Diagnosing Bluetongue virus and vectors to enhance surveillance

Summary

Viruses that are spread by insect vectors (arboviruses) present a disease threat to Australian livestock. They are also a major impediment to trade for both live animals and semen and embryos. Viruses belonging to the bluetongue group generally have the greatest impact. Bluetongue viruses (BTV) currently restrict live ruminant exports to many valuable markets. In other countries, these viruses are an important cause of disease in sheep, causing deaths and loss of production. 
While there are strains of BTV in Australia that have been shown experimentally to cause severe disease and death in sheep, these are currently confined to the far north of Australia. Ultimately the spread of BTV is determined by the movement of their insect vectors which in turn is influenced by climatic conditions, most notably temperature and rainfall. With increasing volatility of weather patterns, particularly rising temperatures, southern extension of the distribution of midges from the genus Culicoides is likely, taking with them a range of arboviruses. If pathogenic strains of bluetongue move further south and east, large sheep populations will be at risk of disease outbreaks. Further, some regions currently certified as bluetongue free for export purposes would become zones of possible virus transmission, rendering them ineligible for trade. 
Recent arbovirus research has also shown that there is occasional entry of exotic bluetongue viruses and vectors into northern Australia in association with severe weather events. Collectively, these changes indicate that the bluetongue situation in Australia is at present unstable and there is potential for these viruses to impact heavily on ruminant health and production. 
The key achievements of this project were: The elaboration of nucleic acid sequence data for the known Culicoides vector species of BTV in Australia as well as the 2 exotic vector species considered as the greatest threat; 
Identification of non-destructive methods for the concurrent purification of DNA from midges and RNA from BTV; 
Development of Culicoides species-specific real time PCR assays that allow the rapid detection and identification of midges; 
Application of midge specific assays to evaluate light trap collections of insects from the National Arbovirus Monitoring Program (NAMP); 
Evaluation of the capacity of real time PCR assays to detect exotic Culicoides species in NAMP collections; 
Capability to quantify the major vector C. brevitarsis in NAMP collections; 
A capacity to detect BTV in insects and to identify insects that are potential vectors of BTV; 
Demonstration of the capacity of these assays to detect BTV in Culicoides collections 
Development of novel assays for the detection and identification of BTV