Evidence for bluetongue virus in Canada: 1976-1979.

Since the identification of approximately 1 400 bovine serological reactors to bluetongue virus in the Okanagan Valley of British Columbia in 1976, there has been no evidence of virus establishment in Canada. No clinical signs suggestive of bluetongue were observed. It was not possible to demonstrate viral activity at the time the seropositive animals were detected and subsequent serological testing supports the hypothesis that the virus has not become endemic or indeed survived in Canadian cattle populations. This combined with the dramatic reduction in prevalence of serological reactors in the years following the initial slaughter suggests that viral activity occurred in the Okanagan Valley prior to 1976 and disappeared. There has been no evidence for transmissions different from that expected of a classical arbovirus; that is, no evidence of "vertical" transmission.