Modelling bluetongue risk in Kazakhstan

Sarsenbay K Abdrakhmanov,Paul R Torgerson,Ablaikhan S Kadyrov,Aigerim Y Zhakenova,Yersyn Y Mukhanbetkaliyev,Altay Y Ussenbayev,Kanatzhan K Beisembayev,Akmetzhan A Sultanov

doi:10.1186/s13071-021-04945-6

Sarsenbay K Abdrakhmanov, Paul R Torgerson + Show 6 more

Open Access

https://doi.org/10.1186/s13071-021-04945-6

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Abstract

BackgroundBluetongue is a serious disease of ruminants caused by the bluetongue virus (BTV). BTV is transmitted by biting midges (Culicoides spp.). Serological evidence from livestock and the presence of at least one competent vector species of Culicoides suggests that transmission of BTV is possible and may have occurred in Kazakhstan.MethodsWe estimated the 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. We plotted the results on isopleth maps of Kazakhstan using interpolation to smooth the irregular data. We also mapped the estimated proportion of the population requiring vaccination to prevent outbreaks of bluetongue.ResultsThe results suggest that transmission of bluetongue in Kazakhstan is not possible in the winter from October 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 July. The risk declined in September and had disappeared by October.ConclusionThese 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. The results also indicate where vaccination efforts should be focussed to prevent outbreaks of disease.Graphical abstract

Highlights

Bluetongue is a serious disease of ruminants caused by the bluetongue virus (BTV)
Bluetongue (BT) is a viral disease of ruminants caused by bluetongue virus (BTV), which has been identified on all continents except Antarctica [1,2,3,4,5]
Adult Culicoides are killed by cold winter temperatures, and BTV infections typically do not last for more than 63 days [13], which is not long enough for BT-infected animals to remain infectious to the vectors for the duration of the winter

Summary

Introduction

Bluetongue is a serious disease of ruminants caused by the bluetongue virus (BTV). The extent of suitable vectors of the virus is unknown, the vector-competent species Culicoides obsoletus has been found in eastern Kazakhstan [11, 12]. In inner Mongolia, which has cold winters, BT appears to be endemic [14], indicating that the virus can continue to transmit following long periods when the vector in inactive. It seems that the virus somehow survives in overwintering midges or animals. Less likely mechanisms include alternative but unknown reservoir hosts or alternative vectors that are better able to overwinter [15]

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