, and the lack of horizontal transmission from clinical cases in bison to herdmates.

Technical Abstract: In December, 2002, a flock of sheep that contained 1.375 seven month-old lambs and 375 aged ewes was pastured for a period of 20 days on the acreage adjacent to a feedlot that contained 1,610 head of bison and approximately 4000 head of beef cattle. The sheep were grazed within 600 yards of the lot during the day, and were bedded down adjacent to the feedlot at night, at a distance of approximately 20 and 30 yards from the nearest bison and cattle, respectively. The sheep were moved away after 20 days. An additional 177 head of bison were moved into the lot 25 days after the departure of the sheep. At about this time, losses from malignant catarrhal fever (MCF) began. Diagnosis was made by detection of the DNA of the ovine strain of MCF virus (OvHV-2) in tissues by PCR, and was confirmed by histologic examination of tissue lesions. Peak losses occurred between 41 and 54 days post mean exposure time (PME), and reached a maximum of 41 head per day. Total mortality at 113 days PME, when losses had slowed to about one per day, was 806 head, or 50.1% of the 1,610 initial head of exposed bison. To reduce losses, exposed but unaffected bison were shipped to slaughter as rapidly as possible during the outbreak, thereby artificially lowering apparent mortality rates. No cases of MCF were observed among the 177 head of bison that arrived in the lot after departure of the sheep. Ten of the involved lambs were randomly sampled and examined by PCR, and all were positive for OvHV-2. Of the several thousand head of beef cattle in the lot during the outbreak, only a single case of MCF was identified. This outbreak illustrates the devastating impact the MCF virus can have on bison under the proper exposure conditions, the high threat posed by adolescent lambs to susceptible species, the significantly greater susceptibility of bison than beef cattle to MCF, and the lack of horizontal transmission from clinical cases in bison to herdmates.

Last Modified: 11/28/2014
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