Molecular tracing of pathogen of three local dengue fever cases originated from imported case in Shenzhen in 2017

Abstract

Objective To trace the origin of pathogens of three local dengue fever cases in Shenzhen in 2017. Methods The epidemiological surveys were conducted and the serum samples were collected from suspected dengue fever patients to detect IgM and IgG against dengue virus, NS1 antigens and nucleic acids. Dengue fever virus was isolated with C6/36 cell line and typing of virus was performed by real-time RT-PCR. The E genes of the virus strains were sequenced after amplification by RT-PCR for the construction of phylogenetic tree. Results The serum samples of three local patients were positive for dengue virus nucleic acids and NS1 antigens. Two dengue virus strains from local cases and one strain from an imported case from Malaysia showed 100% similarity in E gene sequences. The isolated virus strains were confirmed to be dengue virus type-2 (subtype Ⅳ). The stains were the closest to the predominant strain TM280 in 2014 in Malaysia and the similarities of nucleotide sequences and amino acid sequences were 99.7% and 99.8%, respectively, indicating that virus strains might originated from Malaysia. Conclusions Both on-site epidemiological data and laboratory molecular genetic analysis suggested that three local dengue fever cases in Shenzhen in 2017 may be the secondary cases caused by the imported case returned from travelling in Malaysia. Key words: Dengue fever; Local case; Secondary case; E gene; Epidemiology