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) that affects
both ruminant and camelid species. The disease is of significant global importance due to its
economic impact and effect on animal welfare. Bluetongue virus, a dsRNA virus, evolves
through a process of quasispecies evolution that is driven by genetic drift and shift as well as
intragenic recombination. Quasispecies evolution coupled with founder effect and evolutionary
selective pressures has over time led to the establishment of genetically distinct strains of the
virus in different epidemiological systems throughout the world.
Bluetongue virus field strains may differ substantially from each other with regards to their
phenotypic properties (i.e. virulence and/or transmission potential). The intrinsic molecular
determinants that influence the phenotype of BTV have not yet clearly been characterized. It is
currently unclear what contribution each of the viral genome segments have in determining the
phenotypic properties of the virus and it is also unknown how genetic variability in the
individual viral genes and their functional domains relate to differences in phenotype.
In order to understand how genetic variation in particular viral genes could potentially
influence the phenotypic properties of the virus; a closer understanding of the BTV virion, its encoded proteins and the evolutionary mechanisms that shape the diversity of the virus is
required. This review provides a synopsis of these issues and highlights some of the studies that
have been conducted on BTV and the closely related African horse sickness virus (AHSV) that
have contributed to ongoing attempts to identify the molecular determinants that influence the
virus’ phenotype. Different strategies that can be used to generate BTV mutants in vitro and
methods through which the causality between particular genetic modifications and changes in
phenotype may be determined are also described. Finally examples are highlighted where a
clear understanding of the molecular determinants that influence the phenotype of the virus
may have contributed to risk assessment and mitigation strategies during recent outbreaks of
BT in Europe.
