Characterization of Severe Fever with Thrombocytopenia Syndrome in Rural Regions of Zhejiang, China

Abstract

Severe fever with thrombocytopenia syndrome virus (SFTSV) infections have recently been found in rural regions of Zhejiang. A severe fever with thrombocytopenia syndrome (SFTS) surveillance and sero-epidemiological investigation was conducted in the districts with outbreaks. During the study period of 2011–2014, a total of 51 SFTSV infection cases were identified and the case fatality rate was 12% (6/51). Ninety two percent of the patients (47/51) were over 50 years of age, and 63% (32/51) of laboratory confirmed cases occurred from May to July. Nine percent (11/120) of the serum samples from local healthy people without symptoms were found to be positive for antibodies to the SFTS virus. SFTSV strains were isolated by culture using Vero, and the whole genomic sequences of two SFTSV strains (01 and Zhao) were sequenced and submitted to the GenBank. Homology analysis showed that the similarity of the target nucleocapsid gene from the SFTSV strains from different geographic areas was 94.2–100%. From the constructed phylogenetic tree, it was found that all the SFTSV strains diverged into two main clusters. Only the SFTSV strains from the Zhejiang (Daishan) region of China and the Yamaguchi, Miyazakj regions of Japan, were clustered into lineage II, consistent with both of these regions being isolated areas with similar geographic features. Two out of eight predicted linear B cell epitopes from the nucleocapsid protein showed mutations between the SFTSV strains of different clusters, but did not contribute to the binding ability of the specific SFTSV antibodies. This study confirmed that SFTSV has been circulating naturally and can cause a seasonal prevalence in Daishan, China. The results also suggest that the molecular characteristics of SFTSV are associated with the geographic region and all SFTSV strains can be divided into two genotypes.

Low Seroprevalence of Severe Fever with Thrombocytopenia Syndrome Virus Antibodies in Individuals Living in an Endemic Area in Japan

“…Similar to our findings, a previous study reported a low seroprevalence (2/237, 0.8%) of SFTSV antibodies in the general population of Yiyuan County, Shandong Province, China, in which more than 80% of the goats were positive for anti-SFTSV antibodies (16). In contrast, studies conducted in SFTS endemic regions in China have shown a higher seroprevalence (more than 5%) among healthy in- dividuals (17)(18)(19)(20). Furthermore, a recent study in South Korea reported that the seroprevalence of SFTS among patients visiting a tertiary hospital was 2.1%.…”

Seroprevalence of Severe Fever with Thrombocytopenia Syndrome in Southeastern Korea, 2015

“…The SFTSV Seropositivity rate in China is 0.3%–9.2%, depending on the population group and region investigated (678910111213141516). However, no study has addressed the seroprevalence of SFTSV in Korea.…”

Presence of Antibodies against Severe Fever with Thrombocytopenia Syndrome Virus in Non-Endemic Areas of China

“…However, some areas in China, with a similar environment as in endemic areas, SFTS cases have not been found. Furthermore, since 2010, when SFTSV was found to be the pathogen responsible for SFTS (3), serological surveys were conducted to understand SFTSV seroprevalence, which was found to be inconsistent (ranging from 0% to 9.2%) and rare, especially in non-endemic areas (14)(15)(16)20). Therefore, it is urgent to conduct investigations of SFTSV seroprevalence to know the infection status in such areas.…”