Traceability Of Peste Des Petits Ruminants In China And Verification Of Cross-border Import Paths In Western Border Areas

Peste des Petits Ruminants(PPR)is a highly infectious cross-border small ruminant disease caused by Peste des Petits Ruminants virus(PPRV).The world organization for animal health(OIE)lists it as an animal epidemic that must be reported,and China lists it as a class I animal epidemic.China has recorded two epidemics of PPRV,the first of which occurred in Tibet,China,in 2007.The second time occurred in Xinjiang from 2013 to 2014.What is more serious is that the outbreak quickly spread to more than 20 provinces,bringing great trauma to China’s aquaculture industry.At present,Western China is an important endemic and rendezvous area of PPRV.The prevalence of Peste des Petits Ruminants(PPR)has not only brought huge losses to animal husbandry,but also threatened endangered wild animal populations.In the western border area of China,due to the grazing of livestock and the migration of wild animals,there are frequent exchanges between livestock and wild animals,which also promotes the spread of PPRV.In addition,wild animals show obvious clinical symptoms,which also shows that wild animal infection has played an important role in the epidemic of Peste des Petits Ruminants in this area,and the transmission between domestic and wildlifes has also become an obstacle to the complete eradication of PPR in China.It is revealed that the transmission of PPRV between China and surrounding countries is the premise of effective prevention and control.It is necessary to quantitatively monitor the disease transmission between countries,so as to provide reliable means for regional accurate prevention and control.By studying the global pedigree dynamics of the N gene sequence of PPRV,we summarized and analyzed the transmission law,evolution and geographical diffusion characteristics of Peste des Petits Ruminants,and traced the origin of PPRV in China.Then we combined meteorological data,terrain data,vegetation data and human factors to establish a Max Ent model to predict the PPR risk in the western border area of China.In order to solve the error of the results caused by large landscape differences and species distribution differences,we divided the western region into Pamir and Trans-Himalayan region for analysis respectively.At the same time,we also calculated the least-cost path(LCP)of PPR crossing the border,and combined with the distribution range of wildlifes,confirmed the possibility of cross-border activities of wild animals to spread diseases.Finally,in order to determine whether PPRV transmission exists in wild small ruminants and domestic animals in China,we combined with the epidemic situation of wild Pseudois nayaur in Qinghai Province to detect and identify it and analyze the genetic evolution characteristics of N gene.The results of this study can play an important role in monitoring PPR epidemic and blocking its cross-border transmission in the future.The main results are as follows:1.Through Bayesian phylogenetic analysis of global PPRV N gene,we obtained the Bayesian maximum clade credibility(MCC)tree and average evolution rate of Peste des Petits Ruminants virus N gene with time scale.Pedigree dynamics analysis confirmed that West Africa is the origin of Peste des Petits Ruminants and spread from West Africa to the world.China has a high possibility of spreading the epidemic from South Asia,which is consistent with the fact that PPR first broke out in China in the western border area of China.2.In Pamir region of Western China,Max Ent model is applied to accurately predict PPRV high-risk areas and cross-border paths.The results show that there are many high-risk areas in the study area.The risk in China is lower than that in foreign countries,and human activities are an important influencing factor.Five LCPs representing Kazakhstan,Tajikistan,Pakistan,India and China were obtained.It has proved for the first time that wild animals and livestock can spread diseases through cross-border activities.3.Through the prediction of the application of Max Ent model to the trans Himalayan region(THR)in Western China,the key points to prevent PPR are determined.Our results reveal that the low-elevation area of the THR had a higher PPR risk and was mainly dominated by human variables.The high-elevation area had lower risk and was mainly dominated by natural variables.Eight LCPs representing corridors among India,Nepal,Bhutan,Bangladesh,and China were obtained.The predicted potential risk communication between the two livestock systems and landscapes(high and low elevation)might play a role in driving PPR transboundary transmission.4.After PPR diagnosis and identification of wild Pseudois nayaur,we obtained the N gene sequence of PPRV of a Pseudois nayaur.Through comparison with the sequence published by NCBI,through homology and genetic distance analysis,it is concluded that the sequence of Qinghai Pseudois nayaur has a high homology rate with the isolates of domestic animals(KM091959,KX421384,MF443350,KM089830)of the same lineage IV in China from 2013 to 2014,with the highest homology rate of 98.9%.Phylogenetic analysis shows that the N gene of Qinghai Pseudois nayaur is closely related to other Chinese isolates except those isolated in Tibet,indicating that domestic PPRV in China was still prevalent in some areas from 2013 to2014,and there was still transmission between domestic and wild animals.