Phylogeographic analysis of severe fever with thrombocytopenia syndrome virus from Zhoushan Islands, China: implication for transmission across the ocean

Abstract

From June 2011 to August 2014, 21 cases of infection by severe fever with thrombocytopenia syndrome bunyavirus (SFTSV) were confirmed in Zhoushan Islands in the Eastern coast of China. To identify the source of SFTSV in Zhoushan Islands, the whole SFTSV genomes were amplified and sequenced from 17 of 21 patients. The L, M, and S genomic segments of these SFTSV strains were phylogenetically analyzed together with those of 188 SFTSV strains available from GenBank. Phylogenetic analysis demonstrated SFTSV could be classified into six genotypes. The genotypes F, A, and D were dominant in mainland China. Additionally, seven types of SFTSV genetic reassortants (abbreviated as AFA, CCD, DDF, DFD, DFF, FAF, and FFA for the L, M and S segments) were identified from 10 strains in mainland China. Genotype B was dominant in Zhoushan Islands, Japan and South Korea, but not found in mainland China. Phylogeographic analysis also revealed South Korea possible be the origin area for genotype B and transmitted into Japan and Zhoushan islands in the later part of 20(th) century. Therefore, we propose that genotype B isolates were probable transmitted from South Korea to Japan and Zhoushan Islands.

Figure 1. Comparison of monthly distributions of reported SFTS cases between Zhoushan and Mainland China.

Figure 2. Maximum likelihood (ML) phylogenetic trees of SFTSV L(A), M(B), and S(C) genomic segments.

Bootstrap values for ML and NJ tree are shown at corresponding nodes. The red, purple, blue, and green branches represent the strains from Zhoushan, mainland China, Japan, Korea, respectively. The pen diamonds indicate the strains from animals, including ticks, sheep, cows, and dogs. Ten SFTSV reassortants are highlighted by the colored circles, squares, and triangles.

Figure 3. Genotype distribution of SFTSV in China, Korea and Japan.

(A) The location of Zhoushan Islands, (B) Genotype distribution of SFTSV. Arrows indicate the transmission routes of SFTSV genotype B and the transmission routes of SFTSV genotype A from central China to Zhoushan. Two islands where SFTSV was circulating are highlighted in purple. The map was drawn with packages “maps” and “mapdata” in R version 3.1.3(https://cran.r-project.org/web/packages/mapdata/index.html)