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United States Department of Agriculture

Agricultural Research Service

Title: Production of Malignant Catarrhal Fever Virus-Free Sheep

Authors
item Li, Hong
item Snowder, Gary
item Crawford, T - WASHINGTON STATE UNIV

Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 15, 1998
Publication Date: N/A

Interpretive Summary: Sheep-associated malignant catarrhal fever (SA-MCF) is a globally- distributed herpesviral disease of cattle, bison, deer and certain other animals. The traditional recommendation for controlling SA-MCF has been to keep sheep away from cattle, deer or other animals. Since no vaccine for SA-MCF is yet available, production of the SA- MCF virus-free sheep is the only alternative to species isolation. In this study, we examined the variables affecting the success of establishment of SA-MCF virus-free sheep flocks. A total of 38 lambs born to MCF virus-positive ewes were selected and divided into 4 groups. Three groups of 10 lambs each were separated from the positive ewes at 2, 2.5 and 3 months of age, respectively, and maintained in isolation facilities. One group of 8 remained in the positive flock as controls. Blood samples from each lamb were examined regularly by PCR for the viral DNA. All lambs (100%) that were weaned and maintained in isolation from the ages of 2, 2.5 and 3 months remained negative until termination of the experiment at one year of age. One lamb was discovered to be PCR-positive on the day of isolation at 2.5 months of age, and was promptly removed from the isolation group. In contrast, all lambs (100%) that remained with the flock became PCR-positive by 6 months of age. The data confirmed that, with rare exceptions, separation of lambs from SA-MCF virus- infected animals at around 2 months of age reliably yields SA-MCF virus-free sheep. The PCR monitoring is recommended as a safety measure.

Technical Abstract: The study was designed to better define the variables affecting the success of establishment of ovine herpesvirus 2 (OHV-2) free sheep flocks. A total of 38 lambs born to OHV-2 positive ewes were selected and divided into 4 groups. Three groups of 10 lambs each were separated from the positive ewes at 2, 2.5 and 3 months of age, respectively, and maintained in isolation facilities. One group of 8 remained in the positive flock as controls. Peripheral blood samples from each lamb were examined regularly by PCR for OHV-2 DNA. All lambs (100%) that were weaned and maintained in isolation from the ages of 2, 2.5 and 3 months remained negative until termination of the experiment at one year of age. One lamb was discovered to be PCR-positive on the day of isolation at 2.5 months of age, and was promptly removed from the isolation group. In contrast, all lambs (100%) that remained with the flock became PCR-positive by 6 months of age. The data confirmed that, with rare exceptions, separation of lambs from OHV-2 infected animals at around 2 months of age reliably yields OHV-2 free sheep. Appropriate PCR monitoring will enable the rare exceptions to be removed from the group, and is recommended as a safety measure.

Last Modified: 8/27/2014
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