Two confirmed cases of severe fever with thrombocytopenia syndrome with pneumonia: implication for a family cluster in East China

Background

Severe fever with thrombocytopenia syndrome (SFTS) was first reported in China in 2011. Human-to-human transmission of the virus occurred occasionally in family clusters. However, pneumonia as an onset syndrome was not common in most SFTS cases. Our aim is to report a family cluster of SFTS with clinical manifestation of pneumonia in Shanghai.

Methods

Epidemiologic investigations were conducted when a family cluster of severe fever with thrombocytopenia syndrome virus (SFTSV) infection was identified in Shanghai in June 2016. Samples were collected from two secondary cases and two close contacts with fever. SFTSV was detected by Real-Time reverse transcription polymerase chain reaction (RT-PCR).

Results

There were two confirmed STFS cases and one potential index case. The potential index case became ill on 21 May and died on 31 May. Case A had onset from 4 to 23 June and case B from 8 June to 25 June. All the three cases experienced pneumonia at the early stage of SFTSV infection. Three (3) out of thirty two (32) close contacts had symptoms of fever or cough but were detected STFSV negative by real-time RT-PCR. According to epidemiologic investigations, the potential index case had outdoor activities on a nearby hill. A tick bite could have been the reason for the SFTSV infection in the potential index case as ticks were found both in grassland or shrubs on the hill and also found on mice caught in her house. Both cases A and B had provided bedside care for the potential index case without any protection and had contacted with blood and other body fluids.

Conclusion

It was a family cluster of SFTSV infection imported from Jiangsu province located in the east of China. We suggested to become alert to atypical SFTSV infected cases.

A Cluster of Symptomatic and Asymptomatic Infections of Severe Fever with Thrombocytopenia Syndrome Caused by Person-to-Person Transmission

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a novel phlebovirus that was identified to be the etiological pathogen of the emerging infectious disease, severe fever with thrombocytopenia syndrome (SFTS). SFTSV could be transmitted through tick bite. Transmission of SFTSV among humans has also been reported mainly through direct blood contact. In July 2014, a cluster of six suspected SFTS cases occurred in Shandong Province, China. In this cluster, both symptomatic and asymptomatic persons were included. By analyzing the clinical data and results of laboratory tests, and conducting the epidemiological interviews with the cases and their families, risk factors responsible for the transmission were evaluated. The findings suggested that SFTSV transmission among humans may cause asymptomatic infection via personal contact without blood exposure.

Risk factors associated with fatality of severe fever with thrombocytopenia syndrome: a meta-analysis

Severe fever with thrombocytopenia syndrome is an emerging life-threatening infectious disease identified in 2009. Given high case-fatality rate among patients with severe fever with thrombocytopenia syndrome, identification of the risk factors at acute phase associated with fatality is crucial for treatment. Therefore, we aimed to meta-analytically evaluate risk factors of fatal clinical outcome of severe fever with thrombocytopenia syndrome. 238 fatal cases and 873 non-fatal cases from 12 studies were included in this meta-analysis. Elder age and high viral load were significantly associated with fatal clinical outcome. Further, severe fever with thrombocytopenia syndrome patients with fatal clinical outcome had significantly reduced level of albumin and platelet count, higher level of serum alanine aminotransferase, aspirate aminotransferase, lactic acid dehydrogenase and creatinine phosphokinase, and prolonged activated partial thromboplastin time, comparing with mild patients. These disturbed parameters function as predictors to warn fatal clinical outcome of the disease. Moreover, ribavirin has a minimal impact to alleviate disease progression of severe fever with thrombocytopenia syndrome. In conclusion, our finding demonstrates a panel of factors associated with fatality of SFTS disease, which have important implications during clinical practice.

Severe fever with thrombocytopenia syndrome: the disease, caused by the novel phlebovirus

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by a new virus (SFTS virus) reported to be endemic to central and northeastern parts of China. SFTS virus, which is classified into the genus Phlebovirus (the Bunyaviridae family), is suspected to be a tick-borne virus owing to evidence in two species of ticks: Haemaphysalis longicornis and Rhipicephalus microplus. SFTS virus is detected among many species of domestic animals in China. The clinical symptoms of SFTS include fever, thrombocytopenia, leucocytopenia, gastrointestinal symptoms, neural symptoms, bleeding tendency. The fatality rate of SFTS is 6-30%. Person-to-person transmission of SFTS virus is possible through blood contact. Clinical and epidemiological studies of SFTS, the cases of SFTS outside China, person-to-person transmission of SFTS virus, evolutionary and molecular analysis of the emergent SFTS virus, and risk assessment of human infection with a novel phlebovirus are considered in this review.

Seroprevalence of severe fever with thrombocytopenia syndrome virus in China: A systematic review and meta-analysis

Objective

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by a novel bunyavirus-SFTSV. The seroprevalence of anti-SFTSV antibodies including immunoglobulin G (IgG) and immunoglobulin M (IgM), specific to SFTSV in the general population has been investigated in various epidemiological studies with inconsistent results. Here, we clarify this discrepancy and reach a more comprehensive result by mean of a meta-analysis.

Methods

All relevant articles were searched in the electronic databases (PubMed, Web of science, Embase, Chinese National Knowledge Infrastructure database, Chinese Wanfang database) up to November 2016. The pooled seroprevalence and 95% confidence intervals (95% CIs) were calculated by random- or fixed- model on the basis of heterogeneity.

Results

In total, 21 studies containing 23,848 blood samples from 7 provinces were included in this meta-analysis. The minimum and maximum reported seroprevalences of SFTSV among humans in China were 0.23% and 9.17%, respectively. The overall pooled seroprevalence of SFTSV antibodies was 4.3% (95%CI: 3.2%-5.5%). The pooled prevalence was 5.9% (95%CI: 4.7%-7.0%) in Zhejiang province, 4.9% (95%CI: 4.1–5.8%) in Anhui province, 3.9% (95%CI: 1.3%-6.4%) in Shandong province, and 0.7% (95%CI: 0.2%-1.1%) in Jiangsu province. Stratified by occupation, the pooled prevalence of farmer was 6.1% (95%CI: 3.4%-8.9%) and others (mainly are students) was 3.3% (95%CI: 2.4%-4.2%). Additionally, seroprevalence of SFTSV in people who lived in the same village with the patient were higher than that of people who lived in a different village. Seropositive rates in sampling years after 2012 were higher than that before 2012. The prevalence of SFTSV did not differ by age or gender. Sensitive analysis by omitting one study at a time indicated the results of the pooled seroprevalence were robust.

Conclusions

Seroprevalence of SFTSV among healthy population in central and eastern China is high. Surveillance efforts on mild or asymptomatic infections among endemic persons are needed.

The Impact of Emerging Infectious Diseases on Chinese Blood Safety

Emerging infectious diseases (EIDs) have always been one of the major threats to public health. Although the implementation of mandatory testing for 4 classical transfusion-transmitted infectious-human immunodeficiency virus, hepatitis B virus, hepatitis C virus, and syphilis-has reduced the transfusion risk of these pathogens, the potential threat of various EID agents and their constantly evolving variants to blood safety in China is not fully understood. This review presents 9 representative EID agents that are autochthonous and epidemic nationally or regionally in China. The epidemiologic status and distribution of these EID agents among donors and/or healthy populations are summarized. The potential risks of these EID agents to blood safety are discussed. The review also explores strategies to strengthen hemovigilance systems and studies to further evaluate the impact of EID agents on blood safety.

Severe fever with thrombocytopenia syndrome (SFTS) and SFTS virus

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infectious disease caused by the SFTS virus (SFTSV), a novel phlebovirus reported to be endemic to China in 2011. In Japan, the first SFTS patient was identified during the autumn of 2012; since then, over 100 SFTS patients have been reported. The SFTSV has been identified throughout Japan over the past two years; however, SFTS patients are specifically localized to western Japan. The clinical symptoms of SFTS include fever, thrombocytopenia, leukocytopenia, gastrointestinal symptoms, and various other symptoms, including muscular symptoms, neurological abnormalities, and coagulopathy. SFTS is often accompanied by hemophagocytic syndrome. The histopathological findings are characterized by necrotizing lymphadenitis, with infiltration of the virus-infected cells to the local lymph nodes. Pathophysiological analyses of SFTS include studies regarding the kinetics of cytokine production and immune responses in patients with SFTS and in SFTSV-infection animal models. This article aimed to survey the history of SFTS in Japan and to review the clinical, epidemiological, and virological aspects of SFTS and SFTSV infection.

Identification of a candidate standard strain of severe fever with thrombocytopenia syndrome virus for vaccine quality control in China using a cross-neutralization assay

Severe fever with thrombocytopenia syndrome (SFTS) is caused by a phlebovirus of the Bunyaviridae family, which is designated as SFTS virus (SFTSV). To our knowledge, no efficient SFTSV vaccine exists. Here, we report the identification of a standard virus strain for the eight major SFTSV strains circulating in China for use in evaluating the SFTSV vaccine. Rabbits were immunized with the SFTSV strains and the cross-neutralization capacities of SFTSV anti-sera were determined in microculture cytopathic effect (CPE)-inhibition assays. The mean cross-neutralization capacity of the eight SFTSV anti-sera ranged from 62.4 to 142.6%, compared to autologous strains. The HB29 strain demonstrated strong cross-reactivity with heterologous antibodies, and 33 serum samples from SFTS patients efficiently neutralized HB29, suggesting its broad cross-reactivity. In addition, HB29 demonstrated good replication in Vero and MRC-5 cells (8.0 and 6.0 lg 50% cell culture-infectious dose/mL, respectively) and significant CPE, which satisfied the requirements for a standard virus strain. The HB29 isolate was proven identical to the reported HB29 strain by DNA sequencing, and showed high homology in the S segments with other SFTSV strains (94.8-99.7%). Our results suggest that HB29 may be the best candidate standard strain for use in SFTS vaccine development in China.

Novel sub-lineages, recombinants and reassortants of severe fever with thrombocytopenia syndrome virus

Severe fever with thrombocytopenia syndrome virus (SFTSV) has been continuously circulating in Eastern Asia in recent years, without the availability of effective vaccines or antiviral drugs, posing a serious threat to public health, particularly in the central-eastern provinces of China. In this study, we isolated and sequenced four new SFTSV strains from Shandong Province identified in 2015. Phylogenetic analysis, with all publicly available L, M and S gene segments, revealed that the four newly described SFTSV strains belonged to genotype C3. In addition, our phylogenetic analyses also identified two potentially novel sub-lineages of SFTSV, tentatively named C6 and J4. Our comprehensive analysis revealed twenty recombination events in fourteen SFTSV genomes and recombination events were found in the S gene segment for the first time. A total of twenty-six strains were probable SFTSV reassortants, including sixteen which were previously unidentified. We further characterised the genetic constellation of these putative reassortants and classified them into twelve different reassortment forms. Our study revealed multiple evolutionary forces acting on SFTSV, responsible for the increasing genetic diversity of this agent, which could potentially alter the antigenicity and pathogenicity of the virus. This calls for an urgent need for intensified surveillance and the development of vaccines and antiviral drugs against this high-consequence pathogen.

Severe Fever with Thrombocytopenia Syndrome in South Korea, 2013-2015

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease that was recently identified in China, South Korea and Japan. The objective of the study was to evaluate the epidemiologic and clinical characteristics of SFTS in South Korea.

METHODS/PRINCIPAL FINDINGS

SFTS is a reportable disease in South Korea. We included all SFTS cases reported to the Korea Centers for Disease Control and Prevention (KCDC) from January 2013 to December 2015. Clinical information was gathered by reviewing medical records, and epidemiologic characteristics were analyzed using both KCDC surveillance data and patient medical records. Risk factors for mortality in patients with SFTS were assessed. A total of 172 SFTS cases were reported during the study period. SFTS occurred throughout the country, except in urban areas. Hilly areas in the eastern and southeastern regions and Jeju island (incidence, 1.26 cases /105 person-years) were the main endemic areas. The yearly incidence increased from 36 cases in 2013 to 81 cases in 2015. Most cases occurred from May to October. The overall case fatality ratio was 32.6%. The clinical progression was similar to the 3 phases reported in China: fever, multi-organ dysfunction, and convalescence. Confusion, elevated C-reactive protein, and prolonged activated partial thromboplastin times were associated with mortality in patients with SFTS. Two outbreaks of nosocomial SFTS transmission were observed.

CONCLUSIONS

SFTS is an endemic disease in South Korea, with a nationwide distribution and a high case-fatality ratio. Confusion, elevated levels of C-reactive protein, and prolonged activated partial thromboplastin times were associated with mortality in patients with SFTS.

Epidemiological and Clinical Features of Severe Fever with Thrombocytopenia Syndrome in Japan, 2013-2014

Although severe fever with thrombocytopenia syndrome (SFTS) was first reported from Japan in 2013, the precise clinical features and the risk factors for SFTS have not been fully investigated in Japan. Ninety-six cases of severe fever with thrombocytopenia syndrome (SFTS) were notified through the national surveillance system between April 2013 and September 2014 in Japan. All cases were from western Japan, and 82 cases (85%) had an onset between April and August. A retrospective observational study of the notified SFTS cases was conducted to identify the clinical features and laboratory findings during the same period. Of 96 notified cases, 49 (51%) were included in this study. Most case-patients were of advanced age (median age 78 years) and were retired or unemployed, or farmers. These case-patients had a history of outdoor activity within 2 weeks before the onset of illness. The median serum C-reactive protein concentration was slightly elevated at admission. Fungal infections such as invasive aspergilosis were found in 10% of these case-patients. Hemophagocytosis was observed in 15 of the 18 case-patients (83%) whose bone marrow samples were available. Fifteen cases were fatal, giving a case-fatality proportion of 31%. The proportion of neurological abnormalities and serum concentrations of lactate dehydrogenase and aspartate aminotransferase were significantly higher in the fatal cases than in the nonfatal cases during hospitalization. Appearance of neurological abnormality may be useful for predicting the prognosis in SFTS patients.

Epidemiological and Clinical Features of Severe Fever with Thrombocytopenia Syndrome During an Outbreak in South Korea, 2013-2015

Since the first reported case of severe fever with thrombocytopenia syndrome (SFTS) in South Korea in 2013, between 2013 and 2015, we collected 1,697 serum samples from suspected patients who experienced symptoms of SFTS. We performed reverse transcriptase polymerase chain reaction using total RNA extracted from the patients' sera. When viral RNA was detected in the sera, SFTS was diagnosed. Among the 1,697 samples, 170 were positive for SFTS virus. We then analyzed the epidemiologic features of these 170 cases. As a result, we found that the annual number of cases increased steadily. However, the annual case fatality rate exhibited a downward trend. The majority of patients were aged ≥ 60 years, and most cases occurred during May–October in the eastern and southern parts of the country. These results may be useful for effective SFTS control by describing the clinical and epidemiologic features of the disease in South Korea.

Factors associated with Severe Fever with Thrombocytopenia Syndrome infection and fatal outcome

Severe fever with thrombocytopenia syndrome (SFTS) is emerging in China and the incidence increased year by year. In this study, we conducted case control study to explore factors associated with SFTS virus (SFTSV) infection and fatal outcome. In the study of factors associated with SFTSV infection, a total of 216 individuals participated the study, including 72 cases and 144 matched controls. There were significant differences in proportion of history of tick bite and breeding domestic animals between cases and controls. Of note, individuals who were unclear whether they had been bitten by ticks had the highest risk of SFTSV infection and odds ratio (OR) was 10.222. In the study of factors associated with SFTS fatal outcome, a total of 129 cases participated the study including 16 deaths and 113 survivors. Significant differences were observed in body mass index (BMI), intervals from illness onset to confirmation, and proportion of gingival hemorrhage between deaths and survivors, whose ORs of these factors were 3.903, 1.996, and 3.826, respectively. Our results suggest that all patients with fever, thrombocytopenia and leukocytopenia in SFTS endemic areas should be suspected of SFTS, even they don’t have history of tick bite, and more intense treatment should be administered to patients with abnormal BMI before laboratory parameters are detected.

Characteristics and Factors Associated with Death among Patients Hospitalized for Severe Fever with Thrombocytopenia Syndrome, South Korea, 2013

Surveillance for this emerging disease should be expanded to the outpatient setting.

In South Korea, nationwide surveillance for severe fever with thrombocytopenia syndrome (SFTS) began during 2013. Among 301 surveillance cases, 35 hospitalized case-patients in 25 areas were confirmed by using virologic testing, and 16 (46%) case-patients subsequently died. The SFTS cases occurred during May–November and peaked during June (9 cases, 26%). The incidence of SFTS was higher in the southern regions of South Korea. Age and neurologic symptoms, including decreased level of consciousness and slurred speech, were heavily associated with death; neurologic symptoms during the first week after disease onset were also associated with death. Although melena was common among patients who died, no other hemorrhagic manifestations were substantively more common among those who died. No effective treatments, including ribavirin, were identified. Expansion of SFTS surveillance to include the outpatient sector and development of an antibody test would enhance completeness of SFTS detection in South Korea.

Molecular detection of severe fever with thrombocytopenia syndrome and tick-borne encephalitis viruses in ixodid ticks collected from vegetation, Republic of Korea, 2014

Ticks play an important role in transmission of arboviruses responsible for emerging infectious diseases, and have a significant impact on human, veterinary, and wildlife health. In the Republic of Korea (ROK), little is known about information regarding the presence of tick-borne viruses and their vectors. A total of 21,158 ticks belonging to 3 genera and 6 species collected at 6 provinces and 4 metropolitan areas in the ROK from March to October 2014 were assayed for selected tick-borne pathogens. Haemaphysalis longicornis (n=17,570) was the most numerously collected, followed by Haemaphysalis flava (n=3317), Ixodes nipponensis (n=249), Amblyomma testudinarium (n=11), Haemaphysalis phasiana (n=8), and Ixodes turdus (n=3). Ticks were pooled (adults 1-5, nymphs 1-30, and larvae 1-50) and tested by one-step reverse transcription polymerase chain reaction (RT-PCR) or nested RT-PCR for the detection of severe fever with thrombocytopenia virus (SFTSV), tick-borne encephalitis virus (TBEV), Powassan virus (POWV), Omsk hemorrhagic fever virus (OHFV), and Langat virus (LGTV). The overall maximum likelihood estimation (MLE) [estimated numbers of viral RNA positive ticks/1000 ticks] for SFTSV and TBEV was 0.95 and 0.43, respectively, while, all pools were negative for POWV, OHFV, and LGTV. The purpose of this study was to determine the prevalence of SFTSV, TBEV, POWV, OHFV, and LGTV in ixodid ticks collected from vegetation in the ROK to aid our understanding of the epidemiology of tick-borne viral diseases. Results from this study emphasize the need for continuous tick-based arbovirus surveillance to monitor the emergence of tick-borne diseases in the ROK.

Viral shedding from diverse body fluids in a patient with severe fever with thrombocytopenia syndrome

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne disease characterized by high fever, thrombocytopenia, leukopenia, and multiple organ failure and is caused by a novel bunyavirus. Human-to-human transmission has been reported previously, but the mode of transmission has not been clarified thoroughly.

STUDY DESIGN

We identified a case of a 73-year-old woman with SFTS and performed a semi-quantitative real-time reverse transcription PCR (real-time RT-PCR) assay on her blood, tracheal aspirate, gastric aspirate and urine to detect SFTS virus (SFTSV).

RESULTS

During 7-day hospitalization, all the serum samples showed positive Ct values lower than 35 in both the S and M segments, suggesting the presence of the SFTSV RNA. After initiation of plasma exchange, serum SFTSV load markedly decreased, but still remained positive. The SFTS viral RNA was also detected in other body fluids, including tracheal aspirate and gastric aspirate.

CONCLUSION

These results suggest that droplet transmission can occur through close contact with infected patients.

Antibodies against severe fever with thrombocytopenia syndrome virus in healthy persons, China, 2013

In June 2013, a subclinical infection with severe fever with thrombocytopenia syndrome virus (SFTSV) was detected in Zhejiang Province, China, prompting seroprevalence studies in 6 districts within the province. Of 986 healthy persons tested, 71 had IgG antibodies against SFTSV. This finding suggests that most natural infections with SFTSV are mild or subclinical.

Severe fever with thrombocytopenia syndrome presenting as hemophagocytic syndrome: two case reports

Introduction

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease that was first reported in China in 2011. However, it is now endemic in Japan, and the SFTS viruses in Japan and China have evolved independently. Its fatality rate is 26.5 % in Japan, and the viral load is related to morbidity.

Case description

We encountered two patients with SFTS. Case 1 is a 72-year-old woman who visited our hospital owing to severe fatigue, diarrhea, and nausea. Her consciousness level score on the Glasgow Coma Scale was 14 points, and her serum lactate dehydrogenase level was 646 IU/L. Case 2 is an 82-year-old woman who visited our hospital owing to diarrhea and general fatigue. Her consciousness level score on the Glasgow Coma Scale was 11 points, and her serum lactate dehydrogenase level was 935 IU/L.

Discussion and evaluation

Both patients had hemophagocytic syndrome and presented with similar symptoms. Although both were treated with similar drug regimens, their clinical courses were different: after treatment, the 72-year-old woman survived whereas the 82-year-old woman died. In addition to age, the two patients differed in terms of time between symptom onset and treatment initiation, consciousness level, viral load, and extent of elevation of liver enzyme levels.

Conclusions

The viral load, which is a predictor of morbidity, was associated with the level of consciousness and the serum lactate dehydrogenase level, both of which might be useful for predicting death in patients with SFTS.

The prospective evaluation of viral loads in patients with severe fever with thrombocytopenia syndrome

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS), caused by novel bunyavirus (SFTSV) is a potentially fatal disease that was first identified in China. Person to person transmission through contact with blood or body fluids was considered as an important infection route.

OBJECTIVES

The study is designed to investigate the longitudinal viral loads following SFTSV infection and to identify factors affecting viral shedding in SFTS patients.

METHODS

A prospective, observational study was performed on 208 laboratory-confirmed SFTSV infected patients in Xinyang, Henan Province. Sequential serum samples were collected on admission and during the hospitalization for quantification of SFTSV RNA by real-time RT-PCR.

RESULTS

The viral RNA was undetectable in 55.6% of the patients on admission into the hospital, becoming detectable in most cases until three days and attained maximum level on six days after disease onset. This was followed by an obvious decrease thereafter, but maintained detectable for over 20 days. Viral load was independently predictable of severe disease outcome throughout the hospitalization. Viral load of >10(7)copies/mL was predictable of fatal outcome. The serum levels of PLT, WBC, LDH, AST and CK were significantly associated with viral loads level.

CONCLUSIONS

The diagnosis of SFTSV infection based on PCR test should be performed at least three days after disease onset. Peaking viral loads were attained around six days after disease, posing a highest risk of human-to-human transmission.

Phylogeographic analysis of severe fever with thrombocytopenia syndrome virus from Zhoushan Islands, China: implication for transmission across the ocean

From June 2011 to August 2014, 21 cases of infection by severe fever with thrombocytopenia syndrome bunyavirus (SFTSV) were confirmed in Zhoushan Islands in the Eastern coast of China. To identify the source of SFTSV in Zhoushan Islands, the whole SFTSV genomes were amplified and sequenced from 17 of 21 patients. The L, M, and S genomic segments of these SFTSV strains were phylogenetically analyzed together with those of 188 SFTSV strains available from GenBank. Phylogenetic analysis demonstrated SFTSV could be classified into six genotypes. The genotypes F, A, and D were dominant in mainland China. Additionally, seven types of SFTSV genetic reassortants (abbreviated as AFA, CCD, DDF, DFD, DFF, FAF, and FFA for the L, M and S segments) were identified from 10 strains in mainland China. Genotype B was dominant in Zhoushan Islands, Japan and South Korea, but not found in mainland China. Phylogeographic analysis also revealed South Korea possible be the origin area for genotype B and transmitted into Japan and Zhoushan islands in the later part of 20(th) century. Therefore, we propose that genotype B isolates were probable transmitted from South Korea to Japan and Zhoushan Islands.

First Isolation of Severe Fever with Thrombocytopenia Syndrome Virus from Haemaphysalis longicornis Ticks Collected in Severe Fever with Thrombocytopenia Syndrome Outbreak Areas in the Republic of Korea

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infectious disease that is endemic to China, Japan, and the Republic of Korea (ROK). In this study, 8313 ticks collected from SFTS outbreak areas in the ROK in 2013 were used to detect the SFTS virus (SFTSV). A single SFTSV was isolated in cell culture from one pool of Haemaphysalis longicornis ticks collected from Samcheok-si, Gangwon Province, in the ROK. Phylogenetic analysis showed that the SFTSV isolate was clustered with the SFTSV strain from Japan, which was isolated from humans. To the best of our knowledge, this is the first isolation in the world of SFTSV in ticks collected from vegetation.

Association of the Serum Angiotensin II Level with Disease Severity in Severe Fever with Thrombocytopenia Syndrome Patients

OBJECTIVE

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by a novel Bunyavirus. Recent data suggest that the physiological balance of multiple proinflammatory cytokines is substantially changed in cases of severe fever with thrombocytopenia syndrome virus (SFTSV) infection, and the inflammatory response probably plays an important role in disease progression. Angiotensin II is an important active substance of the renin-angiotensin system, and studies have demonstrated that angiotensin II is involved in key events in the inflammatory process and can regulate inflammatory cell responses.

METHODS

In order to elucidate the role of angiotensin II in the pathogenesis of SFTS, we collected serum samples from SFTS patients in the acute or convalescent phase and tested the angiotensin II levels using an enzyme-linked immunosorbent assay as well as SFTSV viral RNA with real-time reverse-transcriptase polymerase chain reaction. Furthermore, we explored possible correlations between the angiotensin II levels and clinical parameters in SFTS patients.

RESULTS

Our data showed that the serum level of angiotensin II was significantly increased in the acute phase compared with that seen in the convalescent phase and the healthy controls, while there were no significant differences between the convalescent cases and healthy controls (p>0.05). A correlation analysis demonstrated that the level of angiotensin II positively correlated with the SFTS viral RNA load. The angiotensin II levels were also found to be correlated with clinical parameters indicating impairments in organ functions. Moreover, we also found that the angiotensin II levels were significantly increased in the severe cases versus the non-severe cases (p<0.001).

CONCLUSION

The serum angiotensin II levels in SFTS patients may be used to stratify the disease severity and are possibly predictive of disease outcomes.

Fatal Severe Fever with Thrombocytopenia Syndrome: An Autopsy Case Report

As of June 2014, among six patients who had severe fever with thrombocytopenia syndrome (SFTS) at our hospital, an 83-year-old man died despite receiving appropriate critical care. An autopsy revealed extensive ischemic damage of the intra-abdominal organs, including the liver, spleen, stomach and gut, due to severe celiac atherosclerotic stenosis and superior mesenteric arterial thrombosis. Many SFTS virus nucleoprotein antigen-immunoreactive cells were detected in a paraaortic node, where necrotizing lymphadenitis was seen, and in the spleen. Fewer such cells were seen in the liver, bone marrow and adrenals.

CONCLUSION

Atherosclerosis, in addition to hemophagocytic lymphohistiocytosis syndrome, can be lethal in elderly SFTS patients.

Experimental and Natural Infections of Goats with Severe Fever with Thrombocytopenia Syndrome Virus: Evidence for Ticks as Viral Vector

Background

Severe fever with thrombocytopenia syndrome virus (SFTSV), the causative agent for the fatal life-threatening infectious disease, severe fever with thrombocytopenia syndrome (SFTS), was first identified in the central and eastern regions of China. Although the viral RNA was detected in free-living and parasitic ticks, the vector for SFTSV remains unsettled.

Methodology/Principal Findings

Firstly, an experimental infection study in goats was conducted in a bio-safety level-2 (BSL-2) facility to investigate virus transmission between animals. The results showed that infected animals did not shed virus to the outside through respiratory or digestive tract route, and the control animals did not get infected. Then, a natural infection study was carried out in the SFTSV endemic region. A cohort of naïve goats was used as sentinel animals in the study site. A variety of daily samples including goat sera, ticks and mosquitoes were collected for viral RNA and antibody (from serum only) detection, and virus isolation. We detected viral RNA from free-living and parasitic ticks rather than mosquitoes, and from goats after ticks’ infestation. We also observed sero-conversion in all members of the animal cohort subsequently. The S segment sequences of the two recovered viral isolates from one infected goat and its parasitic ticks showed a 100% homology at the nucleic acid level.

Conclusions/Significance

In our natural infection study, close contact between goats does not appear to transmit SFTSV, however, the naïve animals were infected after ticks’ infestation and two viral isolates derived from an infected goat and its parasitic ticks shared 100% of sequence identity. These data demonstrate that the etiologic agent for goat cohort’s natural infection comes from environmental factors. Of these, ticks, especially the predominant species Haemaphysalis longicornis, probably act as vector for this pathogen. The findings in this study may help local health authorities formulate and focus preventive measures to contain this infection.

Severe fever with thrombocytopenia syndrome virus (SFTSV), a newly identified bunyavirus, has been found to circulate in mainland China, South Korea, and Japan since 2009. This virus is the etiologic agent for an emerging fatal hemorrhagic fever, severe fever with thrombocytopenia syndrome (SFTS) with high fatality. Although ticks have been implicated as the primary host vector indicated by epidemiological surveys, their role in transmitting this virus to the susceptible hosts, including humans, has not been validated. In this study, we conducted experimental and natural infections of goats with SFTSV to explore the role of ticks for this pathogen’s transmission. In the experimental infection study, we have not found any viral transmission within the cohort by close contact between animals. However, in the natural infection study, every member of a naïve goat cohort was observed to get infected sequentially when they were farmed in a SFTSV-endemic site. We detected viral RNA from free-living and parasitic ticks rather than mosquitoes, and from goats after ticks’ infestation. We also observed sero-conversion in all members of the animal cohort subsequently. More importantly, in the natural infection study, two virus strains isolated from one infected goat and its parasitic ticks showed identical S segment sequences of the viral genome. All these findings indicate that ticks, especially the dominant species Haemaphysalis longicornis, probably act as viral vector for this emerging pathogen, SFTSV.

Emerging tick-borne infections in mainland China: an increasing public health threat

Since the beginning of the 1980s, 33 emerging tick-borne agents have been identified in mainland China, including eight species of spotted fever group rickettsiae, seven species in the family Anaplasmataceae, six genospecies in the complex Borrelia burgdorferi sensu lato, 11 species of Babesia, and the virus causing severe fever with thrombocytopenia syndrome. In this Review we have mapped the geographical distributions of human cases of infection. 15 of the 33 emerging tick-borne agents have been reported to cause human disease, and their clinical characteristics have been described. The non-specific clinical manifestations caused by tick-borne pathogens present a major diagnostic challenge and most physicians are unfamiliar with the many tick-borne diseases that present with non-specific symptoms in the early stages of the illness. Advances in and application of modern molecular techniques should help with identification of emerging tick-borne pathogens and improve laboratory diagnosis of human infections. We expect that more novel tick-borne infections in ticks and animals will be identified and additional emerging tick-borne diseases in human beings will be discovered.

Probable aerosol transmission of severe fever with thrombocytopenia syndrome virus in southeastern China

Some clusters of severe fever with thrombocytopenia syndrome virus (SFTSV) infection were reported in China as of 2010. However, to date, there has been no epidemiologic evidence of aerosol transmission of SFTSV. Epidemiologic investigations were conducted after a cluster of 13 cases of SFTSV in May 2014. A total of 13 cases, including 11 confirmed cases and one clinically diagnosed case, were identified besides the case of the index patient. The index patient experienced onset of SFTSV on 23 April and died on 1 May. The patients with secondary cases had onset from 10 to 16 May, peaking on 13 May. Moreover, eight secondary cases occurred in family members of the index patient, and the other five cases occurred in neighbors of the index patient. According to epidemiologic investigations, patients 1, 3, 4, 5, 6, 7, 9 and 12 contracted the disease through contact with blood of the index patient. Notably, patients 8 and 10 did not have a history of contact with the blood of the index patient, but they stayed in the mourning hall for hours. SFTSV could be transmitted from person to person by direct contact and/or aerosol transmission, and it is important to consider aerosol transmission as a possible transmission route.

Application of recombinant severe fever with thrombocytopenia syndrome virus nucleocapsid protein for the detection of SFTSV-specific human IgG and IgM antibodies by indirect ELISA

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging disease that was first reported in China in 2011. It is caused by SFTS virus (SFTSV) which is a member of the Phlebovirus genus in the Bunyaviridae family. SFTSV has been classified as a BSL3 pathogen. There is a need to develop safe and affordable serodiagnostic methods for proper clinical management of infected patients.

Methods

The full length nucleocapsid (N) gene of SFTSV Yamaguchi strain was amplified by RT-PCR and cloned to an expression vector pQE30. The recombinant (r) SFTSV-N protein was expressed by using Escherichia coli (E. coli) expression system and purified under native conditions. rSFTSV-N protein based indirect IgG and IgM enzyme linked immunosorbent assay (ELISA) systems were established to detect specific human IgG and IgM antibodies, respectively. One hundred fifteen serum samples from clinically suspected-SFTS patients were used to evaluate the newly established systems and the results were compared with the total antibody detecting sandwich ELISA system.

Results

The native form of recombinant (r) SFTSV-N protein was expressed and purified. Application of the rSFTSV-N protein based indirect IgG ELISA to the 115 serum samples showed results that perfectly matched those of the total antibody sandwich ELISA with a sensitivity and specificity of 100 %. The rSFTSV-N protein based indirect IgM ELISA missed 8 positive samples that were detected by the total antibody sandwich ELISA. The sensitivity and specificity of rSFTSV-N-IgM capture ELISA were 90.59 and 100 %, respectively.

Conclusions

The rSFTSV-N protein is highly immunoreactive and a good target for use as an assay antigen in laboratory diagnosis. Its preparation is simpler in comparison with that used for the total antibody sandwich system. Our rSFTSV-N protein-based IgG and IgM ELISA systems have the advantage of distinguishing two types of antibodies and require small volume of serum sample only. They are safe to use for diagnosis of SFTS virus infection and especially fit in large-scale epidemiological investigations.

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.

Effects of ribavirin on severe fever with thrombocytopenia syndrome virus in vitro

Severe fever with thrombocytopenia syndrome (SFTS) is a disease with a high case fatality rate that is caused by infection with the recently identified tick-borne SFTS virus (SFTSV), for which there are no specific countermeasures. We examined the effects of ribavirin and mizoribine, which are nucleoside analogue drugs with broad antiviral activities, on SFTSV proliferation in vitro. When 3 cell lines were treated with these drugs before and during infection with a Chinese SFTSV strain, the 99% effective concentrations (EC99) of ribavirin were 19-64 μg/ml (78-262 μM); in contrast, the EC99 of mizoribine was >500 μg/ml (1,929 μM). Similar levels of inhibitory effects of ribavirin were observed with 4 Japanese SFTSV strains. However, when Vero cells were treated with ribavirin 3 days after inoculation, the inhibitory effect was dramatically decreased, indicating that ribavirin did not effectively reduce virus production in pre-infected cells. These results suggest that ribavirin could be used as post-exposure prophylaxis for the prevention of SFTS.

Severe fever with thrombocytopenia syndrome presenting as acute hepatic failure

Severe fever with thrombocytopenia syndrome (SFTS) is characterized by fever, thrombocytopenia, leukopenia, and altered consciousness, which may also involve multi-organ failure. Initially SFTS mortality was as high as 30%, when diagnosis remained unclear. We present a case of a 53-year- old man with SFTS presenting with acute hepatic failure. On admission, he presented with confusion, elevated serum liver enzyme and ammonia levels, whose serum markers were negative for acute viral hepatitis. He was diagnosed with SFTS based on reverse transcription-polymerase chain reaction identification of the SFTS virus M segment. Percutaneous liver biopsy was performed to identify the degree and extent of necroinflammation and patient prognosis. After recovery, he was followed-up for 12 months with no SFTS-related sequelae. A discordance in severity between biopsy findings and clinical course could explain the rapid clinical improvement. Atypical presentations with multi-organ failure can delay timely diagnosis and management of infected patients.

Efficacy of the Mirasol pathogen reduction technology system against severe fever with thrombocytopenia syndrome virus (SFTSV)

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tickborne virus in the Bunyaviridae family. This virus has recently been found in China, Japan and Korea. The risk of transfusion-transmitted SFTSV infection (TTI-SFTSV) is a concern because person-to-person transmission resulting from contact with SFTSV-contaminated blood has been reported. Therefore, we investigated the efficacy of the Mirasol pathogen reduction technology (PRT) system for inactivating SFTSV in vitro. The Mirasol PRT system achieved a > 4.11 log10 reduction value (LRV) for SFTSV. In conclusion, we showed that the Mirasol PRT system could potentially be used to reduce the risk of TTI-SFTSV.

A national assessment of the epidemiology of severe fever with thrombocytopenia syndrome, China

First discovered in rural areas of middle-eastern China in 2009, severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne zoonosis affecting hundreds of cases reported in China each year. Using the national surveillance data from 2010 to 2013, we conducted this retrospective epidemiological study and risk assessment of SFTS in China. We found that the incidence of SFTS and its epidemic areas are continuing to grow, but the case fatality rate (CFR) has steadily decreased. SFTS most commonly affected elderly farmers who acquired infection between May and July in middle-eastern China. However, other epidemiological characteristics such as incidence, sex ratio, CFR, and seasonality differ substantially across the affected provinces, which seem to be consistent with local agricultural activities and the seasonal abundance of ticks. Spatial scan statistics detected three hot spots of SFTS that accounted for 69.1% of SFTS cases in China. There was a strong association of SFTS incidence with temporal changes in the climate within the clusters. Multivariate modeling identified climate conditions, elevation, forest coverage, cattle density, and the presence of Haemaphysalis longicornis ticks as independent risk factors in the distribution of SFTS, based on which a predicted risk map of the disease was derived.

[Severe fever with thrombocytopenia syndrome in Japan]

Severe fever with thrombocytopenia syndrome (SFTS) is characterized by sudden onset of fever, leukopenia, thrombocytopenia, and gastrointestinal tract symptoms and approximately 12% of patients die from disseminated intravascular coagulation and/or multiple organ failures. Agent of the disease is a novel bunyavirus SFTS virus, and is transmitted by bite of a possible vector tick, Haemaphysalis longicornis, and through direct contact with virus-containing patient body fluids, or through unknown routes. SFTS case reports have been limited in China, and more than two thousand cases were reported in 2011 and 2012. In late 2012, a woman living in Yamaguchi prefecture in Japan showed symptoms reminiscent of those of SFTS and died 6 days after the onset of symptoms. Virus was isolated from her acute serum in Vero cells and a next generation-sequencing identified it as SFTS virus. SFTS viral genome and proteins were detected in the patient's serum. Based on the first demonstration of SFTS in Japan, a retrospective study started. Until March of 2013, totally 8 patients were diagnosed as having SFTS and the most early case was in 2005. Phylogenetic analysis of virus sequences revealed that Japanese isolates form an independent branch distinct from Chinese isolates, indicating that SFTS has been present not only in China but also in Japan.

Severe fever with thrombocytopenia syndrome: a newly discovered emerging infectious disease

Severe fever with thrombocytopenia syndrome (SFTS) is a newly discovered emerging infectious disease that has recently become epidemic in Asia. The causative agent of SFTS is a novel phlebovirus in the family Bunyaviridae, designated SFTS virus (SFTSV). SFTS clinically presents with high fever, thrombocytopenia, leukocytopenia, gastrointestinal disorders, and multi-organ dysfunction, with a high viral load and a high case-fatality rate. In human infection, SFTSV targets microphages, replicates in the spleen of infected mice, and causes thrombocytopenia and a cytokine storm. The tick disseminates virus to humans and animals, forming a special transmission model in nature. Person-to-person transmission though direct contact with patient blood has been frequently reported. Measurements of viral RNA and antibodies have been established for diagnosis, but vaccines and specific therapeutics are not available so far.

Circulating regulatory T cells in patients with severe fever with thrombocytopenia syndrome

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is a newly emerging infectious disease caused by SFTS virus (SFTSV). Immunologic factors have been proved to be related to the occurrence and development of SFTS; however, their role still remains to be further elucidated.

METHODS

Samples from 30 patients with laboratory-confirmed SFTS and 15 healthy controls were subjected to flow cytometry to detect the proportion of CD4+/total lymphocytes, CD4 + CD25+/CD4 + cells and CD4 + CD25+ Foxp3+/CD4 + CD25+ cells in circulating blood and to evaluate their potential function in the development of SFTS.

RESULTS

The data showed that a reduced proportion of CD4+/total lymphocytes and CD4 + CD25+/CD4 + cells was observed in patients with SFTS compared with healthy controls. In contrast, the percentage of CD4 + CD25+ Foxp3+/CD4 + CD25+ cells in the patients in the SFTS group was significantly elevated. Furthermore, we investigated the dynamic changes of the circulating regulatory T cells (Tregs) in patients with SFTS at different stages. The results showed that the proportion of CD4+/total lymphocytes and CD4 + CD25+/CD4 + cells in the non-severe group was prominently higher than that in patients with severe SFTS. Conversely, the proportion of CD4 + CD25+ Foxp3+/CD4 + CD25+ cells was lower in the non-severe group than in the severe group. Additionally, the circulating Tregs reverted to normal ranges during the convalescent phase of SFTSV infection. Moreover, the Tregs level correlated with various clinical parameters.

CONCLUSION

We demonstrated that SFTSV infection resulted in a robust circulating Treg response in patients with SFTS. Our investigation suggested that the proportions of CD4+/total lymphocytes and CD4 + CD25+ Foxp3+/CD4 + CD25+ cells in circulating blood could serve as sensitive indices to evaluate the changes in Tregs in SFTS and predict the progression of SFTS.

Nosocomial transmission of severe fever with thrombocytopenia syndrome in Korea

Of the 27 healthcare workers (HCWs) who had contact with a fatally ill patient with severe thrombocytopenia syndrome in Korea (SFTS), 4 who were involved in cardiopulmonary resuscitation complained of fever and were diagnosed with SFTS via seroconversion. Exposure to respiratory secretions, blood, or gowns soiled by body fluids was significantly associated with infection of HCWs.

A case of severe fever with thrombocytopenia syndrome caused by a novel bunyavirus in Zhejiang, China

Two typical symptoms of severe fever with thrombocytopenia syndrome (SFTS) are fever and thrombocytopenia. Here we report a laboratory confirmed SFTS case with no fever during the entire hospitalization period, in Daishan County, Zhejiang Province, China. A 77-year-old woman was admitted to hospital with symptoms including nausea, retching, and anorexia. Laboratory tests revealed thrombocytopenia, leukopenia, and liver and brain damage. The case was later confirmed as a novel bunyavirus infection. Epidemiological investigations revealed that she had no history of tick bites or skin damage, and no known exposure to persons with a similar illness in the area prior to illness onset. The patient was hospitalized for 15 days, and during the whole admission period, she did not experience any fever. The patient recovered and was discharged.

Age is a critical risk factor for severe fever with thrombocytopenia syndrome

Background

Severe Fever with Thrombocytopenia Syndrome (SFTS) is an emerging infectious disease in East Asia. SFTS is a tick borne hemorrhagic fever caused by SFTSV, a new bunyavirus named after the syndrome. We investigated the epidemiology of SFTS in Laizhou County, Shandong Province, China.

Methods

We collected serum specimens of all patients who were clinically diagnosed as suspected SFTS cases in 2010 and 2011 in Laizhou County. The patients' serum specimens were tested for SFTSV by real time fluorescence quantitative PCR (RT-qPCR). We collected 1,060 serum specimens from healthy human volunteers by random sampling in Laizhou County in 2011. Healthy persons' serum specimens were tested for specific SFTSV IgG antibody by ELISA.

Results

71 SFTS cases were diagnosed in Laizhou County in 2010 and 2011, which resulted in the incidence rate of 4.1/100,000 annually. The patients ranged from 15 years old to 87 years old and the median age of the patients were 59 years old. The incidence rate of SFTS was significantly higher in patients over 40 years old and fatal cases only occurred in patients over 50 years old. 3.3% (35/1,060) of healthy people were positive to SFTSV IgG antibody. The SFTSV antibody positive rate was not significantly different among people at different age groups.

Conclusion

Our results revealed that seroprevalence of SFTSV in healthy people in Laizhou County was not significantly different among age groups, but SFTS patients were mainly elderly people, suggesting that age is the critical risk factor or determinant for SFTS morbidity and mortality.

A cluster of person-to-person transmission cases caused by SFTS virus in Penglai, China

An emerging infectious disease, severe fever with thrombocytopenia syndrome (SFTS), was identified to be associated with a novel SFTS virus (SFTSV). Transmission of the disease among humans has been described, but clinical impact factors and transmission mechanisms still need further study. An outbreak of person-to-person transmission of SFTS in a cluster of nine patients that occurred in an SFTS endemic area, Penglai County, Shandong province, China, was investigated. We found that the onset date of all eight secondary SFTS patients ranged from 7 to 13 days after exposure to the corpse of the index patient, and clinical incubation time was mostly focused on 9-10 days (n = 6). The two dead patients, including the index patient and one secondary infected patient, presented unusually high levels of viral load (6 × 10(8-9) copies/mL), low levels of platelets count (<55 × 10(9)/L), and significant increase of alanine aminotransferase, aspartate aminotransferase, lactate dehydrogenase, and creatine kinase values in the second week, and died on day 10 or 11 after disease onset. Genetic sequencing revealed 100% homology among virus strains isolated from the index patient and five secondary patients. Risk factors assessment of the person-to-person transmission revealed that the major exposure factor was blood contact without personal protection equipment. Information from this study provided solid references of SFTS incubation time, clinical and laboratory parameters related to SFTS severity and outcome, and biosafety issues for preventing person-to-person transmission or nosocomial infection of SFTSV.

Discrimination of novel bunyavirus infection using routine laboratory test

The wide epidemic and high case fatality rate have made severe fever with thrombocytopenia syndrome (SFTS) a significant public health problem. The diagnosis and discrimination of SFTS virus (SFTSV) infection at an early stage of the disease is important for treatment choice. A prospective study was performed in an SFTS reference hospital during 2011-2013. Suspected SFTS patients were recruited and prospectively observed. Comparison between SFTSV-positive and -negative patients was made to identify the parameters that were related to positive detection by discriminant and classification tree analysis. A total of 538 SFTSV-positive and 396 negative patients were recruited and observed. Multiple logistic regression models demonstrated the significant parameters associated with positive detection, including decreased platelet counts and elevated aspartate aminotransferase (AST) level during the first stage (1∼4 days), decreased white blood cell and platelet counts, elevated creatine kinase (CK) and AST levels during the second stage (5∼7 days), and older age, decreased consciousness and elevated CK and AST during the third stage (8-11 days). The classification trees disclosed that the significant predictors for positive SFTSV detection were AST >50.6 U/L and AST/alanine transaminase (ALT) >1.3 at the first stage, CK >257 U/L or 57.7 U/L < CK ≤98.5 U/L with AST/ALT >1.6 at the second stage, as well as CK >630.7 U/L or 114.3 U/L < CK ≤630.7 U/L with decreased consciousness at the third stage. In making the clinically probable diagnosis of SFTS, the supplementation of AST and CK evaluations might remarkably improve the diagnostic capacity of routine laboratory tests, while the leukopenia is of limited use.

Comprehensive molecular detection of tick-borne phleboviruses leads to the retrospective identification of taxonomically unassigned bunyaviruses and the discovery of a novel member of the genus phlebovirus

Until the recent emergence of two human-pathogenic tick-borne phleboviruses (TBPVs) (severe fever with thrombocytopenia syndrome virus [SFTSV] and Heartland virus), TBPVs have been neglected as causative agents of human disease. In particular, no studies have addressed the global distribution of TBPVs, and consequently, our understanding of the mechanism(s) underlying their evolution and emergence remains poor. In order to provide a useful tool for the ecological and epidemiological study of TBPVs, we have established a simple system that can detect all known TBPVs, based on conventional reverse transcription-PCR (RT-PCR) with degenerate primer sets targeting conserved regions of the viral L genome segment. Using this system, we have determined that several viruses that had been isolated from ticks decades ago but had not been taxonomically identified are novel TBPVs. Full-genome sequencing of these viruses revealed a novel fourth TBPV cluster distinct from the three known TBPV clusters (i.e., the SFTS, Bhanja, and Uukuniemi groups) and from the mosquito/sandfly-borne phleboviruses. Furthermore, by using tick samples collected in Zambia, we confirmed that our system had enough sensitivity to detect a new TBPV in a single tick homogenate. This virus, tentatively designated Shibuyunji virus after the region of tick collection, grouped into a novel fourth TBPV cluster. These results indicate that our system can be used as a first-line screening approach for TBPVs and that this kind of work will undoubtedly lead to the discovery of additional novel tick viruses and will expand our knowledge of the evolution and epidemiology of TBPVs.

IMPORTANCE

Tick-borne phleboviruses (TBPVs) have been largely neglected until the recent emergence of two virulent viruses, severe fever with thrombocytopenia syndrome virus and Heartland virus. Little is known about the global distribution of TBPVs or how these viruses evolved and emerged. A major hurdle to study the distribution of TBPVs is the lack of tools to detect these genetically divergent phleboviruses. In order to address this issue, we have developed a simple, rapid, and cheap RT-PCR system that can detect all known TBPVs and which led to the identification of several novel phleboviruses from previously uncharacterized tick-associated virus isolates. Our system can detect virus in a single tick sample and novel TBPVs that are genetically distinct from any of the known TBPVs. These results indicate that our system will be a useful tool for the surveillance of TBPVs and will facilitate understanding of the ecology of TBPVs.

Two autopsy cases of severe fever with thrombocytopenia syndrome (SFTS) in Japan: a pathognomonic histological feature and unique complication of SFTS

We report two autopsy cases of severe fever with thrombocytopenia syndrome (SFTS) with a high fatality rate in aged Japanese patients. Both cases were caused by a tick-bite. The pathognomonic histological feature was necrotizing lymphadenitis of systemic lymphoid tissue with SFTS viruses and SFTSV-RNA copies. Marked fungal infections were also observed in the lungs of both patients. Since cellular immune function may be suppressed in SFTS patients, physicians should be aware of possible fungal infections.