Epidemiology Of African Swine Fever And Analysis Of Its Risk Prevention And Control In China

The Food and Agriculture Organization of the United Nations describes Transboundary Animal Diseases（TADs）as:epidemics that are highly contagious or transmittable and have the potential to spread rapidly.No matter these diseases occur in which country,they will cause serious economic consequences and even public health problems.African swine fever（ASF）is a serious transboundary animal disease that currently causes domestic pigs and wild boars worldwide in danger and threatens the world’s food supply.As the largest pork producer and consumer in the world,China’s pig industry has suffered a heavy loss since the outbreak of ASF in 2018.Although the prevention and control of the epidemic has made a significant success within a short period of time due to the efforts of relevant Chinese departments,the virus will still exist in our country for a long time in the future.As the global ASF epidemic continues to spread,how to prevent the virus from other countries and how to further curb the development of the domestic epidemic have become a new challenge at this stage.In the prevention and control of ASF,the main difficulties are as follows:First,African swine fever virus（ASFV）has strong vitality and can exist for a long time in a variety of environmental and non-biological media,which makes it possible to spread rapidly through various means such as mechanical transmission of biological media and human activities.Second,the existence of wild boar and Ornithodoros ticks,the reservoir hosts of ASFV,makes it more difficult to be eradicated.Third,the number of subclinical and chronic cases will increase when ASF colonized in a certain area,which will make it more difficult to detect the outbreak in time.However,the most important reason is that no effective vaccines and drugs against ASFV have yet been developed,which means spread of the disease can only be blocked through monitoring,culling,epidemiological investigation and trace.Therefore,in this relatively passive defense scenario,it is particularly important to keep abreast of the global and neighboring ASF dynamics,to grasp the latest epidemiological information and transmission characteristics,and to summarize the effective prevention and control experience abroad.However,blindly learning and copying experience are not advisable,and adjustments should be made in due course in the light of the characteristics and progress of the development of the epidemic in our country.In addition,considering human factors play a vital role in the spread of ASF,analysis of specific risk factors based on the actual situation of the country’s breeding industry will make the country’s prevention and control strategies more scientific and effective.This research is composed of three parts.The first part is the analysis of the global epidemic distribution of ASF.Through a comprehensive review and analysis of the global ASF epidemic situation from 2015 to 2020,we explore the characteristics of the epidemic distribution and summarize the experience of foreign epidemic prevention and control.Time series analysis was used to verify and predict the seasonality of global wild boar mortality for the first time.The second part is the analysis of the distribution of ASF in China.This part is based on the information and data of ASF in China from August 2018 to October 2020.It objectively presents the development and development of ASF in China through statistics and modeling.The changes of focus in the ASF prevention and control process will also be explored.The third part is the analysis of the risk factors of ASF in China.The pioneering method of combining principal component analysis and neural network models is used based on the relevant factors of the pig industry.We analyzed the risk factors related to ASF in our country,hoping to provide a scientific basis for the formulation of our national defense control strategy,and help consolidate the results of normalized ASF prevention and control.The specific research content is as follows:1.Analysis of Global Epidemic Distribution of ASFTransboundary animal disease is a collective term for a type of disease that has a major impact on the economy,trade,or food security of most countries.With the acceleration of economic globalization,sharing epidemic information and prevention and control experience,and strengthening regional joint prevention and control have become important strategies for many countries.As there is no effective vaccine against ASF,the ASFV has become a cross-border animal disease with widespread global impact by virtue of its strong survival ability and complex transmission relationship between infected hosts.From 2015 to 2020,ASF was reported in 42 countries on 4 continents;the number of infected animals has increased year by year,exceeding 200,000 for the first time in 2018.Among them,the number of reported epidemics in wild boars is significantly higher than that of domestic pigs,but domestic pigs are the host that is absolutely affected by ASF.Through time series analysis,we verified the seasonality of the global wild boar mortality,established a simple seasonal model（R²=80.2%,P=0.282）and predicted the wild boar mortality in 2021.2.Analysis of Epidemic Distribution of ASF in ChinaASF was first reported in Kenya,and has been prevalent in Africa,Europe,and other countries for the past century.The disease seriously endangers the food security and trade exports of infected countries,and may even cause a series of social problems.On August 3,2018,the first case of ASF in China and Asia was confirmed in Shenyang,Liaoning Province,which caused widespread concern in the international community.As of the end of October2020,in addition to Hong Kong,Macau and Taiwan,182 cases of ASF have been reported in 31 provinces（municipalities,autonomous regions）in China,including 176 cases of domestic pigs and 6 cases of wild boars.Five provincial-level administrative regions have reported more than 10 cases,and more than half of the provinces have reported fewer than 5cases;the total number of culleds in the 10 provincial-level administrative regions is more than 10,000,and more than half of the provinces have a risk stock of less than 5,000.In the past two years,the prevention and control of the epidemic has been based on passive reporting,and large-scale breeding farms have been the hardest hit area for the ASF epidemic in my country.In addition,we also established a mathematical model to simulate and analyze the development trend of the epidemic in a macroscopic way.3.Risk Factor Analysis of ASF in ChinaIn order to explore the risk factors that affect the occurrence of ASF in my country,we first conducted multiple principal component analysis on 34 variables related to pig production,deleted and merged the variables based on correlation and collinearity,and finally combined the remaining 20 variables Divided into three types of principal components,it can explain 77.6%of the data variation of the original variable.Subsequently,we tried to establish a linear regression model with the extracted three principal components as independent variables and the number of risk stocks in 31 provincial administrative units in China as dependent variables,but the results showed that F（3,27）=0.247,P=0.863>0.05,That is,the model is not statistically significant,and there is no linear correlation between the parameters.Finally,we re-divided 2 risk levels based on the differences in the number of risk stocks in 31 provinces,and combined the extracted 3 principal components to construct a 3-layer artificial neural network model.Analysis shows that the model has a strong predictive ability on samples and is most affected by the principal component Z₂.