Assessment On High-risk Areas And Incoming Risk Of Bluetongue In China

Bluetongue is an infectious disease of ruminants caused by Bluetongue virus(BTV)infection,which is mainly transmitted by the bite of Culicoides.Among domestic ruminants,sheep are most susceptible to BTV and often have severe clinical symptoms,including fever,submandibular hyperemia and edema,oral erosions and ulcers,cyanotic tongue,and lameness until severe disease progression and death.Before the 1940 s,Bluetongue was endemic in South Africa.Bluetongue spread to the Asian continent for the first time since 1943.From 2006 to 2008,BTV-8 caused one of the most economically devastating Bluetongue outbreaks in Europe.In 2018,BTV-8,which ravaged Europe,spread to Turkey,posing a major challenge to the prevention and control of Bluetongue in Asian countries.Bluetongue is listed as a notifiable animal disease by the Office International Des Epizooties(OIE),and the Ministry of Agriculture of China classifies it as a Class I animal disease.At present,although China is a country free from Bluetongue recognized by the OIE,since the BTV was first isolated from domestic sheep in Yunnan Province in 1979,positive samples for pathogens or serological antibodies have been detected in many provinces.The scale of China’s animal husbandry industry is huge,and the amount of cattle and sheep raised and the quality of animal products are closely related to the economy and people’s livelihood.Since the Bluetongue serotypes are complex and have no cross-protective effect,and ruminants are not required to implement mandatory immunization against Bluetongue in China,domestic animals such as cattle and sheep in China are generally weak against BTV.In addition to pathogens and susceptible animal populations,vectors are also one of the necessary conditions for the prevalence of Bluetongue.Culicoides,as an important vector in the transmission of Bluetongue,is widely distributed in China.Once genetic variation,gene recombination or foreign virus strains of BTV are introduced into China,it can constitute a new transmission chain of "infection source-transmission vector-susceptible animals" and form a potential risk of Bluetongue outbreaks.With the increasingly frequent trade between China and other countries in the world,it is important to remain vigilant about potential outbreaks and introduction risks of Bluetongue.However,at present,there is insufficient understanding of the local epidemic situation and the imported risk of Bluetongue in China,and it is difficult to carry out targeted prevention and control of Bluetongue.For countries in non-endemic areas,epidemiological modeling is an effective tool to study the potential risk of Bluetongue outbreaks.Therefore,based on the epidemiological characteristics of Bluetongue,this study focused on modeling prediction and risk assessment of high-risk areas and incoming risks of Bluetongue in China.The specific research contents include:(1)Based on the international Bluetongue epidemic information from 2004 to 2021,the spatial and temporal distribution characteristics and epidemic regularity of Bluetongue were analyzed using spatial epidemiological methods.The results of descriptive analysis showed that the current international outbreaks of Bluetongue are mainly distributed in Europe,Africa and West Asia,and all showed obvious seasonal epidemics;the results of spatiotemporal clustering scanning showed that nine spatiotemporal aggregation areas were detected,and their centers are all located in the traditional bluetongue epidemic areas;the results of the directional distribution analysis show that the BTV-1 and BTV-4 epidemics were mainly prevalent in northern Africa and southern Europe,and the epidemic spread from southwest to northeast.The BTV-8 and BTV-16 epidemics were prevalent in western Europe and southern Europe,respectively,and the spread of the epidemic is in the northwest-southeast direction.In addition,based on the distribution data of BTV infection in Chinese livestock published in domestic and foreign literature,the results of Hotspot analysis showed that the hotspot of Bluetongue infection in China was Yunnan Province.(2)based on the data of the existence of the pathogen of Bluetongue in domestic and foreign literature records,and the bioclimatic variables under the current and future climatic conditions,a maximum entropy model for predicting the pathogen distribution of Bluetongue in China was established.The results show that the AUC value of the model is 0.857,and the prediction effect is good.Under the current climatic conditions,the potential environmental suitable area of BTV was mainly concentrated in the south of China,and the environmental suitable areas of BTV will expand to the northern high latitudes in varying degrees under the future climate scenarios.(3)Based on the BTV environment suitable area under the current climatic conditions,ruminant distribution density,vector distribution density and vegetation index in China,a spatial model for risk distribution prediction of Bluetongue was established by using multi-criteria decision analysis technique.The results showed that the high-risk areas of Bluetongue in China were mainly concentrated in South China and part regions of Southwest China,including Hainan Province,Guangxi Zhuang Autonomous Region,Guangdong Province,and Yunnan Province.In addition,there were also high-risk distributions in East China and Central China.Sensitivity analysis showed that the most sensitive risk factors were sheep distribution density,normalized vegetation index and BTV environmental suitability.Uncertainty analysis showed that the model was stable.(4)Based on the ecological characteristics and meteorological data of Culicoides,using the Hybrid Single-Particle Lagrangian Integrated Trajectory model to realize the trajectory calculation and trajectory clustering analysis of the long-distance transmission of Culicoides.The results show that,in Yunnan Province,from June to September 2017,Culicoides were transported along the trajectory of the airflow from the border to the inland,and the main transmission trend was southwest-northeast.(5)Based on the epidemiological characteristics of Bluetongue and port trade policies,qualitative risk analysis was used to assess the risk of imported ruminants and their products from Europe.The results show that under the condition of missing inspection in quarantine supervision,the risk level of BTV introduced into China with imported live animals or frozen semen is "high",but under the strict implementation of quarantine supervision measures,the risk level of BTV into China is "low".(6)Based on the principle of the classic warehouse model,a simulation system of Bluetongue transmission dynamics was established.The system can predict the spatial and temporal transmission trends of BTV in a specific area,and based on hypothetical scenarios,evaluate the effect of vector control in the prevention and control of Bluetongue.The results showed that preventive measures of insecticide can reduce the prevalence of Bluetongue and effectively control the occurrence of Bluetongue.In conclusion,this study systematically analyzed the potential high-risk areas and incoming risks of Bluetongue in China using a variety of spatiotemporal distribution characteristic analysis methods and infectious disease early warning and prediction techniques.The environmental suitable areas for the pathogen and risk areas of Bluetongue in China are predicted,and targeted pathogen surveillance and disease prevention and control can be carried out in the high-risk areas according to the prediction results;This paper discusses the risk of the introduction of Bluetongue into China from the perspectives of wind-borne vectors,ruminants and their products trade,which provides evidence of air flow for the introduction risk theory of Bluetongue in China,and reveals the importance of quarantine supervision measures and vector surveillance;Through the hypothetical simulation of the Bluetongue transmission dynamics system,the transmission trend of Bluetongue in a specific area is predicted,the spatial heterogeneity of BTV and the impact of intervention measures on the epidemic are explored,which provided scientific basis and decision support for the formulation of Bluetongue prevention and control strategies.