Distribution And Shifting Mechanism Of The Dominant Genotype Of Japanese Encephalitis Virus

Japanese encephalitis(JE)is mainly prevalent in Asian-Pacific region,including China.According to WHO around 68,000 JE cases are reported annually across the globe,about half of them occur in China.The causative agent of JE is a mosquito-borne Japanese encephalitis virus(JEV).Culex tritaeniorhynchus is considered as most competent vector for JEV transmission.Swine and wading birds are considered as most important amplifying hosts.JEV is classified into one serotype and five genotypes(G).Before 21 st century,G III JEV was the most dominant strain in nature.Currently,some studies have revealed that G I JEV strains isolated from all over the world is gradually increasing.Many countries including India,Korea and Taiwan have claimed that G III JEV has been displaced by G I JEV and has become the most dominant JEV strain.Many G I JEV strains has been identified in China,one of which was isolated from a boy inoculated with G III JEV vaccine.There are no scientific estimations for G I JEV invasion and the public health risk caused by JEV genotype shifting.Up till now,we are not clear about the distribution of the dominant genotype of JEV.Moreover,shifting mechanism of the dominant genotype of JEV also needs to be illustrated.In this study,according to an article,we established an ELISA method to screen the sera of swine infected by G I or G III JEV.2232 samples were collected for this purpose from 12 provinces of china,including The Inner Mongolia Autonomous region,The Guangxi Zhuang Autonomous region,The Xinjiang Uygur Autonomous region,Jiangsu province and so forth.The seroepidemiology result showed that the average seropositive rates of antibody against JEV varies from 26.43% to 58.72%.Average positive rate of JEV antibody in southern China was found relatively high.The seropositive rates of antibody against JEV in Guangdong province and Hunan province was found 59.5% and 53.2% respectively,whereas annual positive rate of JEV antibody is Xinjiang was just 28.3% which is located in northwest of China.Furthermore,the ratio of positive sample we confirmed as GI to the numbers we confirmed as GIII is between 1.3 to 2.8.The highest rate of 2.8 was found in Qinghai province which was contrary to the lowest rate of 1.3 in Hunan,Jiangsu and Inner Mongolia.Although,all the ratios were more than 1.Therefore,it can be said that G I JEV is the dominant strain circulated in China.To illustrate potential mechanisms about JEV dominant genotype shifting,we collected and analyzed some ecology factors,like climate,latitude,longitude and so on,but we could not find any significant relationship among the distribution of dominant genotype JEV strain and domestic climate.To make sure if the JEV dominant genotype shifting is related to the host tropism of JEV,multi-step growth curve test was conducted.There is no significant difference on the amplification of 3 strains of GI JEV and 4 GIII JEV strains in C6/36 cells and in PIEC cells.Interestingly,in DF-1 cells,the growth curve is significantly different between 3 GI JEV strains and 4 GIII JEV strains.To validate the phenomenon,animal experiments were carried out.We selected 6 strain JEV,including 3 strains of GI JEV and 4 strains of GIII JEV.Same dose of viral load(10,000 PFU)was used to infect Sheldrake ducklings of 2-3 days of age.The duck blood was collected in order to detect the level of viremia.The results showed that GI JEV produced higher titer and longer duration viremia in ducks than GIII JEV.Mosquitoes that feed on blood with higher titer of viremia are easier to infect,disseminate and transmit JEV,which facilitate the circulation of GI JEV in nature environment.Our study illustrated that GI JEV is the dominant strain in pigs of China,and there is no direct connection between the distribution of GI JEV strains with domestic climate in the sight of seroepidemiology.Wading birds are a kind of important amplifying host and play a crutial role in the circulation of JEV.Unlike GIII JEV,GI JEV strains can make Sheldrake develop a more serious viremia with the higher titer of virus,which suggest that the phenomenon facilitate the displacement from GIII JEV to GI JEV in nature.To sum up,Our research data improved the understanding of the mechanism of the dominant genotype shifting of JEV and could supply the basal data to analyze the potential public health risk caused by the shifting.Also our research would help improvising the control of JE in China.