Modelling Bluetongue Risk in Kazakhstan

Abstract

Background: Bluetongue is a serious disease of ruminants transmitted by biting midges (Culicoides spp). Serological evidence from livestock and the presence of at least one vector competent spp of Culicoides suggests that transmission of bluetongue is possible and may have occurred in Kazakhstan. Methods: We estimated the relative risk of transmission using a mathematical model of the reproduction number R0 for bluetongue. This model depends on livestock density and climatic factors which affect vector density. Data on climate and livestock numbers from the 2466 local communities were used. This together with previously published model parameters was used to estimate R0 for each month of the year, which was rescaled to give a relative risk of transmission. These relative risks were mapped using kernal density estimates using R statistical software and mapping tools.Results: The results suggest that transmission of bluetongue in Kazakhstan is not possible in the winter from November to March. Assuming there are vector competent species of Culicoides endemic in Kazakhstan, then low levels of risk first appear in the south of Kazakhstan in April before spreading north and intensifying reaching maximum levels in northern Kazakhstan in August. The risk decline in September with only a low risk of transmission in October.Conclusion: These results should aid in surveillance efforts for the detection and control of bluetongue in Kazakhstan by indicating where and when outbreaks of bluetongue are most likely to occur.