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United States Department of Agriculture

Agricultural Research Service

Title: Transmission of Ovine Herpesvirus 2 among Adult Sheep

Authors
item Li, Hong
item Snowder, Gary
item O'Toole, D - UNIV OF LARAMIE
item Crawford, T - WASHINGTON STATE UNIV

Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 11, 1999
Publication Date: N/A

Interpretive Summary: Management program for production of malignant catarrhal fever (MCF) virus-free sheep was established as an alternative strategy in control of the disease. The question of whether the virus could be transmitted between adult sheep was critical to the feasibility of preserving the virus-free status of the sheep flock. In this study, we examined two potential routes of transmission: 1) direct inoculation of either viable blood leukocytes or whole blood from MCF virus positive sheep, and 2) horizontal transmission through natural contact with the positive sheep. Two groups of MCF virus negative adult sheep were inoculated with material from infected sheep, one with 5 x 108 viable blood leukocytes, and the other with 100 ml of whole blood. None of 3 sheep inoculated with the blood leukocytes were infected during the 20 weeks following inoculation. In the group of 5 sheep inoculated with whole blood, two became infected at 7 and 8 weeks post-inoculation, respectively, and the remaining 3 sheep maintained uninfected until termination of the experiment at 20 weeks post-inoculation. In 2 experiments with a total of 20 adult sheep to examine horizontal transmission by contact, all animals became infected within 12 months of mixing of the uninfected and infected animals. The results indicated: 1) adult sheep remain fully susceptible to MCF virus infection, 2) horizontal contact is the predominant mode for the transmission, and 3) transmission by inoculation of blood cells or whole blood is much less efficient than contact transmission.

Technical Abstract: Previous studies from this laboratory have defined the pattern of acquisition of ovine herpesvirus 2 (OHV-2) in lambs under natural flock conditions. This study examines the question of whether OHV-2 could be transmitted between adult sheep. Two potential routs of transmission were examined: 1) direct inoculation of either viable leukocytes or whole blood from OHV-2 positive sheep, and 2) horizontal transmission through natural contact with OHV-2 positive sheep. Two groups of OHV-2 negative adult sheep were inculated with material from infected sheep, one with 5 x 108 viable peripheral blood leukocytes (PBL), and the other with 100 ml of whole peripheral blood. No PCR signals were detected in any of 3 sheep inoculated with the PBL during the 20 weeks following inoculation. In the group of 5 sheep inoculated with whole blood, two became PCR-position at 7 and 8 weeks post-inoculation, respectively, and the remaining sheep maintained their negative status until termination of the experiment at 20 weeks post-inoculation. In 2 experiments conducted in different flocks, a total of 20 adult sheep were used to examine horizontal transmission by contact, all animals became PCR-position within 12 months of mixing of the uninfected and infected animals. The results of these experiments support two conclusions. First, the susceptibility of OHV-2 is not limited to young lambs; adult sheep remain fully susceptible. Second, the fact that whole blood, but not PBL, from infected sheep was able to transmit the infection to only 2 of 5 inoculated sheep suggests that the infection in peripheral blood cells may be largely non-productive.

Last Modified: 10/1/2014
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