Schmallenberg virus: a seroprevalence survey in cattle and sheep, France, winter 2011-2012

In France, a national surveillance plan to monitor congenital Schmallenberg virus (SBV) outbreaks was set up in January 2012, and has shown that SBV had become widespread throughout the country since mid-2011. However, the number of SBV-infected farms cannot accurately be estimated through congenital SBV reporting alone. Therefore, GDS France (National Animal Health Farmers' Organization) conducted serological investigations in cattle and sheep holdings in several departments in spring 2012 to assess SBV exposure in 2011. A serological study was also conducted in the department of Saône-et-Loire (southern Burgundy) to establish an accurate local overview of circulation of virus in 2011 among cattle. The study was conducted following guidelines elaborated by the French Platform for animal health surveillance. Results indicated differences in within-herd seroprevalence between cattle herds and sheep herds in departments where outbreaks of congenital SBV were reported in early 2012 and a great heterogeneity in seroprevalence between areas (even between areas geographically close to each other). In departments which had been severely affected in early 2012, the overall impact of SBV infection in cattle herds during the 2012-2013 calving season will probably be low. On the other hand, given the low proportion of immunised ewes in sheep SBV outbreaks, sheep flocks which were already affected in early 2012 may once again face congenital cases of SBV.