Surveillance of vector-borne diseases in cattle with special emphasis on bluetongue disease in Switzerland

Due to previous climatic conditions in Switzerland, vector-borne diseases were not of primary importance to the Swiss Federal Veterinary Office. It has now been established that global warming has had a major impact on vector species ecology due to temperature shifts, humidity and precipitation changes amongst many factors, which influence vector habitats and their distribution, and allowed in some instances for vectors already present in an area to transmit a disease, or aid in the extension of habitats of exotic vectors species. In Switzerland, several vector-borne diseases have and are emerging, causing alarm due to the eventual consequences in health and economic matters that they can bring with them. Such examples are Bluetongue disease (BT), cattle anaplasmosis and cattle babesiosis, which have, at the time of writing, now all been reported in Switzerland. In order to aid decision and policy makers in planning eventual surveillance, prevention and control measures, disease surveillance needs to be focused on aspects of vector ecology and the epidemiology of the mentioned diseases. In this study, surveillance took form as a sentinel herd strategy through serological and entomological sampling over the past three years. The aim was to establish an early warning system for the primary incursion of BT virus via infected Culicoides species vectors, or the reemergence of anaplasmosis and babesiosis through endemic tick species. Hence, as a risk based approach, it was important to identify areas considered at higher likelihood of disease occurrence located within Switzerland. This was achieved through the collection of climatic, environmental, altitude, entomological and vector population dynamics data. These data were incorporated into a Geographic Information System and a mathematical model and finally developed into a Scenario Tree pathway to help decide upon different surveillance system components. Models developed in this study through the collected data have proved useful as the first cases of reported BT disease in Switzerland were in areas highlighted by the suitability maps, as well as mirroring calculated prevalence estimates. Results from this study were also implemented into a national surveillance plan for bluetongue disease in Switzerland.