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ARS Home » Pacific West Area » Pullman, Washington » Animal Disease Research » Research » Publications at this Location » Publication #86061
Title: TRANSMISSION OF OVINE HERPESVIRUS 2 IN LAMBS

Author
item Li, Hong
item Snowder, Gary
item O'TOOLE, D - UNIVERSITY OF WY
item CRAWFORD, T - WASHINGTON STATE UNIV.

Submitted to: Journal of Clinical Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/27/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Sheep are natural carriers of a herpesvirus designated as ovine herpesvirus 2 (OHV-2), the causative agent of sheep-associated malignant catarrhal fever (SA-MCF) in cattle, deer and certain other animals. Relatively little information is known about the transmission of this virus in sheep. In this study, we used two recently-developed assays (CI-ELISA and PCR) to examine the pattern of transmission of OHV-2 in lambs. Placental infection of OHV-2 in sheep was uncommon (only 2 out of 77 of newborn lambs were PCR-positive before nursing). Majority of lambs was not infected until sometime after 3 months of age. Comparison of pattern of appearance of viral DNA (genomic material) in peripheral blood and in nasal secretions with humoral response suggested the tissues in nasal cavity might support the viral replication. In an attempt to define the time of infection of OHV-2 in lambs, two groups were weaned at 2.5 and 3.5 months of age respectively, and raised without contact with other sheep. Of 5 lambs separated from the flock at 2.5 months of age, all remained uninfected until the termination of the experiment at one year of age. In contrast, lambs weaned and returned to the flock were all infected by 3.5 months of age. Weaning and separation from flock at 3.5 months of age did not prevent infection. The data showed that OHV-2 infection does not commonly occur in perinatal lambs and OHV-2-free sheep can be established by separation of lambs at the proper time, which has important implications for potential control measures.

Technical Abstract: In this study, the pattern of acquisition of ovine herpesvirus 2 (OHV- 2) infection in lambs was examined. Newborn lambs (n=108) did not exhibit antibody at birth. Viral DNA in PBL was detected in only 3% (n=77) of newborn lambs before suckling. After nursing, viral DNA was sporadically present in about 10 to 20% of lambs until about 3 months of age. Thereafter, strong DNA signals began to appear in increasing numbers of lambs, reaching 100% by 5.5 months of age. Viral DNA in nasal secretions began to be detectable in about 30% of lambs at 5.5 months of age, achieved significant levels in 88% of lambs by 7.5 months of age, and then declined. The kinetics of the humoral immune response in lambs paralleled those of viral DNA in nasal secretions, but not its presence in blood leukocytes, suggesting that OHV-2 infection in leukocytes is non-permissive, and that tissues of nasopharynx are productively infected, which leads to stimulation of the immune system. In isolation study, 5 lambs separated from the flock at 2.5 months of age and raised without contact with other sheep, all remained uninfected until the termination of the experiment at one year of age. In contrast, lambs weaned and returned to the flock were all infected by 3.5 months of age. Weaning and separation from the flock at 3.5 months of age did not prevent infection. The study showed that OHV-2 infection does not commonly occur in perinatal lambs and OHV-2-free sheep can be established by separation of lambs at the proper time, which has important implications for potential control measures.