Bluetongue: Aetiology, Epidemiology, Pathogenesis, Diagnosis and Control (chapter 1)

Bluetongue (BT) is an emerging and re-emerging vector-borne viral disease of domestic and wild ruminants, caused by viruses classified within the species bluetongue virus (BTV), genus Orbivirus, family Reoviridae. There are 27 recognized serotypes of BTV (with two more recently discovered ‘putative’ serotypes) as well as multiple geographic variants (topotypes) and many different strains and genotypes, most of which are transmitted between their vertebrate hosts by certain ‘vector-competent’ biting midges of the genus Culicoides. Bluetongue is an economically important transboundary disease that is listed by the World Organisation for Animal Health, reflecting the ability of BTV to (a) infect all ruminants, including important domesticated species; (b) cause severe disease, with high fatality rates in sheep and certain species of deer; and (c) cause large economic losses due to fatalities, reduced productivity and reproductive performance, animal movement and trade restrictions and surveillance and control strategies (including vaccination). The plurality of BTV serotypes and strains, the involvement of multiple host and vector species and the potential for (re)introduction of exotic BTV strains make the control and eradication of BT very complex and difficult to achieve. In this chapter, we review the current understanding of BTV biology, bluetongue epidemiology, pathogenesis and pathology, laboratory techniques to diagnose the disease and identify the virus, experimental animal models to study the disease and to evaluate vaccines and methods for the control and/or eradication of bluetongue.