Outdoor and indoor monitoring of livestock-associated Culicoides spp. to assess vector-free periods and disease risks

BACKGROUND Within the last few decades Culicoides spp. (Diptera: Ceratopogonidae) emerged Europe-wide as a major vector for epizootic viral diseases e.g. caused by Bluetongue (BT) or Schmallenberg virus. In accordance with the EU regulation 1266/2007, veterinary authorities are requested to determine vector-free periods for loosing trade and movement restrictions of susceptible livestock. Additionally, the widely used basic reproduction number [Formula: see text] is optionally applied for risk assessment of vector-borne diseases. Values of R0 < 1 indicate periods with no disease transmission risk. For the determination of vector-free period and R0 a continuously operating daily Culicoides spp. monitoring in Vienna (Austria) was established. It covered the period 2009-2013 and depicts the seasonal vector abundance indoor and outdoor. Future BT and African horse sickness (AHS) outbreak risks were estimated by projecting R0 to climate change scenarios. Therefore, temperature-dependent vector parameters were applied. RESULTS The vector-free period lasted about 100 days inside stables, while less than five Culicoides were trapped outdoors on 150 days per season, i.e. winter half year. Additionally, the potential outbreak risk was assessed for BT and AHS. For BT, a basic reproduction number of R0 > 1 was found each year between June and August. The periods without transmission risk, i.e. R0 < 1, were notably higher (200 days). Contrary, values of R0 < 1 were estimated for AHS during the whole period. Finally, the basic reproduction numbers were projected to the future by using temperature forecasts for the period 2014-2100. While the mean summer peak values for BT increase from of R0 = 2.3 to R0 = 3.4 until 2100 (1.1/100 years), no risk for AHS was estimated even under climate warming assumptions. CONCLUSIONS Restrictions to trade and movement are always associated with an economic impact during epidemic diseases. To minimize these impacts, risk assessments based on the vector-free period or the basic reproduction number R0 can essentially support veterinary authorities to improve protection and control measurements.