Study On The Circulatory Cycle Of Japanese Encephalitis Virus In Huaihua City Of Hunan Province

The Japanese encephalitis virus(JEV), a mosquito-borne zoonotic pathogen, is one of the major causes of viral encephalitis worldwide. JEV is mainly prevalent in East, South, and Southeast Asia, and is also found in the south Pacific region, including Australia. JEV has epidemiced in China for over 60 years, since the first JEV isolate was reported in 1949. Although vaccination have now dramatically reduced the number of JE cases, it remains a major public health problem. Huaihua County is located in southwestHunan(N27°48’09.57 ", E109°95’39.61") bordering Guangxi and Guizhou Provinces. Huaihua lies in the subtropical monsoon climate zone and is the biggest county in Hunan province. Its warm sunny climate and abundant rainfall provide Culex tritaeniorhynchus(Giles) with excellent breeding conditions. There has been very little recent research on Cx. tritaeniorhynchus, which is the dominant JEV vector in the Huaihua County. Detailed investigations of basic aspects of the ecology of this species such as, population density and seasonal population fluctuations have yet to be done. Moreover, it remains unknown if Cx. tritaeniorhynchus is still the dominant species after ongoing urbanization and development in the Huaihua region, including gradual reduction in rice cultivation and standardization of pig husbandry. In addition, the lack of in depth research on common JEV strains in this region limits our current understanding of local JEV genotypes and their etiology. For example, China’s JEV monitoring database shows a gradual replacement of the JEV Type III genotype by the Type I genotype over the past 30 years, but the relative prevalence of different JEV genotypes in the Huaihua region remains unclear.We here present the study of mosquito species diversity, seasonal population fluctuations of Cx. tritaeniorhynchus and mosquito-borne pathogens in Huaihua County. Also, the genotypes and molecular characteristics of current, common JEV genotype in this region was conducted. The results are as follows.Research on mosquito species diversity in different habitats in the Huaihua region revealed that community composition was relatively simple, the main species being Culex pipiens, Cx. tritaeniorhynchus and Anopheles sinensis. Cx. tritaeniorhynchus was clearly the dominant species comprising 94.2%~98.6% of all specimens and was always the most common species captured in pig pens and human dwellings. The seasonal abundance of Cx. tritaeniorhynchus was relatively even with a single seasonal peak in late August. The lowest JEV infection ratios among mosquitoes captured in 2012 and 2013 were 1: 3858 and 1: 2381, respectively. The genetic affinities of the Huaihua JEV strain were determined by analyzing C/Pr M and E gene variation. The results show that The Huaihua JEV strain is of the Type III genotype, and most closely related to the live, attenuated vaccine strains SA14, SAl4-14-2 and YN0901. The Huaihua E protein shares 98.8% similarity at the nucleotide level, and 99.98% similarity at the amino acid level, with the SA14-14-2 vaccine. Although we found that the E gene sequences of the Huaihua JEV strain and the SAl4-14-2 vaccine differed at 11 amino acid sites, key sites associated with JEV virulence were identical. According to the results, the following conclusions are:Research on mosquito species diversity in different habitats in the Huaihua region revealed that community composition was relatively simple, the main species being Culex pipiens, Cx. tritaeniorhynchus and Anopheles sinensis. Cx. tritaeniorhynchus was clearly the dominant species comprising 94.2%~98.6% of all specimens and was always the most common species captured in pig pens and human dwellings. The seasonal abundance of Cx. tritaeniorhynchus was relatively even with a single seasonal peak in late August.The Minimum JEV infection ratios among mosquitoes captured in 2012 and 2013 were 1: 3858 and 1: 2381, respectively. 3. The results show that The Huaihua JEV strain isolated in mosquito and pig were of the Type III genotype, and most closely related to the live, attenuated vaccine strains SA14, SAl4-14-2 and YN0901. The Huaihua E protein shares 98.8% similarity at the nucleotide level, and 99.98% similarity at the amino acid level, with the SA14-14-2 vaccine. Although we found that the E gene sequences of the Huaihua JEV strain and the SAl4-14-2 vaccine differed at 11 amino acid sites, key sites associated with JEV virulence were identical.Comparison of sequence data revealed that, although the Huaihua JEV strain isolated in mosquito and pig and the SA-14-14-2 vaccine differed at 11 shared amino acid sites, key regions that determine antigenic activity were identical. This suggests that the Huaihua JEV strain’s antigenicity is the same as that of the SA-14-14-2 vaccine strain. In theory, the currently used SA-14-14-2 vaccine should be effective in protecting against infection by the Huaihua JEV strain.