Identification of Endemic Region for Severe Fever with Thrombocytopenia Syndrome in an Alluvial Plain of Hebei Province, China.

Severe fever with thrombocytopenia syndrome (SFTS), an emerging infectious tick-borne viral disease, is increasingly affecting human beings worldwide. SFTS monitoring has been carried out since 2010 in mainland China. Since 2022, an increase in local cases has been noted in the central coastal plain region of Hebei Province. This study aimed to identify the endemic region in the central coastal plain region by epidemiological characteristics, antibody surveillance and molecular characterization. Case data were obtained from the Chinese Disease Control and Prevention Information System. Serum samples from suspected or clinically diagnosed cases, the indigenous healthy population and native domesticated animals were collected for laboratory tests, along with ticks in the central coastal plain region of Hebei Province, China. The local cases were mainly distributed in Cangzhou City, located at the central coastal plain region of Hebei Province. The 0.68% of IgM antibody detection rate and 1.71% of IgG antibody detection rate in this study showed the potential existence of subclinical or mild infections in Cangzhou. Phylogenetic analysis indicated that all sequences from patients, ticks and sheep clustered within the F subtype, exhibiting a close evolutionary relationship and the possible circulation of SFTSV having established among animal hosts and ticks in Cangzhou. These findings first identify the natural focus of SFTSV in the central plain region of Hebei Province, highlighting enhanced surveillance measures for preventing and controlling SFTSV.