Investigation on an outbreak of dengue serotype 2 virus in Xishuangbanna prefecture of Yunnan province in 2015

Abstract

Objective To understand the epidemiologic features of an outbreak of dengue fever (DF) in Xishuangbanna prefecture of Yunnan province in 2015, with its viral serum-type and transmission source. Methods The data of DF cases in Xishuangbanna prefecture were collected. The serum samples from acute stage of these patients were collected to detect the viral nucleic acid by RT-PCR assay. The phylogenetic tree was generated and analyzed based on the nucleotide sequences of C/PrM gene fragments of dengue virus (DENV). Results A total of 1 132 cases of DF were reported in Xishuangbanna prefecture in 2015. Of them, 1 089 were indigenous cases (96.20%), 43 were imported cases (3.80%), i. e., 38 from Myanmar, 3 from Laos and 2 from Thailand. Autochthonous DF occurred in urban area and Gasa towan of Jinghong city that there was distribution of Aedes aegypti mosquitoes. Epidemic month of DF was from July to December. The majority of patients were aged from 20 to 49 years-old, with the youngest 2 years old and the eldest 93 years old. The male to female ratio was 1: 1.05. The results of virus nucleic acid detection and sequencing indicated that nucleotide sequences of C/PreM of 33 virus strains were obtained from the DF cases. Phylogenetic analysis indicated that the 33 strains belonged to DENV serotype 2 (DENV-2), and the strain from the imported cases of Thailand shared high homology with the strains from indigenous cases as well as belonged to same clade. These DENV-2 strains from Xishuangbanna had a closer genetic relationship with the strains isolated from Southeast Asia, Fujian and Guangdong provinces of China, however, distant relatives with DENV-2 strains from Ruili city of Yunnan province in 2014. Conclusions The autochthonous DF epidemic occurred in Xishuangbanna in 2015 was caused by DENV-2. The study also suggests that the transmission of DF from Thailand to Xishuangbanna of China was the main cause of the autochthonous DF epidemic, and Aedes aegypti mosquito was the main transmitting vector in the local. Should strengthen surveillance and management on the imported cases and indigenous cases of DF and mosquito control in this region is the key measures to prevent prevalence of the disease once again. Key words: Dengue fever; Dengue virus; Phylogenetic analysis; Epidemiology