Behavioural and immunological control methods for Culicoides biting midges in the UK

Culicoides biting midges are the most important biological vectors of arboviruses of ruminants in Europe, where they act as vectors of bluetongue and Schmallenberg viruses and potentially other emerging threats. This studentship tests the following hypotheses which are relevant to reducing the impact of Culicoides-borne arboviruses. 1. The presence of adult Culicoides in animal housing has a major role in overwintering and spread of arboviruses, but can be addressed in part through vector-proof accommodation. 2. Immunological responses to over-exposure of vector salivary proteins can be harnessed to reduce the survival of bloodfeeding Culicoides with future potential for vaccine design. The student will examine Culicoides populations at cattle holdings in the UK already established by The Pirbright Institute (TPI: Academic lead) and APS Biocontrol (Industrial Partner). Winter survival of adult Culicoides within animal housing will be investigated using standardised suction trap and vacuum surveys. Results from this direct sampling will be compared with models of seasonal abundance based on outside light-suction trap sampling already conducted by TPI. To improve our understanding of biosecurity in animal housing, the efficacy of ultraviolet-based traps and air curtains will then be examined using behavioural assays in the laboratory to complement testing of insecticide impregnated screens already completed at TPI. In the subsequent two field seasons, at time of peak transmission of Culicoides-borne arboviruses,
efforts will be made across selected sites to exclude Culicoides from housing through implementation of optimized procedures and the degree of bio-containment assessed by the abundance of Culicoides versus outside collections.

The studentship will also examine development of vaccines based on responses of hosts to unnaturally high doses of arthropod saliva. Preliminary data in collaboration with Dr Alasdair Nisbet of the Moredun Institute demonstrated that inoculated of sheep with a Culicoides extract produce elevated levels of serum antibodies. Feeding on the blood of postvaccination sheep reduces survival in Culicoides when compared to unvaccinated controls. Serum from naturally exposed cattle and sheep will initially be screened for anti-Culicoides antibody levels, assessing the seasonality of exposure and the likely degree of saliva protein cross-recognition between Culicoides species. Sampling will compare hosts in areas known to be dominated by specific Culicoides fauna and saliva proteins purified from colony-reared lines with homologous field-collected species extractions. Conserved immunogenic Culicoides saliva proteins across samples will be identified by western blot assays and proteomics. A vaccination trial of sheep with purified Culicoides saliva proteins will then analyse immunological responses (e.g. titre and isotype(s) of serum antibodies and the potential presence of cytokines). Cell mediated immune responses will be examined using proliferation assays and cytokine production of in vitro exposed peripheral blood cells from vaccinated sheep to saliva proteins (combined and fractionated). Laboratory survival and fecundity rates of Culicoides blood-fed on vaccinated and control sheep will then be statistically assessed. The student placement will last three months and will aim to devise techniques for the collection of saliva from C.impunctatus, utilizing the expertise of Dr Alison Blackwell (APS Biocontrol) with this species. This will provide a significant resource for all collaborating partners in the project and is enabled by geographic distance between the partners with APS being based in Scotland. In addition, the student will also work with the APS team to estimate commercial potential for containment facilities in the UK which was a major area of discussion during the 2007 incursion of bluetongue virus when movement restrictions were implemented.