Clinical signs and pathology shown by British sheep and cattle infected with bluetongue virus serotype 8 derived from the 2006 outbreak in northern Europe

Four poll Dorset sheep and four Holstein-Friesian cattle were infected with the northern European strain of bluetongue virus (BTV), BTV-8, to assess its pathogenicity in UK breeds. The time course of infection was monitored in both species by using real-time reverse transcriptase-PCR (RT-PCR), conventional RT-PCR and serology. Two of the sheep developed severe clinical signs that would have been fatal in the field; the other two were moderately and mildly ill, respectively. The cattle were clinically unaffected, but had high levels of viral RNA in their bloodstream. Real-time RT-PCR detected viral RNA as early as one day after infection in the cattle and three days after infection in the sheep. Antibodies against BTV were detected by six days after infection in the sheep and eight days after infection in the cattle. Postmortem examinations revealed pathology in the cattle that was more severe than suggested by the mild clinical signs, but the pathological and clinical findings in the sheep were more consistent.