Serologic evidence for Schmallenberg virus circulation at high altitude, Central Portugal, 2015–2016

Summary A few years after the initial 2011 large scale Schmallenberg virus ( SBV ) epidemic that affected Europe, a subsequent decrease in new SBV infections was observed presumably associated with natural substitution of previously exposed animals. In the present work, a 2‐year prospective serosurvey was performed to evaluate SBV circulation in a population of sheep living at high altitude in the central region of Portugal and with restricted movement. Blood from a representative sample of 168 autochthonous sheep was collected in 2015 and again in 2016, and tested for the presence of anti‐ SBV IgG by ELISA . Of the 2015 sample collection, seven animals tested positive for anti‐ SBV IgG, corresponding to a seroprevalence of 4.2% while of the 2016 sample collection, 10 presented SBV antibodies, showing a seroprevalence of 6.0% ( p  = 0.619). Results show that SBV is endemic in sheep of central Portugal, even in herds at high altitude locations. When comparing anti‐ SBV seroprevalences of 2015/2016 found in this study, to one detected in 2014 in the same region, a steep decrease could be observed ( p  <   0.001). This is in accordance with what has been documented in Western European countries, where a decrease in the number of SBV ‐infected sheep has been found, a fact which may pose a new threat for SBV re‐emergence.