Chapter 16 - Bluetongue virus and climate change

Abstract

This chapter describes the shifted pattern of Bluetongue (BT) epidemics in Europe and summarizes the strands of evidence that link this emergence to climate change. The biological mechanisms underlying this response to climate change may include increased virus persistence over winter, the northward expansion of the primary Old World vector—Culicoides imicola—and, beyond this vector's range, transmission by indigenous European Culicoides species. This chapter considers these potential mechanisms in more detail, focusing on questions that remain to be answered and their consequences for the spread of BT in Europe. Vector-borne pathogens are particularly sensitive to climate because they are transmitted between vertebrate hosts by small, poikilothermic, blood-sucking insects or ticks. This has led to widespread and continued speculation that anthropogenic climate change will increase the incidence and intensity of their transmission. Bluetongue virus (BTV) replicates in all ruminant species but severe disease is mostly restricted to certain breeds of sheep and some species of deer. In cattle, BTV causes long-lived sub-clinical infections making these ruminants the main reservoir host. Bluetongue virus is transmitted between its ruminant hosts, primarily by certain species of Culicoides biting midges. Finally, this chapter speculates on the features of the European BTV–Culicoides ‘episystem’ that made it particularly sensitive to climate change.