| Rift Valley fever(RVF)is an acute and febrile infectious disease of ruminants and humans,which is caused by the infection of Rift Valley fever virus(RVFV).It is a vector-borne disease which mainly transmitted by mosquitoes.It first outbroke in the Rift Valley of Kenya in 1930.Subsequently,its widely spreading in Africa has caused a huge blow to the ruminant economy in Africa.In 2000,the epidemic of RVF reached Eurasia for the first time.It outbroke in Saudi Arabia and Yemen,which sounded an alarm for the prevention and control of RVF in Asia and Europe.Moreover,as RVF is a zoonosis,it not only threatens animal health,but also threatens human health.The first imported human case of RVF in China was reported in 2016.RVF is one of the OIE-Listed diseases,infections and infestations in force.RVF has been listed as one of the thirteen exotic animal diseases that need to be prevented in the National Medium and Long-Term Animal Disease Control Plan(2012-2020)of China.China's ruminant industry has a huge scale.Products such as beef,mutton,milk and wool are closely related to people's livelihood and economy.Ruminant economy accounts for a considerable proportion in China's animal husbandry.For RVF,an exotic animal disease,the ruminant population in China is lack of resistance.In addition to susceptible animal populations,the presence of vectors is also a necessary condition for the outbreak of RVF.There are a variety species of mosquitoes in China that have been proved to be able to transmit RVFV.Once the infectious source enters China,a complete transmission chain of "Infectious source-Vector-Susceptible animals" is expected to be formed.According to the OIE's criteria for identifying the risk level of RVF,our country should be regarded as “Infection free countries at risk”.OIE suggests that countries at this risk level should strengthen import quarantine,vector control and public health system staff's awareness of this disease in order to detect and contain the epidemic as early as possible.The potential introduction of RVF poses a huge threat to ruminant breeding industry of China.Once an outbreak occurs in China,the epidemic prevention and control work is facing a great challenge.Today,with international traffic and trade becoming increasingly frequent and tight,China should always be vigilant against the risk of RVF.However,at present,there is insufficient understanding of the potential risk of RVF in China,as well as insufficient understanding of its vector ecology.It is difficult to carry out targeted prevention and control work for RVF.This study intends to start with the basic links of the epidemic of vector-borne infectious diseases.The distributions of potential RVF vectors in China were modelled,the risk of RVF occurrence and transmission in China was assessed,and a dynamic simulation system of RVF transmission based on mathematical model was established.It can guide the formulation of control strategies and the implementation of control measures for RVF in China.The research contents of this study are as follows:(1)Based on the international RVF animal outbreaks from 2004 to 2019,the spatiotemporal distribution characteristics and epidemic regularity were analyzed by using the spatial epidemiology method of spatialtemporal analysis.The results of directional distribution analysis showed that the RVF animal outbreaks from 2004 to 2019 presented in turn as sporadics in parts of northwest Africa(2004-2005),large-scale epidemics in southeast Africa(2006-2009),pandemics in parts of southern Africa(2010-2011),and large-scale sporadics in central Africa(2013-2019).Distribution direction showed different degrees of northwest-southeast direction;The results of space-time scanning showed that there were eight statistically significant spatiotemporal clusters from 2004 to 2019.The first three clusters were located in the east,south and southeast of the African continent,covering most of RVF cases and outbreaks during the study period,and were also historical RVF traditional epidemic areas.(2)Based on occurrence records in international literatures and GBIF database,as well as current and future high-resolution meteorological factors reflecting China's climatic conditions,an ecological niche model for predicting the suitability of RVF vectors in China was established by using Maxent.The model revealed the current distribution suitability of six potential RVF vectors in China,Aedes aegypti,Aedes albopictus,Aedes vexans,Culex pipiens pallens,Culex pipiens quinquefasciatus and Culex tritaeniorhynchus and habitat shifts under future climate change.The results showed that AUC values were 0.801?0.992 which indicated good performance.Suitable habitats of the six vectors are currently distributed in different regions of China,and they will all have a tendency to expand to the high latitude areas in northern China in the future.(3)Based on the international RVF animal outbreaks from 2004 to 2019 and high-resolution meteorological factors reflecting the climatic conditions of the epidemic area,a Maxent model was established to reveal the key meteorological factors affecting the occurrence of RVF and extrapolate to China.The results showed that AUC value was 0.897 which indicated good performance.Vast areas of southern China were predicted to have similar climatic conditions as those in the African RVF epidemic area.Using GIS technology,combined with China's ruminant distribution density and vector distribution index,high-risk areas in China that are favorable for the occurrence of RVF was revealed.Based on AHP,the risk of RVF spreading on a large spatial scale caused by traffic and trade factors(highways,railways,waterways and livestock trading markets),host and vector distribution in China was comprehensively evaluated.Finally,the risk of occurrence and spreading were superimposed,and a comprehensive risk map of RVF in China was obtained.(4)Based on the principle of classical compartment model and according to the epidemiological characteristics of RVF,a dynamic simulation system of RVF transmission was established by using computer technology,which can be used to simulate the transmission and spread trend of local possible RVF epidemics.Based on the hypothetical scenarios,the epidemic development without intervention and with intervention was simulated,and the effects of artificial interventions including mosquito control,immunization and culling in epidemic prevention and control were explored.The results showed that in the hypothetical scenarios in this study,preventive measures(preventive immunization and mosquito control)could effectively reduce the intensity of the outbreak and reduce livestock losses;and emergency response measures(emergency immunization and mosquito control)could effectively accelerate the end of the outbreak and reduce livestock losses.In summary,a variety of spatial epidemiological research methods and mathematical modelling technology were used to conduct a pioneering systematic analysis of the potential risk of Rift Valley fever,an exotic animal disease,entering a non endemic country like China.The current and future suitable habitats of various potential RVF vectors in China were predicted,the gap in the knowledge of eco-informatics of RVF vectors was filled and targeted monitoring of vectors and pathogens can be carried out according to the predicted results.According to the obtained comprehensive RVF risk map of China,targeted prevention and control work can be carried out in areas identified as having the risk of RVF occurrence and transmission.Through the established dynamic simulation system of RVF transmission,the development trend of possible RVF epidemic can be predicted and analyzed,and the effect of intervention measures on epidemic prevention and control can be evaluated,thus providing scientific basis for the formulation of prevention and control strategies. |
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