Study On The Temporal-spatial Distribution And Epidemic Risk Of African Horse Sickness

African Horse Sickness(AHS)is an acute or subacute insect-borne disease by African Horse Sickness Virus(AHSV).Equine animals are the most susceptible in all,the fatality rate can be as high as 95%.The World Organization for Animal Health(OIE)lists it as an animal disease that must be reported,China also lists it as the first class of animal disease.Epidemic mainly occurred in southern Africa,and once spreaded to North Africa,the Middle East,the Arabian Peninsula,Southwest Asia and countries in the Mediterranean region.The outbreak of AHS in Thailand was first reported to OIE on March 27 2020.In September of the same year,African Horse Sickness epidemic occurred in Malaysia.China has been recognized historically free of African Horse Sickness by OIE,but the threat from neighboring countries increases.AHS is transmitted by biting insects such as Culidiodes imicola.Climate have a significant impact on the distribution and abundance of C.imicola.AHS occurs in areas where C.imicola exist and in seasons which is conducive to C.imicola activity.Insect vectors of AHS have been detected in China,therefore there is a high risk of the epidemic being introduced into China.With the increasingly close international traffic and trade,China should always be vigilant against the risk of AHS.This study analyze the time-space distribution of AHS based on international epidemic data,starting from the basic links of the prevalence of insect-borne diseases,the potential vector distribution of AHS in China was modeled and predicted,and the occurrence risk of AHS in China was comprehensively assessed,so as to provide reference and measures for the development of prevention and control strategies of AHS in China.The specific contents of the research include:(1)Based on global animal epidemic situation AHS records from 2007 to 2020,using standard deviation ellipse method to analyze epidemic prevalence,the result shows that directional distribution at three different stages respectively is northwest-southeast,no obvious directivity,southwest-northeast.in general,it presents the characteristic of west-east distribution,spreading from Africa to Asia.(2)Based on global records of AHS from 2007 to 2020 world records,the results of space-time scanning analysis show that there are four statistically significant spatiotemporal cluster,the center of the spatiotemporal community located respectively in Nigeria,Senegal,South Africa,Ethiopia.(3)Based on the distribution records of C.imicola,a vector of AHS from the literature and database,combined with the bioclimatic variables in World Clim database,which reflected the current and future climate conditions,the maximum entropy niche model was used to predict the distribution niche of C.imicola in China.The results show that the AUC value of the model is 0.973,the prediction result is good.Under the current climate conditions,the potential habitats of C.imicola were mainly distributed in Hainan,Taiwan,Guangdong,Fujian,Guangxi and Yunnan.In the future,climate conditions will be more conducive to the habitat of C.imicola.The habitat area of C.imicola will be increased and the suitable level will be improved.The first three environmental contributing significantly factors are respectively Isothermality,Min Temperature of Coldest Month,Mean temperature of Coldest Quarter.(4)Based on AHS epidemic and combined with the biological climate variable data,the global C.imicola distribution data and equine density.The AHS risk map showed that high risk areas are distributed in Yunnan Hainan,Taiwan and Tibet Province.The variables contribute most are Isothermality,Precipitation Seasonality,Precipitation of Wettest Quarter,Precipitation of Coldest Quarter.In summary,conclusions can be drawn as follows:(1)The annual number of outbreaks of AHS is not large and the epidemic intensity is not strong,the scope is expanding year by year.At first it only occurred in Senegal in northern Africa,and then extended to many countries in eastern and southern Africa,indicating that the epidemic of AHS has a large spread trend in Africa.In the end,the epidemic was not confined to African continent,but spread to Thailand and Malaysia in Asia,indicating that the spread of AHS was further expanded and the thread to China was intensified.(2)The climate of spatio-temporal clusters is characterized by distinct dry and wet seasons.Three clusters are located in the Sudanese steppe in the south of the Sahara Desert,one is located in Ethiopian Plateau.(3)Some areas of Yunnan are highly suitable for C.imicola,C.imicola is highly likely to be distributed in these areas.The habitats are moderately suitable for in Hainan,Taiwan,and southeast coastal areas.(4)Most areas of Yunnan area are at risk of AHS,and the northern part of Yunnan is at high risk of AHS,Hainan,Taiwan,Tibet are also at risk to a certain extent.