Overview of the immunological mechanism underlying severe fever with thrombocytopenia syndrome (Review)

Multi-omics analysis of SFTS virus infection in Rhipicephalus microplus cells reveals antiviral tick factors

The increasing prevalence of tick-borne arboviral infections worldwide necessitates advanced control strategies, particularly those targeting vectors, to mitigate the disease burden. However, the cellular interactions between arboviruses and ticks, especially for negative-strand RNA viruses, remain largely unexplored. Here, we employ a proteomics informed by transcriptomics approach to elucidate the cellular response of the Rhipicephalus microplus-derived BME/CTVM6 cell line to severe fever with thrombocytopenia syndrome virus (SFTSV) infection. We generate the de novo transcriptomes and proteomes of SFTSV- and mock-infected tick cells, identifying key host responses and regulatory pathways. Additionally, interactome analysis of the viral nucleoprotein (N) integrated host responses with viral replication and dsRNA-mediated gene silencing screen reveals two anti-SFTSV effectors: the N interacting RNA helicases DHX9 and UPF1. Collectively, our results provide insights into the antiviral responses of R. microplus vector cells and highlight critical SFTSV restriction factors, while enriching transcriptomic and proteomic resources for future research.

Gn-modified biomimetic nanospheres for targeted siRNA delivery and their in vitro activity against severe fever with thrombocytopenia syndrome virus

Severe fever with thrombocytopenia syndrome virus (SFTSV) has a high mortality rate, particularly in regions such as South Korea. Although vaccines and antiviral drugs are available, their effectiveness is limited, and they often have significant side effects. This study presents a novel therapeutic strategy aimed at effectively inhibiting SFTSV gene expression through the use of biomimetic nanospheres designed for siRNA delivery. In this study, we developed a biomimetic nanosphere for siRNA delivery by combining Gn-modified Vero cell membrane with siRNA-cationic peptide nanocomplexes. The biomimetic nanospheres exhibited an average size of ∼175 nm, a ζ-potential of +20 mV, and an IC50 of 18.44 nM, demonstrating high antiviral efficacy against SFTSV.

Genome-wide CRISPR screening identifies LRP1 as an entry factor for SFTSV

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne disease caused by the SFTS virus (SFTSV), which has high mortality rates and poses a significant threat to public health. To identify potential therapeutic targets against SFTSV, we conduct genome-wide knockout screening, which identifies the previously known host factor CCR2, and reveals prolow-density lipoprotein receptor-related protein 1 (LRP1) as an entry factor for SFTSV. Knockdown or knockout of LRP1 significantly attenuate SFTSV infection in mouse embryonic fibroblasts (MEFs). Additionally, inhibition of LRP1 suppresses SFTSV pseudovirus infection in MEFs, suggesting its role in viral entry. The interaction between the SFTSV glycoprotein Gn and LRP1 via the CLI and CLII domains is revealed by co-IP and surface plasmon resonance (SPR). Moreover, LRP1 antagonists and neutralizing antibodies effectively attenuate SFTSV infection in MEFs. Administration of an LRP1-neutralizing antibody in a lethal male mouse model reduces the viral load, mitigates tissue damage, and improves survival. This study identifies LRP1 as a host entry receptor for SFTSV, providing a target for therapeutic strategy development.

Mitochondrial fission regulates midgut muscle assembly and tick feeding capacity

Ticks ingest over 100 times their body weight in blood. As the primary tissue for blood storage and digestion, the tick midgut's regulation in response to this substantial blood volume remains unclear. Here, we show that blood intake triggers stem cell proliferation and mitochondrial fission in the midgut of Haemaphysalis longicornis. While inhibiting stem cell proliferation does not impact feeding behavior, disruption of mitochondrial fission impairs tick feeding capacity. Mitochondrial fission mediated by dynamin 2 (DNM2) regulates ATP generation, which in turn influences the expression of the tropomyosin-anchoring subunit troponin T (TNT). Knockdown of TNT disrupts muscle fiber assembly, hindering midgut enlargement and contraction, thereby preventing blood ingestion. These findings underscore the indispensable role of musculature in facilitating midgut expansion during feeding in ticks.

Prognostic nutritional index as an early predictor of mortality in patients with severe fever with thrombocytopenia syndrome: multicenter retrospective study in South Korea

BACKGROUND AND AIM

Severe fever with thrombocytopenia syndrome (SFTS) is a fatal tick-borne infectious disease lacking effective treatments or vaccines. Early identification of prognostic factors is essential for optimizing clinical management. This study investigated the predictors for mortality in SFTS patients.

METHODS

We conducted a retrospective multicenter cohort study of 413 SFTS patients hospitalized in South Korea from 2013 to 2024. Clinical and laboratory data were comprehensively analyzed to evaluate associations between in-hospital mortality and various inflammatory, immune, and nutritional biomarkers. Cox regression and time-dependent receiver operating characteristic (ROC) analyses were performed to identify risk factors.

RESULTS

413 patients diagnosed with SFTS were included and In-hospital mortality was 17% (70/413). Multivariate Cox regression identified older age (HR: 1.042; 95% CI: 1.014-1.071), elevated PT(INR) (HR: 109.57; 95% CI: 19.79-606.57), and lower prognostic nutritional index (PNI) (HR: 0.937; 95% CI: 0.886-0.990) as early predictors of mortality. Time-dependent ROC analysis demonstrated predictive accuracy, with AUCs of 0.512 for age, 0.857 for PT(INR), and 0.694 for PNI at 30 days. Kaplan-Meier analysis revealed significant survival differences for patients stratified by PNI (< 40.75), PT(INR) (≥ 0.97), and age (≥ 59 years).

CONCLUSIONS

PNI, PT(INR), and age were identified as key early predictors of mortality in SFTS. PNI, as a novel biomarker, was found to be a useful index for risk level and treatment strategies in SFTS patients.

CLINICAL TRIAL NUMBER

Not applicable.

Identification of early prediction biomarkers of severity in patients with severe fever with thrombocytopenia syndrome based on plasma proteomics

Background

Severe fever with thrombocytopenia syndrome (SFTS) is a newly emerging infectious disease. Given its rapid disease progression and high mortality rate, early warning is crucial in improving the outcomes, However, to date, relevant comprehensive predictors or an effective prediction model are still poorly explored.

Methods

A plasma proteomic profile was performed at early stages in patients with SFTS. Functional clustering analysis was used to select the candidate proteins and then validate their expression by ELISA. A cohort consisting of 190 patients with SFTS was used to develop the predictive model for severe illness and subsequently validate it in a new cohort consisting of 93 patients with SFTS.

Results

A significant increase in plasma proteins associated with various functional clusters, such as the proteasomal protein catabolic process, phagocytosis, and humoral immune response, was observed in severe SFTS patients. High levels of four proteins including NID1, HSP90α, PSMA1, and VCAM1 were strongly correlated with multi-organ damage and disease progression. A prediction model was developed at the early stage to accurately predict severe conditions with the area under the curve of 0.931 (95% CI, 0.885, 0.963).

Conclusion

The proteomic signatures identified in this study provide insights into the potential pathogenesis of SFTS. The predictive models have substantial clinical implications for the early identification of SFTS patients who may progress to severe conditions.

Developing a Prognostic Model for Predicting the Risk of Outcome in Patients With Novel Bunyavirus Infection: A Retrospective Study

The study aims to investigate the key risk factors influencing the prognosis of patients with severe fever with thrombocytopenia syndrome (SFTS) and develop a prognostic warning model based on these factors. A total of 264 SFTS patients treated at Tongji Hospital from April 1, 2023, to July 30, 2024, were included as the research sample. Retrospective analysis was conducted based on the final prognostic status of the patients, dividing them into a survival group (n = 165) and a death group (n = 99). Univariate and multivariate analyses were performed along with LASSO and logistic regression on baseline information and the first laboratory indicators within 24 h after admission to identify independent risk factors affecting prognosis. A warning model was constructed based on these factors. The analysis revealed that age (OR = 1.098, 95% CI: 1.054-1.149, p < 0.001), presence of consciousness disorders (OR = 2.506, 95% CI: 1.042-6.187, p = 0.042), BUN (OR = 1.248, 95% CI: 1.154-1.369, p < 0.001), and viral load (OR = 3.598, 95% CI: 2.572-5.288, p < 0.001) were identified as independent risk factors significantly impacting the prognosis of SFTS patients. A nomogram warning model was developed incorporating these four risk factors, which demonstrated excellent predictive performance (ROC = 0.917, 95% CI: 0.882-0.948, p < 0.001). The prognostic risk prediction model successfully established for SFTS patients in this study exhibits robust predictive performance, and it is anticipated to serve as a practical clinical tool for predicting disease progression and prognosis in SFTS patients.

Dabie bandavirus and Mycoplasma pneumoniae co-infection: a case report

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by Dabie bandavirus (DBV). We report a case of DBV and Mycoplasma pneumoniae (MP) co-infection.

CASE PRESENTATION

Here we reported a 57-year-old healthy male who was admitted with the presentations of fever, cough, hemoptysis, and hypotension. Laboratory investigations revealed thrombocytopenia, leukopenia, and organ dysfunction of liver and kidney. Seroconversion from Mycoplasma IgM antibody to IgG was recorded, and SFTS was confirmed through metagenomic next-generation sequencing. In addition, hemophagocytic lymphohistiocytosis was diagnosed in the context of DBV and MP coinfection. The patient exhibited a rapid recovery following treatment with omadacycline and essential symptomatic and supportive treatment.

CONCLUSIONS

We firstly reported a case with DBV and MP coinfection, which reminded us that the symptoms of DBV infection were bewildering and easy to miss diagnosis when it was co-infection with other etiologies.

Development of 111In-Labeled Monoclonal Antibodies Targeting SFTSV Structural Proteins for Molecular Imaging of SFTS Infectious Diseases by SPECT

No effective vaccines or treatments are currently available for severe fever with thrombocytopenia syndrome (SFTS), a fatal tick-borne infectious disease caused by the SFTS virus (SFTSV). This study evaluated the potential of 111In-labeled anti-SFTSV antibodies targeting SFTSV structural proteins as single-photon emission computed tomography (SPECT) imaging agents for the selective visualization of SFTSV-infected sites. This study used nuclear medicine imaging to elucidate the pathology of SFTS and assess its therapeutic efficacy. Immunostaining experiments confirmed that the anti-SFTSV antibody (N-mAb), which targets the N protein, specifically accumulated in SFTSV-infected Vero E6 cells. 111In-labeled N-mAb was successfully prepared using a diethylenetriaminepentaacetic acid (DTPA) chelator, resulting in [111In]In-DTPA-N-mAb with high radiochemical purity exceeding 95% and a radiochemical yield of 55%. Cell-binding assays using SFTSV-infected Vero E6 cells demonstrated that [111In]In-DTPA-N-mAb binding was detectable even without membrane permeabilization, with the binding intensity correlating with infection levels. In vivo studies using SFTSV-infected A129 mice showed high spleen accumulation of [111In]In-DTPA-N-mAb (87.5% ID/g), consistent with SFTSV tropism, compared to 12.3% ID/g in mock-infected mice. SPECT/CT imaging clearly revealed high radioactivity in these regions. Although nonspecific accumulation was noted in the liver and spleen, this issue may be mitigated through antibody modifications such as fragmentation or PEGylation. Overall, [111In]In-DTPA-N-mAb is a promising imaging agent for non-invasive visualization of SFTSV-infected sites and may aid in elucidating SFTS pathology and assessing therapeutic efficacy.

Limitations of a proper SFTSV mouse model using human C-type lectin receptors

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne virus with a human mortality rate of up to 30%, posing a significant threat to public health. However, the lack of suitable research models has impeded the development of effective human vaccines. In this study, we engineered transgenic mice (3xTg) using a novel construct that simultaneously expresses three C-type Lectin receptors, identified as critical SFTSV entry receptors. While this construct substantially enhanced viral binding and infection in BJAB cells, the 3xTg mice exhibited only limited SFTSV replication in the lymph nodes and spleen, without significant impacts on morbidity or mortality. These findings highlight that the overexpression of entry receptors alone is insufficient to fully recapitulate human SFTSV infection in mice. Moreover, our results reveal that the introduction of multiple entry receptors does not necessarily translate to enhanced infection efficacy. This underscores the need for further investigation into the interplay between SFTSV entry mechanisms and host factors to develop more robust mouse models. Advancing such models will be crucial for unraveling the pathogenesis of SFTS pathology and improving strategies for its prevention and treatment in humans.

Development and validation of a clinical and laboratory-based nomogram to predict mortality in patients with severe fever with thrombocytopenia syndrome

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging global infectious disease with a high mortality rate. Clinicians lack a convenient tool for early identification of critically ill SFTS patients. The aim of this study was to construct a simple and accurate nomogarm to predict the prognosis of SFTS patients.

METHODS

We retrospectively analyzed the clinical data of 372 SFTS patients collected between May 2015 and June 2023, which were divided 7:3 into a training set and an internal validation set. We used LASSO regression to select predictor variables and multivariable logistic regression to identify independent predictor variables. Prognostic nomograms for SFTS were constructed based on these factors and analysed for concordance index, calibration curves and area under the curve (AUC) to determine the predictive accuracy and consistency of the model.

RESULTS

In the training set, LASSO and multivariate logistic regression analyses showed that age, SFTSV RNA, maximum body temperature, pancreatitis, gastrointestinal bleeding, pulmonary fungal infection (PFI), BUN, and PT were independent risk factors for death in SFTS patients. There was a strong correlation between neurological symptoms and mortality (P < 0.001, OR = 108.92). Excluding neurological symptoms, nomograms constructed based on the other eight variables had AUCs of 0.937 and 0.943 for the training and validation sets, respectively. Furthermore, we found that age, gastrointestinal bleeding, PFI, bacteraemia, SFTSV RNA, platelets, and PT were the independent risk factors for neurological symptoms, with SFTSV RNA having the highest diagnostic value (AUC = 0.785).

CONCLUSIONS

The nomogram constructed on the basis of eight common clinical variables can easily and accurately predict the prognosis of SFTS patients. Moreover, the diagnostic value of neurological symptoms far exceeded that of other predictors, and SFTSV RNA was the strongest independent risk factor for neurological symptoms, but these need to be further verified by external data.

Risk assessment of human-to-human transmission of severe fever with thrombocytopenia syndrome virus based on 10-year clustered analysis

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an acute infectious disease, which was first reported in 2009 in China. Previous studies have rarely quantitatively assessed the transmission and fatal risk of SFTS clusters.

Methods

Epidemiological information regarding SFTS clusters in Yantai city of Shandong province during 2013-2022 was obtained from the National Public Health Emergency Event Surveillance System (PHEESS) for Disease Control and Prevention information system. The secondary attack rate (SAR) and relative risk (RR) were used to assess the risk of human-to-human transmission of SFTS.

Results

A total of 20 SFTS clusters involving 51 laboratory-confirmed patients were reported between 2013 and 2022 in Yantai city, Shandong province. Most of the clusters occurred from May to October, and the patients were mainly distributed in four counties. Contact with blood or other fluids [RR = 14.06, 95% confidence interval (CI) = 3.29-70.65, p < 0.001] and using no personal protection equipment (PPE) [11.63% (10/86) vs. 2.22% (2/90), RR = 5.74, 95% CI = 1.17-55.44, p = 0.013] were significantly related with an increased risk of SFTS virus (SFTSV) transmission.

Conclusion

Our study may provide direct guidance on health education and behavioral interventions for the accompanying relatives and personnel of SFTS patients, both during their hospital stay and upon returning home after discharge.

The hnRNP A2B1 is important for the replication of SFTSV and other RNA viruses

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.

Establishment and validation of a clinical risk scoring model to predict fatal risk in SFTS hospitalized patients

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infection with a high case fatality rate. Significant gaps remain in studies analyzing the clinical characteristics of fatal cases.

METHODS

From January 2017 to June 2023, 427 SFTS cases were included in this study. A total of 67 variables about their demographic, clinical, and laboratory data were collected. Univariate logistic regression and the least absolute shrinkage and selection operator (LASSO) method was used to screen predictors from the cohort. Multivariate logistic regression was used to identify independent predictors and nomograms were developed. Calibration, decision curves and area under the curve (AUC) were used to assess model performance.

RESULTS

The multivariate logistic regression analysis screened out the four most significant factors, including age > 70 years (p = 0.001, OR = 2.516, 95% CI 1.452-4.360), elevated serum PT (p < 0.001, OR = 1.383, 95% CI 1.143-1.673), high viral load (p < 0. 001, OR = 1.496, 95% CI 1.290-1.735) and high level of serum urea (> 8.0 μmol/L) (p < 0.001, OR = 4.433, 95% CI 1.888-10.409). The AUC of the nomogram based on these four factors was 0.813 (95% CI, 0.758-0.868). The bootstrap resampling internal validation model performed well, and decision curve analysis indicated a high net benefit.

CONCLUSIONS

The nomogram based on age, elevated PT, high serum urea level, and high viral load can be used to help early identification of SFTS patients at risk of fatality.

A nomogram including admission serum glycated albumin/albumin ratio to predict mortality in patients with severe fever with thrombocytopenia syndrome

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is a novel tick-borne infectious disease with a high fatality rate. Although several nomograms based on demographic and laboratory data have been reported to predict the prognosis of SFTS in recent studies, baseline serum glycated albumin (GA)/albumin (ALB) ratio included risk model has not been evaluated for the prediction of clinical outcome.

METHODS

A total of 214 SFTS patients with integral data admitted to our hospital from May, 2020 to November, 2022 were included in this study. SFTS infection was confirmed by real time fluorescent quantitative PCR (qRT-PCR). The demographic characteristics, clinical and laboratory data were collected with in 24 h of admission and 1 to 2 days before discharge and were analysed retrospectively.

RESULTS

Fiffty-seven patients (26.6%) died. Multivariate logistic regression analysis showed that age, aspartate aminotransferase (AST), blood glucose (GLU), GA/ALB ratio, neutrophil counts (NEU) and lymphocyte percentage (LYM%) were the independent risk factors for mortality. A nomogram by these factors was created using RMS package in the R program. Area under the receiver operating characteristic (ROC) curve (AUC) of this nomogram was 0.88 (95% CI: 0.83, 0.93). This model showed the excellent net benefit, as revealed by the decision curve analysis. GA/ALB ratios were also independent risk factors for poor out clinical come in subgroups of patients with hyperglycemia on admission and with diabetes history. Nomograms were constructed by the independent risk factors in the subgroups. AUCs of the nomograms in the subgroups showed high predictive values for adverse prognosis.

CONCLUSIONS

GA/ALB ratios were independent risk factors for mortality in all SFTS patients and subgroups of with hyperglycemia on admission and diabetes history. The nomograms including GA/ALB ratio had high predictive value for adverse clinical outcome.The nomograms provide a basis for clinical decision-making for the treatment of SFTS patients in different clinical settings.

A broadly protective antibody targeting glycoprotein Gn inhibits severe fever with thrombocytopenia syndrome virus infection

Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging bunyavirus that causes severe viral hemorrhagic fever and thrombocytopenia syndrome with a fatality rate of up to 30%. No licensed vaccines or therapeutics are currently available for humans. Here, we develop seven monoclonal antibodies (mAbs) against SFTSV surface glycoprotein Gn. Mechanistic studies show that three neutralizing mAbs (S2A5, S1G3, and S1H7) block multiple steps during SFTSV infection, including viral attachment and membrane fusion, whereas another neutralizing mAb (B1G11) primarily inhibits the viral attachment step. Epitope binning and X-ray crystallographic analyses reveal four distinct antigenic sites on Gn, three of which have not previously been reported, corresponding to domain I, domain II, and spanning domain I and domain II. One of the most potent neutralizing mAbs, S2A5, binds to a conserved epitope on Gn domain I and broadly neutralizes infection of six SFTSV strains corresponding to genotypes A to F. A single dose treatment of S2A5 affords both pre- and post-exposure protection of mice against lethal SFTSV challenge without apparent weight loss. Our results support the importance of glycoprotein Gn for eliciting a robust humoral response and pave a path for developing prophylactic and therapeutic antibodies against SFTSV infection.

Early predictors of Epstein-Barr virus infection in patients with severe fever with thrombocytopenia syndrome

BACKGROUND

Epstein-Barr virus (EBV) can be reactivated and proliferated with fatal outcome in immuno-compromised people, but the clinical consequences of EBV infection in patients with severe fever with thrombocytopenia syndrome (SFTS) remain uncertain. In this study, we investigated the infection rate, the influence and the early predictors of EBV infection in SFTS patients.

METHODS

In this retrospective study, SFTS patients who were treated in the First Affiliated Hospital of Nanjing Medical University from May 2011 to August 2021 were enrolled and divided into infected and non-infected groups. We compared the demographic characteristics, clinical manifestations and signs, laboratory tests and prognosis, and explored the risk factors of EBV infection by receiver operating characteristic (ROC) curve and logistic regression.

RESULTS

A total of 120 hospitalized SFTS patients with EBV-DNA testing were enrolled in this study. Patients with EBV infection had statistically significant higher mortality rate (32.0% vs. 11.43%, P = 0.005). Compared with the non-infected group, the EBV-infected group had higher levels of C-reactive protein (CRP), creatine-kinase (CK), fasting blood glucose (FBG), blood urea nitrogen (BUN), D-dimer, and CD56+ cell counts, lower levels of immunoglobulin G (IgG), IgM, complement 3 (C3), and C4. The proportion of patients with age ≥ 60 years and ferritin > 1500.0 ng/ml in the EBV-infected group was significantly higher than that in the non-infected group. The results of ROC analysis showed that the cut-off values of CRP, IgG, C3, C4, and CD56+ cell counts to predict EBV infection were 13.2 mg/l, 12.5 g/l, 1.1 g/l, 0.6 g/l, 0.3 g/l, and 94.0 cells/µl. Multivariable logistic analysis showed that age ≥ 60 years old, CRP > 13.2 mg/l, BUN > 5.4 mmol/l, ferritin > 1500.0 ng/ml, IgG < 12.5 g/l, IgM < 1.1 g/l, C4 < 0.3 g/l, and CD56+ cell counts > 94.0 cells/µl were the independent risk factors of EBV infection in SFTS patients.

CONCLUSIONS

SFTS combined with EBV infection is associated with high morbidity and mortality. It is necessary to strengthen screening for EBV infection and its early predictive markers after admission in SFTS patients.

The first diagnosis of Severe Fever with Thrombocytopenia Syndrome caused by tick-borne Severe Fever with Thrombocytopenia Syndrome virus in Chongqing, China: A case report and literature review

BACKGROUND

Severe Fever with Thrombocytopenia Syndrome (SFTS) is a tick-borne disease caused by the SFTS virus (SFTSV) which has the potential to become a pandemic and is currently a major public health concern.

CASE PRESENTATION

We present the case of a 74-year-old female from an urban area of Chongqing, with leukocytopenia, thrombocytopenia, organ function, inflammatory, blood coagulation, and immune abnormalities. SFTSV infection was confirmed through molecular detection and metagenomic next-generation sequencing (mNGS) analysis, indicating a diagnosis of SFTS due to the patient's history of tick bites. The patient received symptomatic and supportive therapy, including antibiotics, antiviral treatment, and antifungal therapy, and finally discharged from the hospital on day 18.

CONCLUSIONS

This study highlights the need for increased awareness, early diagnosis, and prompt treatment for tick-borne SFTS. It also provides a comprehensive understanding of the disease's characteristics, pathogenesis, detection methods, and available treatments.

Differential short-term and long-term metabolic and cytokine responses to infection of severe fever with thrombocytopenia syndrome virus

INTRODUCTION

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by the SFTS virus (SFTSV), which has a wide geographic distribution. The primary clinical manifestations of SFTS are fever and thrombocytopenia, with multiorgan failure being the leading cause of death. While most patients recover with treatment, little is known about the potential long-term metabolic effects of SFTSV infection.

OBJECTIVES

This study aimed to shed light on dysregulated metabolic pathways and cytokine responses following SFTSV infection, which pose significant risks to the short-term and long-term health of affected individuals.

METHODS

Fourteen laboratory-confirmed clinical SFTS cases and thirty-eight healthy controls including 18 SFTSV IgG-positive and 20 IgG-negative individuals were recruited from Taizhou city of Zhejiang province, Eastern China. Inclusion criteria of healthy controls included residing in the study area for at least one year, absence of fever or other symptoms in the past two weeks, and no history of SFTS diagnosis. Ultrahigh-performance liquid chromatography-mass spectrometry (UHPLC-MS) was used to obtain the relative abundance of plasma metabolites. Short-term metabolites refer to transient alterations present only during SFTSV infection, while long-term metabolites persistently deviate from normal levels even after recovery from SFTSV infection. Additionally, the concentrations of 12 cytokines were quantified through fluorescence intensity measurements. Differential metabolites were screened using orthogonal projections to latent structures discriminant analysis (OPLS-DA) and the Wilcoxon rank test. Metabolic pathway analysis was performed using MetaboAnalyst. Between-group differences of metabolites and cytokines were examined using the Wilcoxon rank test. Correlation matrices between identified metabolites and cytokines were analyzed using Spearman's method.

RESULTS AND CONCLUSIONS

We screened 122 long-term metabolites and 108 short-term metabolites by analytical comparisons and analyzed their correlations with 12 cytokines. Glycerophospholipid metabolism (GPL) was identified as a significant short-term metabolic pathway suggesting that the activation of GPL might be linked to the self-replication of SFTSV, whereas pentose phosphate pathway and alanine, aspartate, and glutamate metabolism were indicated as significant long-term metabolic pathways playing a role in combating long-standing oxidative stress in the patients. Furthermore, our study suggests a new perspective that α-ketoglutarate could serve as a dietary supplement to protect recovering SFTS patients.

N-glycosylation of viral glycoprotein is a novel determinant for the tropism and virulence of highly pathogenic tick-borne bunyaviruses

Severe fever with thrombocytopenia syndrome (SFTS) virus, a tick-borne bunyavirus, causes a severe/fatal disease termed SFTS; however, the viral virulence is not fully understood. The viral non-structural protein, NSs, is the sole known virulence factor. NSs disturbs host innate immune responses and an NSs-mutant SFTS virus causes no disease in an SFTS animal model. The present study reports a novel determinant of viral tropism as well as virulence in animal models, within the glycoprotein (GP) of SFTS virus and an SFTS-related tick-borne bunyavirus. Infection with mutant SFTS viruses lacking the N-linked glycosylation of GP resulted in negligible usage of calcium-dependent lectins in cells, less efficient infection, high susceptibility to a neutralizing antibody, low cytokine production in macrophage-like cells, and reduced virulence in Ifnar-/- mice, when compared with wildtype virus. Three SFTS virus-related bunyaviruses had N-glycosylation motifs at similar positions within their GP and a glycan-deficient mutant of Heartland virus showed in vitro and in vivo phenotypes like those of the SFTS virus. Thus, N-linked glycosylation of viral GP is a novel determinant for the tropism and virulence of SFTS virus and of a related virus. These findings will help us understand the process of severe/fatal diseases caused by tick-borne bunyaviruses.

Kinetics and Prognostic Significance of Laboratory Markers in Patients With Severe Fever With Thrombocytopenia Syndrome: Insight From a Comprehensive Analysis

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with significant mortality. Identifying prognostic factors that influence patient outcomes is crucial for effective clinical management. In this study, we assessed the dynamic changes of laboratory markers and their association with outcomes in 93 SFTS patients. We found that age and hypertension were significantly associated with poor outcomes in SFTS patients. The deceased group exhibited lower platelet counts, elevated liver and kidney function markers, coagulation profiles, inflammatory markers, and cytokines compared to the survival group. Kinetic analysis showed that these markers gradually normalized in the survival group, while they remained persistently abnormal in the deceased group. Furthermore, hypertension, elevated aspartate aminotransferase, procalcitonin, and interleukin 10 were identified as independent risk factors for predicting poor prognosis of SFTS patients. These findings provide valuable insights into the prognostic significance of laboratory markers and highlight the importance of early identification of high-risk SFTS patients.

Seroprevalence study in humans and molecular detection in Rhipicephalus sanguineus ticks of severe fever with thrombocytopenia syndrome virus in Thailand

Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging tick-borne virus with a mortality rate of up to 30%. First identified in China in 2009, it was later reported in other Asian countries, including Thailand in 2020. SFTSV has been detected in several tick species, including Rhipicephalus sanguineus, known for infesting dogs. We conducted a seroprevalence study of SFTSV in Bangkok and Nong Khai, Thailand, by analyzing 1162 human samples collected between 2019 and 2023. The testing method relied on IgG detection using ELISA and confirmed though a virus seroneutralization test. The results indicated that out of the participants, 12 (1.1%) tested positive for anti-SFTSV IgG antibodies; however, none exhibited positive results in the seroneutralization assay. Additionally, molecular detection of SFTSV, Crimean-Congo hemorrhagic fever (CCHF), Coxiella spp., Bartonella spp., and Rickettsia spp. was performed on 433 Rh. sanguineus ticks collected from 49 dogs in 2023 in Chachoengsao Province, Thailand. No evidence of these pathogens was found in ticks. These findings highlight the importance of exploring viral cross-reactivity. Furthermore, it is important to conduct additional studies to isolate SFTSV from animals and ticks in order to identify the potential transmission routes contributing to human and animal infections in Thailand.

The Effect of Tryptophan-to-Tyrosine Mutation at Position 61 of the Nonstructural Protein of Severe Fever with Thrombocytopenia Syndrome Virus on Viral Replication through Autophagosome Modulation

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 with central nervous system symptom onset: a case report and literature review

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is a natural focal disease transmitted mainly by tick bites, and the causative agent is SFTS virus (SFTSV). SFTS can rapidly progress to severe disease, with multiple-organ failure (MOF) manifestations such as shock, respiratory failure, disseminated intravascular coagulation (DIC) and death, but cases of SFTS patients with central nervous system (CNS) symptoms onset and marked persistent involuntary shaking of the perioral area and limbs have rarely been reported.

CASE PRESENTATION

A 69-year-old woman with fever and persistent involuntary shaking of the perioral area and limbs was diagnosed with SFTS with CNS symptom onset after metagenomic next-generation sequencing (mNGS) of cerebrospinal fluid (CSF) and peripheral blood identified SFTSV. The patient developed a cytokine storm and MOF during the course of the disease, and after aggressive antiviral, glucocorticoid, and gamma globulin treatments, her clinical symptoms improved, her laboratory indices returned to normal, and she had a good prognosis.

CONCLUSION

This case gives us great insight that when patients with CNS symptoms similar to those of viral encephalitis combined with thrombocytopenia and leukopenia are encountered in the clinic, it is necessary to consider the possibility of SFTS involving the CNS. Testing for SFTSV nucleic acid in CSF and blood (mNGS or polymerase chain reaction (PCR)) should be carried out, especially in critically ill patients, and treatment should be given accordingly.

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.

Tick symbiosis

As obligate blood-feeders, ticks serve as vectors for a variety of pathogens that pose threats on both human and livestock health. The microbiota that ticks harbor play important roles in influencing tick nutrition, development, reproduction, and vector. These microbes also affect the capacity of ticks to transmit pathogens (vector competence). Therefore, comprehending the functions of tick microbiota will help in developing novel and effective tick control strategies. Here, we summarize the effects of main tick symbiotic bacteria on tick physiology and vector competency.

The Adaptive Immune Response against Bunyavirales

The Bunyavirales order includes at least fourteen families with diverse but related viruses, which are transmitted to vertebrate hosts by arthropod or rodent vectors. These viruses are responsible for an increasing number of outbreaks worldwide and represent a threat to public health. Infection in humans can be asymptomatic, or it may present with a range of conditions from a mild, febrile illness to severe hemorrhagic syndromes and/or neurological complications. There is a need to develop safe and effective vaccines, a process requiring better understanding of the adaptive immune responses involved during infection. This review highlights the most recent findings regarding T cell and antibody responses to the five Bunyavirales families with known human pathogens (Peribunyaviridae, Phenuiviridae, Hantaviridae, Nairoviridae, and Arenaviridae). Future studies that define and characterize mechanistic correlates of protection against Bunyavirales infections or disease will help inform the development of effective vaccines.

The change of Siglec-9 expression in peripheral blood NK cells of SFTS patients can affect the function of NK cells

OBJECTIVES

To investigate the changes and mechanism of Siglec-9 on NK cells in peripheral blood of patients with severe fever with thrombocytopenia syndrome (SFTS).

METHODS

First, we used single-cell RNA sequencing to analyze the frequency of NK cells in Peripheral Blood Mononuclear Cells (PBMCs) of SFTS patients and healthy controls (HCs), as well as the differences in the genes on NK cells. Secondly, we analyzed the expression of Siglec-9 and other receptors on NK cells by flow cytometry. Thirdly, we analyzed the correlation between Siglec-9 on NK cells and DBV viral load in plasma.

RESULTS

Compared with HCs, the frequency of NK cells in peripheral blood of SFTS patients was significantly decreased, and the activating receptors on NK cells were reduced. The expression of Siglec-9 on NK cells and the frequency of Siglec-9+NK cells decreased significantly in SFTS patients. The expression of Siglec-9 on CD16+CD56dim NK cells was negatively correlated with DBV viral load. In addition, Siglec-9+NK cells expressed higher levels of activating receptors and exhibited stronger effector functions than Siglec-9-NK cells.

CONCLUSIONS

The decreased expression of Siglec-9 on NK cells predicts NK cell dysfunction in SFTS patients, suggesting that Siglec-9 may be a potential marker for functional NK cell subsets in SFTS patients.

Fatal outcome of severe fever with thrombocytopenia syndrome (SFTS) and severe and critical COVID-19 is associated with the hyperproduction of IL-10 and IL-6 and the low production of TGF-β

Severe fever with thrombocytopenia syndrome virus (SFTSV) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can cause the hyperproduction of inflammatory cytokines, which have pathological effects in patient including severe or fatal cytokine storms. To characterize the effect of SFTSV and SARS-CoV-2 infection on the production of cytokines in severe fever with thrombocytopenia syndrome (SFTS) and COVID-19 patients, we performed an analysis of cytokines in SFTS and COVID-19 patients and also investigated the role of interleukin-10 (IL-10) in vitro studies: lipopolysaccharide-induced THP-1-derived macrophages, SFTSV infection of THP-1 cells, and SARS-CoV-2 infection of THP-1 cells. In this study, we found that levels of both IL-10 and IL-6 were significantly elevated, the level of transforming growth factor-β (TGF-β) was significantly decreased and IL-10 was elevated earlier than IL-6 in severe and critical COVID-19 and fatal SFTS patients, and inhibition of IL-10 signaling decreased the production of IL-6 and elevated that of TGF-β. Therefore, the hyperproduction of IL-10 and IL-6 and the low production of TGF-β have been linked to cytokine storm-induced mortality in fatal SFTS and severe and critically ill COVID-19 patients and that IL-10 can play an important role in the host immune response to severe and critical SARS-CoV-2 and fatal SFTSV infection.

Construction and Characterization of Severe Fever with Thrombocytopenia Syndrome Virus with a Fluorescent Reporter for Antiviral Drug Screening

Severe fever with thrombocytopenia syndrome (SFTS) caused by a novel bunyavirus (SFTSV) is an emerging infectious disease with up to 30% case fatality. Currently, there are no specific antiviral drugs or vaccines for SFTS. Here, we constructed a reporter SFTSV in which the virulent factor nonstructural protein (NSs) was replaced by eGFP for drug screening. First, we developed a reverse genetics system based on the SFTSV HBMC5 strain. Then, the reporter virus SFTSV-delNSs-eGFP was constructed, rescued, and characterized in vitro. SFTSV-delNSs-eGFP showed similar growth kinetics with the wild-type virus in Vero cells. We further detected the antiviral efficacy of favipiravir and chloroquine against wild-type and recombinant SFTSV by the quantification of viral RNA, and compared the results with that of fluorescent assay using high-content screening. The results showed that SFTSV-delNSs-eGFP could be used as a reporter virus for antiviral drug screening in vitro. In addition, we analyzed the pathogenesis of SFTSV-delNSs-eGFP in interferon receptor-deficient (IFNAR^-/-) C57BL/6J mice and found that unlike the fatal infection of the wild-type virus, no obvious pathological change or viral replication were observed in SFTSV-delNSs-eGFP-infected mice. Taken together, the green fluorescence and attenuated pathogenicity make SFTSV-delNSs-eGFP a potent tool for the future high-throughput screening of antiviral drugs.

Disinfection, Sterilization, and Decontamination of Pathogens in Medicine

The ongoing coronavirus disease (COVID-19) pandemic caused by SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) is putting our public health services under enormous strain [...].

Research Progress of Fever with Thrombocytopenia Syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is a new infectious disease first discovered in Ta-pieh Mountains in central China in 2009. It is caused by a novel bunyavirus infection (SFTSV). Since the first discovery of SFTSV, there have been case reports and epidemiological studies on SFTS in several East Asian countries, such as South Korea, Japan, Vietnam and so on. With the rising incidence of SFTS and the rapid spread of the novel bunyavirus around the world, it is clear that the virus has a pandemic potential and may pose a threat to global public health in the future. Early studies have suggested that ticks are an important medium for the transmission of SFTSV to humans; in recent years, it has been reported that there is also human-to-human transmission. In endemic areas, potential hosts include a variety of livestock and wildlife. When people are infected with SFTV, the main clinical manifestations are high fever, thrombocytopenia, leukocytopenia, gastrointestinal symptoms, liver and kidney function damage, and even MODS, with a mortality rate of about 10-30%. This article reviews the latest progress of novel bunyavirus, including virus transmission vector, virus genotypic diversity and epidemiology, pathogenesis, clinical manifestation and treatment.

Severe fever with thrombocytopenia syndrome virus trends and hotspots in clinical research: A bibliometric analysis of global research

BACKGROUND

Since severe fever with thrombocytopenia syndrome virus (SFTSV) was first reported in 2009, a large number of relevant studies have been published. However, no bibliometrics analysis has been conducted on the literature focusing on SFTSV. This study aims to evaluate the research hotspots and future development trends of SFTSV research through bibliometric analysis, and to provide a new perspective and reference for future SFTSV research and the prevention of SFTSV.

METHODS

We retrieved global publications on SFTSV from the Web of Science Core Collection (WoSCC) and Scopus databases from inception of the database until 2022 using VOSviewer software and CiteSpace was used for bibliometric analysis.

RESULTS

The number of SFTSV-related publications has increased rapidly since 2011, peaking in 2021. A total of 45 countries/regions have published relevant publications, with China topping the list with 359. The Viruses-Basel has published the most papers on SFTSV. In addition, Yu et al. have made the greatest contribution to SFTSV research, with their published paper being the most frequently cited. The most popular SFTSV study topics included: (1) pathogenesis and symptoms, (2) characteristics of the virus and infected patients, and (3) transmission mechanism and risk factors for SFTSV.

CONCLUSIONS

In this study, we provide a detailed description of the research developments in SFTSV since its discovery and summarize the SFTSV research trends. SFTSV research is in a phase of explosive development, and a large number of publications have been published in the past decade. There is a lack of collaboration between countries and institutions, and international collaboration and exchanges should be strengthened in the future. The current research hotpots of SFTSV is antiviral therapy, immunotherapy, virus transmission mechanism and immune response.