Effect of Culicoides sonorensis salivary proteins on clinical disease outcome in experimental bluetongue virus serotype 8 infection of Dorset sheep.

The severity of Bluetongue clinical disease in ruminants varies greatly depending on the outbreak serotype/strain, animal species/breed, and immune status of the herd. To predict disease risk from any of the 26 Bluetongue virus (BTV) serotypes identified to date, experimental animal susceptibility studies are often conducted. Although sheep are the most susceptible livestock species in the US, infection of domestic breeds by injection of field isolates rarely produces the level of clinical disease observed in natural Culicoides midge-transmitted outbreaks. Thus, outbreak risk assessments based on experimental animal infections can underestimate the severity posed by a potential outbreak with a given virus serotype or strain. The aim of this study was to determine whether secreted Culicoides salivary proteins injected simultaneously with virus, to more closely mimic midge-delivered virus, would affect clinical disease outcome in a BTV-8 sheep susceptibility study. Eight sheep were intradermally inoculated with BTV-8; 4 received virus mixed with secreted Culicoides salivary proteins (BTV-8 + Cu SP), 4 received virus alone. Clinical signs were monitored daily for type, severity and duration. In sheep receiving the BTV-8 + Cu SP inoculum, clinical signs were more varied, more severe, and duration was three times longer compared to sheep receiving virus alone. These results suggest that Culicoides salivary proteins may play a contributing role in BTV pathology and that use of these proteins in experimental animal infections may allow development of a more robust target-host animal model.