Using behavioural and immunological tools to study the seasonality of Culicoides biting midges in the UK

Abstract

Culicoides biting midges are biological vectors of arthropod-borne viruses (arboviruses) of international importance. The emergence of bluetongue virus (BTV) and Schmallenberg virus (SBV) in Europe has highlighted the vulnerability of the UK to incursions. Persistence of Culicoides-borne viruses through adverse conditions in the cold winter months (“overwintering”) contributes to their economic and welfare impact and is a major source of uncertainty in policy response. Understanding the role of temperature in adult Culicoides activity, particularly in colder months, will inform policy on the likely risk of transmission. Reducing exposure to Culicoides biting is an important factor in controlling the spread of Culicoides-borne viruses following an incursion and immunological responses to the Culicoides bite may provide a novel approach to measuring the exposure of susceptible hosts to Culicoides. This thesis investigates adult Culicoides seasonal activity and biting in the UK using both field and laboratory-based studies, focusing on the impact of winter. Culicoides activity, examined directly using ultraviolet-baited light-suction traps, was limited to days when maximum temperatures were >7°C in a field study. An experimental system that tested movement of adult Culicoides within a controlled environment further demonstrated the effect of temperature, with the minimum temperature for flight activity varying according to collection location, time of year of collection and species. Furthermore, immunoassays were developed to detect the presence of antibodies against Culicoides salivary proteins in host sera and to indirectly infer Culicoides blood-feeding activity. This work demonstrated that horses, cattle and sheep in the UK produce detectable levels of antibodies recognising Culicoides salivary protein antigens for the first time, as a result of natural biting exposure in the field environment. These findings have direct implications in future surveillance programs and policy decision making, particularly when defining vector-free periods of adult activity.