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Severe fever with thrombocytopenia syndrome virus (SFTSV), recently named as Dabie bandavirus, belongs to the family Phenuiviridae of the order Bunyavirales, is a newly-identified bunyavirus with a case fatality rate of up to 30%, posing a serious threat to public health. Lipid rafts on plasm membranes are important for the entry of enveloped viruses; however, the role of lipid rafts in bunyavirus entry remains unclear. In this study, we found that methyl-beta-cyclodextrin (MβCD), a drug that disrupts cholesterol in lipid rafts of cell membranes, inhibits SFTSV infection. Additionally, there is a back-complementary effect of SFTSV infection upon the addition of cholesterol. Moreover, the concentration of SFTSV particles in lipid rafts during entry directly indicated the role of lipid rafts as a gateway, whereas MβCD could inhibit SFTSV entry by affecting the structure of lipid rafts. In an in vivo study, MβCD also reduced the susceptibility of mice to SFTSV infection. Our results suggest that SFTSV can interact with Talin1 proteins on lipid rafts to enter host cells by endocytosis of lipid rafts and reveal the potential therapeutic value of MβCD for SFTSV infection., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

The heterogeneous nuclear ribonucleoprotein (hnRNP A2B1) is a key component of the hnRNP complex involving RNA modulation in eukaryotic cells and it has also been reported to be involved in the replication of the hepatitis E virus, influenza A virus, and hepatitis B virus. However, it is not clear whether the role of the hnRNP A2B1 in viral replication is conserved among RNA viruses and what is the mechanism of hnRNP A2B1 in RNA virus replication. In this study, we first used severe fever with thrombocytopenia syndrome virus (SFTSV), a tick-borne RNA virus that causes a severe viral hemorrhagic fever as well as other RNA viruses including VSV-GFP, SeV, EV71, and ZIKV to demonstrate that knockout hnRNPA2B1 gene inhibited viral RNA replication and overexpression of hnRNP A2B1 could restore the RNA levels of all tested RNA viruses. These results suggest that hnRNPA2B1 upregulation of viral replication is conserved among RNA viruses. Next, we demonstrated that hnRNP A2B1 was translocated from the nucleus to the cytoplasm under RNA virus infection including SFTSV, VSV-GFP, SeV, EV71, and ZIKV, suggesting translocation of hnRNP A2B1 from the nucleus to the cytoplasm is crucial for RNA virus replication. We then used SFTSV as a model to demonstrate the mechanism of hnRNP A2B1 in the promotion of RNA virus replication. We found that overexpression of SFTSV nucleoprotein can also cause hnRNP A2B1 translocation from the nucleus to the cytoplasm and that the SFTSV NP interacted with the RNA recognition motif 1 domain of hnRNP A2B1. We further demonstrated that the hnRNP A2B1 interacted with the 5' UTR of SFTSV RNA. In conclusion, we revealed that the hnRNP A2B1 upregulation of viral RNA replication is conserved among RNA viruses; the mechanism of hnRNP A2B1 in promotion of SFTSV viral RNA replication is that SFTSV NP interacted with the hnRNPA2B1 to retain it in the cytoplasm where the hnRNP A2B1 interacted with the 5' UTR of SFTSV RNA to promote the viral RNA replication.IMPORTANCESevere fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne RNA virus with a high mortality rate of up to 30%. In this study, we first used SFTSV as a model to demonstrate that the role of hnRNPA2B1 in viral replication is conserved in SFTSV. Then we used other RNA viruses, including VSV-GFP, SeV, EV71, and ZIKV, to repeat the experiment and demonstrated the same results as SFTSV in all tested RNA viruses. By knocking out the hnRNPA2B1 gene, SFTSV RNA replication was inhibited, and overexpression of hnRNPA2B1 restored RNA levels of SFTSV and other tested RNA viruses. We revealed a novel mechanism where the SFTSV nucleoprotein interacts with hnRNPA2B1, retaining it in the cytoplasm. This interaction promotes viral RNA replication by binding to the 5' UTR of SFTSV RNA. The findings suggest that targeting hnRNPA2B1 could be a potential strategy for developing broad-spectrum antiviral therapies, given its conserved role across different RNA viruses. This research provides significant insights into the replication mechanisms of RNA viruses and highlights potential targets for antiviral interventions., Competing Interests: The authors declare no conflict of interest.

Severe fever with thrombocytopenia syndrome virus (SFTSV) nonstructural protein (NSs) is an important viral virulence factor that sequesters multiple antiviral proteins into inclusion bodies to escape the antiviral innate immune response. However, the mechanism of the NSs restricting host innate immunity remains largely elusive. Here, we found that the NSs induced complete macroautophagy/autophagy by interacting with the CCD domain of BECN1, thereby promoting the formation of a BECN1-dependent autophagy initiation complex. Importantly, our data showed that the NSs sequestered antiviral proteins such as TBK1 into autophagic vesicles, and therefore promoted the degradation of TBK1 and other antiviral proteins. In addition, the 8A mutant of NSs reduced the induction of BECN1-dependent autophagy flux and degradation of antiviral immune proteins. In conclusion, our results indicated that SFTSV NSs sequesters antiviral proteins into autophagic vesicles for degradation and to escape antiviral immune responses.

Severe fever with thrombocytopenia syndrome (SFTS) has a high mortality rate compared to other infectious diseases. SFTS is particularly associated with a high risk of mortality in immunocompromised individuals, while most patients who die of SFTS exhibit symptoms of severe encephalitis before death. However, the region of brain damage and mechanisms by which the SFTS virus (SFTSV) causes encephalitis remains unknown. Here, we revealed that SFTSV infects the brainstem and spinal cord, which are regions of the brain associated with respiratory function, and motor nerves in IFNAR1 -/- mice. Further, we show that A1-reactive astrocytes are activated, causing nerve cell death, in infected mice. Primary astrocytes of SFTSV-infected IFNAR1 -/- mice also induced neuronal cell death through the activation of A1-reactive astrocytes. Herein, we showed that SFTSV induces fatal neuroinflammation in the brain regions important for respiratory function and motor nerve, which may underlie mortality in SFTS patients. This study provides new insights for the treatment of SFTS, for which there is currently no therapeutic approach., (© 2024 The Author(s). Journal of Medical Virology published by Wiley Periodicals LLC.)

In our prior investigations, we elucidated the role of the tryptophan-to-tyrosine substitution at the 61st position in the nonstructural protein NSsW61Y in diminishing the interaction between nonstructural proteins (NSs) and nucleoprotein (NP), impeding viral replication. In this study, we focused on the involvement of NSs in replication via the modulation of autophagosomes. Initially, we examined the impact of NP expression levels, a marker for replication, upon the infection of HeLa cells with severe fever thrombocytopenia syndrome virus (SFTSV), with or without the inhibition of NP binding. Western blot analysis revealed a reduction in NP levels in NSsW61Y-expressing conditions. Furthermore, the expression levels of the canonical autophagosome markers p62 and LC3 decreased in HeLa cells expressing NSsW61Y, revealing the involvement of individual viral proteins on autophagy. Subsequent experiments confirmed that NSsW61Y perturbs autophagy flux, as evidenced by reduced levels of LC3B and p62 upon treatment with chloroquine, an inhibitor of autophagosome-lysosome fusion. LysoTracker staining demonstrated a decrease in lysosomes in cells expressing the NS mutant compared to those expressing wild-type NS. We further explored the mTOR-associated regulatory pathway, a key regulator affected by NS mutant expression. The observed inhibition of replication could be linked to conformational changes in the NSs, impairing their binding to NP and altering mTOR regulation, a crucial upstream signaling component in autophagy. These findings illuminate the intricate interplay between NSsW61Y and the suppression of host autophagy machinery, which is crucial for the generation of autophagosomes to facilitate viral replication.

Severe fever with thrombocytopenia syndrome (SFTS) is a life-threatening disease caused by a novel bunyavirus (SFTSV), mainly transmitted by ticks. With no effective therapies or vaccines available, understanding the disease's mechanisms is crucial. Recent studies found increased expression of programmed cell death-1 (PD-1) on dysfunctional T cells in SFTS patients. However, the role of the PD-1/programmed cell death-ligand 1 (PD-L1) pathway in SFTS progression remains unclear. We investigated PD-1 blockade as a potential therapeutic strategy against SFTSV replication. Our study analyzed clinical samples and performed in vitro experiments, revealing elevated PD-1/PD-L1 expression in various immune cells following SFTSV infection. An anti-PD-1 nanobody, NbP45, effectively inhibited SFTSV infection in peripheral blood mononuclear cells (PBMCs), potentially achieved through the mitigation of apoptosis and the augmentation of T lymphocyte proliferation. Intriguingly, subcutaneous administration of NbP45 showed superior efficacy compared to a licensed anti-PD-1 antibody in an SFTSV-infected humanized mouse model. These findings highlight the involvement of the PD-1/PD-L1 pathway during acute SFTSV infection and suggest its potential as a host target for immunotherapy interventions against SFTSV infection., (© 2024. The Author(s).)

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a bunyavirus that causes SFTS, with a case fatality rate of up to 30 %. The innate immune system plays a crucial role in the defense against SFTSV; however, the impact of viral propagation of STFSV on the innate immune system remains unclear. Although proteomics analysis revealed that the expression of the downregulator of transcription 1 (DR1) increased after SFTSV infection, the specific change trend and the functional role of DR1 during viral infection remain unelucidated. In this study, we demonstrate that DR1 was highly expressed in response to SFTSV infection in HEK 293T cells using qRT-PCR and Western blot analysis. Furthermore, viral replication significantly increased the expression of various TLRs, especially TLR9. Our data indicated that DR1 positively regulated the expression of TLRs in HEK 293T cells, DR1 overexpression highly increased the expression of numerous TLRs, whereas RNAi-mediated DR1 silencing decreased TLR expression. Additionally, the myeloid differentiation primary response gene 88 (MyD88)-dependent or TIR-domain-containing adaptor inducing interferon-β (TRIF)-dependent signaling pathways were highly up- and downregulated by the overexpression and silencing of DR1, respectively. Finally, we report that DR1 stimulates the expression of TLR7, TLR8, and TLR9, thereby upregulating the TRIF-dependent and MyD88-dependent signaling pathways during the SFTSV infection, attenuating viral replication, and enhancing the production of type I interferon and various inflammatory factors, including IL-1β, IL-6, and IL-8. These results imply that DR1 defends against SFTSV replication by inducing the expression of TLR7, TLR8, and TLR9. Collectively, our findings revealed a novel role and mechanism of DR1 in mediating antiviral responses and innate immunity., Competing Interests: Declaration of Competing Interest The authors declare no conflicts of interest., (Copyright © 2023. Published by Elsevier GmbH.)

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with high case mortality rates, which is caused by Dabie bandavirus (DBV), a novel pathogen also termed as SFTS virus (SFTSV). Currently, no specific therapeutic drugs or vaccines are available for SFTS. Myxovirus resistance protein A (MxA) has been shown to inhibit multiple viral pathogens; however, the role of MxA in DBV infection is unknown. Here, we demonstrated that DBV stimulates MxA expression which, in turn, restricts DBV infection. Mechanistic target analysis revealed that MxA specifically interacts with the viral nucleocapsid protein (NP) in a manner independent of RNA. Minigenome reporter assay showed that in agreement with its targeting of NP, MxA inhibits DBV ribonucleoprotein (RNP) activity. In detail, MxA interacts with the NP N-terminal and disrupts the interaction of NP with the viral RNA-dependent RNA polymerase (RdRp) but not NP multimerization, the critical activities of NP for RNP formation and function. Furthermore, MxA N-terminal domain was identified as the functional domain inhibiting DBV infection, and, consistently, then was shown to interact with NP and obstruct the NP-RdRp interaction. Additionally, threonine 103 within the N-terminal domain is important for MxA inhibition to DBV, and its mutation (T103A) attenuates MxA binding to NP and obstruction of the NP-RdRp interaction. This study uncovers MxA inhibition of DBV with a series of functional and mechanistical analyses, providing insights into the virus-host interactions and probably helping inform the development of antiviral agents in the future.IMPORTANCEDBV/SFTSV is an emerging high-pathogenic virus. Since its first identification in China in 2009, cases of DBV infection have been reported in many other countries, posing a significant threat to public health. Uncovering the mechanisms of DBV-host interactions is necessary to understand the viral pathogenesis and host response and may advance the development of antiviral therapeutics. Here, we found that host factor MxA whose expression is induced by DBV restricts the virus infection. Mechanistically, MxA specifically interacts with the viral NP and blocks the NP-RdRp interaction, inhibiting the viral RNP activity. Further studies identified the key domain and amino acid residue required for MxA inhibition to DBV. Consistently, they were then shown to be important for MxA targeting of NP and obstruction of the NP-RdRp association. These findings unravel the restrictive role of MxA in DBV infection and the underlying mechanism, expanding our knowledge of the virus-host interactions., Competing Interests: The authors declare no conflict of interest.

Importance: One of the conserved mechanisms at the stage of genome transcription of segmented negative-strand RNA viruses (sNSVs) is the cap-snatching process, which is vital for sNSVs transcription and provides drugable targets for the development of antivirals. However, the specificity of RNAs snatched by sNSV is still unclear. By transcriptomics analysis of whole blood samples from SFTS patients, we found WNT-CTNNB1 signaling pathway was regulated according to the course of the disease. We then demonstrated that L protein of severe fever with thrombocytopenia syndrome virus (SFTSV) could interact with mRNAs of WNT-CTNNB1 signaling pathway-related gene, thus affecting WNT-CTNNB1 signaling pathway through its cap-snatching activity. Activation of WNT-CTNNB1 signaling pathway enhanced SFTSV replication, while inhibition of this pathway decreased SFTSV replication in vitro and in vivo . These findings suggest that WNT-associated genes may be the substrate for SFTSV "cap-snatching", and indicate a conserved sNSVs replication mechanism involving WNT-CTNNB1 signaling., Competing Interests: The authors declare no conflict of interest.

Severe fever with thrombocytopenia syndrome (SFTS) is a new infectious disease caused by bunyavirus, and the critically cases conform to the definition of sepsis. In order to compare the differences between SFTS sepsis and non-SFTS sepsis, a retrospective analysis was performed. Thirty-seven SFTS sepsis and 96 non-SFTS sepsis patients were enrolled. The clinical characteristics, laboratory results were compared between the two groups and independent prognostic risk of mortality were investigated respectively. Compared with non-SFTS sepsis, SFTS cases had lower white blood cell, neutrophil and platelet counts, prolonged activated partial thromboplastin time and decreased fibrinogen, slightly elevated inflammatory indicators. Interleukin-6 (IL-6), and acute physiology and chronic health evaluation Ⅱ (APACHE II) score were independent prognostic risk factors in non-SFTS sepsis. The mortality risk of STFS sepsis was related to the viral clearance. There was no difference in viral load between SFTS survivors and non-survivors on admission. However, the differences were significant on 5th, 7th, 10th, and 14th day, and all SFTS non-survivors died within 14 days. Viral clearance rate on 7th day was an independent risk factor for mortality in SFTS sepsis. The mortality risk of STFS sepsis was related to the viral clearance rate., Competing Interests: Declaration of Competing Interest The authors declare no conflict of interest., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Pathogens co-evolved with ticks to facilitate blood collection and pathogen transmission. Although tick saliva was recently found to be rich in bioactive peptides, it is still elusive which saliva peptide promotes virus transmission and which pathways are invovled. Here, we used a saliva peptide HIDfsin2 and a severe fever with thrombocytopenia syndrome virus (SFTSV) both carried by the tick Haemaphysalis longicornis to elucidate the relationship between tick saliva components and tick-borne viruses. HIDfsin2 was found to promote the replication of SFTSV in a dose-dependent manner in vitro. HIDfsin2 was further revealed to MKK3/6-dependently magnify the activation of p38 MAPK. The overexpression, knockdown and phosphorylation site mutation of p38α indicated that p38 MAPK activation facilitated SFTSV infection in A549 cells. Moreover, the blockade of p38 MAPK activation significantly suppressed SFTSV replication. Differently, HIDfsin2 or pharmacological inhibition of p38 MAPK activation had no effect on a mosquito-borne Zika virus (ZIKV). All these results showed that HIDfsin2 specifically promoted SFTSV replication through the MKK3/6-dependent enhancement of p38 MAPK activation. Our study provides a new perspective on the transmission of tick-borne viruses under natural conditions, and supports that the blockade of p38 MAPK activation can be a promising strategy against the mortal tick-borne virus SFTSV., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Severe fever with thrombocytopenia syndrome virus (SFTSV), which has been reported in China, Korea, Japan, Vietnam, and Taiwan, is a causative agent of severe fever thrombocytopenia syndrome. This virus has a high mortality and induces thrombocytopenia and leukocytopenia in humans, cats, and aged ferrets, whereas immunocompetent adult mice infected with SFTSV never show symptoms. Anti-SFTSV antibodies have been detected in several animals-including goats, sheep, cattle, and pigs. However, there are no reports of severe fever thrombocytopenia syndrome in these animals. Previous studies have reported that the nonstructural protein NSs of SFTSV inhibits the type I interferon (IFN-I) response through the sequestration of human signal transducer and activator of transcription (STAT) proteins. In this study, comparative analysis of the function of NSs as IFN antagonists in human, cat, dog, ferret, mouse, and pig cells revealed a correlation between pathogenicity of SFTSV and the function of NSs in each animal. Furthermore, we found that the inhibition of IFN-I signaling and phosphorylation of STAT1 and STAT2 by NSs depended on the binding ability of NSs to STAT1 and STAT2. Our results imply that the function of NSs in antagonizing STAT2 determines the species-specific pathogenicity of SFTSV., Competing Interests: Conflict of interest The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Negative-strand RNA viruses (NSVs) represent one of the most threatening groups of emerging viruses globally. Severe fever with thrombocytopenia syndrome virus (SFTSV) is a highly pathogenic emerging virus that was initially reported in 2011 from China. Currently, no licensed vaccines or therapeutic agents have been approved for use against SFTSV. Here, L-type calcium channel blockers obtained from a U.S. Food and Drug Administration (FDA)-approved compound library were identified as effective anti-SFTSV compounds. Manidipine, a representative L-type calcium channel blocker, restricted SFTSV genome replication and exhibited inhibitory effects against other NSVs. The result from the immunofluorescent assay suggested that manidipine inhibited SFTSV N-induced inclusion body formation, which is believed to be important for the virus genome replication. We have shown that calcium possesses at least two different roles in regulating SFTSV genome replication. Inhibition of calcineurin, the activation of which is triggered by calcium influx, using FK506 or cyclosporine was shown to reduce SFTSV production, suggesting the important role of calcium signaling on SFTSV genome replication. In addition, we showed that globular actin, the conversion of which is facilitated by calcium from filamentous actin (actin depolymerization), supports SFTSV genome replication. We also observed an increased survival rate and a reduction of viral load in the spleen in a lethal mouse model of SFTSV infections after manidipine treatment. Overall, these results provide information regarding the importance of calcium for NSV replication and may thereby contribute to the development of broad-scale protective therapies against pathogenic NSVs. IMPORTANCE SFTS is an emerging infectious disease and has a high mortality rate of up to 30%. There are no licensed vaccines or antivirals against SFTS. In this article, L-type calcium channel blockers were identified as anti-SFTSV compounds through an FDA-approved compound library screen. Our results showed the involvement of L-type calcium channel as a common host factor for several different families of NSVs. The formation of an inclusion body, which is induced by SFTSV N, was inhibited by manidipine. Further experiments showed that SFTSV replication required the activation of calcineurin, a downstream effecter of the calcium channel. In addition, we identified that globular actin, the conversion of which is facilitated by calcium from filamentous actin, supports SFTSV genome replication. We also observed an increased survival rate in a lethal mouse model of SFTSV infection after manidipine treatment. These results facilitate both our understanding of the NSV replication mechanism and the development of novel anti-NSV treatment.

Severe fever with thrombocytopenia syndrome virus (SFTSV), an emerging tick-borne bunyavirus, causes mild-to-moderate infection to critical illness or even death in human patients. The effect of virus variations on virulence and related clinical significance is unclear. We prospectively recruited SFTSV-infected patients in a hotspot region of SFTS endemic in China from 2011 to 2020, sequenced whole genome of SFTSV, and assessed the association of virus genomic variants with clinical data, viremia, and inflammatory response. We identified seven viral clades (I-VII) based on phylogenetic characterization of 805 SFTSV genome sequences. A significantly increased case fatality rate (32.9%) was revealed in one unique clade (IV) that possesses a specific co-mutation pattern, compared to other three common clades (I, 16.7%; II, 13.8%; and III, 11.8%). The phenotype-genotype association (hazard ratios ranged 1.327-2.916) was confirmed by multivariate regression adjusting age, sex, and hospitalization delay. We revealed a pronounced inflammation response featured by more production of CXCL9, IL-10, IL-6, IP-10, M-CSF, and IL-1β, in clade IV, which was also related to severe complications. We observed enhanced cytokine expression from clade IV inoculated PBMCs and infected mice. Moreover, the neutralization activity of convalescent serum from patients infected with one specified clade was remarkably reduced to other viral clades. Together, our findings revealed a significant association between one specific viral clade and SFTS fatality, highlighting the need for molecular surveillance for highly lethal strains in endemic regions and unravelled the importance of evaluating cross-clade effect in development of vaccines and therapeutics.

Severe fever with thrombocytopenia syndrome (SFTS) has been acknowledged as an emerging infectious disease that is caused by the SFTS virus (SFTSV). The main clinical features of SFTS on presentation include fever, thrombocytopenia, leukocytopenia and gastrointestinal symptoms. The mortality rate is estimated to range between 5‑30% in East Asia. However, SFTSV infection is increasing on an annual basis globally and is becoming a public health problem. The transmission cycle of SFTSV remains poorly understood, which is compounded by the pathogenesis of SFTS not being fully elucidated. Since the mechanism underlying the host immune response towards SFTSV is also unclear, there are no effective vaccines or specific therapeutic agents against SFTS, with supportive care being the only realistic option. Therefore, it is now crucial to understand all aspects of the host‑virus interaction following SFTSV infection, including the antiviral states and viral evasion mechanisms. In the present review, recent research progress into the possible host immune responses against SFTSV was summarized, which may be useful in designing novel therapeutics against SFTS.

Severe fever with thrombocytopenia syndrome (SFTS) virus (SFTSV) is an emerging tick-borne phlebovirus with a high fatality rate of 12-30%, which has an expanding endemic and caused thousands of infections every year. Central nervous system (CNS) manifestations are an important risk factor of SFTS outcome death. Further understanding of the process of how SFTSV invades the brain is critical for developing effective anti-SFTS encephalitis therapeutics. We obeserved changes of viral load in the brain at different time points after intraperitoneal infection of SFTSV in newborn C57/BL6 mice. The virus invaded the brain at 3 h post-infection (hpi). Notably, the viral load increased exponentially after 24 hpi. In addition, it was found that in addition to macrophages, SFTSV infected neurons and replicated in the brain. These findings provide insights into the CNS manifestations of severe SFTS, which may lead to drug development and encephalitis therapeutics., (© 2022. The Author(s).)

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tickborne disease in East Asia that is causing high mortality. The Gn glycoprotein of the SFTS virus (SFTSV) has been considered to be an essential target for virus neutralization. However, data on anti-Gn glycoprotein antibody kinetics are limited. Therefore, we investigated the kinetics of Gn-specific antibodies compared to those of nucleocapsid protein (NP)-specific antibodies. A multicenter prospective study was performed in South Korea from January 2018 to September 2021. Adult patients with SFTS were enrolled. Anti-Gn-specific IgM and IgG were measured using an enzyme-linked immunosorbent assay. A total of 111 samples from 34 patients with confirmed SFTS were analyzed. Anti-Gn-specific IgM was detected at days 5-9 and peaked at day 15-19 from symptom onset, whereas the anti-NP-specific IgM titers peaked at days 5-9. Median seroconversion times of both anti-Gn- and NP-specific IgG were 7.0 days. High anti-Gn-specific IgG titers were maintained until 35-39 months after symptom onset. Only one patient lost their anti-Gn-specific antibodies at 41 days after symptom onset. Our data suggested that the anti-Gn-specific IgM titer peaked later than anti-NP-specific IgM, and that anti-Gn-specific IgG remain for at least 3 years from symptom onset.

Severe fever with thrombocytopenia syndrome (SFTS) is a novel tick-borne infectious disease caused by a new type of SFTS virus (SFTSV). Here, a longitudinal sampling study is conducted to explore the differences in transcript levels after SFTSV infection, and to characterize the transcriptomic and epigenetic profiles of hospitalized patients. The results reveal significant changes in the mRNA expression of certain genes from onset to recovery. Moreover, m 6 A-seq reveals that certain genes related with immune regulation may be regulated by m 6 A. Besides the routine tests such as platelet counts, serum ALT and AST levels testing, distinct changes in myocardial enzymes, coagulation function, and inflammation are well correlated with the clinical data and sequencing data, suggesting that clinical practitioners should monitor the above indicators to track disease progression and guide personalized treatment. In this study, the transcript changes and RNA modification may lend a fresh perspective to our understanding of the SFTSV and play a significant role in the discovery of drugs for effective treatment of this disease., (© 2021. The Author(s).)

Sand flies transmit Leishmania infantum , which is responsible for causing leishmaniasis, as well as many phleboviruses, including the human pathogenic Toscana virus. We screened sand flies collected from a single site between 2017 and 2020 for the presence of both phleboviruses and Leishmania . The sand flies were sampled with attractive carbon dioxide traps and CDC light traps between May and October. We collected more than 50,000 sand flies; 2826 were identified at the species level as Phlebotomus perfiliewi (98%) or Phlebotomus perniciosus (2%). A total of 16,789 sand flies were tested in 355 pools, and phleboviruses were found in 61 pools (6 Toscana virus positive pools, 2 Corfou virus positive pools, 42 Fermo virus positive pools, and 7 Ponticelli virus positive pools, and 4 unidentified phlebovirus positive pools). Leishmania was found in 75 pools and both microorganisms were detected in 16 pools. We isolated nine phleboviruses from another 2960 sand flies (five Ponticelli viruses and for Fermo viruses), not tested for Leishmania ; the complete genome of a Fermo virus isolate was sequenced. The simultaneous detection in space and time of the Fermo virus and L. infantum is evidence that supports the co-circulation of both microorganisms in the same location and partial overlap of their cycles. A detailed characterization of the epidemiology of these microorganisms will support measures to limit their transmission.

With global warming and lush forest change, vector-borne infections are expected to increase in the number and diversity of agents. Since the first report of severe fever with thrombocytopenia syndrome (SFTS) in 2013, the number of reported cases has increased annually in South Korea. However, although tick-borne encephalitis virus (TBEV) was detected from ticks and wild rodents, there is no human TBE case report in South Korea. This study aimed to determine the seroprevalence of TBEV and SFTS virus (SFTSV) among forest and field workers in South Korea. From January 2017 to August 2018, a total 583 sera were obtained from the forest and field workers in South Korea. IgG enzyme-linked immunosorbent assay (ELISA) and neutralization assay were conducted for TBEV, and indirect immunofluorescence assay (IFA) and neutralization assay were performed for SFTSV. Seroprevalence of TBEV was 0.9% (5/583) by IgG ELISA, and 0.3% (2/583) by neutralization assay. Neutralizing antibody against TBEV was detected in a forest worker in Jeju (1:113) and Hongcheon (1:10). Only 1 (0.2%) forest worker in Yeongju was seropositive for SFTSV by IFA (1:2,048) and neutralizing antibody was detected also. In conclusion, this study shows that it is necessary to raise the awareness of physicians about TBEV infection and to make efforts to survey and diagnose vector-borne diseases in South Korea., Competing Interests: I have read the journal’s policy and the authors of this manuscript have the following competing interests: JYS received a grant that was underwritten by Pfizer. The other authors declare that no competing interests exist.

Severe fever with thrombocytopenia syndrome (SFTS) is an acute febrile illness characterized by fever, leukopenia, thrombocytopenia, and gastrointestinal symptoms such as diarrhea, nausea, and vomiting resulting from infection with the SFTS virus (SFTSV). The SFTSV is transmitted to humans by tick bites, primarily from Haemaphysalis longicornis , Amblyomma testudinarium , Ixodes nipponensis , and Rhipicephalus microplus . Human-to-human transmission has also been reported. Since the first report of an SFTS patient in China, the number of patients has also been increasing. The mortality rate of patients with SFTS remains high because the disease can quickly lead to death through multiple organ failure. In particular, an average fatality rate of approximately 20% has been reported for SFTS patients, and no treatment strategy has been established. Therefore, effective antiviral agents and vaccines are required. Here, we aim to review the epidemiology, clinical manifestations, laboratory diagnosis, and various specific treatments (i.e., antiviral agents, steroids, intravenous immunoglobulin, and plasma exchange) that have been tested to help to cope with the disease.

Viral non-structural proteins, such as NSs of the newly emerging severe fever with thrombocytopenia syndrome virus, are well established virulence factors, mediating viral pathogenesis and disease progression through various mechanisms. NSs has been described as a potent interferon antagonist and NF-κB agonist, two divergent signaling pathways in many immune responses upon a viral encounter. In this review, we highlight the many mechanisms used by NSs on the host that promote viral replication and hyper-inflammation. Understanding these host-pathogen interactions is crucial for antiviral therapy development.

Aspergillus-related disease was confirmed to be associated with immune disorders in patients, severe patients with severe fever with thrombocytopenia syndrome (SFTS) infected by novel phlebovirus were confirmed to have severe immune damage including cellular immunosuppression and cytokine storms. Secondary invasive pulmonary aspergillosis (IPA) in severe SFTS patients can increase fatality rate. This study investigated early-warning predictive factors of secondary IPA in severe SFTS patients. Receiver operating characteristic analysis was used to assess the value of immune parameters to predict IPA in SFTS patients. The cut-off values of CD4 + and CD8 + T-cell counts to predict IPA were 68 and 111 cells/mm 3 , with sensitivities of 82.6% and 72%, and specificities of 56.7% and 83.3%, respectively. Cut-off values of IL-6, TNF-α, IL-8, and IL-10 to predict IPA incidence in critically ill SFTS patients were 99 pg/mL, 63 pg/mL, 120 pg/mL, and 111 pg/mL, with sensitivities of 90.0%, 86.7%, 83.3% and 90.0% and specificities of 80.4%, 71.7%, 82.6% and 65.2%, respectively. Lower CD4 + and CD8 + T-cells counts, higher levels of IL-6, TNF-α, IL-8 and IL-10, higher incidence of pancreatic and renal damage, early antibacterial therapy of carbapenems, and intensive care unit admission were risk factors of IPA in SFTS patients. Multivariate logistic regression analysis indicated counts of CD4 + T-cells <68 cells/mm 3 combined with CD8 + T-cells <111 cells/mm 3 (odds ratio [OR] 0.218, 95% confidence interval [CI] 0.059-0.803, p =0.022), IL-6 >99 pg/ml combined with IL-10 >111 pg/ml (OR 17.614, 95% CI 2.319-133.769, p =0.006), and brain natriuretic peptide level >500 pg/ml (OR 13.681, 95% CI 1.994-93.871, p =0.008) were independent risk factors for IPA in SFTS patients. The mortality in the IPA group was significantly higher than in the non-IPA group ( p =0.001). Early antifungal treatment of IPA patients was significantly associated with improved survival (log-rank, p =0.022). Early diagnosis of IPA and antifungal treatment can improve the prognosis of SFTS patients. Besides, we speculate SFTS may be as a host factor for IPA., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Hu, Kong, Yue, Xu, Xia, Bian, Liu, Zhang, Ma, Yin, Sun, Gao, Ye and Li.)

An emerging infectious disease first identified in central China in 2009, severe fever with thrombocytopenia syndrome (SFTS) was found to be caused by a novel phlebovirus. Since SFTSV was first identified, epidemics have occurred in several East Asian countries. With the escalating incidence of SFTS and the rapid, worldwide spread of SFTSV vector, it is clear this virus has pandemic potential and presents an impending global public health threat. In this review, we concisely summarize the latest findings regarding SFTSV, including vector and virus transmission, genotype diversity and epidemiology, probable pathogenic mechanism, and clinical presentation of human SFTS. Ticks most likely transmit SFTSV to animals including humans; however, human-to-human transmission has been reported. The majority of arbovirus transmission cycle includes vertebrate hosts, and potential reservoirs include a variety of both domestic and wild animals. Reports of the seroprevalence of SFTSV in both wild and domestic animals raises the probability that domestic animals act as amplifying hosts for the virus. Major clinical manifestation of human SFTS infection is high fever, thrombocytopenia, leukocytopenia, gastrointestinal symptoms, and a high case-fatality rate. Several animal models were developed to further understand the pathogenesis of the virus and aid in the discovery of therapeutics and preventive measures.

Background: Severe fever with thrombocytopenia syndrome (SFTS) was listed as one of the most severe infectious disease by world health organization in 2017. It can mostly be transmitted by tick bite, while human-to-human transmission has occurred on multiple occasions. This study aimed to explore the epidemiological and clinical characteristics and make risk analysis of SFTS human-to-human transmission., Methods: Descriptive and spatial methods were employed to illustrate the epidemiological and clinical characteristics of SFTS human-to-human transmission. The risk of SFTS human-to-human transmission was accessed through secondary attack rate (SAR) and basic reproductive number (R0). Logistic regression analysis was used to identify the associated risk factors., Results: A total of 27 clusters of SFTS human-to-human transmission were reported in China and South Korea during 1996-2019. It mainly occurred among elder people in May, June and October in central and eastern China. The secondary cases developed milder clinical manifestation and better outcome than the index cases. The incubation period was 10.0 days (IQR:8.0-12.0), SAR was 1.72%-55.00%, and the average R0 to be 0.13 (95%CI:0.11-0.16). Being blood relatives of the index case, direct blood/bloody secretion contact and bloody droplet contact had more risk of infection (OR = 6.35(95%CI:3.26-12.37), 38.01 (95%CI,19.73-73.23), 2.27 (95%CI,1.01-5.19))., Conclusions: SFTS human-to-human transmission in China and South Korea during 1996-2019 had obvious spatio-temporal distinction. Ongoing assessment of this transmission risk is crucial for public health authorities though it continues to be low now., Competing Interests: The authors have declared that no competing interests exist.

Severe fever with thrombocytopenia syndrome (SFTS) has a high fatality rate and is caused by SFTS virus (SFTSV). Currently, SFTS is endemic to some areas in western Japan, and wild animals are considered to play important roles in the circulation of SFTSV in the environment. Previous retrospective surveys using samples mainly obtained between 2006 and 2015 revealed serological evidence of SFTSV infection in wild animals; however, seroprevalence before 2006 remains unclear. In this study, we investigated the presence of anti-SFTSV antibodies in a total of 521 serum samples from nine wild animal species collected from 11 prefectures in central and eastern Japan between 1980 and 2000. All samples yielded negative results for antibodies to SFTSV, suggesting that there had been few or no SFTSV infections before 2000 in the sampled areas., (© 2020 The Authors Veterinary Medicine and Science Published by John Wiley & Sons Ltd.)

Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging tick-borne virus that causes hemorrhagic fever. Previous studies showed that SFTSV-infected patients exhibited elevated levels of pro-inflammatory cytokines like interleukin-1β (IL-1β), indicating that SFTSV infection may activate inflammasomes. However, the detailed mechanism remains poorly understood. Herein, we found that SFTSV could stimulate the IL-1β secretion in the infected human peripheral blood mononuclear cells (PBMCs), human macrophages, and C57/BL6 mice. We demonstrate that the maturation and secretion of IL-1β during SFTSV infection is mediated by the nucleotide and oligomerization domain, leucine-rich repeat-containing protein family, pyrin-containing domain 3 (NLRP3) inflammasome. This process is dependent on protease caspase-1, a component of the NLRP3 inflammasome complex. For the first time, our study discovered the role of NLRP3 in response to SFTSV infection. This finding may lead to the development of novel drugs to impede the pathogenesis of SFTSV infection., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Liu, Chu, Jiao, Zhou, Qi and Yu.)

Phenuiviridae is a large family of arthropod-borne viruses with over 100 species worldwide. Several cause severe diseases in both humans and livestock. Global warming and the apparent geographical expansion of arthropod vectors are good reasons to seriously consider these viruses potential agents of emerging diseases. With an increasing frequency and number of epidemics, some phenuiviruses represent a global threat to public and veterinary health. This review focuses on the early stage of phenuivirus infection in mammalian host cells. We address current knowledge on each step of the cell entry process, from virus binding to penetration into the cytosol. Virus receptors, endocytosis, and fusion mechanisms are discussed in light of the most recent progress on the entry of banda-, phlebo-, and uukuviruses, which together constitute the three prominent genera in the Phenuiviridae family.

Severe fever with thrombocytopenia syndrome virus (SFTSV) is the causative agent of SFTS, an emerging tick-borne disease in East Asia, and is maintained in enzootic cycles involving ticks and a range of wild animal hosts. Direct transmission of SFTSV from cats and dogs to humans has been identified in Japan, suggesting that veterinarians and veterinary nurses involved in small-animal practice are at occupational risk of SFTSV infection. To characterize this risk, we performed a sero-epidemiological survey in small-animal-practice workers and healthy blood donors in Miyazaki prefecture, which is the prefecture with the highest per capita number of recorded cases of SFTS in Japan. Three small-animal-practice workers were identified as seropositive by ELISA, but one had a negative neutralization-test result and so was finally determined to be seronegative, giving a seropositive rate of 2.2% (2 of 90), which was significantly higher than that in healthy blood donors (0%, 0 of 1000; p < 0.05). The seroprevalence identified here in small-animal-practice workers was slightly higher than that previously reported in other high-risk workers engaged in agriculture and forestry in Japan. Thus, enhancement of small-animal-practice workers' awareness of biosafety at animal hospitals is necessary for control of SFTSV.

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a novel bunyavirus. Since 2007, SFTS disease has been reported in China with high fatality rate up to 30%, which drew high attention from Centre for Disease Control and Prevention and government. SFTSV is endemic in the centra l and eastern China, Korea and Japan. There also have been similar cases reported in Vietnam. The number of SFTSV infection cases has a steady growth in these years. As SFTSV could transmitted from person to person, it will expose the public to infectious risk. In 2018 annual review of the Blueprint list of priority diseases, World Health Organisation has listed SFTSV infection as prioritised diseases for research and development in emergency contexts. However, the pathogenesis of SFTSV remains largely unclear. Currently, there are no specific therapeutics or vaccines to combat infections of SFTSV. This review discusses recent findings of epidemiology, transmission pathway, pathogenesis and treatments of SFTS disease.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging lethal tick-borne disease that has been widely prevalent in East Asia in recent years, and raised an important public health problem in China. However, a comprehensive and thorough understanding of the current SFTS epidemic areas in Shandong Province is not available. Accordingly, a descriptive analysis was applied to explore the demographic and spatio-temporal features of SFTS cases in Shandong Province from 2010 to 2015. The division between epidemic areas and non-epidemic areas was given by maximum entropy niche model (MaxEnt) based on environmental factors such as temperature and precipitation. There were 1,786 SFTS cases between 2010 and 2015 in Shandong, mainly involving middle-aged and elderly individuals (age:40-80) and farmers (84.6 %). May-October was the high-incidence period and the SFTS cases were mostly clustered in the central and eastern regions of Shandong Province. In light of MaxEnt, 3 specific environmental features between dichotomous areas were identified, including 1) most epidemic areas are covered by acidic soils (Constituent ratio: 63.8 %) while 29.1 % coverage appears in non-epidemic areas, 2) compared with non-epidemic areas, the identical kinds of agricultural areas accounted for a higher constituent ratio (64.9 % vs. 42.7 %), and 3) lower level of annual temperature in epidemic areas compared to non-epidemic areas [Median: 13.2℃ vs. 14.2℃; (25th IQR, 75th IQR): (12.5, 13.7) vs. (13.6, 14.9)]. Our study suggests middle-aged and elderly farmers are high-risk population to be focused on in future prevention and acidic soils, agricultural activities as well lower temperature that may be related to increased SFTS incidence., (Copyright © 2020 Elsevier GmbH. All rights reserved.)

Severe fever with thrombocytopenia syndrome virus subclone B7 shows strong plaque formation and cytopathic effect induction compared with other subclones and the parental strain YG1. Compared to YG1 and the other subclones, only B7 possesses a single substitution in the L protein at the amino acid position 1891, in which N is changed to K (N1891K). In this study, we evaluate the effects of this mutation on L protein activity via a cell-based minigenome assay. Substitutions of N with basic amino acids (K or R) enhanced polymerase activity, while substitutions with an acidic amino acid (E) decreased this activity. Mutation to other neutral amino acids showed no significant effect on activity. These results suggest that the characteristic of the amino acid at position 1891 of the L protein are critical for its function, especially with respect to the charge status. Our data indicate that this C-terminal domain of the L protein may be crucial to its functions in genome transcription and viral replication.

Interferon-induced transmembrane proteins (IFITMs) are transmembrane proteins induced by interferon that can provide broad-spectrum antiviral activities. However, there are few reports on the antiviral activity of monkey-derived IFITMs. In this study, the IFITM1 and IFITM3 genes of African green monkey (AGM) were cloned and overexpressed in Vero cells, followed by infection with mouse norovirus (MNV) and severe fever with thrombocytopenia syndrome virus (SFTSV). The results showed that monkey IFITM1 and IFITM3 can be stably overexpressed in Vero cells. Both IFITM1 and IFITM3 from AGM could effectively restrict infection by SFTSV, and the viral inhibition rate of IFITM3 was more obvious compared with IFITM1. However, both monkey IFITM1 and IFITM3 had no significant effect on the replication of MNV. These results indicate that different IFITMs have different functions, which may be related to the structure of the host IFITMs and the types of pathogens.

Severe fever with thrombocytopenia syndrome (SFTS) is a disease with a high case-fatality rate that is caused by infection with the SFTS virus (SFTSV). Five electronic databases were systematically searched to identify relevant articles published from 1 January 2011 to 1 December 2019. The pooled rates with 95% confidence interval (CI) were calculated by a fixed-effect or random-effect model analysis. The results showed that 92 articles were included in this meta-analysis. For the confirmed SFTS cases, the case-fatality rate was 0.15 (95% CI 0.11, 0.18). Two hundred and ninety-six of 1384 SFTS patients indicated that they had been bitten by ticks and the biting rate was 0.21 (95% CI 0.16, 0.26). The overall pooled seroprevalence of SFTSV antibodies among the healthy population was 0.04 (95% CI 0.03, 0.05). For the overall seroprevalence of SFTSV in animals, the seroprevalence of SFTSV was 0.25 (95% CI 0.20, 0.29). The infection rate of SFTSV in ticks was 0.08 (95% CI 0.05, 0.11). In conclusion, ticks can serve as transmitting vectors of SFTSVs and reservoir hosts. Animals can be infected by tick bites, and as a reservoir host, SFTSV circulates continuously between animals and ticks in nature. Humans are infected by tick bites and direct contact with patient secretions.

Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging human pathogen, endemic in areas of China, Japan, and the Korea (KOR). It is primarily transmitted through infected ticks and can cause a severe hemorrhagic fever disease with case fatality rates as high as 30%. Despite its high virulence and increasing prevalence, molecular and functional studies in situ are scarce due to the limited availability of high-titer SFTSV exposure stocks. During the course of field virologic surveillance in 2017, we detected SFTSV in ticks and in a symptomatic soldier in a KOR Army training area. SFTSV was isolated from the ticks producing a high-titer viral exposure stock. Through the use of advanced genomic tools, we present here a complete, in-depth characterization of this viral stock, including a comparison with both the virus in its arthropod source and in the human case, and an in vivo study of its pathogenicity. Thanks to this detailed characterization, this SFTSV viral exposure stock constitutes a quality biological tool for the study of this viral agent and for the development of medical countermeasures, fulfilling the requirements of the main regulatory agencies.

RNA-activated protein kinase (PKR) is a major innate immune factor that senses viral double-stranded RNA (dsRNA) and phosphorylates eukaryotic initiation factor (eIF) 2α. Phosphorylation of the α subunit converts the eIF2αβγ complex into a stoichiometric inhibitor of eukaryotic initiation factor eIF2B, thus halting mRNA translation. To escape this protein synthesis shutoff, viruses have evolved countermechanisms such as dsRNA sequestration, eIF-independent translation by an internal ribosome binding site, degradation of PKR, or dephosphorylation of PKR or of phospho-eIF2α. Here, we report that sandfly fever Sicilian phlebovirus (SFSV) confers such a resistance without interfering with PKR activation or eIF2α phosphorylation. Rather, SFSV expresses a nonstructural protein termed NSs that strongly binds to eIF2B. Although NSs still allows phospho-eIF2α binding to eIF2B, protein synthesis and virus replication are unhindered. Hence, SFSV encodes a unique PKR antagonist that acts by rendering eIF2B resistant to the inhibitory action of bound phospho-eIF2α. IMPORTANCE RNA-activated protein kinase (PKR) is one of the most powerful antiviral defense factors of the mammalian host. PKR acts by phosphorylating mRNA translation initiation factor eIF2α, thereby converting it from a cofactor to an inhibitor of mRNA translation that strongly binds to initiation factor eIF2B. To sustain synthesis of their proteins, viruses are known to counteract this on the level of PKR or eIF2α or by circumventing initiation factor-dependent translation altogether. Here, we report a different PKR escape strategy executed by sandfly fever Sicilian virus (SFSV), a member of the increasingly important group of phleboviruses. We found that the nonstructural protein NSs of SFSV binds to eIF2B and protects it from inactivation by PKR-generated phospho-eIF2α. Protein synthesis is hence maintained and the virus can replicate despite ongoing full-fledged PKR signaling in the infected cells. Thus, SFSV has evolved a unique strategy to escape the powerful antiviral PKR., (Copyright © 2020 Wuerth et al.)

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a novel phlebovirus in the Bunyaviridae family, causing SFTS with high mortality rate. Haemaphysalis longicornis ticks has been demonstrated as a competent vector of SFTSV by experimental transmission study and field study. However, there has been query whether other tick species that infest human beings in the SFTS endemic regions are capable of transmitting the pathogen. Here by performing experimental transmission study, we compared the capable of transmitting SFTSV among Ixodes sinensis, Ixodes persulcatus and Dermacentor silvarum ticks. The transovarial transmission was seen in the I. sinensis ticks with a rate of 40%, but neither in I. persulcatus nor in D. silvarum ticks. I. sinensis ticks also have the ability to transmit SFTSV horizontally to uninfected mice at 7 days after feeding, but not for I. persalcatus or D. silvarum ticks. In the transstadial transmission of I. persulcatus and D. silvarum ticks, I. persulcatus ticks were tested negative from larvae to adults. But the D. silvarum ticks were tested positive from larvae to nymphs, with the positive rate of 100% (10/10) for engorged larval ticks and 81.25% (13/16) for molted nymphs. However, the mice bitten by SFTSV-infected D. silvarum nymphs were negative for SFTSV detection. Therefore, there is not enough evidence to prove the transstadial transmission of SFTSV in I. persalcatus and D. silvarum ticks., Competing Interests: The authors have declared that no competing interests exist.

The identification of host cell factors for virus entry is useful for the molecular explanation of viral tropisms and often leads to a more profound understanding of virus-induced diseases. Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by SFTS virus. No countermeasures against the disease exist. In this report, we show an efficient method using virus-like particles for the functional screening of a cellular cDNA library to identify SFTS virus entry factors. Two variants encoding dendritic cell-specific ICAM-3 grabbing non-integrin related (DC-SIGNR), a calcium-dependent lectin known to enhance SFTS virus infection, were successfully identified from a human liver cDNA library. We will discuss applications for yet unidentified factor(s) for SFTS virus entry and for entry factor(s) for other viruses related to SFTS virus.

Severe fever with thrombocytopenia syndrome (SFTS) virus (SFTSV) is an emerging tick-borne virus that carries a high fatality rate of 12%-50%. In-depth understanding of the SFTSV-induced pathogenesis mechanism is critical for developing effective anti-SFTS therapeutics. Here, we report transcriptomic analysis of blood samples from SFTS patients. We observe a strong correlation between inflammatory responses and disease progression and fatal outcome. Quantitative proteomic analysis of SFTSV infection confirms the induction of inflammation and further reveals virus-induced mitochondrial dysfunction. Mechanistically, SFTSV infection triggers BCL2 antagonist/killer 1 (BAK) upregulation and BAK/BCL2-associated X (BAX) activation, leading to mitochondrial DNA (mtDNA) oxidization and subsequent cytosolic release. The cytosolic mtDNA binds and triggers NLRP3 inflammasome activation. Notably, the BAK expression level correlates with SFTS disease progression and fatal outcome. These findings provide insights into the clinical features and molecular underpinnings of severe SFTS, which may aid in patient care and therapeutic design, and may also be conserved during infection by other highly pathogenic viruses., Competing Interests: Declaration of Interests The authors declare no competing interests., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging zoonotic tick-borne disease caused by SFTS virus, which circulates among ticks and their host animals, including wildlife. However, few studies have examined SFTS virus infection in wildlife present in the Republic of Korea (ROK). We evaluated SFTS virus infection in tissue samples from Korean water deer (Hydropotes inermis argyropus), one of the most common wild ungulates in ROK. In this study, we evaluated tissue samples of 129 water deer carcasses collected in 2017 and detected SFTS viral RNA by conventional PCR. SFTS viral RNA was found in 3 of the 129 carcasses, showing a prevalence of 2.3 %; 2 of which were collected in Gyeongsangnam-do and 1 of which was in the Gangwon-do region. Among the 6 internal organs studied, only the spleen samples were positive. Phylogenetic analysis revealed close relationships between deer- and human-derived strains. The medium segments of the three positive cases clustered with genotype B, which is the predominant genotype in ROK. In the small segment, two cases clustered with genotype B, samples 17WD044 and 17WD065. The third sample, 17WD068 from Gangwon-do province, showed genotype A, which circulates mainly in China. The disagreement in the genotypes of the two tested segments suggests a potential reassortment between genotype A and B, resulting in genetic recombination as observed in sample 17WD068, which may be co-circulating in China and Korea. Further studies in wildlife and humans are necessary to understand the genetic characteristics of SFTS viruses circulating in ROK., Competing Interests: Declaration of Competing Interest None., (Copyright © 2019 Elsevier GmbH. All rights reserved.)

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a newly identified phlebovirus associated with severe hemorrhagic fever in humans. While many viruses subvert the host cell cycle to promote viral growth, it is unknown whether this is a strategy employed by SFTSV. In this study, we investigated how SFTSV manipulates the cell cycle and the effect of the host cell cycle on SFTSV replication. Our results suggest that cells arrest at the G 2 /M transition following infection with SFTSV. The accumulation of cells at the G 2 /M transition did not affect virus adsorption and entry but did facilitate viral replication. In addition, we found that SFTSV NSs, a nonstructural protein that forms viroplasm-like structures in the cytoplasm of infected cells and promotes virulence by modulating the interferon response, induces a large number of cells to arrest at the G 2 /M transition by interacting with CDK1. The interaction between NSs and CDK1, which is inclusion body dependent, inhibits formation and nuclear import of the cyclin B1-CDK1 complex, thereby leading to cell cycle arrest. Expression of a CDK1 loss-of-function mutant reversed the inhibitive effect of NSs on the cell cycle, suggesting that this protein is a potential antiviral target. Our study provides new insight into the role of a specific viral protein in SFTSV replication, indicating that NSs induces G 2 /M arrest of SFTSV-infected cells, which promotes viral replication. IMPORTANCE Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne pathogen that causes severe hemorrhagic fever. Although SFTSV poses a serious threat to public health and was recently isolated, its pathogenesis remains unclear. In particular, the relationship between SFTSV infection and the host cell cycle has not been described. Here, we show for the first time that both asynchronized and synchronized SFTSV-susceptible cells arrest at the G 2 /M checkpoint following SFTSV infection and that the accumulation of cells at this checkpoint facilitates viral replication. We also identify a key mechanism underlying SFTSV-induced G 2 /M arrest, in which SFTSV NSs interacts with CDK1 to inhibit formation and nuclear import of the cyclin B1-CDK1 complex, thus preventing it from regulating cell cycle progression. Our study highlights the key role that NSs plays in SFTSV-induced G 2 /M arrest., (Copyright © 2020 American Society for Microbiology.)

The seasonal abundance of hard ticks that transmit severe fever with thrombocytopenia syndrome virus was monitored with a collection trap method every April to November during 2015-2018 and with a flagging method every July and August during 2015-2018 in Ganghwa-do (island) of Incheon Metropolitan City, Republic of Korea. This monitoring was performed in a copse, a short grass field, coniferous forest and broad-leaved forest. A total of 17,457 ticks (8,277 larvae, 4,137 nymphs, 3,389 females, and 1,654 males) of the ixodid ticks comprising 3 species (Haemaphysalis longicornis, H. flava, and Ixodes nipponensis) were collected with collection traps. Of the identified ticks, H. longicornis was the most frequently collected ticks (except larval ticks) (94.26%, 8,653/9,180 ticks (nymphs and adults)), followed by H. flava (5.71%, 524/9,180) and Ix. nipponensis (less than 0.04%, 3/9,180). The ticks collected with collecting traps were pooled and assayed for the presence of SFTS virus with negative results. In addition, for monitoring the prevalence of hard ticks, a total of 7,461 ticks (5,529 larvae, 1,272 nymphs, 469 females, and 191 males) of the ixodid ticks comprising 3 species (H. longicornis, H. flava, and Ix. nipponensis) were collected with flagging method. H. longicornis was the highest collected ticks (except larval ticks) (99.53%, 1,908/1,917 ticks (nymphs and adults)), followed by H. flava (1.15%, 22/1,917).

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.

Rationale: Severe fever with thrombocytopenia syndrome (SFTS) is a recently recognized fatal infectious disease caused by the SFTS virus, and severe cases are complicated by the presence of hemophagocytic lymphohistiocytosis (HLH) associated with a cytokine storm. Herein, we report on serial changes of serum cytokine levels and viral load in a severe case of SFTS., Patient Concerns: A 63-year-old Japanese woman presented with high-grade fever, abdominal pain, diarrhea, impaired consciousness, leukocytopenia, and thrombocytopenia., Diagnosis: SFTS was diagnosed based on a positive serum test for SFTS virus RNA and electroencephalogram (EEG) findings of encephalopathy., Interventions: The patient was treated with supportive therapy, including steroid pulse therapy (intravenous methylprednisolone 1 g/d for 3 days) for HLH and intravenous recombinant thrombomodulin 19200 U/d for 7 days for disseminated intravascular coagulation., Outcomes: Treatment for 7 days improved both symptoms and abnormal EEG findings, and SFTS virus RNA disappeared from the serum at day 10 from the onset of symptoms. The serum cytokines and chemokines analysis during the clinical course revealed 2 distinct phases: the acute phase and the recovery phase. The cytokines and chemokines elevated in the acute phase included interleukin (IL)-6, IL-10, interferon (IFN)-α2, IFN-γ, tumor necrosis factor-α, interferon-γ-induced protein-10, and fractalkine, while the IL-1β, IL-12p40, IL-17, and vascular endothelial growth factor levels were higher in the recovery phase., Conclusion: These observations suggest that the cytokines and chemokines elevated in the acute phase may reflect the disease severity resulted in a cytokine storm, while those in the recovery phase may be attributed to T-cell activation and differentiation.

Severe fever with thrombocytopenia syndrome (SFTS), an emerging tick-borne infectious disease caused by a novel phlebovirus (SFTS virus, SFTSV), was listed among the top 10 priority infectious diseases by the World Health Organization due to its high fatality of 12%-50% and possibility of pandemic transmission. Currently, effective anti-SFTSV intervention remains unavailable. Here, by screening a library of FDA-approved drugs, we found that benidipine hydrochloride, a calcium channel blocker (CCB), inhibited SFTSV replication in vitro. Benidipine hydrochloride was revealed to inhibit virus infection through impairing virus internalization and genome replication. Further experiments showed that a broad panel of CCBs, including nifedipine, inhibited SFTSV infection. The anti-SFTSV effect of these two CCBs was further analyzed in a humanized mouse model in which CCB treatment resulted in reduced viral load and decreased fatality rate. Importantly, by performing a retrospective clinical investigation on a large cohort of 2087 SFTS patients, we revealed that nifedipine administration enhanced virus clearance, improved clinical recovery, and remarkably reduced the case fatality rate by >5-fold. These findings are highly valuable for developing potential host-oriented therapeutics for SFTS and other lethal acute viral infections known to be inhibited by CCBs in vitro.

Severe fever with thrombocytopenia syndrome (SFTS) is an infectious disease with a high fatality rate, caused by SFTS virus (SFTSV). Because little is known about the nature of SFTSV, basic studies are required for the developments of vaccines and effective therapies. In the present study, we identified the amino acid residue important for membrane fusion induced by the SFTSV glycoprotein (GP). Syncytium formations were observed in cells expressing the GPs of SFTSV Japanese strain (YG-1 and SPL030). In contrast, no or only weak syncytium formations were induced in cells expressing GP of SFTSV Chinese strain (HB29). The replacement of arginine at amino acid residue 962 with serine in HB29 GP (R962S) induced membrane fusion, while the replacement of serine at residue 962 with arginine in YG1 GP (S962R) did not. These data indicate that serine at residue 962 in the SFTSV-GP is critical for inducing membrane fusion and viral infection., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging hemorrhagic fever caused by the SFTS phlebovirus (SFTSV). SFTS patients were first reported in China, followed by Japan and South Korea. In 2017, cats were diagnosed with SFTS for the first time, suggesting that these animals are susceptible to SFTSV. To confirm whether or not cats were indeed susceptible to SFTSV, animal subjects were experimentally infected with SFTSV. Four of the six cats infected with the SPL010 strain of SFTSV died, all showing similar or more severe symptoms than human SFTS patients, such as a fever, leukocytopenia, thrombocytopenia, weight loss, anorexia, jaundice and depression. High levels of SFTSV RNA loads were detected in the serum, eye swab, saliva, rectal swab and urine, indicating a risk of direct human infection from SFTS-infected animals. Histopathologically, acute necrotizing lymphadenitis and hemophagocytosis were prominent in the lymph nodes and spleen. Severe hemorrhaging was observed throughout the gastrointestinal tract. B cell lineage cells with MUM-1 and CD20, but not Pax-5 in the lesions were predominantly infected with SFTSV. The present study demonstrated that cats were highly susceptible to SFTSV. The risk of direct infection from SFTS-infected cats to humans should therefore be considered.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious zoonosis caused by the SFTS virus. Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening syndrome associated with excessive immune activation. Cytokine storms are often seen in both SFTS and HLH, resulting in rapid disease progression and poor prognosis. The aim of this study was to identify whether SFTS cases complicated by HLH are related to higher rates of mortality. Descriptive analysis of the frequency of clinical and laboratory data, complications, treatment outcomes, and HLH-2004 criteria was performed. Cases presenting with five or more clinical or laboratory findings corresponding to the HLH-2004 diagnostic criteria were defined as SFTS cases complicated by HLH. Eighteen cases of SFTS were identified during a 2-year study period, with a case-fatality proportion of 22.2% (4 among 18 cases, 95% confidence interval 9%-45.2%). SFTS cases complicated by HLH were identified in 33.3% (6 among 18 cases). A mortality rate of 75% (3 among 4 cases) was recorded among SFTS cases complicated by HLH. Although there were no statistically significant differences in outcomes, fatal cases exhibited more frequent correlation with HLH-2004 criteria than non-fatal cases [3/14 (21.4%) vs. 3/4 (75%), p =0.083]. In conclusion, the present study suggests the possibility that SFTS cases complicated by HLH are at higher risk of poor prognosis., Competing Interests: The authors have no potential conflicts of interest to disclose., (© Copyright: Yonsei University College of Medicine 2019.)

The large diversity of new tick-borne phleboviruses, and the negative impacts of the virulent viruses on human/animal health have led to a growing interest in their analysis. In this report, new insights are brought out into the diversity of putative phleboviruses circulating in Portugal (both the continental territory and the islands of São Miguel, in the Azores, and Madeira), as well as in the Spanish western regions of Extremadura and Castilla and León. Phlebovirus sequences were frequently detected (L-segment) from both questing and feeding ticks, but especially in Rhipicephalus sanguineus sensu lato (s.l.) specimens. These sequences were detected in adult ticks, as well as nymphs and eggs, supporting the hypothesis of viral maintenance by vertical transmission. Though multiple genetic groups could be identified in phylogenetic trees (AnLuc, KarMa, RiPar virus 1, and Spanish group 1 and 2), all the sequences from Portugal and Spain shared common ancestry with other viral sequence obtained from samples collected over a large geographic coverage. Spatiotemporal analysis placed Middle-East as the geographic origin of the most recent common ancestor (MRCA) of all phleboviruses analysed in the present study. More recent viral transitions might include migrations from Spain to continental Portugal, and from there to the Portuguese Islands. Our findings suggest that the time of the MRCA of phleboviruses was dated around 225 years ago [95% HPD: 124-387 year before the last sampling date]., (Copyright © 2019 Elsevier GmbH. All rights reserved.)