In the initial outbreak in 2012/13 the virus likely arrived in the UK with windblown midges in south eastern counties and then spread inland and north. At the end of 2013 the APHA had confirmed virus infection on 656 holdings, though subsequent serology testing indicated that all areas of the UK below the Scottish borders had been exposed, with 25- 75% of animals having antibodies to the virus (depending on county). Individual herd or flock losses of neonates due to Schmallenberg vary but on average SBV affected flocks report an extra 3% lamb mortality than those flocks not affected. Some flocks however experience 50-60% losses due to SBV. Following the initial outbreak, sheep born in 2014/15 in southern counties did not seroconvert to the virus at all, indicating that the virus did not circulate in those years. As a consequence total herd immunity dropped.
Follow the link for more of the latest information http://apha.defra.gov.uk/documents/surveillance/diseases/guidance-schmallenberg-virus.pdf