Genetic Susceptibility Is One of the Determinants for Severe Fever with Thrombocytopenia Syndrome Virus Infection and Fatal Outcome: An Epidemiological Investigation

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease in China and case-fatality rate of SFTS is very high (approximately 10%). However, genetic susceptibility for SFTS virus (SFTSV) infection and fatal outcome of SFTSV infection in humans are unclear. In this study, we investigated the clinical, laboratory and epidemiological features of SFTS in a cluster of three sisters who died of SFTSV infection between late April and mid-May 2014. Before disease onset, two of the sisters (Case A and case B) had common exposure history for ticks by working together in a field to pick tea leaves from April 8 to April 12. The third sister (Case C) did not live or work together with case A and B, but had ticks in her living environment. SFTSV RNA sequences were amplified from three cases were not identical, suggesting that the three sisters were most likely infected with SFTSV through tick bite rather than through person-to-person transmission of SFTSV. The sequence of SFTSV from case C was identical to SFTSV sequences from 3 groups of ticks collected around the residential area of case C. Seroprevalence of SFTSV IgG antibody among healthy population in the area where the patients resided was 4.05% (3/74). The majority of SFTSV infections were mild cases and all three sisters died of SFTSV infection suggested that they were highly susceptible to SFTSV. Our findings indicated that genetic susceptibility was a risk factor for SFTSV infection and fatal outcome.