In the present study, the risk of a potential African horse sickness outbreak, caused by the African horse sickness virus, was estimated for the Veterinary University of Vienna. The African horse sickness is an endemic infectious disease on the African continent and occurred in Southern Europe so far only occasionally. The virus is transmitted by biting midges of the genus Culicoides spp..
The risk was calculated using the basic reproduction number R0 for the years 2009-2011. The basic reproduction number R0 describes the expected number of secondary cases produced by a typical infected individual during its entire period of infectiousness in a completely susceptible population. R0 depends on the density of horses and midges, the recovery and death rate of horses caused by the infection, the transmission probability form host to vector and backwards, as well as the temperature-dependent midge biting- and mortality rate and the virus reproduction rate.
The results comprise values R0 > 1 only for a short period during the hot summer months leading to a decreased risk of infection with the African horse sickness at the Veterinary University of Vienna. Depending on transmission probabilities pM and pE proposed by different authors, R0 is greater than 1 for max. 82 days (high pM and pE) during 2009-2011. Maximum values for R0 were estimated in 2010 and will remain for a long period in this critical range.