Epidemiologic characteristics of bluetongue virus serotype 8 laboratory-confirmed outbreaks in The Netherlands in 2007 and a comparison with the situation in 2006

A major epidemic of bluetongue virus serotype 8 (BTV-8) occurred in Western Europe in 2006. During 2007 it became evident that BTV-8 had survived the winter and a re-emerging epidemic quickly developed. The objective of this study was to describe the severity and clinical impact of the BTV-8 epidemic in 2007 in The Netherlands in laboratory-confirmed outbreaks and to compare this with the situation in 2006. The relative frequency of clinical signs in BTV-8 affected sheep flocks and cattle herds in 2007 and 2006 was similar. The most prominent changes were a higher proportion of sheep flocks with lameness and a much higher proportion of cattle herds reporting a decrease in milk yield in 2007. BTV-8 associated morbidity and mortality incidence rates in sheep flocks and cattle herds were significantly (P < 0.001) higher in 2007 than in 2006. Both in sheep flocks and cattle herds, BTV-8 associated case fatality was significantly (P < 0.001) lower in 2007, which was probably due to better medical treatment of sick animals. There were significantly (P < 0.001) more fertility problems associated with BTV-8 infection in outbreak cattle herds in 2007 compared to 2006.