First Isolation of Severe Fever with Thrombocytopenia Syndrome Virus from Haemaphysalis longicornis Ticks Collected in Severe Fever with Thrombocytopenia Syndrome Outbreak Areas in the Republic of Korea

Abstract

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infectious disease that is endemic to China, Japan, and the Republic of Korea (ROK). In this study, 8313 ticks collected from SFTS outbreak areas in the ROK in 2013 were used to detect the SFTS virus (SFTSV). A single SFTSV was isolated in cell culture from one pool of Haemaphysalis longicornis ticks collected from Samcheok-si, Gangwon Province, in the ROK. Phylogenetic analysis showed that the SFTSV isolate was clustered with the SFTSV strain from Japan, which was isolated from humans. To the best of our knowledge, this is the first isolation in the world of SFTSV in ticks collected from vegetation.

Keywords: Haemaphysalis longicornis; Isolate; Republic of Korea; SFTSV.

FIG. 1.

Geographical location of collection sites in this study. Open circles show the sites in which positive tick pools for SFTSV were detected. GG, Gyeonggi Province; GW, Gangwon Province; CB, Chungcheongbuk Province; CN, Chungcheongnam Province; JB, Jeonllabuk Province; JN, Jeonllanam Province; GB, Gyeongsangbuk Province; GN, Gyeongsangnam Province; JJ, Jeju Special Autonomous Province.

FIG. 2.

Identification of severe fever with thrombocytopenia syndrome virus (SFTSV) isolated from ticks and phylogenetic analysis of SFTSV strains. (A) Detection of SFTSV M segment gene (560 bp) from the supernatant of the KAGWT-infected cell culture after three passages by RT-PCR. Lane M, 1-kb DNA plus ladder. Identification of antigenicity by indirect immunofluorescent assay (IFA) (B) and immunoblotting (C) for Vero E6 cells infected with KAGWT using anti-SFTSV nucleoprotein (NP) monoclonal antibody. Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) was used as a protein loading control. (D) Transmission electron microscopy (TEM) image of Vero E6 cells infected with the KAGWT strain (arrows). Scale bar in the image indicates 200 nm. Magnification, 80,000×. (E) Phylogenetic analysis of SFTSV strains based on the partial M segment sequences. Phylogenetic trees constructed using the neighbor-joining (NJ) method based on the p-distance model in MEGA version 6 (5000 bootstrap replicates). The phylogenetic branches were supported with greater than 70% bootstrap values in this analysis. Uukuniemi virus, Rift Valley fever virus, Heartland virus, Hunter Island Group virus, and Sandfly virus were used as outgroups. The scale bar indicates the nucleotide substitutions per position. Each strain is identified by strain name followed by GenBank accession number, source of virus, and geographical origin, except for the five outgroups. The Korean strain isolated in this study is marked with a closed circle.