Weaker pathogenicity means clinical signs may be fewer
Vets are being reminded of the risk of bluetongue virus, as serotype 8 re-emerges in northern Europe.
According to an APHA briefing, there have been reports from France of calves being born small and blind, dying at just a few days old, since mid-December 2018. There has been a considerable increase in reports since January this year.
The affected animals have been positive by PCR on blood and spleen for BTV-8. APHA said the detection of BTV-8 in calves of around a week old, during the culicoides vector-free period, suggests transplacental infection.
Since the first reports of cases, 418 samples have tested positive for BTV-8 by PCR, with between two and 15 per cent of newborn calves affected on some farms.
Further studies using experimental midge infection suggest that the current BTV-8 strain in France has a reduced culicoides vector competence.
Official veterinarians are being urged to consider BTV-8 as a possible cause of malformed calves or abortion, and to be aware that the re-emerging strain in northern Europe could cause transplacental transmission and infection of foetuses in cattle.
Owing to the weaker pathogenicity of the re-emerging strain, there may be fewer clinical signs than the 2007 strain, so APHA says an increase in awareness is important.