Close Correlation between Development of MODS during the Initial 72h of Hospitalization and Hospital Mortality in Severe Fever with Thrombocytopenia Syndrome

An emerging infectious disease was identified as severe fever with thrombocytopenia syn- drome （SFTS） in central China since late March 2009. We found the patients with SFTS had severe clinical symptoms, and progressed rapidly to multiple organ dysfunction syndrome （MODS） with high fatality rate of 25%-30%. The aim of this study was to assess the significance of risk factors predicting the development of MODS and death in SFTS patients. Consecutive SFTS admissions between May 2009 and September 2011 were analyzed for parameters of organ function during hospitalization using Marshall scoring system for MODS, and platelet counts were recorded on admission and at 24, 48, 72 h and one week after admission. We investigated the kinetics of organ failures and analyzed the associa- tion between age, platelet count and development of MODS or death. A total of 92 SFTS patients were enrolled in this study. Among them, 32 patients with dysfunction of over 4 organs were identified, 45% of them died within 72 h, 72% died within 5 days, and 76% died within 7 days after admission. We also found cumulative Marshall score was significantly higher in death patients （11.76＋2.05） than in survival patients （4.22~1.98） （P〈0.001）. In addition, SFTS patients had older age and lower platelet counts in MODS and death groups. Furthermore, we also observed that there was a close correlation between platelet count on admission and Marshall score （P〈0.001）. High Marshall score, advanced age and lower platelet counts were the main risk factors for the development of MODS, and those factors could predict mortality in SFTS patients, suggesting prompt treatment and close monitoring of severe complications, especially MODS, are of great importance in saving patients＇ lives.

View Point on Severe Fever with Thrombocytopenia Syndrome

Severe fever with thrombocytopenia syndrome (SFTS), a new disease of zoonotic natural foci has been increasing in recent years. In this review, the disease of human granulocytic anaplasmosis infection due to tick-borne and new Bunia virus infection, have similar clinical symptoms. Total of 11 articles were retrieved. The emergence, etiology, nomenclature and pathogenic mechanisms, clinical diagnosis and genotyping of SFTS were summarized, and the current situation of treatment was also evaluated. In conclusion, early detection, identiifcation and treatment are the key points to SFTS, but how to reduce the mortality of critically ill patients is still the focus in the future.

Laboratory indicators of death in severe fever with thrombocytopenia syndrome:a metaanalysis and systematic review

Background:Severe fever with thrombocytopenia syndrome(SFTS)is a tick-borne disease characterized by a fever-induced by severe fever with thrombocytopenia syndrome virus(SFTSV)infection.Methods:We systematically searched the literature on Web of Science,PubMed,Cochrane Library,Embase,Chinese National Knowledge Infrastructure databases,Sinomed Database,Wan Fang Data,and VIP Database,which describing the death characteristics SFTS(published between January 1,2009 and May 5,2021)and used STATA version 15.0 software to combine data from the selected study.Results:In the 14150 identified studies,23 were eligible and were included in our analysis.The death characteristics of SFTS are associated with old age,high viral load,high neutrophil ratio,low lymphocyte ratio,low platelet count,elevated liver enzymes,high serum potassium,and high blood urea nitrogen.Conclusions:The results of this meta-analysis can improve our knowledge of the death features of SFTS and necessitate increased attention to the above laboratory indicators to improve the understanding and therapeutic strategies of SFTS.

Hsp90βis critical for the infection of severe fever with thrombocytopenia syndrome virus

Severe fever with thrombocytopenia syndrome(SFTS)caused by the SFTS virus(SFTSV)is an emerging disease in East Asia with a fatality rate of up to 30%.However,the viral-host interaction of SFTSV remains largely unknown.The heat-shock protein 90(Hsp90)family consists of highly conserved chaperones that fold and remodel proteins and has a broad impact on the infection of many viruses.Here,we showed that Hsp90 is an important host factor involved in SFTSV infection.Hsp90 inhibitors significantly reduced SFTSV replication,viral protein expression,and the formation of inclusion bodies consisting of nonstructural proteins(NSs).Among viral proteins,NSs appeared to be the most reduced when Hsp90 inhibitors were used,and further analysis showed that their translation was affected.Co-immunoprecipitation of NSs with four isomers of Hsp90 showed that Hsp90βspecifically interacted with them.Knockdown of Hsp90βexpression also inhibited replication of SFTSV.These results suggest that Hsp90βplays a critical role during SFTSV infection and could be a potential target for the development of drugs against SFTS.

A new luciferase immunoprecipitation system assay provided serological evidence for missed diagnosis of severe fever with thrombocytopenia syndrome

Severe fever with thrombocytopenia syndrome(SFTS),caused by SFTS virus(SFTSV)infection,was first reported in 2010 in China with an initial fatality of up to 30%.The laboratory confirmation of SFTSV infection in terms of detection of viral RNA or antibody levels is critical for SFTS diagnosis and therapy.In this study,a new luciferase immunoprecipitation system(LIPS)assay based on p REN2 plasmid expressing SFTSV NP gene and tagged with Renilla luciferase(Rluc),was established and used to investigate the levels of antibody responses to SFTSV.Totally 464 serum samples from febrile patients were collected in the hospital of Shaoxing City in Zhejiang Province in 2019.The results showed that 82 of the 464 patients(17.7%)had antibody response to SFTSV,which were further supported by immunofluorescence assays(IFAs).Further,q RT-PCR and microneutralization tests showed that among the 82 positive cases,15 patients had viremia,10 patients had neutralizing antibody,and one had both(totally 26 patient).However,none of these patients were diagnosed as SFTS in the hospital probably because of their mild symptoms or subclinical manifestations.All the results indicated that at least the 26 patients having viremia or neutralizing antibody were the missed diagnosis of SFTS cases.The findings suggested the occurrence of SFTS and the SFTS incidence were higher than the reported level in Shaoxing in 2019,and that LIPS may provide an alternative strategy to confirm SFTSV infection in the laboratory.

Establishment of a Reverse Genetic System of Severe Fever with Thrombocytopenia Syndrome Virus Based on a C4 Strain

Severe fever with thrombocytopenia syndrome virus(SFTSV)is an emerging tick-borne bunyavirus that causes hemorrhagic fever-like disease(SFTS)in humans with a case fatality rate up to 30%.To date,the molecular biology involved in SFTSV infection remains obscure.There are seven major genotypes of SFTSV(C1-C4 and J1-J3)and previously a reverse genetic system was established on a C3 strain of SFTSV.Here,we reported successfully establishment of a reverse genetics system based on a SFTSV C4 strain.First,we obtained the 5’-and 3’-terminal untranslated region(UTR)sequences of the Large(L),Medium(M)and Small(S)segments of a laboratory-adapted SFTSV C4 strain through rapid amplification of cDNA ends analysis,and developed functional T7 polymerase-based L-,M-and S-segment minigenome assays.Then,fulllength cDNA clones were constructed and infectious SFTSV were recovered from co-transfected cells.Viral infectivity,growth kinetics,and viral protein expression profile of the rescued virus were compared with the laboratory-adapted virus.Focus formation assay showed that the size and morphology of the foci formed by the rescued SFTSV were indistinguishable with the laboratory-adapted virus.However,one-step growth curve and nucleoprotein expression analyses revealed the rescued virus replicated less efficiently than the laboratory-adapted virus.Sequence analysis indicated that the difference may be due to the mutations in the laboratory-adapted strain which are more prone to cell culture.The results help us to understand the molecular biology of SFTSV,and provide a useful tool for developing vaccines and antivirals against SFTS.

Prevalence of severe fever with thrombocytopenia syndrome virus in animals in Henan Province, China

Severe fever with thrombocytopenia syndrome(SFTS)is an emerging infectious disease caused by severe fever with thrombocytopenia syndrome virus(SFTSV).SFTSV has been found in humans,ticks and animals,and SFTS has high mortality and increasing prevalence in East Asia.In the study,the samples(heart,liver,lung,kidney,spleen,brain tissue and serum)were collected from 374 domestic animals and 241 wild animals in Pingqiao District and Xinxian County of Xinyang in Henan Province,China.275(44.72%,275/615)animals were positive for anti-SFTSV antibodies,the anti-SFTSV antibodies positive ratios of domestic and wild animals were 43.58%(163/374)and 46.47%(112/241),respectively.There was no significant difference in domestic and wild animals,but significant differences were detected among different species of animals(x^2=112.59,P<0.0001).Among 615 animals,105(17.07%,105/615)animals were positive for SFTSV RNA,and only one SFTSV strain was isolated from heart tissue of a yellow weasel.The phylogenetic analysis shows that the sequence from animals belonged to the same group with viral sequences obtained from humans.The animals maybe play a reservoir host in maintaining the life cycle of SFTSV in nature.

Proteasome Inhibitor PS-341 Effectively Blocks Infection by the Severe Fever with Thrombocytopenia Syndrome Virus

Severe fever with thrombocytopenia syndrome(SFTS)is an emerging hemorrhagic fever disease caused by SFTSV,a newly discovered phlebovirus that is named after the disease.Currently,no effective vaccines or drugs are available for use against SFTSV infection,as our understanding of the viral pathogenesis is limited.Bortezomib(PS-341),a dipeptideboronic acid analog,is the first clinically approved proteasome inhibitor for use in humans.In this study,the antiviral efficacy of PS-341 against SFTSV infection was tested in human embryonic kidney HEK293T(293T)cells.We employed four different assays to analyze the antiviral ability of PS-341 and determined that PS-341 inhibited the proliferation of SFTSV in 293T cells under various treatment conditions.Although PS-341 did not affect the virus absorption,PS-341 treatment within a non-toxic concentration range resulted in a significant reduction of progeny viral titers in infected cells.Dual-luciferase reporter assays and Western blot analysis revealed that PS-341 could reverse the SFTSV-encoded nonstructural protein(NS)mediated degradation of retinoic acid-inducible gene-1(RIG-I),thereby antagonizing the inhibitory effect of NSs on interferons and blocking virus replication.In addition,we observed that inhibition of apoptosis promotes virus replication.These results indicate that targeting of cellular interferon pathways and apoptosis during acute infection might serve as the bases of future therapeutics for the treatment of SFTSV infections.

Transmission and mortality risk assessment of severe fever with thrombocytopenia syndrome in China:results from 11-years’study

Background: The transmission and fatal risk of severe fever with thrombocytopenia syndrome (SFTS), an emerging infectious disease first discovered in China in 2009, still needed further quantification. This research aimed to analyze the SFTS clusters and assess the transmission and mortality risk for SFTS.Methods: Both epidemiological investigation and case reports regarding SFTS clusters in China during 2011-2021 were obtained from the Public Health Emergency Information Management System of the Chinese Center for Disease Control and Prevention Information System. The transmission risk was evaluated by using the secondary attack rate (SAR) and relative risk (RR). Mortality risk factors were analyzed using a logistic regression model.Results: There were 35 SFTS clusters during 2011-2021 involving 118 patients with a fatality rate of 22.0%. The number of clusters annually increased seasonally from April to September. The clusters mainly occurred in Anhui (16 clusters) and Shandong provinces (8 clusters). The SAR through contact with blood or bloody fluids was much higher than that through contact with non-bloody fluids (50.6% vs 3.0%;χ^(2) = 210.97,P < 0.05), with anRR of 16.61 [95% confidence interval (CI): 10.23-26.97]. There was a statistically significant difference in the SAR between exposure to the blood of a deceased person during burial preparation and exposure to the living patients’ blood (66.7% vs 34.5%;χ^(2)= 6.40,P < 0.05), with anRR of 1.93 (95%CI: 1.11-3.37). The mortality risk factors were a long interval from onset to diagnosis [odds ratio (OR)= 1.385), 95%CI: 1.083-1.772,P= 0.009) and advanced age (OR: 1.095, 95%CI: 1.031-1.163,P= 0.01).Conclusions: The SFTS clusters showed a high mortality rate and resulted in a high SAR. Contact with a bleeding corpse was associated with a higher infection risk, compared with contacting the blood from living patients. It is important to promote early detection and appropriate case management of patients with SFTS, as well as improved handling of their corpses, to prevent further transmission and mortality.

Depletion but Activation of CD56dimCD16+ NK Cells in Acute Infection with Severe Fever with Thrombocytopenia Syndrome Virus

Severe fever with thrombocytopenia syndrome(SFTS)is an emerging infectious disease with high mortality(12%–30%).The mechanism by which the SFTS bunyavirus(SFTSV)causes severe illness remains unclear.To evaluate the phenotypic and functional characteristics of the NK cell subsets in SFTS patients,twenty-nine SFTS patients were sequentially sampled from admission until recovery.Phenotypic and functional characteristics of NK cell subsets in circulating blood were analysed via flow cytometry.Then,correlations between NK cell subset frequencies and the SFTS index(SFTSI)were evaluated in all SFTS patients(15 mild,14 severe)upon admission.The frequencies of CD56dimCD16+NK cells were greatly decreased in early SFTSV infection and were negatively correlated with disease severity.Additionally,higher Ki-67 and granzyme B expression and relatively lower NKG2 A expression in CD56dimCD16+NK cells were observed in acute infection.Moreover,the effector function of CD56dimNK cells was increased in the acute phase compared with the recovery phase in nine severe SFTS patients.Additionally,interleukin(IL)-15,interferon(IFN)-a,IL-18 and IFN-c secretion was markedly increased during early infection.Collectively,despite depletion of CD56dimCD16+NK cells,activation and functional enhancement of CD56dimCD16+NK cells were still observed,suggesting their involvement in defence against early SFTSV infection.

Seroprevalence of Severe Fever with Thrombocytopenia Syndrome Phlebovirus in Domesticated Deer in South Korea

Severe fever with thrombocytopenia syndrome phlebovirus(SFTSV)has a wide host range.Not only has it been found in humans,but also in many wild and domesticated animals.The infection of breeding deer on farms is a particularly worrisome public health concern due to the large amount of human contact and the diverse use of deer products,including raw blood.To investigate the prevalence of breeding domesticated deer,we examined the SFTSV infection rate on deer farms in South Korea from 2015 to 2017.Of the 215 collected blood samples,0.9%(2/215)were found to be positive for viral RNA by PCR,and sequence analysis showed the highest homology with the KADGH human isolate.Both SFTSVspecific recombinant N and Gn protein-based ELIS As revealed that 14.0%(30/215)and 7.9%(17/215)of collected blood specimens were positive for SFTSV antibody.These results demonstrate that the breeding farm deer are exposed to SFTSV and could be a potential infection source for humans through direct contact or consumption of byproducts.

Antigenicity of severe fever with thrombocytopenia syndrome virus nucleocapsid protein and its potential application in the virus serodiagnosis

Dear Editor,Severe fever with thrombocytopenia syndrome virus(SFTSV)is a newly identified viral pathogen of the genus Phlebovirus in the family Bunyaviridae(Sun et al.,2012).SFTSV was first identified from patient serum samples in China(Li et al.,2013;Ning et al.,2015).SFTSV can cause a severe hemorrhagic fever-like disease with a reported case fatality rate ranging from 2.5%

Experimental infections of mosquitoes with severe fever with thrombocytopenia syndrome virus

Background:Severe fever with thrombocytopenia syndrome(SFTS)is a newly identified emerging infectious disease,which is caused by a novel bunyavirus(termed SFTSV)in Asia.Although mosquitoes have not been identified as the primary vectors,as revealed by epidemiological surveys,their role in transmitting this SFTSV as a suspicious vector has not been validated.Findings:In this study,we conducted experimental infections of mosquitoes with SFTSV to examine the role of mosquitoes in the transmission of the virus.We did not detect viral replication in Culex pipiens pallens,Aedes aegyptis and Anopheles sinensis as revealed by qRT-PCR assay.In addition,we failed to isolate SFTSV from the Vero cells cultured with suspensions of SFTSV-infected mosquitoes.Conclusion:The results of the present study demonstrate little possibility that mosquitoes act as vectors for the emerging pathogen SFTSV.

Quantitative assessment on the epidemic characteristics of severe fever with thrombocytopenia syndrome virus infection in China

Severe fever with thrombocytopenia syndrome(SFTS)was first detected in China in 2009.The incidence of SFTS increases year by year,and there is no effective treatment.Considering that the reported prevalence of SFTSV infection varies from region to region,we aimed to quantitatively evaluate the epidemic characteristics of SFTSV infection in China from 2010 to 2020,including the distribution differences in infectious season,sex,age,occupation,and region.A meta-analysis framework was used to search for the related published data with keywords in electronic databases(CNKI,WanFang,CBM,and PubMed).According to the PRISMA statement,the studies that included SFTS diagnosed in China were analyzed.Furthermore,we used Revman and Stata to merge statistical effects,and used I2 and P-values for heterogeneity test and quality assessment.Eleven studies containing 4,932 cases confirmed by SFTSV infection were included in this meta-analysis.The ratio of male-to-female is 1.04 to 1.Cases were concentrated between 40 and 80 years of age(MD=92%,95%CI:91%–93%).Farmers are at the highest risk of SFTSV infection(MD=84%,95%CI:77%–90%).The risk of infection for consecutive period of April-August was significantly higher than the sum of the remaining months(MD=82%,95%CI:78%–85%).In addition,the patient has an extensive history of exposure,including living in the mountains,exposure to ticks,livestock,mouse and the patient.We came to the conclusion that SFTSV is transmitted primarily through tick bites in China,so middle-aged and older adults living in mountains regions are at the highest risk for SFTSV infection in April through August each year.

Severe fever with thrombocytopenia syndrome with re-infection in China: a case report

Background:Severe fever with thrombocytopenia syndrome(SFTS),an emerging tickborne infectious disease caused by a novel banyangvirus(SFTS virus,SFTSV),was endemic in several Asian countries with a high mortality up to 30%.Until recently,SFTSV-associated re-infection have not been reported and investigated.

Liver Function Derangement in Patients with Severe Fever and Thrombocytopenia Syndrome

Background and Aims:Patients with severe fever with thrombocytopenia syndrome(SFTS)commonly show liver function impairment.This study aimed to characterize the liver function indices in SFTS patients and investigate their association with mortality.Methods:Clinical information and laboratory results of 459 laboratory-confirmed SFTS patients,including 78 deceased and 381 surviving patients,were retrospectively analyzed.To explore the infectivity of SFTS caused by novel Bunyavirus(SFTSV)in hepatocytes,Huh7 human hepatoma cells were infected with various concentrations of SFTSV in vitro.Results:The proportion of SFTS patients developing liver injury during hospitalization was 73.2%(336/459);the hepatocellular injury was the predominant type.The median time to occurrence of liver injury from disease onset was 8 d.Liver injury in the deceased group occurred earlier than that in the surviving group.Alanine aminotransferase(ALT)level between 2–5 times upper limit of normal(ULN)at 4–6 d and between 5–15 ULN at 7–12 d of disease course were independent predictors of mortality.Alkaline phosphatase(ALP)>2 ULN at 7–9 d and elevated ALP at 10–12 days after disease onset were risk factors for death.ALT and aspartate transaminase(AST)levels were correlated with lymphocyte count and platelet-to-lymphocyte ratio(PLR).Total bilirubin(TB),ALT,AST levels showed positive correlation with viral load.In the in vitro experiment,SFTSV infected and replicated inside Huh7 cells.Conclusions:Liver injury is common in SFTS patients.ALT and ALP were independent predictors of SFTS-related mortality.Frequent monitoring and evaluation of liver function indices are needed for SFTS patients.

Reactivation of Epstein-Barr virus in SFTSV infected patients

Background:Severe fever with thrombocytopenia syndrome(SFTS)is an emerging hemorrhagic fever caused by a tick-borne bunyavirus SFTSV with case fatality up to 30%.The reactivation of Epstein-Barr virus(EBV)has been proven to occur in individuals with various immune suppression conditions.Methods:Here,we diagnosed 22 SFTSV infected patients with PCR in a hospital in Shandong Province,China in 2020.To understand the consequences of SFTSV infection leading to EBV reactivation,we examined EBV reactivation in SFTSV-infected patients with PCR and RT-PCR.Results:We found that EBV was reactivated in 18.2%(4/22)of SFTS patients,suggesting that EBV reactivation is common in SFTS patients.Compared with SFTS patients without EBV reactivation,SFTS patients with EBV-reactivation had a significantly lower median level of serum albumin(32.45 g/L vs.26.95 g/L,p=0.03)and a significantly higher median number of urine red blood cells(0 cells/μL vs.9 cells/μL,p=0.04).Conclusion:SFTS infection can reactivate EBV in patients,which may make the clinical condition of patients worsen.

Novel SFTSV Phylogeny Reveals New Reassortment Events and Migration Routes

Severe fever with thrombocytopenia syndrome virus(SFTSV),the causative agent of a febrile human disease,was first identified from central and eastern provinces in China,and later in Japan and South Korea.Hubei Province is one of the major SFTS epidemic areas in the central part of China.This study reported the isolation of 11 new SFTSV strains from patients in Hubei Province collected in 2017.Extensive phylogenetic analyses were conducted based on the complete coding sequences of SFTSV segments including the new strains.It was suggested that five different SFTSV genotypes were circulating in Hubei,and 15 reassortment patterns and migration pathways correlated with each genotype were identified,which was more than previously recognized.Hubei Province was more involved in the evolutionary events of SFTSV than that previously thought in which the evolutionary events of SFTSV were reported to be independent from those in other epidemic regions.Further divergence of SFTSV strains was suggested by pairwise comparison of SFTSV sequences from each genotype and sequence identity normalized to representative strain in genotype C1.Subsequently,amino acid variations specific for genotype(s),strain(s),or cluster(s)were inspected,which may be related to differential biological activity of SFTSV strains/genotypes.In conclusion,we analyzed the current status of SFTSV phylogeny in Hubei Province and discussed the possible events correlated to SFTSV evolution.It provided an in-depth insight into SFTSV evolution,raising concerns for the use of proper SFTSV strains in future studies.

SNX11 Identified as an Essential Host Factor for SFTS Virus Infection by CRISPR Knockout Screening

Severe fever with thrombocytopenia syndrome virus(SFTSV)is a highly pathogenic tick-borne bunyavirus that causes lethal infectious disease and severe fever with thrombocytopenia syndrome(SFTS)in humans.The molecular mechanisms and host cellular factors required for SFTSV infection remain uncharacterized.Using a genome-wide CRISPR-based screening strategy,we identified a host cellular protein,sorting nexin 11(SNX11)which is involved in the intracellular endosomal trafficking pathway,as an essential cell factor for SFTSV infection.An SNX11-KO HeLa cell line was established,and SFTSV replication was significantly reduced.The glycoproteins of SFTSV were detected and remained in later endosomal compartments but were not detectable in the endoplasmic reticulum(ER)or Golgi apparatus.pH values in the endosomal compartments of the SNX11-KO cells increased compared with the pH of normal HeLa cells,and lysosomal-associated membrane protein 1(LAMP1)expression was significantly elevated in the SNX11-KO cells.Overall,these results indicated that penetration of SFTSV from the endolysosomes into the cytoplasm of host cells was blocked in the cells lacking SNX11.Our study for the first time provides insight into the important role of the SNX11 as an essential host factor in the intracellular trafficking and penetrating process of SFTSV infection via potential regulation of viral protein sorting,membrane fusion,and other endocytic machinery.