FIGURE 2-18 Progression of bluetongue viruses emergence in Europe. Created by Rick Hayes, School of Veterinary Medicine, University of California, Davis.

were different, possibly C. dewulfi and C. obsoletus complex, and appeared to be the primary vectors in Germany, France, the Netherlands, Belgium, and Luxembourg (Meiswinkel et al., 2004). These vectors are well-adapted and acclimated to northern Europe. The other environmental factors that appear to have played a role were global warming and more importantly, the unusual flow of warm weather from southern Europe. The temperature in northern Europe was 3°C warmer during the 2006 autumn than had been recorded before (WMO, 2007). Also, the vector season was extended into November because of unusually warm temperatures. This elevated temperature may have permitted virogenesis to easily occur in C. dewulfi and C. obsoletus complex.

Another factor of interest was the appearance of BTV serotype 8 in northern European countries. Serotype 8 had not been reported north of Nigeria. It is unusual for serotypes to move over such a great distance. The explanation for the appearance of serotype 8 in northern Europe has not been resolved.

It is of interest that BT disease has been reasonably well controlled in eastern and southern Europe; whether this is due to the effectiveness of vaccines or whether BTVs 1, 2, 4, 9, and l6 have not been able to become established with C. imicola, C. obsoletus, and/or C. pulicaris in that environment, only time will tell.