An outbreak of dengue serotype 1 virus in Xishuangbanna prefecture of Yunnan province, China, 2017

ObjectiveTo understand the epidemiologic, virologic and genetic characteristics of an outbreak of dengue fever in Xishuangbanna prefecture of Yunnan province in 2017.

MethodsThe incidence data of dengue fever in Xishuangbanna were collected. The serum samples from acute patients were collected to detect the nucleic acid of dengue virus by reverse transcription- polymerase chain reaction(RT-PCR) assay. Coding regions of C/prM and E genes of dengue virus were amplified by RT-PCR and sequenced. The phylogenetic tree was constructed by Neighbor-Joining methods of MEGA 5.0 software.

ResultsA total of 1 348 laboratory confirmed dengue fever cases were reported in Xishuangbanna in 2017, in which 1 231 were indigenous cases (91.32%), 117 were imported cases (8.68%). Imported cases from Laos and Myanmar were reported in Jinghong, Mengla and Menghai counties of Xishuangbanna, and indigenous cases occurred in Jinghong (1 030, 83.67%) and Mengla (201, 16.33%). The epidemic of dengue fever lasted from May to December. The majority of patients were aged 20－54 years, the youngest was 2 year-old and the oldest was 89 year-old. The male to female ratio of the cases was 1∶1.16. Phylogenetic analysis on nucleotide sequences of C/PrM of 48 virus strains obtained from the serum samples of dengue fever cases indicated that the 46 strains belonged to dengue virus serotype 1 (DENV-1), in which 33 from Jinghong, 10 from Mengla and 3 from Menghai and 2 strains belonged to dengue virus serotype 2 (DENV-2), in which 1 from Mengla and 1 from Menghai. The DENV-1 strains from imported cases of Laos shared high homology with the strains from indigenous cases.These DENV-1 strains from Xishuangbanna had closer genetic relationship with the DENV-1 strains isolated from Ruili county of Dehong prefecture and Gengma county of Lincang prefecture of Yunnan and the countries of southeastern Asia in recent years.

ConclusionThe dengue fever epidemic occurred in Xishuangbanna in 2017 was mainly caused by DENV-1. The imported dengue fever cases from Laos were the main sources for the indigenous transmission of dengue fever in Xishuangbanna. It is necessary to strengthen control of the cross-border spread of dengue fever in this area.