Bluetongue virus and Culicoides in the UK: the impact of research on policy

Bluetongue virus (BTV) is an arbovirus (arthropod-borne virus) that is spread between its ruminant hosts by vector species of Culicoides biting midges (Diptera: Ceratopogonidae). Culicoides are among the smallest of haematophagous flies, with a wingspan that rarely exceeds 4mm, making them extremely challenging subjects for experimental research. In susceptible ruminants (primarily fine wool breeds of sheep), infection with BTV can cause a haemorrhagic disease (bluetongue: BT). Since 2006, the international profile of the virus has risen substantially as a result of a widespread and economically damaging incursion of a sub-Saharan strain of BTV serotype 8 (BTV-8) into north-western Europe, a region where the virus had never previously been recorded. This step-change in the epidemiology of the virus is thought to be a consequence both of globalisation of trade (although a specific pathway of introduction for BTV-8 has not been definitively identified), and the influence of climate within those affected regions in driving virus transmission. The effect of the BTV-8 incursion was initially most obvious in sheep holdings where mortality due to BT was observed. In addition, however, many cattle in northern Europe were also significantly affected with widespread cases of infertility, abortion and reduced milk yield, impacting directly upon the efficient operation of beef and dairy holdings. The full impact of these clinical cases and the animal movement restrictions imposed to reduce spread of the virus is poorly characterised, but from small scale studies is likely to amount to 100s of millions of Euros. From as early as the late 1970s, the UK was unique among north-western European countries in funding a sustained and continuous research programme on BTV and on Culicoides as vectors of animal pathogens. Following the appearance of BTV-8 in northern Europe in 2006, many of the findings that had been achieved as part of this programme were used to devise responses to the incursion, at both an EU and UK level. In this paper, the UK's response to the incursion and which areas of entomological research proved useful in predicting, monitoring and mitigating against BTV outbreaks are considered.