Session 2. 곤충매개 인수공통전염병: Vectorborne Zoonotic Diseases : S2-2 ; Severe Fever with Thrombocytopenia Syndrome: Molecular and Serological Diagnosis

Severe fever with thrombocytopenia syndrome (SFTS) is a new emerging viral infectious disease, first reported in China in 2010. Patients with SFTS have been reported recently in South Korea and Japan in 2013. Totally 36 cases of SFTS were identified in Korea in 2013 with case fatality rate of 47%. The SFTS is characterized by acute febrile illness, thrombocytopenia, leucopenia, gastrointestinal symptoms, elevated serum enzymes and multi-organ failure which are not specific signs and symptoms for SFTS. The SFTS virus (SFTSV) causing SFTS belongs to the genus Phlebovirus in the family Bunyaviridae. Heartland viruses and Hunter Island Group virus (HIGV) which are related to but distinctly different from SFTSV were isolated from patients in the US and ticks in Australia, respectively. The patients infected with Heartland virus presented a similar signs and symptoms to SFTS. HIGV was isolated from ticks collected from shy albatross on Albatross Island, a small island in the Hunter Island Group in northwestern Tasmania, Australia. The SFTSV has been detected in Haemaphysalis longicornis and Rhipicephalus microplus ticks suggesting that the causative agent of SFTS, SFTSV is transmitted possibly to humans by ticks, such as H. longicornis which is considered as the principal vector of SFTSV. Recently Amblyomma testudinarium and Ixodes nipponensis are also implicated as the vector of SFTSV. Although cases of person-to-person transmission through contact with infected patient’s blood or mucous have also been reported in China, transmission of SFTSV takes place by biting of ticks infected with SFTSV. The SFTS presents with clinical manifestations similar to those of other infectious vector-borne diseases, such as hemorrhagic fever with renal syndrome (HFRS), scrub typhus, leptospirosis and anaplasmosis, strongly suggesting the need for differential diagnosis of SFTS from other infectious diseases. HFRS, leptospirosis and anaplasmosis are caused by Hantavirus, Leptospira interrogans and Anaplasma phagocytophilum, respectively. Wild rodents (Apodemus agrarius) play the role of the primary natural reservoir for these pathogens. HFRS, scrub typhus and leptospirosis are endemic in eastern and south-east Asia including Korea. In terms of distribution of hosts and reservoirs of vector-borne pathogens in the environment, and current coexistence of these diseases in the same epidemic area, concurrent infections of these vector-borne diseases can occur. Therefore, a reliable SFTSV detection tool is urgently required to provide early diagnosis of SFTS to support clinical care, infection control and epidemiological surveillance. Laboratory diagnosis of SFTSV infection is carried out by various ways, including nucleic acid amplification, detection of viral antigen, virus isolation and antibody detection to SFTSV using by real-time RT-PCR, Vero E6 cell culture, enzyme-linked immunosorbent assay (ELISA) and indirect fluorescent assay (IFA). Conventional RT-PCR and real-time RT-PCR was developed in our laboratory and applied to detect SFTSV from hospitalized patients who presented SFTS symptoms. The SFTSVs were detected from 35 specimens among more than 300 serum specimens in 2013 and the nucleotide sequence was analyzed for identification of the SFTSV. The Korean isolates of SFTSV showed 93-98% similarityof the nucleotide sequences to Chinese and Japanese isolates of SFTSV and were distinctly different from Heartland virus. SFTSVs were also isolated by Vero E6 cell culture and identified by the nucleotide sequence, IFA using monoclonal antibodies, and electron microscopy. As reported, antibody to SFTSV can be detected as early as 2 to 4 days after illness onsets by serological assays and persists in some patients even one year after recovery. Seroconversion against SFTS V in patients with SFTS occurs mostly more than 3 weeks after onsets of illness. We developed IFA for laboratory diagnosis and determined serologic cross reactivity of SFTSV to Hantavirus and rickets. Slides for IFA were prepared with Vero E6 cells infected with SFTSV and Hantaan virus (HTNV). Commercial IFA kits for Anaplasma, Ehrlichia, Leptosira and Origentia spp were also used in the study. Serum specimens of SFTSV patients, sera of HTNV IgG antibody of more than 512 and paired sera of scrub typhus patients were tested with IFA. None of sera specimens showed specific antibody reaction to SFTSV infected cells and antigens assayed by IFA. IgG titers to each homogeneous antigen of HTNV and O.tsutsugamushi assayed by IFA were ranged from 512 to 4,096 and from 0 to 8,192. These results suggest that SFTSV does not have cross reactivity to at least, HTNV and O. tsutsugamushi. Considered currently occurrence of SFTSV, HTNV and O. tsutsugamushi in the same epidemic of the country, concurrent infection can be identified by serological assays. In the presentation, we report a case of coinfection with SFTSV and Hantavirus in humans. To the best of our knowledge, this is the first case report of coinfection with SFTSV and Hantavirus. A 66-year-old farm-dwelling woman was admitted to the hospital with a 6-day history of worsening fever and myalgia. Neutropenia and thrombocytopenia were evident on admission to the intensive care unit. SFTSV infection was suspected based on clinical findings and laboratory test results, although the patient had no recollection of a tick bite and there was no evidence of tick bites. She was treated with plasma exchange and oral ribavirin (4.0g/day) after 10 days of illness onset and had fully recovered at 15 days after illness onset Considering the concurrence of SFTS, HFRS and ricketiisial diseases in the endemic area and the higher possibility of exposure to pathogens due to the patient’s area of residence and occupation as a farmer, coinfection with SFTSV, hantavirus and ricketiisial agents in the patient is suggested. Determining the effects of coinfection on disease prognosis and laboratory diagnosis could be helpful in deciding patient treatment and management.