Genomic diversity among eastern and western topotypes of bluetongue virus serotype 16 based on whole genome sequence analysis

Abstract

Bluetongue (BT) is a noncontagious, vector-borne disease of domestic and wild ruminants. The causative agent bluetonguevirus (BTV) is a double stranded RNAvirus belonging to genus Orbivirus within family Reoviridae. Eradication of BTVfromendemic regions like India is not an easy task due to the widely distributed Culicoides spp. midge vectors, the ubiquitousdistribution of vertebrate hosts and existence of a large number of serotypes of the virus (at least 26 till date). The completegenomes (19,193 base-pairs) of several strains of bluetongue virus serotype 16 (BTV-16) originated from Australia, China,Indian subcontinent, Mediterranean basin, Middle East, Africa (Nigeria) and Europe, were compared. These analysis showedthat all ten genome segments of a Nigerian strain are derived from a western lineage, showing only 77% - 84% nt identity withthe eastern topotype reference strain 'RSArrrr/16' (and its derivative 'RSAvvvv/16', a vaccine strain) that was originallyisolated in Pakistan, 76.4% - 83% with eastern BTV-16 strain from Australia (DPP96) and 77% - 89% with a reassortant strainfrom India. These detailed comparisons involving global strains showed that there is a very high degree of variation (up to24%) between BTV-16 strains from eastern and western geographical regions. These data confirm the value of whole genomesequencing for characterization of novel BTV isolates and has helped to identify representative suitable 'reference-strain' ofeastern topotype (BTV-16e), western topotype (BTV-16w), as well as 'cross-topotype' reassortant strain (BTV-16r) that aregenerated in the field for further serological, phylogenetic and molecular epidemiology studies.

Keywords

• Bluetongue virus
• BTV-16
• eastern
• Orbivirus
• reference strain
• western
• topotype
• whole genome sequencing