Severe fever with thrombocytopenia syndrome, South Korea, 2012

Outbreak of Natural Severe Fever with Thrombocytopenia Syndrome Virus Infection in Farmed Minks, China

We isolated severe fever with thrombocytopenia syndrome virus (SFTSV) from farmed minks in China, providing evidence of natural SFTSV infection in farmed minks. Our findings support the potential role of farmed minks in maintaining SFTSV and are helpful for the development of public health interventions to reduce human infection.

Pancreatic Injury Is Associated with Poor Prognosis in Severe Fever with Thrombocytopenia Syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease. Previous studies have primarily focused on the epidemiological and clinical characteristics of patients with SFTS, whereas pancreatic injury has received little attention. This study investigated the effects of pancreatic injury on the prognosis of patients with SFTS. A total of 156 patients diagnosed with SFTS between April 2016 and April 2022 were included in the analysis. Multivariate logistic regression analysis showed that pancreatic injury (odds ratio [OR] = 3.754, 95% confidence interval [CI]: 1.361-79.036, P = 0.024) and neurological symptoms (OR = 18.648, 95% CI: 4.921-70.668, P < 0.001) were independent risk factors for mortality. The receiver operating characteristic curve indicated that serum pancreatic enzymes were predictive of progression to death in patients with SFTS. The area under the curve (AUC) for amylase was 0.711, with an optimal cutoff value of 95.5 U/L, sensitivity of 96.4%, and specificity of 35.9%. Lipase had an AUC of 0.754, an optimal cutoff value of 354.75 U/L, sensitivity of 75%, and specificity of 67.2%. Thus, pancreatic injury was associated with a poor prognosis of SFTS and can be used as an important reference for SFTS determination and prognostic assessment.

6-Thioguanine inhibits severe fever with thrombocytopenia syndrome virus through suppression of EGR1

The severe fever with thrombocytopenia syndrome virus (SFTSV) is a novel phlebovirus, recently being officially renamed as Dabie bandavirus, and a causative agent for an emerging infectious disease associated with high fatality. Effective therapeutics and vaccines are lacking and disease pathogenesis is yet to be fully elucidated. In our effort to identify new SFTSV inhibitory molecules, 6-Thioguanine (6-TG) was found to potently inhibit SFTSV infection. 6-TG has been widely used as therapeutic agent since the approval of the Food and Drug Administration in the 1960s. In the current study, we showed that 6-TG was a potent inhibitor of SFTSV infection with 50% effective concentrations (EC50) of 3.465 μM in VeroE6 cells, and 1.848 μM in HUVEC cells. The selectivity index (SI) was > 57 in VeroE6 cells and > 108 in HUVEC cells, respectively. The SFTSV RNA transcription, protein synthesis, and progeny virions were reduced in a dose dependent manner by the presence of 6-TG in the in vitro infection assay. Further study on the mechanism of the anti-SFTSV activity showed that 6-TG downregulated the production of early growth response gene-1 (EGR1). Using gene silencing and overexpression, we further confirmed that EGR1 was a host restriction factor against SFTSV. Meanwhile, treatment of infected experimental animals with 6-TG inhibited SFTSV infection and alleviated multi-organ dysfunction. In conclusion, we have identified 6-TG as an effective inhibitor of SFTSV replication via the inhibition of EGR1 expression. Further studies are needed to evaluate of 6-TG as a potential therapeutic for treating SFTS.

Direct transmission of severe fever with thrombocytopenia syndrome virus from farm-raised fur animals to workers in Weihai, China

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease. SFTS virus (SFTSV) is transmitted by tick bites and contact with the blood or body fluids of SFTS patients. Animal-to-human transmission of SFTS has been reported in Japan, but not in China. In this study, the possible transmission route of two patients who fed and cared for farm-raised fur animals in a mink farm was explored.

METHOD

An epidemiological investigation and a genetic analysis of patients, animals and working environment were carried out.

RESULTS

It was found that two patients had not been bitten by ticks and had no contact with patients infected with SFTS virus, but both of them had skinned the dying animals. 54.55% (12/22) of the farm workers were positive for SFTS virus antibody. By analyzing the large, medium and small segments sequences, the viral sequences from the two patients, animals and environments showed 99.9% homology.

CONCLUSION

It is suspected that the two patients may be directly infected by farm-raised animals, and that the virus may have been transmitted by aerosols when skinning dying animals. Transmission by direct blood contacts or animal bites cannot be ignored.

A nomogram to predict mortality in patients with severe fever with thrombocytopenia syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is an acute infectious disease caused by a novel Bunyavirus infection with low population immunity and high mortality rate. Lacking specific therapies, the treatment measures vary with the severity of the disease, therefore, a case control study involved 394 SFTS patients was taken to determine risk factors for mortality. Comparative clinical data from the first 24 h after admission was collected through the electronic medical record system. Independent risk factors for death of SFTS were identified through univariate and multivariate binary logistic regression analyses. The results of the logistic regression were visualized using a nomogram which was created by downloading RMS package in the R program. In our study, four independent mortality risk factors were identified: advanced age(mean 70.45 ± 7.76 years), MODS, elevated APTT, and D-dimer. The AUC of the nomogram was 0.873 (0.832, 0.915), and the model passes the calibration test namely Unreliability test with P = 0.958, showing that the model's predictive ability is excellent. The nomogram to determine the risk of death in SFTS efficiently provide a basis for clinical decision-making for treatment.

Computer-aided designing of a novel multi‑epitope DNA vaccine against severe fever with thrombocytopenia syndrome virus

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne viral disease caused by the SFTS virus (Dabie bandavirus), which has become a substantial risk to public health. No specific treatment is available now, that calls for an effective vaccine. Given this, we aimed to develop a multi-epitope DNA vaccine through the help of bioinformatics. The final DNA vaccine was inserted into a special plasmid vector pVAX1, consisting of CD8+ T cell epitopes, CD4+ T cell epitopes and B cell epitopes (six epitopes each) screened from four genome-encoded proteins--nuclear protein (NP), glycoprotein (GP), RNA-dependent RNA polymerase (RdRp), as well as nonstructural protein (NSs). To ascertain if the predicted structure would be stable and successful in preventing infection, an immunological simulation was run on it. In conclusion, we designed a multi-epitope DNA vaccine that is expected to be effective against Dabie bandavirus, but in vivo trials are needed to verify this claim.

Structural snapshots of phenuivirus cap-snatching and transcription

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a human pathogen that is now endemic to several East Asian countries. The viral large (L) protein catalyzes viral transcription by stealing host mRNA caps via a process known as cap-snatching. Here, we establish an in vitro cap-snatching assay and present three high-quality electron cryo-microscopy (cryo-EM) structures of the SFTSV L protein in biologically relevant, transcription-specific states. In a priming-state structure, we show capped RNA bound to the L protein cap-binding domain (CBD). The L protein conformation in this priming structure is significantly different from published replication-state structures, in particular the N- and C-terminal domains. The capped-RNA is positioned in a way that it can feed directly into the RNA-dependent RNA polymerase (RdRp) ready for elongation. We also captured the L protein in an early-elongation state following primer-incorporation demonstrating that this priming conformation is retained at least in the very early stages of primer extension. This structural data is complemented by in vitro biochemical and cell-based assays. Together, these insights further our mechanistic understanding of how SFTSV and other bunyaviruses incorporate stolen host mRNA fragments into their viral transcripts thereby allowing the virus to hijack host cell translation machinery.

Gn protein expressed in plants for diagnosis of severe fever with thrombocytopenia syndrome virus

Severe fever with thrombocytopenia syndrome virus (SFTSV) causes the highly fatal disease in humans. To facilitate diagnosis, the native form of subunit glycoprotein (Gn), a prime target for potential vaccines and therapies, was produced in Nicotiana benthamiana using a Bamboo mosaic virus-based vector system. By fusion with secretory signal tags, SSExt, derived from the extension protein, and the (SP)10 motif, the yield of the recombinant Gn (rGn) was remarkably increased to approximately 7 mg/kg infiltrated leaves. Ultimately, an rGn-based ELISA was successfully established for the detection of SFTSV-specific antibodies in serum samples from naturally infected monkeys. As validated with the reference method, the specificity and sensitivity of rGn-ELISA were 94% and 96%, respectively. In conclusion, utilizing well-suited fusion tags facilitates rGn production and purification in substantial quantities while preserving its antigenic properties. The rGn-ELISA, characterized by its commendable sensitivity and specificity could serve as a viable alternative diagnostic method for assessing SFTSV seroprevalence. KEY POINTS: • SFTSV Gn, fused with secretory signal tags, was expressed by the BaMV-based vector. • The plant fusion tags increased expression levels and eased the purification of rGn. • The rGn-ELISA was established and validated; its specificity and sensitivity > 94%.

Prevalence and impact of viral myocarditis in patients with severe fever with thrombocytopenia syndrome

To explore the association and impact between viral myocarditis and mortality in patients with severe fever with thrombocytopenia syndrome. A dynamic analysis was conducted between fatal group and nonfatal group regarding the daily epidemiology data, clinical symptoms, and electrocardiogram (ECG), echocardiogram, and laboratory findings. Outcomes of patients with and without viral myocarditis were compared. The association between viral myocarditis and mortality was analyzed. Among 183 severe fever with thrombocytopenia syndrome patients, 32 were in the fatal group and 151 in the nonfatal group; there were 26 (81.25%) with viral myocarditis in the fatal group, 66 (43.70%) with viral myocarditis in the nonfatal group (p < 0.001), 79.35% of patients had abnormal ECG results. The abnormal rate of ECG in the fatal group was 100%, and in the nonfatal group was 74.83%. Univariate analysis found that the number of risk factors gradually increased on Day 7 of the disease course and reached the peak on Day 10. Combined with the dynamic analysis of the disease course, alanine aminotransferase, aspartate aminotransferase, creatine kinase, creatine kinase fraction, lactate dehydrogenase, hydroxybutyrate dehydrogenase, neutrophil count, serum creatinine, Na, Ca, carbon dioxide combining power, amylase, lipase, activated partial thromboplastin time and thrombin time had statistically significant impact on prognosis. The incidence of fever with thrombocytopenia syndrome combined with viral myocarditis is high, especially in the fatal group of patients. Viral myocarditis is closely related to prognosis and is an early risk factor. The time point for changes in myocarditis is Day 7 of the course of the disease.

Difference in Intraspecies Transmissibility of Severe Fever with Thrombocytopenia Syndrome Virus Depending on Abrogating Type 1 Interferon Signaling in Mice

Severe fever with thrombocytopenia syndrome (SFTS), a tick-borne zoonotic disease, is caused by infection with SFTS virus (SFTSV). A previous study reported that human-to-human direct transmission of SFTSV can occur. However, potential animal-to-animal transmission of SFTSV without ticks has not been fully clarified. Thus, the objective of this study was to investigate potential mice-to-mice transmission of SFTSV by co-housing three groups of mice [i.e., wild-type mice (WT), mice injected with an anti-type I interferon-α receptor-blocking antibody (IFNAR Ab), and mice with knockout of type I interferon-α receptor (IFNAR KO)] as spreaders or recipients with different immune competence. As a result, co-housed IFNAR Ab and IFNAR KO mice showed body weight loss with SFTS viral antigens detected in their sera, extracorporeal secretions, and various organs. Based on histopathology, white pulp atrophy in the spleen was observed in all co-housed mice except WT mice. These results obviously show that IFNAR Ab and IFNAR KO mice, as spreaders, exhibited higher transmissibility to co-housed mice than WT mice. Moreover, IFNAR KO mice, as recipients, were more susceptible to SFTSV infection than WT mice. These findings suggest that type I interferon signaling is a pivotal factor in mice intraspecies transmissibility of SFTSV in the absence of vectors such as ticks.

Downregulation of transcription 1 hinders the replication of Dabie bandavirus by promoting the expression of TLR7, TLR8, and TLR9 signaling pathway

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.

The Vector Competence of Asian Longhorned Ticks in Langat Virus Transmission

Haemaphysalis longicornis (the longhorned tick), the predominant tick species in China, serves as a vector for a variety of pathogens, and is capable of transmitting the tick-borne encephalitis virus (TBEV), the causative agent of tick-borne encephalitis. However, it is unclear how these ticks transmit TBEV. Langat virus (LGTV), which has a reduced pathogenicity in humans, has been used as a surrogate for TBEV. In this study, we aimed to investigate the vector competence of H. longicornis to transmit LGTV and demonstrate the efficient acquisition and transmission of LGTV between this tick species and mice. LGTV localization was detected in several tick tissues, such as the midgut, salivary glands, and synganglion, using quantitative PCR and immunohistochemical staining with a polyclonal antibody targeting the LGTV envelope protein. We demonstrated the horizontal transmission of LGTV to different developmental stages within the same generation but did not see evidence of vertical transmission. It was interesting to note that we observed mice acting as a bridge, facilitating the transmission of LGTV to neighboring naïve ticks during blood feeding. In conclusion, the virus-vector-host model employed in this study provides valuable insights into the replication and transmission of LGTV throughout its life cycle.

Elucidation of prognostic factors in the acute phase of feline severe fever with thrombocytopenia syndrome virus infection

Severe fever with thrombocytopenia syndrome (SFTS) is a potentially fatal tick-borne zoonotic disease, endemic to Asian regions, including western Japan. Cats appear to suffer a particularly severe form of the disease; however, feline SFTS is not clinically well characterized. Accordingly, in this study, we investigated the associations of, demographic, hematological and biochemical, immunological, and virological parameters with clinical outcome (fatal cases vs. survivors) in SFTSV-positive cats. Viral genomic analysis was also performed. Viral load in blood, total bilirubin, creatine phosphokinase, serum amyloid A, interleukin-6, tumor necrotic factor-α, and virus-specific IgM and IgG differed significantly between survivors and fatal cases, and thus may have utility as prognosticators. Furthermore, survivor profiling revealed high-level of viremia with multiple parameters (white blood cells, platelet, total bilirubin, glucose, and serum amyloid A) beyond the reference range in the 7-day acute phase, and signs of clinical recovery in the post-acute phase (parameters returning to, or tending toward, the reference range). However, SFTSV was still detectable from some survived cats even 14 days after onset of disease, indicating the risk of infection posed by close-contact exposure may persist through the post-acute phase. This study provides useful information for prognostic assessments of acute feline SFTS, and may contribute to early treatment plans for cats with SFTS. Our findings also alert pet owners and animal health professionals to the need for prolonged vigilance against animal-to-human transmission when handling cats that have been diagnosed with SFTS.

Pathological and virological findings of type I interferon receptor knockout mice upon experimental infection with Heartland virus

Heartland virus (HRTV) causes generalized symptoms, severe shock, and multiple organ failure. We previously reported that interferon-α/β receptor knockout (IFNAR-/-) mice infected intraperitoneally with 1 × 107 tissue culture-infective dose (TCID50) of HRTV died, while those subcutaneously infected with the same dose of HRTV did not. The pathophysiology of IFNAR-/- mice infected with HRTV and the mechanism underlying the difference in disease severity, which depends on HRTV infection route, were analyzed in this study. The liver, spleen, mesenteric and axillary lymph nodes, and gastrointestinal tract of intraperitoneally (I.P.) infected mice had pathological changes; however, subcutaneously (S.C.) infected mice only had pathological changes in the axillary lymph node and gastrointestinal tract. HRTV RNA levels in the mesenteric lymph node, lung, liver, spleen, kidney, stomach, intestine, and blood were significantly higher in I.P. infected mice than those in S.C. infected mice. Chemokine ligand-1 (CXCL-1), tumor necrosis factor (TNF)-α, interleukin (IL)-12, interferon (IFN)-γ, and IL-10 levels in plasma of I.P. infected mice were higher than those of S.C. infected mice. These results indicated that high levels of viral RNA and the induction of inflammatory responses in HRTV-infected IFNAR-/- mice may be associated with disease severity.

Host factor MxA restricts Dabie bandavirus infection by targeting the viral NP protein to inhibit NP-RdRp interaction and ribonucleoprotein activity

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.

Changes in Cytokine Levels in Patients with Severe Fever with Thrombocytopenia Syndrome Virus

Purpose

To characterize the cytokine profile of patients with severe fever with thrombocytopenia syndrome (SFTS) in relation to disease severity.

Patients and Methods

60 laboratory-confirmed SFTS patients and 12 healthy individuals from multi-centers in Shandong Province of China were included, and all patients were divided into fatal patients (9) and recovered patients (51) due to their final outcomes. Multiplex-microbead immunoassays were conducted to estimate levels of 27 cytokines in the sera of patients and controls.

Results

The results showed that levels of IL-2, IL-4, IL-6, IL-7, IL-8, IL-15, IL-1RA, G-CSF, GM-CSF, IFN-γ, TNF-α, basic FGF, PDGF-BB, RANTES, IP-10, MIP-1α, MIP-1β, MCP-1, and Eotaxin differed significantly among the SFTS fatal patients, recovered patients, and the healthy controls (all p<0.05). Compared to the healthy controls, the fatal patients and recovered patients had reduced levels of IL-2, IL-4, IL-7, PDGF-BB, RANTES, and Eotaxin, while the levels of PDGF-BB and RANTES were significantly lower in fatal patients compared to recovered patients. The increasing levels of IL-6, IL-8, IL-15, IL-1RA, G-CSF, GM-CSF, IFN-γ, TNF-α, basic FGF, IP-10, MIP-1α, MIP-1β, and MCP-1 were observed in fatal patients (all p<0.05), and the levels of IL-6, IP-10, MIP-1α, and MCP-1 were significantly higher than other two groups. The Spearman correlation analysis indicated a positive correlation between platelet count and PDGF-BB levels (p<0.05), while the white blood cell count had a negative correlation with MIP-1 level (p<0.05).

Conclusion

The research exhibited that the SFTS virus (SFTSV) caused an atypical manifestation of cytokines. The levels of IL-6, IP-10, MIP-1α, and MCP-1 had been observed a positive association with the severity of the illness.

Seroprevalence and transmission of severe fever with thrombocytopenia syndrome virus in a coastal endemic area in Southeastern China

Severe fever with thrombocytopenia syndrome (SFTS) is a newly emerged tick-borne viral zoonosis and widely prevalent in China, Japan and South Korea. Most reported SFTS cases have been identified in mountainous and hilly areas, with a few in island areas. In this study, we conducted a systematic investigation about natural infection of SFTS virus (SFTSV) among humans, animals and ticks in a coastal endemic prefecture, containing island, plains and mountain settings, in Zhejiang Province, Southeastern China. From July 2020 to June 2021, 1117 participants completed a survey with questionnaire interview and serum testing. Meanwhile, 862 serum samples of domestic animals, 275 spleen tissue samples of wild animals and 829 ticks representing five species (predominantly Haemaphysalis longicornis and Rhipicephalus sanguineus sensu lato) were collected. The seroprevalence of anti-SFTSV total antibody and IgM antibody among the participants was 4.8 % (54/1117) and 0.6 % (7/1117), respectively. Multivariate logistic regression analysis indicated that living in the island area (OR=2.66; 95 %CI: 1.04-6.80; P = 0.041) was significantly associated with seropositivity of total antibody to SFTSV. Furthermore, a higher seroprevalence was observed in domestic animals (36.1 %), while the SFTSV-RNA infection rate was 0.4 % in wild animals and the minimum infection rate (MIR) was 0.8 % for all tick species combined. The only tick species infected with SFTSV was H. longicornis. The prevalence of SFTSV infection in the island area, manifested by anti-SFTSV total antibody (P = 0.012) and IgM antibody (P = 0.004) among humans, anti-SFTSV total antibody (P<0.001) among domestic animals, and SFTSV-RNA among ticks (P = 0.022), was significantly higher than that in the mountainous area and the plain area. Furthermore, phylogenetic analysis showed that SFTSV sequences obtained from ticks in the island area were clustered with reported strains in Japan and South Korea. These results suggest that islands in the study area might be an important natural focus of SFTSV.

Cardiac injury in hospitalized patients with severe fever and thrombocytopenia syndrome

Severe fever with thrombocytopenia syndrome (SFTS), an emerging infectious disease with a high fatality rate. Cardiac injury in SFTS patients is a major concern. This study aimed to evaluate the prevalence of cardiac injury and its association with mortality in hospitalized patients infected with novel Bunyavirus. Cardiac injury was defined as the presence of any of the following abnormalities: (1) blood levels of cardiac biomarkers (creatine kinase-MB, troponin-I, B-type natriuretic peptide or N-terminal pro-B-type natriuretic peptide); (2) new abnormalities in electrocardiography. The 203 SFTS patients were included in the final analysis. The proportion of SFTS patients developing cardiac injury during hospitalization was 71.4% (145/203). Compared with the uninjured group, the cardiac injury group had the severity of cardiac injury was underscored by higher median hospital costs (31420 vs. 12911, p < 0.001), higher proportion of intensive care units admissions (13.1% vs. 3.4%, p = 0.041), and higher hospital mortality rate (33.8% vs. 6.9%, p < 0.001). Multivariable-adjusted Cox proportional hazards regression analysis showed that cardiac injury was associated with higher mortality during hospitalization (hazards ratio, 7.349; 95% CI: 2.352-22.960). Cardiac injury is common among hospitalized SFTS patients, and it is associated with higher risk of mortality.

Association of Deforestation With Severe Fever With Thrombocytopenia Syndrome

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) virus was first isolated in China in 2009 and has since spread to several Asian countries. SFTS is closely related to environmental factors that accelerate vector growth. We evaluated the associations of SFTS and deforestation with environmental variables.

METHODS

For this observational study, we generated multiple Poisson models using national SFTS outbreak data (2013-2018) and official environmental data for Korea. We included established risk factors as variables. Deforestation was used as the main variable. All variables were analyzed according to their spatial characteristics using the R-INLA package.

RESULTS

SFTS cases increased over time and peaked in 2017, at 272, followed by a decrease in 2018. Disease mapping showed a high incidence of SFTS nationwide, with particular risks in Gangwon and Gyeonggi Provinces in the north, and Jeju in the south of South Korea. Deforestation was significantly associated with a higher risk of SFTS in the final model (relative risk, 1.751 [95% confidence interval, 1.125-2.743]).

CONCLUSIONS

SFTS outbreaks are associated with deforestation. Therefore, deforestation in Gyeonggi, Gangwon, and Jeju provinces of South Korea needs to be considered in vector-control strategies and active surveillance of SFTS occurrence.

Novel nomograms to predict risk and prognosis in hospitalized patients with severe fever with thrombocytopenia syndrome

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging and life-threatening infectious disease caused by SFTS virus. Although recent studies have reported the use of nomograms based on demographic and laboratory data to predict the prognosis of SFTS, no study has included viral load, which is an important factor that influences the prognosis, when compared with other risk factors. Therefore, this study aimed to develop a model that predicts SFTS prognosis before it reaches the critical illness stage and to compare the predictive ability of groups with and without viral load.

Methods

Two hundred patients with SFTS were enrolled between June 2018 and August 2023. Data were sourced from the first laboratory results at admission, and two nomograms for mortality risk were developed using multivariate logistic regression to identify the risk variables for poor prognosis in these patients. We calculated the area under the receiver operating characteristic curve (AUC) for the two nomograms to assess their discrimination, and predictive abilities were compared using net reclassification improvement (NRI) and integrated discrimination improvement (IDI).

Results

The multivariate logistic regression analysis identified four independent risk factors: age, bleeding manifestations, prolonged activated partial thromboplastin time, and viral load. Based on these factors, a final nomogram predicting mortality risk in patients with SFTS was constructed; in addition, a simplified nomogram was constructed excluding the viral load. The AUC [0.926, 95% confidence interval (CI): 0.882-0.970 vs. 0.882, 95% CI: 35 0.823-0.942], NRI (0.143, 95% CI, 0.036-0.285), and IDI (0.124, 95% CI, 0.061-0.186) were calculated and compared between the two models. The calibration curves of the two models showed excellent concordance, and decision curve analysis was used to quantify the net benefit at different threshold probabilities.

Conclusion

Two critical risk nomograms were developed based on the indicators for early prediction of mortality risk in patients with SFTS, and enhanced predictive accuracy was observed in the model that incorporated the viral load. The models developed will provide frontline clinicians with a convenient tool for early identification of critically ill patients and initiation of a better personalized treatment in a timely manner.

Serologic and Molecular Prevalence of Severe Fever with Thrombocytopenia Syndrome Virus Among Poultry in the Republic of Korea

Background: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by Dabie bandavirus, which belongs to the genus Bandavirus, family Phenuiviridae, and order Bunyavirales. It has been found in tick species, various animals, and humans. The aim of this study was to detect RNA of antigens and antibodies against SFTS virus (SFTSV) among poultry such as chickens, ducks, and wild geese from five provinces in the Republic of Korea (ROK). Materials and Methods: A one-step reverse transcriptase (RT)-PCR and nested PCR were performed after viral RNA extraction. The phylogenetic tree was constructed after sequencing data were analyzed and aligned. An indirect enzyme-linked immunosorbent assay (ELISA) and a neutralization test (NT) were performed to test for IgG antibodies of SFTSV. Results: Of a total of 606 poultry serum samples collected, 568 and 539 serum samples were used to perform ELISA and NT, respectively. Of a total of 606 serum samples tested by RT-PCR targeting the S segment, 15 (2.5%) were positive for SFTSV. From the 15 positive serum samples for the SFTSV antigen, three from chickens, three from ducks, and one from wild geese were classified as genotype B-2; one from chickens was classified as genotype B-3; and three from chickens and four from wild geese were classified as genotype D. Of the 568 serum samples tested by ELISA, 83 (28.0%) from chickens, 81 (32.9%) from ducks, and 8 (30.8%) from wild geese were seropositive. Of the 539 serum samples for which an NT was performed, 113 (38.6%) from chickens and 75 (30.5%) from ducks were positive for SFTSV antibodies. Conclusions: The results of this study provide useful information regarding detection of SFTSV RNA and antibodies among poultry and the possibility of SFTSV transmission in various types of poultry, including chickens, ducks, and wild geese, in the ROK.

Epidemiology of Severe Fever with Thrombocytopenia Syndrome in Dogs and Cats in Taiwan

Severe Fever with Thrombocytopenia Syndrome (SFTS), caused by the SFTS Virus (SFTSV), is a global health threat. SFTSV in Taiwan has only been reported in ruminants and wild animals. Thus, we aimed to investigate the infection statuses of dogs and cats, the animals with closer human interactions. Overall, the SFTSV RNA prevalence was 23% (170/735), with dogs showing a 25.9% (111/429) prevalence and cats at 19.3% (59/306) prevalence. Noticeably, the prevalence in stray animals (39.8% 77/193) was significantly higher than in domesticated ones (17.2%, 93/542). Among the four categories analyzed, the highest SFTSV prevalence was found in the stray dogs at 53.9% (120/193), significantly higher than the 24.2% prevalence noted in stray cats. In contrast, domesticated animals exhibited similar prevalence rates, with 17.1% for dogs and 17.2% for cats. It is noteworthy that in the domesticated animal groups, a significantly elevated prevalence (45%, 9/20) was observed among cats exhibiting thrombocytopenia compared to those platelet counts in the reference range (4.8%, 1/21). The high infection rate in stray animals, especially stray dogs, indicated that exposure to various outdoor environments influences the prevalence of infections. Given the higher human interaction with dogs and cats, there is a need for proactive measures to reduce the risk associated with the infection of SFTSV in both animals and humans.

Emerging tickborne viruses vectored by Amblyomma americanum (Ixodida: Ixodidae): Heartland and Bourbon viruses

Heartland (HRTV) and Bourbon (BRBV) viruses are newly identified tick-borne viruses, isolated from serious clinical cases in 2009 and 2014, respectively. Both viruses originated in the lower Midwest United States near the border of Missouri and Kansas, cause similar disease manifestations, and are presumably vectored by the same tick species, Amblyomma americanum Linnaeus (Ixodida: Ixodidae). In this article, we provide a current review of HRTV and BRBV, including the virology, epidemiology, and ecology of the viruses with an emphasis on the tick vector. We touch on current challenges of vector control and surveillance, and we discuss future directions in the study of these emergent pathogens.

Long-Term Detection and Isolation of Severe Fever with Thrombocytopenia Syndrome (SFTS) Virus in Dog Urine

Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne infection caused by the SFTS virus (SFTSV), with a high fatality rate of approximately 30% in humans. In recent years, cases of contact infection with SFTSV via bodily fluids of infected dogs and cats have been reported. In this study, clinical and virological analyses were performed in two dogs in which SFTSV infection was confirmed for the first time in the Toyama prefecture. Both dogs recovered; however, one was severely ill and the other mildly ill. The amount of the SFTSV gene was reduced to almost similar levels in both dogs. In the dogs' sera, the SFTSV gene was detected at a low level but fell below the detection limit approximately 2 weeks after onset. Notably, the SFTSV gene was detected at levels several thousand times higher in urine than in other specimens from both dogs. Furthermore, the gene was detected in the urine for a long period of >2 months. The clinical signs disappeared on days 1 or 6 after onset, but infectious SFTSV was detected in the urine up to 3 weeks later. Therefore, it is necessary to be careful about contact with bodily fluids, especially urine, even after symptoms have disappeared.

Infection and transovarial transmission of severe fever with thrombocytopenia syndrome virus in Rhipicephalus sanguineus in Hainan Island, China

Severe fever with thrombocytopenia syndrome virus (SFTSV) RNA level increased in female ticks after injection with SFTSV. Furthermore, SFTSV RNA was detected in the eggs and larvae that originated from the virus-infected female ticks.

Identification and Analysis of a Four-Gene Set for Diagnosing SFTS Virus Infection Based on Machine Learning Methods and Its Association with Immune Cell Infiltration

Severe Fever with thrombocytopenia syndrome (SFTS) is a highly fatal viral infectious disease that poses a significant threat to public health. Currently, the phase and pathogenesis of SFTS are not well understood, and there are no specific vaccines or effective treatment available. Therefore, it is crucial to identify biomarkers for diagnosing acute SFTS, which has a high mortality rate. In this study, we conducted differentially expressed genes (DEGs) analysis and WGCNA module analysis on the GSE144358 dataset, comparing the acute phase of SFTSV-infected patients with healthy individuals. Through the LASSO-Cox and random forest algorithms, a total of 2128 genes were analyzed, leading to the identification of four genes: ADIPOR1, CENPO, E2F2, and H2AC17. The GSEA analysis of these four genes demonstrated a significant correlation with immune cell function and cell cycle, aligning with the functional enrichment findings of DEGs. Furthermore, we also utilized CIBERSORT to analyze the immune cell infiltration and its correlation with characteristic genes. The results indicate that the combination of ADIPOR1, CENPO, E2F2, and H2AC17 genes has the potential as characteristic genes for diagnosing and studying the acute phase of SFTS virus (SFTSV) infection.

Cryo-EM structure of severe fever with thrombocytopenia syndrome virus

The severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne human-infecting bunyavirus, which utilizes two envelope glycoproteins, Gn and Gc, to enter host cells. However, the structure and organization of these glycoproteins on virion surface are not yet known. Here we describe the structure of SFTSV determined by single particle reconstruction, which allows mechanistic insights into bunyavirus assembly at near-atomic resolution. The SFTSV Gn and Gc proteins exist as heterodimers and further assemble into pentameric and hexameric peplomers, shielding the Gc fusion loops by both intra- and inter-heterodimer interactions. Individual peplomers are associated mainly through the ectodomains, in which the highly conserved glycans on N914 of Gc play a crucial role. This elaborate assembly stabilizes Gc in the metastable prefusion conformation and creates some cryptic epitopes that are only accessible in the intermediate states during virus entry. These findings provide an important basis for developing vaccines and therapeutic drugs.

Coinfection With Severe Fever With Thrombocytopenia Syndrome and Scrub Typhus in Korea

Background

Scrub typhus and severe fever with thrombocytopenia syndrome (SFTS) are the 2 most common tick-borne infectious diseases in Korea. Every year, an increasing number of cases are reported, which is a public health concern. Therefore, we aimed to investigate the prevalence of SFTS-scrub typhus coinfection in patients with SFTS.

Methods

Clinical samples were collected from 129 patients with SFTS. One-step reverse-transcription polymerase chain reaction (PCR) was performed to identify the SFTS virus (SFTSV), and real-time PCR followed by nested PCR was performed to detect the Orientia tsutsugamushi gene for scrub typhus. Phylogenetic analysis was conducted to confirm the evolutionary relationships among different species.

Results

Among 129 SFTS cases, 2 patients with SFTSV were positive for O. tsutsugamushi with a prevalence of coinfection of 1.6% (95% confidence interval, .001-.06). Phylogenetic analysis confirmed these as O. tsutsugamushi strain Boryong.

Conclusions

Our study found that 1.6% of patients were coinfected with SFTS and scrub typhus infection. We believe that this information will add a new dimension to clinical diagnosis, which should be considered for better public health management. Further research is needed to better understand the ecological transmission dynamics and geographical distribution of SFTSV and O. tsutsugamushi in endemic countries.

Emerging Tick-Borne Dabie bandavirus: Virology, Epidemiology, and Prevention

Severe Fever with Thrombocytopenia Syndrome (SFTS), caused by Dabie bandavirus (SFTSV), is an emerging infectious disease first identified in China. Since its discovery, infections have spread throughout East Asian countries primarily through tick bites but also via transmission between animals and humans. The expanding range of ticks, the primary vectors for SFTSV, combined with migration patterns of tick-carrying birds, sets the stage for the global spread of this virus. SFTSV rapidly evolves due to continuous mutation and reassortment; currently, no approved vaccines or antiviral drugs are available. Thus, the threat this virus poses to global health is unmistakable. This review consolidates the most recent research on SFTSV, including its molecular characteristics, transmission pathways through ticks and other animals, as well as the progress in antiviral drug and vaccine development, encompassing animal models and clinical trials.

Genetic Diversity, Regional Distribution, and Clinical Characteristics of Severe Fever with Thrombocytopenia Syndrome Virus in Gangwon Province, Korea, a Highly Prevalent Region, 2019-2021

Severe fever with thrombocytopenia syndrome (SFTS) is an arthropod-borne viral disease with a high mortality rate with high fever and thrombocytopenia. We investigated the clinical and epidemiological characteristics and viral genotypes from 2019 to 2021 in Gangwon Province, Korea. Of the 776 suspected cases, 62 were SFTS. The fatality rate was 11.5-28.6% (average rate, 19.4%), and the frequent clinical symptoms were high fever (95.2%), thrombocytopenia (95.2%), and leukopenia (90.3%). Hwacheon had the highest incidence rate per 100,000 persons at 8.03, followed by Inje and Yanggu (7.37 and 5.85, respectively). Goseong, Yangyang, and Hoengseong had rates of 2 or higher; Samcheok, Hongcheon, Jeongsen, and Yeonwol were 1.70-1.98, and Wonju, Gangneung, and Donghae were slightly lower, ranging from 0.31 to 0.74. Of the 57 cases with identified genotypes, eight genotypes (A, B1, B2, B3, C, D, E, and F) were detected, and the B2 genotype accounted for 54.4% (31 cases), followed by the A genotype at 22.8% (13 cases). The B2 and A genotypes were detected throughout Gangwon Province, and other genotypes, B1, B3, C, D, and F, were discovered in a few regions. In particular, genotype A could be further classified into subtypes. In conclusion, SFTS occurred throughout Gangwon Province, and Hwacheon had the highest incidence density. Multiple genotypes of SFTS were identified, with B2 and A being the most common. These findings provide important insights for the understanding and management of SFTS in this region.

Rapid and portable bunyavirus SFTSV RNA testing utilizing catalytic hairpin assembly coupled with lateral flow immunoassay

Severe fever with thrombocytopenia syndrome (SFTS) is a prevalent, life-threatening, emergent infectious disease. Currently, reverse transcription-polymerase chain reaction is the gold standard for diagnosing SFTS virus (SFTSV) infection, which requires sophisticated equipment and professional personnel that are frequently unavailable in most SFTS endemic rural areas. Here, we reported a simple, rapid nucleic acid amplification system that combined the catalytic hairpin assembly (CHA) with a lateral flow immunoassay (LFIA) strip-based detection method for SFTSV detection. The detection of SFTSV RNA could be realized by generation of H1-H2 hybrid duplexes labeled with biotin and digoxin, which subsequently added to the LFIA test strips containing streptavidin conjugated with Alexa Fluor 647 as well as anti-digoxin antibodies. Our CHA-based LFIA assay offered high amplification efficiency and specificity with a detection limit of 1 aM. Crucially, this method enabled stable detection of 500 copies/mL of SFTSV within 30 min using clinical serum samples. Therefore, our CHA-based LFIA approach provided a potential useful tool to facilitate early and precise diagnosis of SFTS patients in poorly resourced SFTS endemic areas.IMPORTANCESevere fever with thrombocytopenia syndrome (SFTS) is an emerging and potentially fatal infectious disease prevalent in China. Here we report a simple, rapid nucleic acid amplification system, the catalytic hairpin assembly (CHA) in conjunction with a lateral flow immunoassay (LFIA) strip-based detection method for SFTS virus detection, which demonstrated high amplification efficiency and specificity with limit of detection of 1 aM. Most importantly, we also validate our CHA-based LFIA assay using the clinical serum samples, which was fully compatible with reverse transcription-PCR results. Therefore, our strategy provides a potential useful tool to facilitate early and precise diagnosis of SFTS patients especially in poorly resourced SFTS endemic areas.

Antibody production and characterization of the nucleoprotein of sever fever with thrombocytopenia syndrome virus (SFTSV) for effective diagnosis of SFTSV

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an infectious disease caused by the Dabie bandavirus, [or SFTS virus (SFTSV)] that has become increasingly widespread since it was first reported in 2009. The SFTSV comprises three essential single-stranded RNA gene segments, with the S segment encoding the nucleocapsid (N) protein. Since the N protein is the most abundant and stable viral protein, it is a useful diagnostic marker of infection. Various SFTSV N-protein-based detection methods have been developed. However, given the limited research on antibodies of an SFTSV N-protein, here we report the characterization of the antibodies against SFTSV N protein especially their mapping results which is essential for more efficient and optimized detection of SFTSV.

METHODS

To generate SFTSV-N-protein-specific monoclonal antibodies, recombinant full-length SFTSV N protein was expressed in E. coli, and the purified N protein was immunized to mice. The binding epitope positions of the antibodies generated were identified through binding-domain mapping. An antibody pair test using a lateral flow immunoassay (LFIA) was performed to identify effective diagnostic combinations of paired antibodies.

RESULTS

Nine monoclonal antibodies specific for the SFTSV N protein were generated. Antibodies #3(B4E2) and #5(B4D9) were specific for sequential epitopes, while the remainder were specific for conformational epitopes. Antibody #4(C2G1) showed the highest affinity for the SFTSV N protein. The binding domain mapping results indicated the binding regions of the antibodies were divided into three groups. The antibody pair test demonstrated that #3(B4E2)/#4(C2G1) and #4(C2G1)/#5(B4D9) were effective antibody pairs for SFTSV diagnosis.

CONCLUSIONS

Effective virus detection requires at least two strong antibodies recognizing separate epitope binding sites of the virus antigen. Here, we generated SFTSV-N-protein-specific monoclonal antibodies and subsequently performed epitope mapping and an antibody pair test to enhance the diagnostic efficiency and accuracy of SFTSV. Confirmation of epitope mappings and their combination immune response to the N protein provide valuable information for effective detection of SFTSV as well as can respond actively to detect a variant SFTSV.

Dynamics of neutralizing antibodies against severe fever with thrombocytopenia syndrome virus

OBJECTIVES

Severe fever with thrombocytopenia syndrome (SFTS) virus (SFTSV) is an emerging tick-borne bunyavirus with a high pathogenicity. Little is known about the longitudinal dynamics of the SFTSV-specific neutralizing antibody (NAb) and the related factors in patients with SFTS.

METHODS

A prospective cohort study of patients with laboratory-confirmed SFTS were conducted. Antiglomerulonephritis-immunoglobulin G (anti-Gn-IgG) and NAb titers were examined in serially collected serum samples, and their dynamic features were analyzed.

RESULTS

NAb was initially detected at 15 days after symptom onset in surviving patients with SFTS, with positive rates of 37.21% (16/43), whereas neither anti-Gn-IgG antibody nor NAb was detected in patients with fatal SFTS during their hospitalization. The NAb levels reached the peak at 2 months after symptom onset, and then gradually declined, with a rapid downward trend from 6 months to 4 years and a relatively slow downward trend from 5 to 10 years. There was a positive correlation between NAb and anti-Gn-IgG titers in surviving patients with SFTS (r = 0.699, P <0.001). Patients with a mild illness or low viral load experienced early NAb seroconversion. Six different dynamic patterns of NAb were noted in surviving patients.

CONCLUSION

These data provide useful information regarding the dynamic changes in NAb in patients with SFTS during the acute and convalescent phases and the follow-up period.

Analysis of severe fever with thrombocytopenia syndrome cluster in east China

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is a common tick-borne, natural focal disease. SFTS virus (SFTSV) transmission can occur between family members through close contact with an infected patient. In this study, we explored the possible transmission route of an outbreak cluster in east China.

METHOD

A case-control study was carried out to analyze the potential risk factors for person-to-person transmission. Bunia virus was detected by IgM antibody, enzyme-linked immunosorbent assay, and reverse transcription polymerase chain reaction. Chi-square, univariate, and multivariate analyses were performed to calculate the association of possible risk factors for SFTSV transmission.

RESULTS

Two patients had a clear history of blood and aerosols contact, and one may be exposed to aerosols in a closed environment. Five close contacts of the Index patient were IgM-positive and three were IgM and SFTSV RNA positive. Exposure to a poorly ventilated space where the corpse was stored (χ2 = 5.49, P = 0.019) and contact with the Index patient's contaminated items (χ2 = 15.77, P < 0.001) significantly associated with SFTSV infection.

CONCLUSION

We suspect that the cluster outbreak was possibly a person-to-person transmission of SFTSV, which may have been transmitted by directly contacting with blood of SFTS patient. The propagation of aerosols in closed environments is also an undeniable transmission.

Developing and characterizing monoclonal antibodies of Guertu bandavirus nucleoprotein for developing methods of Guertu bandavirus and severe fever with thrombocytopenia syndrome virus detection

Belonging to genus Bandavirus in Phenuiviridae family, Guertu bandavirus (GTV) is a potential pathogen closely related to severe fever with thrombocytopenia syndrome virus (SFTSV) and heartland virus (HRTV) associated with human diseases. Although the medical significance of GTV is not clear, there was serological evidence suggesting past infection with this virus has occurred, indicating its potential threat to human health. So, it is important to prepare for detection of GTV infection so as to control virus transmission and promote disease diagnosis and treatment. This study is aimed at obtaining monoclonal antibodies (mAbs) against GTV nucleoprotein (NP) and evaluating their activities in recognizing viral antigens from genetic-related bandaviruses, SFTSV and HRTV. Eight mAbs were obtained and four of them (22G1, 25C2, 25E2, and 26F8) recognize linear epitopes of GTV NP. The four mAbs showed cross-reactivity to SFTSV but were unable to react with HRTV. Two fine epitopes were identified by the four mAbs, ENP1 (194YNSFRDPLHAAV205) and ENP2 (226GPDGLP231), which are highly conserved in the NPs of GTV and SFTSV but are distinct in HRTV NP. The features of epitopes, including their hydrophilicity, antibody accessibility, flexibility, antigenicity, and spatial locations, were predicted and analyzed, and their potential functional impacts on virus infection and replication and their use for virus detection were discussed. Our results promote the understanding of the molecular basis of GTV and SFTSV NP in inducing antibody responses. The NP-specific mAbs generated in this study are promising fundamental materials for developing viral antigen detection methods for GTV and SFTSV.

Severe fever with thrombocytopenia syndrome virus induces platelet activation and apoptosis via a reactive oxygen species-dependent pathway

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infectious disease caused by the SFTS virus (SFTSV) and with a high fatality rate. Thrombocytopenia is a major clinical manifestation observed in SFTS patients, but the underlying mechanism remains largely unclear. Here, we explored the effects of SFTSV infection on platelet function in vivo in severely infected SFTSV IFNar-/- mice and on mouse and human platelet function in vitro. Results showed that SFTSV-induced platelet clearance acceleration may be the main reason for thrombocytopenia. SFTSV-potentiated platelet activation and apoptosis were also observed in infected mice. Further investigation showed that SFTSV infection induced platelet reactive oxygen species (ROS) production and mitochondrial dysfunction. In vitro experiments revealed that administration of SFTSV or SFTSV glycoprotein (Gn) increased activation, apoptosis, ROS production, and mitochondrial dysfunction in separated mouse platelets, which could be effectively ameliorated by the application of antioxidants (NAC (N-acetyl-l-cysteine), SKQ1 (10-(6'-plastoquinonyl) decyltriphenylphosphonium) and resveratrol). In vivo experiments showed that the antioxidants partially rescued SFTSV infection-induced thrombocytopenia by improving excessive ROS production and mitochondrial dysfunction and down-regulating platelet apoptosis and activation. Furthermore, while SFTSV and Gn directly potentiated human platelet activation, it was completely abolished by antioxidants. This study revealed that SFTSV and Gn can directly trigger platelet activation and apoptosis in an ROS-MAPK-dependent manner, which may contribute to thrombocytopenia and hemorrhage during infection, but can be abolished by antioxidants.

Advancements in the Worldwide Detection of Severe Fever with Thrombocytopenia Syndrome Virus Infection from 2009 to 2023

Severe fever with thrombocytopenia syndrome (SFTS) is a growing concern as an emerging tick-borne infectious disease originating from the SFTS virus (SFTSV), a recent addition to the Phlebovirus genus under the family of bunyaviruses. SFTS is typically identified by symptoms such as fever, thrombocytopenia, leukopenia, and gastrointestinal problems, accompanied by a potentially high case fatality rate. Thus, early and accurate diagnosis is essential for effective treatment and disease management. This review delves into the existing methodologies for SFTS detection, including pathogenic, molecular, and immunological technologies.

Corticosteroid Therapy for Patients With Severe Fever With Thrombocytopenia Syndrome: A Nationwide Propensity Score-Matched Study in Japan

Background

Severe fever with thrombocytopenia syndrome (SFTS) is a life-threatening infectious disease for which no effective treatment strategy has been established. Although corticosteroids (CSs) are widely administered to patients with SFTS, their efficacy remains uncertain. This study aimed to assess the impact of CS therapy on the in-hospital mortality of patients with SFTS.

Methods

In this nationwide observational study using the Japanese Diagnosis Procedure Combination database, patients hospitalized for SFTS from April 2013 to March 2021 were reviewed. We compared patients who were treated with CSs to those who were treated without them after propensity score matching to adjust for their background, disease severity, and combination therapy.

Results

We included 494 patients with SFTS, and 144 pairs of them were analyzed after propensity score matching. No significant difference in the 30-day mortality (19% vs 15%, P = .272) and the number of survival days (log-rank test, P = .392) was found between the CS treatment group and the non-CS treatment group. However, in subgroup analyses, the CS treatment group tended to have better survival among patients with impaired consciousness on admission and/or shock status within 7 days after admission.

Conclusions

CS therapy does not seem effective for all patients with SFTS; however, the impact might be altered by disease severity assessed by the consciousness level and shock status. A large-scale interventional study is required to determine its efficacy, especially for critically ill patients with SFTS.

Study of Viral Coinfection of the Ixodes persulcatus Ticks Feeding on Humans in a Natural Focus of the South of the Far East

The phenomenon of pathogen co-infection detected in a half-fed Ixodes persulcatus tick taken from a human in the south of the Far East was studied. Research was carried out on PEK, Vero, and Vero-E6 cell lines, outbred mice, and chicken embryos using ELISA, PCR, IMFA, plaque formation, and electron microscopy. The tick contained an antigen and a genetic marker of the tick-borne encephalitis virus (TBEV). The patient had post-vaccination antibodies in a titer of 1:200, as a result of which, obviously, an antibody-dependent elimination of TBEV occurred. The tick-borne co-isolate also contained an unknown pathogen (Kiparis-144 virus), which, in our opinion, was a trigger for the activation of chronic infection in suckling white mice. In the laboratory co-isolate, ectromelia virus was present, as evidenced by paw edema during the intradermal infection of mice, characteristic rashes on the chorioallantoic envelope of chicken embryos, and typical plaques on Vero-E6. The Kiparis-144 virus was not pathogenic for white mice and chicken embryos, but it successfully multiplied in the PEK, Vero, and Vero-E6 lines. Viral co-infection was confirmed by electron microscopy. Passaging on mice contributed to an increase in the virulence of the co-isolate, whose titer increased by 10,000 times by the fifth passage, which poses an epidemiological danger.

Recurrent rhabdomyolysis in a patient with a history of rhabdomyolysis due to severe fever with thrombocytopenia syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is a hemorrhagic fever syndrome that is endemic to East Asia. Here, we describe a case of rhabdomyolysis, thought to have been caused by pemafibrate (which was prescribed for hyperlipidemia) or bacterial infection, in a patient who had experienced SFTS-induced rhabdomyolysis 4 years ago. This case suggests that SFTS causes muscle degeneration and can lead to recurrent rhabdomyolysis as a long-term complication.

Coinfection of Severe Fever With Thrombocytopenia Syndrome Virus and Coxiella burnetii in Developmental Stage of Hard Ticks in Subtropical Region of Korea

BACKGROUND

Severe fever with thrombocytopenia syndrome virus (SFTSV) is transmitted through tick bites. Ticks are potential vectors for the bacterium Coxiella burnetii that causes Query fever. Here, we analyzed SFTSV and C. burnetii co-infection rates in ticks in rural areas of Jeju Island, South Korea.

METHODS

Free ticks were collected from the natural environment of the island between 2016 and 2019, and SFTSV RNA was extracted. Additionally, ribosomal RNA gene sequencing was used to identify Coxiella species.

RESULTS

Haemaphysalis longicornis was the most common tick species followed by H. flava. Tick number gradually increased from April, peaked in August, and was lowest in March. Of all the collected ticks, 82.6% (2,851/3,458) were nymphs, 17.9% (639/3,458) adults, and 0.1% (4/3,458) larvae. SFTSV-infected ticks comprised 12.6% of all ticks; their numbers were the lowest in November-December, increased from January, and were mostly identified in the adult stage during June-August. C. burnetii infections were detected in 4.4% of the SFTSV-infected H. longicornis ticks. C. burnetii co-infection was mainly observed in the nymph stage of H. longicornis, with the highest infection rate in January, followed by December and November.

CONCLUSION

Our findings suggest that Jeju Island has a high SFTSV and potential C. burnetii infection in ticks. This study provides important insights regarding SFTS and Q fever risk to humans in South Korea.

The SFTSV Nonstructural Proteins Induce Autophagy to Promote Viral Replication via Interaction with Vimentin

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a newly identified phlebovirus associated with severe hemorrhagic fever in humans. Studies have shown that SFTSV nucleoprotein (N) induces BECN1-dependent autophagy to promote viral assembly and release. However, the function of other SFTSV proteins in regulating autophagy has not been reported. In this study, we identify SFTSV NSs, a nonstructural protein that forms viroplasm-like structures in the cytoplasm of infected cells as the virus component mediating SFTSV-induced autophagy. We found that SFTSV NSs-induced autophagy was inclusion body independent, and most phenuivirus NSs had autophagy-inducing effects. Unlike N protein-induced autophagy, SFTSV NSs was key in regulating autophagy by interacting with the host's vimentin in an inclusion body-independent manner. NSs interacted with vimentin and induced vimentin degradation through the K48-linked ubiquitin-proteasome pathway. This negatively regulating Beclin1-vimentin complex formed and promoted autophagy. Furthermore, we identified the NSs-binding domain of vimentin and found that overexpression of wild-type vimentin antagonized the induced effect of NSs on autophagy and inhibited viral replication, suggesting that vimentin is a potential antiviral target. The present study shows a novel mechanism through which SFTSV nonstructural protein activates autophagy, which provides new insights into the role of NSs in SFTSV infection and pathogenesis. IMPORTANCE Severe fever with thrombocytopenia syndrome virus (SFTSV) is a newly emerging tick-borne pathogen that causes multifunctional organ failure and even death in humans. As a housekeeping mechanism for cells to maintain steady state, autophagy plays a dual role in viral infection and the host's immune response. However, the relationship between SFTSV infection and autophagy has not been described in detail yet. Here, we demonstrated that SFTSV infection induced complete autophagic flux and facilitated viral proliferation. We also identified a key mechanism underlying NSs-induced autophagy, in which NSs interacted with vimentin to inhibit the formation of the Beclin1-vimentin complex and induced vimentin degradation through K48-linked ubiquitination modification. These findings may help us understand the new functions and mechanisms of NSs and may aid in the identification of new antiviral targets.

Recent Advances in the Study of the Immune Escape Mechanism of SFTSV and Its Therapeutic Agents

Sever fever with thrombocytopenia syndrome (SFTS) is a new infectious disease that has emerged in recent years and is widely distributed, highly contagious, and lethal, with a mortality rate of up to 30%, especially in people with immune system deficiencies and elderly patients. SFTS is an insidious, negative-stranded RNA virus that has a major public health impact worldwide. The development of a vaccine and the hunt for potent therapeutic drugs are crucial to the prevention and treatment of Bunyavirus infection because there is no particular treatment for SFTS. In this respect, investigating the mechanics of SFTS-host cell interactions is crucial for creating antiviral medications. In the present paper, we summarized the mechanism of interaction between SFTS and pattern recognition receptors, endogenous antiviral factors, inflammatory factors, and immune cells. Furthermore, we summarized the current therapeutic drugs used for SFTS treatment, aiming to provide a theoretical basis for the development of targets and drugs against SFTS.

Calcium Influx Regulates the Replication of Several Negative-Strand RNA Viruses Including Severe Fever with Thrombocytopenia Syndrome Virus

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.

Development and evaluation of a mouse model susceptible to severe fever with thrombocytopenia syndrome virus by rAAV-based exogenous human DC-SIGN expression

Experimental animal model is indispensable to evaluate the prophylactic and therapeutic candidates against severe fever with thrombocytopenia syndrome virus (SFTSV). To develop a suitable mouse model for SFTSV infection, we delivered human dendritic cell-specific ICAM-3-grabbing non-integrin (hDC-SIGN) by adeno-associated virus (AAV2) and validated its susceptibility for SFTSV infection. Western blot and RT-PCR assays confirmed the expression of hDC-SIGN in transduced cell lines and a significantly increased viral infectivity was observed in cells expressing hDC-SIGN. The C57BL/6 mice transduced with AAV2 exhibited a stable hDC-SIGN expression in the organs for 7 days. Upon SFTSV challenge with 1 × 10⁵ FAID₅₀, the mice transduced with rAAV-hDC-SIGN showed a 12.5% mortality and reduced platelet and white blood cell count in accordance with higher viral titer than control group. Liver and spleen samples collected from the transduced mice had pathological signs similar to the IFNAR^-/- mice with severe SFTSV infection. Collectively, the rAAV-hDC-SIGN transduced mouse model can be used as an accessible and promising tool for studying the SFTSV pathogenesis and pre-clinical evaluation of vaccines and therapeutics against the SFTSV infection.

Analysis of fatal cases of severe fever with thrombocytopenia syndrome in Jiangsu province, China, between 2011 and 2022: A retrospective study

Introduction

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by the SFTS virus (SFTSV), which has a high fatality rate. This disease has become increasingly prevalent in recent years in Jiangsu province, with a noticeable rise in its incidence. Notably, fatal cases have also been increasing. Our study aimed to analyze the epidemiological characteristics and risk factors associated with the fatal cases of SFTS in Jiangsu province from 2011 to September 2022.

Methods

A retrospective study was performed among 698 SFTS cases during 2011-2022 in Jiangsu Province, China. Cox regression analyses were used to determine the dependent and independent risk factors that affected patient survival time. ArcGIS 10.7 was used for the visualization of the geographical distribution of the deaths from SFTS.

Results

There were 698 SFTS cases reported, with an increasing incidence, over the 12-year period. Among these cases, 43 deaths were reported. Fatal cases of SFTS were reported in 12 district counties from 2011 to 2022. Notably, most of the deaths occurred in Lishui county of Nanjing City. The median age of those who died was 69 years, with age ranges from 50 to 83 years. Multivariable Cox regression analysis showed that older age (>70) and living in Lishui county were risk factors for death from SFTS in Jiangsu province. Therefore, older adults aged over 70 years and residing in Lishui county were the high-risk group for SFTS mortality.

Discussion

Over the past 12 years, we have observed a consistent rise in the incidence of SFTS, accompanied by a relatively high case fatality rate, making it a critical public health issue. Therefore, it is urgently necessary to study the impact of meteorological factors on SFTS epidemics and devise prevention and control strategies.

Two Point Mutations in the Glycoprotein of SFTSV Enhance the Propagation Recombinant Vesicular Stomatitis Virus Vectors at Assembly Step

Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging tick-borne pathogen for which approved therapeutic drugs or vaccines are not available. We previously developed a recombinant vesicular stomatitis virus-based vaccine candidate (rVSV-SFTSV) by replacing the original glycoprotein with Gn/Gc from SFTSV, which conferred complete protection in a mouse model. Here, we found that two spontaneous mutations, M749T/C617R, emerged in the Gc glycoprotein during passaging that could significantly increase the titer of rVSV-SFTSV. M749T/C617R enhanced the genetic stability of rVSV-SFTSV, and no further mutations appeared after 10 passages. Using immunofluorescence analysis, we found that M749T/C617R could increase glycoprotein traffic to the plasma membrane, thus facilitating virus assembly. Remarkably, the broad-spectrum immunogenicity of rVSV-SFTSV was not affected by the M749T/C617R mutations. Overall, M749T/C617R could enhance the further development of rVSV-SFTSV into an effective vaccine in the future.

Epidemiological and spatiotemporal analysis of severe fever with thrombocytopenia syndrome in Eastern China, 2011-2021

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease, which is caused by severe fever with thrombocytopenia syndrome virus (SFTSV) with high fatality. Recently, the incidence of SFTS increased obviously in Jiangsu Province. However, the systematic and complete analysis of spatiotemporal patterns and clusters coupled with epidemiological characteristics of SFTS have not been reported so far.

METHODS

Data on SFTS cases were collected during 2011-2021. The changing epidemiological characteristics of SFTS were analyzed by adopting descriptive statistical methods. GeoDa 1.18 was applied for spatial autocorrelation analysis, and SaTScan 10.0 was used to identify spatio-temporal clustering of cases. The results were visualized in ArcMap.

RESULTS

The annual incidence of SFTS increased in Jiangsu Province from 2011 to 2021. Most cases (72.4%) occurred during May and August with the obvious peak months. Elderly farmers accounted for most cases, among which both males and females were susceptible. The spatial autocorrelation and spatio-temporal clustering analysis indicated that the distribution of SFTS was not random but clustered in space and time. The most likely cluster was observed in the western region of Jiangsu Province and covered one county (Xuyi county) (Relative risk = 8.18, Log likelihood ratio = 122.645, P < 0.001) located in southwestern Jiangsu Province from January 1, 2017 to December 31, 2021. The Secondary cluster also covered one county (Lishui county) (Relative risk = 7.70, Log likelihood ratio = 94.938, P < 0.001) from January 1, 2017 to December 31, 2021.

CONCLUSIONS

The annual number of SFTS cases showed an increasing tendency in Jiangsu Province from 2011 to 2021. Our study elucidated regions with SFTS clusters by means of ArcGIS in combination with spatial analysis. The results demonstrated solid evidences for the orientation of limited sanitary resources, surveillance in high-risk regions and early warning of epidemic seasons in future prevention and control of SFTS in Jiangsu Province.

Identification of surfactin as an anti-severe fever with thrombocytopenia syndrome virus multi-target compound extracted from the culture broth of marine microbes

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne virus first identified in China in 2011 and later reported in other Asian countries. Significant efforts have been made to develop anti-SFTSV compounds; however, there are no approved vaccines or antivirals against SFTSV infections. Marine organisms provide nearly unlimited biological resources to produce therapeutic drugs for the treatment and control of disease. In this study, we aimed to identify anti-SFTSV chemical compounds from the culture broth extracts of marine microbes collected from the coasts of the Nagasaki Prefecture, Japan. Of the 80 extracts, two showed an anti-SFTSV effect. One of them, which exhibited low cell toxicity, was used for further characterization. Chemical analysis combined with the anti-SFTSV effect identified surfactin as one of the main components of the selected extract. Our study showed a proof-of-concept to identify novel antiviral compounds from marine microbes against the virus of interest. Further analysis showed that surfactin affected the integrity of the virion membrane and inhibited SFTSV infection-induced membrane fusion at low pH conditions. Furthermore, surfactin inhibits the post-entry step of viral replication in the cell, which is a novel mode of antiviral action of surfactin. These results indicate that surfactin can target multiple steps of SFTSV replication in cells.