Ecology of the Tick-Borne Phlebovirus Causing Severe Fever with Thrombocytopenia Syndrome in an Endemic Area of China.

Zhifeng Li,Carol J Cardona,Xiaochen Wang,Fenyang Tang,Jianli Hu,Xuejian Liu,Jiangang Zhou,Yefei Zhu,Changjun Bao,Xian Qi,Hongjun Zhao,Luxun Li,Lei Zhang,Zhengmin Ji,Zheng Xing,Ai-Hua Shen ,Winston Tan ,Zhi Chun Feng ,Wendong Li

doi:10.1371/journal.pntd.0004574

Abstract

BackgroundSevere fever with thrombocytopenia syndrome (SFTS) is caused by SFTS virus (SFTSV), a tick-borne phlebovirus in family Bunyaviridae. Studies have found that humans, domestic and wildlife animals can be infected by SFTSV. However, the viral ecology, circulation, and transmission remain largely unknown.Methodology/Principal FindingsSixty seven human SFTS cases were reported and confirmed by virus isolation or immunofluorescence assay between 2011 and 2014. In 2013–2014 we collected 9,984 ticks from either vegetation or small wild mammals in the endemic area in Jiangsu, China, and detected SFTSV-RNA by real-time RT-PCR in both questing and feeding Haemaphysalis longicornis and H. flava. Viral RNA was identified in larvae of H. longicornis prior to a first blood meal, which has never been confirmed previously in nature. SFTSV-RNA and antibodies were also detected by RT-PCR and ELISA, respectively, in wild mammals including Erinaceus europaeus and Sorex araneus. A live SFTSV was isolated from Erinaceus europaeus captured during the off tick-feeding season and with a high SFTSV antibody titer. Furthermore, SFTSV antibodies were detected in the migratory birds Anser cygnoides and Streptopelia chinensis using ELISA.Conclusions/SignificanceThe detection of SFTSV-RNA in non-engorged larvae indicated that vertical transmission of SFTSV in H. longicornis might occur in nature, which suggests that H. longicornis is a putative reservoir host of SFTSV. Small wild mammals such as Erinaceus europaeus and Sorex araneus could be infected by SFTSV and may serve as natural amplifying hosts. Our data unveiled that wild birds could be infected with SFTSV or carry SFTSV-infected ticks and thus might contribute to the long-distance spread of SFTSV via migratory flyways. These findings provide novel insights for understanding SFTSV ecology, reservoir hosts, and transmission in nature and will help develop new measures in preventing its rapid spread both regionally and globally.

Highlights

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with a relatively high mortality, caused by the SFTS virus (SFTSV), a recently identified phlebovirus in the family Bunyaviridae [1]
Studies have found that a variety of domestic and wildlife animals can be infected by SFTS virus (SFTSV), but the natural reservoir host for the virus remains unclear
The SFTSV-RNA was identified in certain species of ticks or their larvae, contamination from their host animals cannot be excluded to be the source

Summary

Introduction

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with a relatively high mortality, caused by the SFTS virus (SFTSV), a recently identified phlebovirus in the family Bunyaviridae [1]. The death rates reported have varied from 2.5 to 30%. By the end of 2014, over 5,000 cases of human SFTS had been reported in 23 provinces in China [3]. The disease was reported from Japan and Korea, where SFTSV strains were isolated, and a closely related virus called Heartland virus was isolated from patients with similar symptoms in the United States, which could be transmitted by ticks [6,7,8]. Severe fever with thrombocytopenia syndrome (SFTS) is caused by SFTS virus (SFTSV), a tick-borne phlebovirus in family Bunyaviridae. The viral ecology, circulation, and transmission remain largely unknown

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