Unchanged Schmallenberg virus seroprevalence in the Belgian sheep population after the vector season of 2014 and 2015 despite evidence of virus circulation

Schmallenberg virus (SBV) emerged in North-Western Europe in 2011 and induces congenital defects in ruminants. Many epidemiological studies were undertaken to study the spread of the virus during the first two years after its emergence, but little data is available on the current antibody protection rate against SBV. A cross-sectional seroprevalence study was therefore carried out in the Belgian sheep population and showed that the total seroprevalence against SBV was 26% (CI95%: 21-32) at the end of the vector season of 2015, being significantly lower than the seroprevalence of 84% detected after the outbreak in 2011. Nevertheless, 63% (CI95%: 51-73) of the Belgian sheep flocks still had a certain level of protection against SBV. Despite the fact that PCR detection of SBV in aborted calves in April 2016 evidenced that SBV had circulated in 2015, no change in seroprevalence between 2014 and 2015 was found in the Belgian sheep population.