Detection of antibodies against Schmallenberg virus in wild boars, Belgium, 2010-2012

In the summer/fall of 2011, a nonspecific febrile syndrome characterized by hyperthermia and drop in milk production with occasional reports of watery diarrhea and abortion was reported among dairy cows on farms in northwestern Europe. Further, in November 2011, an enzootic outbreak of malformed neonates emerged in several European countries, with stillbirth and birth at term of lambs, kids and calves with neurological signs or malformations of the head, spine, or limbs. Both syndromes were associated with the presence in the blood (adults) or in the central nervous system (newborns) of a new Shamonda/Sathuperi-like orthobunyavirus, provisionally named Schmallenberg virus (SBV) after the town in Germany where the first positive clinical samples were identified. Defining as precisely as possible the host range of the newcomer is a key point to predict the outcome of the emergence of SBV disease in Europe. In this respect, it must be pointed out that orthobunyaviruses infect more animal species than those in which the foetus is damaged. Recently, serological evidence for SBV infection in wild ruminant species (Cervus elaphus and Capreolus capreolus) was reported (Linden et al., 2012). In the present study, the objective was to seek after serological evidence of SBV infection among wild boars living in a geographical area where exposure to infected insect vectors was high in 2011, as judged from the very high seroprevalence reported among cattle in that region. About 700 animals were sampled during the 2010-2012 hunting seasons. All serum samples collected during the fall of 2010 were seronegative. On the contrary, apparent seroprevalence among wild boars in 2011 was ~27% and started to decline in 2012 (~11%). Acquired immunity against the new virus was thus already very high in the wild boar populations sampled in the fall 2011, suggesting that the new virus had quickly spread throughout the region since its emergence about 250 km northeast in the late summer 2011. The drop in seroprevalence recorded in 2012 suggests that the virus was no more circulating in the region.