1 Introduction
Severe fever with thrombocytopenia syndrome (SFTS) is a new acute infectious disease caused by the severe fever with thrombocytopenia syndrome virus (SFTSV) (Yu et al., 2011)belonging to a a novel phlebovirus (SFTS virus, SFTSV) in the family Phenuiviridae of the order Bunyavirales (Li et al., 2019). It was first reported in 2009 in the rural areas of the Hubei and Henan Provinces in Central China, and the population is generally susceptible. Since then, the incidence of SFTS has been successively reported in more than 10 provinces and cities in China(Zhang et al., 2013), and its epidemic area has a tendency to spread. The disease is also widely distributed in South Korea (Denic et al., 2011; Yun et al., 2016) and Japan(Takahashi et al., 2014), and cases of SFTS have also been reported in the United States (McMullan et al., 2012; Muehlenbachs et al., 2014). The main clinical manifestations of the disease are high fever, anorexia, muscle pain, chills, lymphadenopathy, leukopenia, thrombocytopenia, and multiple organ failure (Sun et al., 2019). Severe cases can lead to death.
SFTSV is an arbovirus mainly carried by ticks(Liu et al., 2012). The SFTSV virus genome is composed of three independent gene segments: L segment (6,368 bp; encodes the RNA-dependent RNA polymerase), M segment (3,378 bp; encodes the membrane protein precursor), and the ambisense S segment (1,744 bp; encodes the non-structural S protein and nucleocapsid protein)(Sun et al., 2014).
Rickettsiosis is a zoonotic disease mainly spread by ticks and is considered an important global emerging zoonotic disease (Parola, Paddock, & Raoult, 2005). Humans are infected by the bite of ticks that carry rickettsial bacteria. Due to human factors such as lifestyle changes and population rates, and to environmental factors such as climate change, people have become more exposed to ticks. Rickettsiosis in humans usually refer to infections caused by bacterial species belonging to the genus Rickettsia andOrientia . It can be classified into typhus, spotted fever, and tsutsugamushi disease(Adem, 2019). Clinically, human serum rickettsia antibodies are used to determine whether the human body is infected withRickettsia . The typical clinical features of these diseases include: fever, fatigue, anorexia, nausea, headache, and rash, and the bite of the tick has eschar formation (Liu et al., 2016). These symptoms usually appear within 1‒2 weeks after infection(Liu et al., 2016). The clinical manifestations of typhus and SFTS are similar, thereby complicating diagnosis.
In 2019, our laboratory carried out clinical analysis, laboratory diagnosis, and traceability studies of SFTSV in suspected cases in the Infectious Disease Hospital of Shenyang City to characterize SFTSV in patients in Northeast China. Molecular diagnosis and antibody testing for Rickettsia were also performed to determine the rates ofRickettsia coinfection with other tick-borne diseases, especially with SFTSV. The results we present here provide insights into the characteristics of SFTSV in Northeast China. Further, our findings can guide clinicians in the diagnosis of tick-borne diseases.