Reconstruction of the Schmallenberg virus epidemic in Belgium: Complementary use of disease surveillance approaches.

Schmallenberg virus (SBV) emerged across Europe in 2011 and Belgium was among the first countries affected. In this study, published findings are combined with new data from veterinary surveillance networks and the Belgian reference laboratory for SBV at the Veterinary and Agrochemical Research centre (CODA-CERVA) to reconstruct the epidemic in Belgium. First retrospective cases of SBV were reported by veterinarians that observed decreased milk yield and fever in dairy cattle in May 2011. The number of SBV suspicions subsequently increased in adult cattle in August 2011. That month, first SBV positive pools of Culicoides were detected and extensive virus circulation occurred in Belgium during late summer and autumn 2011. As a consequence, most pregnant ruminants were infected and their fetuses exposed to the virus. This resulted in an outbreak of abortions, still-births and malformed new-borns observed between January and April 2012. The number of cases drastically diminished in 2012-2013, although multiple lines of evidence obtained from cross-sectional serological surveys, analyses on aborted foetuses, sentinel herd surveillance and surveillance of SBV in vectors prove that SBV was still circulating in Belgium at that time. Virus circulation was then probably strongly reduced in 2013-2014, while increasing evidence indicates its recirculation in 2014-2015 in Belgium. Based on the experience gathered with the closely related Akabane virus, recurrent outbreaks of congenital events can be expected for a long period. Vaccination of seronegative animals before the first mating could be used to prevent the deleterious effects of SBV. During this epidemic, different surveillance approaches including syndromic surveillance, sentinel herd surveillance, cross-sectional seroprevalence studies and pathogen surveillance in vectors have proven their utility and should be considered to continue in the future.