Bluetongue virus reassortment, an overlooked aspect of viral evolution with potentially serious implications

Abstract

Bluetongue virus (BTV) is the prototype member of the Orbivirus genus in the family Reoviridae and is the aetiological agent of the arthropod transmitted disease, bluetongue (BT), which affects ruminant and camelid species. The disease is of significant global importance due to its economic impact and effects on animal welfare. Bluetongue virus, a segmented dsRNA virus, exists as a genetically and phenotypically heterogeneous entity in nature and has the ability to reassort its genome segments in vertebrate or vector cells which have concurrently been infected with more than one strain or serotype of the virus. Although the kinetics of BTV reassortment has been described in both in vivo and in vitro studies, relatively little is known about the consequences which the reassortment of different genome segments may have on the phenotypic properties of the virus. It has been speculated that the reassortment of genome segments between phenotypically distinct strains may result in the generation of novel reassortant viruses, which may display either enhanced virulence or transmission characteristics. The purpose of this review is to provide an overview of the mechanisms of viral evolution which underlie the generation of genetic and phenotypic differences among BTV field strains, to discuss the kinetics of BTV reassortment and to highlight documented examples of the effects of reassortment on the phenotype of the virus. Methods by which BTV reassortants may be generated in vitro, as well as possible approaches for evaluating the consequences of reassortment on the phenotypic properties of the virus are also discussed.