Evidence for transplacental and contact transmission of bluetongue virus in cattle.

This paper presents evidence that a field strain of bluetongue virus serotype 8 (BTV-8) was transmitted transplacentally and that it was also spread by a direct contact route. Twenty pregnant heifers were imported from the Netherlands into Northern Ireland during the midge-free season. Tests before and after the animals were imported showed that eight of them had antibodies to bluetongue virus, but no viral RNA was detected in any of them by reverse transcriptase-PCR (RT-PCR). Two of the seropositive heifers gave birth to three calves that showed evidence of bluetongue virus infection (RT-PCR-positive), and one of the calves was viraemic. Two further viraemic animals (one newly calved Dutch heifer, and one milking cow originally from Scotland) were also found to have been infected with BTV-8 and evidence is presented that these two animals may have been infected by direct contact, possibly through the ingestion of placentas infected with BTV-8.