Re-Emergence of Schmallenberg Virus
Recently we have received reports of Schmallenberg virus (SBV) resurfacing in Holland and Belgium with clinical presentations of milk drop and diarrhoea in dairy cows and abortion with foetal deformities. The Dutch reports suggest that clinically affected cows have been PCR positive for SBV and have also shown evidence of seroconversion.
This has been followed by the recent detection of SBV virus from a deformed calf in Cornwall and evidence of seroconversion as part of routine screening in cattle in Cheshire. APHA figures confirm there were no diagnosed cases of SBV in the UK in 2015 and no evidence of SBV infection in Scotland since 2013. Scotland would be considered to be towards the edge of the vector risk area.
Transmission of this orthobunyavirus by biting midges is followed by viraemia lasting around 6 days. In cattle this can be accompanied by pyrexia, diarrhoea and milk drop with recovery after a few days.
Foetal deformities can occur if pregnant cattle are infected during months three and four of gestation. The danger period for ewes is month two.
In spring 2013 congenital malformations due to SBV were confirmed in six calves in Dumfries and Galloway. Typical findings include arthrogryposis, hydrancephaly and narrowing of the spinal cord. No cases were seen in lambs.
Vet practitioner involvement in cases of foetal deformity is highly likely because of dystokia and we would suggest that such foetuses are submitted for testing and screening for SBV.
If you suspect acute disease with a cluster of cases of significant milk drop, pyrexia, with or without diarrhoea we would suggest that you sample up to 6 affected animals. Please collect EDTA bloods for PCR testing and clotted blood samples for paired serology with convalescent sample collected three weeks later. For Scottish farms the Scottish Government have indicated that they will subsidise this testing of acute cases.
If SBV virus is circulating locally spring calving suckler cows, dairy cows served through the late summer and ewes tupped in August/September are most at risk of foetal abnormalities. There is also a potential risk associated with the purchase of dairy heifer replacements from Northern Europe.
If you wish to discuss potential cases / outbreaks, please do not hesitate to get in touch with you nearest Disease Surveilance Centre.