Multi-locus markers identify possible routes of introduction of Culicoides brevitarsis to Australia and their dispersal within the continent

Background: Biting midges (Culicoides spp.) are the vectors of bluetongue virus (BTV), the agent of a disease that results in significant global economic losses. C. brevitarsis is the major vector of BTV in Australia and the most geographically widespread. Despite absence of clinical BTV in Australia, there are concerns that introduction of novel virulent serotypes via overseas dispersal of the species into northern Australia, or the movement of BTV into southern sheep grazing regions, could result in disease outbreaks and seriously affect Australia’s livestock trade. Use of multi-locus genetic markers to identify source origins and population structure of C. brevitarsisin Australia can provide insights into the likelihood of these threats. This study described the isolation and use of DNA microsatellites to determine population genetic connectivity between Australia and its northern neighbors.

Methodology/Principal findings: A novel genomic enrichment method was used  to isolate 11 microsatellite DNA markers and utilized for population genetic studies of C. brevitarsis from Australia, north Papua New Guinea (PNG) and Timor-Leste. Significant (P < 0.05) population genetic subdivision was observed between all paired regions, though the highest levels of genetic sub-division involved pair-wise tests with PNG. STRUCTURE analysis identified a most probable two-cluster population model, which separated PNG specimens from a cluster containing specimens from Timor-Leste and Australia. Both analyses show panmixia between northern and eastern sampled Australian populations.

Conclusions/significance: The source of incursions of this species in Australia is more likely to be Timor-Leste than PNG. Future incursions of BTV positive C. brevitarsis into Australia may be genetically identified to their source populations using these microsatellite loci. This study has been able to overcome huge technical constraint due to the very tiny size of this vector and has developed technical workflow easily translatable to many other insect vectors of important diseases.