Transmission of ovine herpesvirus 2 among adult sheep

Previous studies from this laboratory have defined the pattern of acquisiti on of ovine herpesvirus 2 (OHV-2) in lambs under natural flock conditions. This study examined the question of whether OHV-2 could be transmitted betw een adult sheep. Two potential routes of transmission were examined: (1) di rect inoculation of either viable leukocytes or whole blood from OHV-2 posi tive sheep, and (2) horizontal transmission through natural contact with OH V-2 positive sheep. Two groups of OHV-2 negative adult sheep were inoculate d with material from infected sheep, one with 5 x 10(8) viable peripheral b lood leukocytes (PBL), and the other with 100 ml of whole peripheral blood. No PCR signals were detected in any of the three sheep inoculated with the PBL during the 20 weeks following inoculation, In the group of five sheep inoculated with whole blood, two became PCR-positive at 7 and 8 weeks post- inoculation, respectively, and the remaining three sheep maintained their n egative status until termination of the experiment at 20 weeks post-inocula tion. In two experiments conducted in different flocks, a total of 20 adult sheep were used to examine horizontal transmission by contact; all animals became PCR-positive within 12 months of mixing the uninfected and infected animals. The results of these experiments support two conclusions. First, the susceptibility to OHV-2 is not limited to young lambs; adult sheep rema in fully susceptible. Second, the fact that whole blood, but not PBL, from infected sheep was able to transmit the infection to only two of five inocu lated sheep suggests that the infection in peripheral blood cells may be la rgely non-productive. (C) 2000 Elsevier Science B.V. All rights reserved.