Three years of bluetongue disease in central Europe with special reference to Germany: what lessons can be learned?

Abstract

With few exceptions, vector-borne diseases have long been considered of minor importance in central and northern Europe. Since the advent of bluetongue disease (BTD) in 2006 and the 2007 chikungunya fever outbreak in Italy this attitude has changed. It is due to continuing globalization rather than to climate change that even central and northern Europe are at risk of new pathogens as well as vectors of disease entering and establishing. BTD was the first 'exotic' disease to arrive: it did not slowly spread northwards but jumped in through a still unknown entry point. Although indigenous Culicoides biting midge species had formerly been considered to be the vectors of the bluetongue virus (BTV) in the Mediterranean, nobody had expected BTD in more northern European areas free of C. imicola. When the disease broke out, the authorities were completely unprepared, particularly as neither data on the putative vectors nor biting midge specialists were available. Starting with about 2000 affected ruminant farming facilities in 2006 in the central western part of Europe, the virus managed to overwinter and spread in all directions in 2007, producing almost 60,000 outbreaks (farms affected) in ten European countries up to early 2008. At that time, vaccine administration against BTV serotype 8 was initiated, significantly decreasing the total number of holdings affected in the third transmission season (May 2008 to April 2009). From May 2009 onwards, relatively few cases of BTV-8 infections were notified in a total of only six European countries. Unfortunately, while the further fate of BTV-8 in Europe remains to be awaited, BTV-1 appears to be approaching from the south, with some 4900 outbreaks in France in 2008. Meanwhile, the results from various entomological monitoring projects have suggested biting midges of the C. obsoletus and C. pulicaris complexes as well as some other ceratopogonid species as the most likely BTV vectors in central Europe. The lesson to be learned from the BTD epidemic is once again that in the long term pro-action is better than mere reaction as it can considerably support and facilitate reaction: to avoid and manage outbreaks of emerging vector-borne diseases, essential prerequisites are to monitor the indigenous hematophagous arthropod fauna, to identify potential vectors and acquire knowledge on their biology, to educate medical entomologists and vector biologists, and to implement better control of imported goods and animals for pathogens and arthropod vectors.