| Objective:At present,dengue fever has been reported in more than 100 countries,and dengue fever has become a public health problem in the world.Since 2008,the epidemic of dengue fever has been continuously occurring in Yunnan.In 2017,an outbreak of dengue fever was caused by DENV-1 in Xishuangbanna,Yunnan,with 1348 confirmed cases.In this study,the molecular characteristics of dengue epidemic strains in Xishuangbanna,Yunnan,2017 were analyzed in order to find out the relationship between the evolution of virus strain and dengue fever epidemic.Methods:A statistical analysis were conducted based on Dengue Fever infection cases in Yunnan from 2010 to 2017.200 serum samples of dengue fever patients were selected during 2017 dengue outbreak in Xishuangbanna Dai Autonomous Prefecture.The sample were use for extraction of nucleic acids,serotype identification.Then the NS1 gene and whole genome sequence of Dengue virus were obtained,respectively,followed by evolution and mutation analysis.Results:Total number of infected cases reached 6524 from 2010 to 2017.The number of infected cases of Xishuangbanna Dai Autonomous Prefecture,Dehong Dai Jingpo Autonomous Prefecture and Lincang City was in the top three,with a cumulative number of 3856,1938 and 517 cases,respectively,each accounted for 59.1%,29.7%,7.9%of the province’s cumulative cases.Xishuangbanna Dai Autonomous Prefecture,Lincang City showed a large outbreak every other year.While,there are more than 100 cases of dengue fever patients each year in Dehong Dai Jingpo Autonomous Prefecture since 2013.all patients were identified as DENV-1 infection.The NS1 genes of DENV-1 isolates originated from 2017 dengue outbreak in Xishuangbanna Dai Autonomous Prefecture was closely related to 2011-China Guangdong(JQ048541).And the NS1 genes of the 16 viruses were more conservative.The complete genome sequences of the five isolates were 10,735 nucleotides in length.Phylogenetic analysis classified all five isolates as genotype I of DENV-1,while isolates of local residents and Burmese travelers belonged to different branches.The three locally isolates were most similar to the Dongguan strain in 2011,and the other two isolates from Burmese travelers were most similar to the Laos strain in 2008.Comparing,twenty-four amino acid substitutions were important in eight evolutionary tree branches.Comparison with DENV-1 SS,658 base substitutionswere observed in local isolates,resulting in 87 synonymous mutations.Compared with the local isolates,52 amino acid mutations occurred in the CDS of two isolates from Burmese travelers.Comparing MY21 with MY22,17 amino acid mutations were observed,all these mutations occurred in the CDS of non-structured proteins.Secondary structure prediction revealed 46 changes in the potential nucleotide and protein binding sites of the CDSs in local isolates.RNA secondary structure prediction also showed base changes in the 3’UTR of local isolates,leading to two significant changes in the RNA secondary structure.Conclusion:In 2017,the Dengue Type 1 strain of Xishuangbanna,Yunnan may have originated in Southeast Asia,and the Myanmar strain may have originated in Laos.Amino acid analysis revealed that the substitution of 24 amino acids played an important role in the branching of evolutionary trees,and may be a key site for the dengue epidemic.In addition,amino acid substitution in the E protein region of Banna strain may enhance the virulence of the strain. |
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