Tick-borne severe fever with thrombocytopenia syndrome virus (SFTSV) is a novel Phlebovirus in the family of Bunyaviridae and a causative agent of an emerging infectious disease in China, Japan, and the Republic of Korea (ROK). SFTS is mainly characterized by fever, leukopenia and thrombocytopenia in human. The purpose of this study is to investigate the circulation of SFTSV in the natural environments. The results of this study will provide the circulation and phylogenetic relationship among SFTS Phlebovirus ioslates.
To investigate the prevalence of SFTSV in the ROK, a total of 4,223 ticks were collected by flagging from Deogyusan National Park from 2015 to 2018. Animal sera were collected from domestic, wild and companion animals during 2013-2018. Viral RNA was extracted from ticks and sera using viral RNA extraction kit. One-step RT-nested PCR was performed to amplify the S segment of the SFTS virus. The sequence data were analyzed using Chromas and were aligned using CLUSTAL X. The phylogenetic analysis was constructed using the neighbor-joining method in MEGA7.
SFTSV was detected from all of the developmental stages, unfed lava, nymph and adult ticks. Haemaphysalis longicornis (3611, 85.5%) were the most abundant, followed by H. flava (502, 11.88%), Ixodes nipponensis (109, 2.5%), and Ixodes ovatus (1, 0.02%). The infection rate of SFTSV in total ticks was 5.8% (245/4,223), and the infection annual rate was 3.69% in 2015, 7.97% in 2016, 5.08% in 2017 and 4.68% in 2018. Three of 103 (2.9%) military dogs, 6 of 101 (5.9%) feral cats, 5 of 127 (3.9%) house cats, 32 of 1,005 (3.2%) black goats, 4 of 240 (1.7%) domesticated pigs, and 12 of 99 (12.1%) cattle were positive for SFTSV. Based on phylogenetic analysis, SFTSV is generally classified into Japanese and Chinese clades. In 36 sequences obtained from this study, 34 (94.4%) sequences were included in Japanese clade and only 2 (5.6%) sequences were included in Chinese clade.
These results indicates that SFTS Phlebovirus may have been circulated and distributed to several tick species and variety animals in the natural environments in Korea.