Wild boars inhabit fields, hills, and farms across Japan, where they are fed on by numerous arthropods, including mosquitoes and ticks. Consequently, they are frequently exposed to arthropod-borne pathogens. In Toyama Prefecture, blood samples from captured wild boars have long been collected for classical swine fever virus antibody testing, with detailed records kept on the capture locations. In this study, we investigated the prevalence of antibodies against Japanese encephalitis virus (JEV) and severe fever with thrombocytopenia syndrome virus (SFTSV) using 3059 serum samples collected from wild boars over the past six years. A previously developed single-round infectious particles (SRIPs) assay system was employed for the analysis. We also examined the geographic distribution of antibody-positive wild boars. The results showed that antibody positivity rates for both JEV and SFTSV increased annually from 2019 to 2024. Geographical analysis revealed that JEV antibody-positive wild boars were distributed throughout Toyama Prefecture, whereas SFTSV antibody-positive wild boars were concentrated mainly in the northwestern region and along the western prefectural border. These findings suggest that JEV continue to pose an infection risk across the entire prefecture, while SFTSV has been actively spreading in the northwestern area during 2023–2024, raising concern over an increasing risk of human infection.

Screening and detection of IgG antibodies against severe fever with thrombocytopenia syndrome virus among blood donors in southwestern part of Japan.

Severe fever with thrombocytopenia syndrome virus NSs: amultifaceted viral protein in host-virus interactions.

Severe fever with thrombocytopenia syndrome virus (SFTSV) infection is associated with poor clinical outcomes and defective humoral immunity yet the immunometabolic mechanisms underlying B cell dysfunction remain incompletely defined. Through integrated single-cell RNA sequencing and B cell receptor (BCR) repertoire profiling of peripheral B cells from SFTS patients, we dissected the molecular signatures between survivors and fatal cases. Functional validation and metabolic flux analysis were further performed. Seven transcriptionally distinct B cell subsets were identified. Fatal cases exhibited a marked expansion of CXCR3+Ki-67+CXCR5- extrafollicular plasmablasts, coupled with depletion of naïve and memory B cells. These plasmablasts exhibited hyperactivation of interferon-response genes (IFI27, ISG15), upregulation of inflammatory mediators (S100A8/A9), and contraction of BCR diversity, with skewed usage of λ-light chains. Pseudotime trajectory analysis and metabolic scoring revealed progressive upregulation of oxidative phosphorylation, glycolysis and endoplasmic reticulum stress during terminal differentiation. In fatal cases, B cells exhibited suppressed antigen presentation capacity and impaired immunoglobulin gene expression, alongside heightened oxidative stress and elevated CD39 levels. Furthermore, analysis of SFTSV-infected versus uninfected B cells revealed that infected plasmablasts displayed enhanced inflammatory and migratory features, including upregulated CXCR3 and CCR10 expression, suggesting direct viral modulation of B cell function and trafficking. Our study reveals that dysfunctional, metabolically reprogrammed plasmablasts underlie humoral immune failure in fatal SFTS. These findings provide mechanistic insight into B cell-mediated immunopathogenesis and highlight potential targets for prognostic evaluation and immunomodulatory intervention.

CRISPR/Cas12a is extensively utilized for pathogen detection owing to its high specificity and efficiency. However, traditional single-CRISPR/Cas12a encounters challenges due to its limited sensitivity, requiring pre-amplification of nucleic acids. This increases the complexity of the procedure and the potential for cross-contamination and false positives. Herein, a modular dual-CRISPR approach was developed coupled with hybridization chain reaction (HCR) for the universal and sensitive detection of pathogen nucleic acids without the need for pre-amplification. The system comprises two core modules: the first CRISPR/Cas12a recognition module specifically identifies pathogen targets and releases the activating agent, while the second CRISPR/Cas12a signal module is activated by this agent to initiate the HCR reaction for generating a strong fluorescent signal through DNA nanostructure self-assembly. Through rational design, we demonstrate the ability of this dual-CRISPR system to achieve attomolar (aM) level sensitivity for pathogen nucleic acid detection without pre-amplification, showing over six-order-of-magnitude higher sensitivity than a traditional single-CRISPR/Cas12a system. Additionally, the flexibility and versatility of the modular dual-CRISPR system have been confirmed for diverse pathogen targets, such as African swine fever virus (ASFV), severe fever with thrombocytopenia syndrome virus (SFTSV), and human papillomavirus type 16 (HPV-16) DNA. The system's practicality was demonstrated by examining ASFV quality control samples in complex environments. The exploration of the pre-amplification-free dual-CRISPR system offers a new perspective on enhancing pathogen nucleic acid detection systems.

Severe Fever with Thrombocytopenia Syndrome Virus (SFTSV) is an emerging tick-borne pathogen with a high case-fatality rate and no approved vaccine, posing a global health threat. Human codon-optimized viral antigens can enhance mRNA vaccine efficacy by improving antigen expression but often requires high mRNA doses, increasing the risk of side effects. In this study, we introduce a codon optimization strategy using Herpes Simplex Virus 1 glycoprotein B (HSVgB) codon usage to develop an mRNA lipid nanoparticle (LNP) vaccine targeting the neutralizing Gn-H domain of SFTSV (sGn-H). The HSVgB codon-optimized mRNA vaccine [sGn-H (HSVgB)] achieved higher antigen expression and elicited stronger humoral and cellular immune responses than a human codon-optimized counterpart [sGn-H (human)]. Notably, sGn-H (HSVgB) induced more bone marrow-resident antibody-secreting cells and conferred superior protection against SFTSV at lower doses. These findings highlight HSVgB codon optimization may represent a promising strategy for enhancing the immunogenicity with low-dose mRNA immunization.

Introduction/Background: Severe fever with thrombocytopenia syndrome virus (SFTSV) poses a threat to global public health with a mortality rate of up to 30%. However, there is currently no commercialized SFTSV vaccine. This study focused on the construction of DNA vaccines with different structures based on the surface glycoproteins Gn and Gc to identify the immunodominant conformations. Methods: The DNA vaccines encoding secretory proteins including Gn or Gc monomer, heterodimer of Gn and Gc (dimer), two forms of hexamer composed of the Gn and Gc heterodimer (hexamer-1 and hexamer-2) or ferritin nanoparticles of Gn, and non-secretory proteins including Gn (Gn-TM) and Gc (Gc-TM) were constructed. Western blot confirmed the expression level and the specificity of those DNA vaccines. After vaccinating mice with those DNA vaccines, its induced humoral and cellular immunity were comprehensively evaluated. Results: The DNA vaccines were constructed successfully. The DNA vaccines of Gn and polymers including dimer, hexamer-2, and ferritin nanoparticles inducing stronger binding antibody, neutralizing antibody, and antibody-dependent cellular cytotoxicity (ADCC) activity. The neutralizing antibody induced by these constructs was also cross-recognized by other five SFTSV pseudovirus strains. However, the T cell response induced by Gc, dimer or hexamer-2 DNA vaccines were significantly higher than those in most other groups, including Gn. Conclusion: The DNA vaccines encoding dimer or hexamer-2 demonstrated superior immunogenicity over other conformations, after taking the results of humoral and cellular responses into account. This study revealed the advantages of using polymer conformations in SFTSV vaccine design and provided new targets in SFTSV vaccine development.

Severe fever with thrombocytopenia syndrome (SFTS), caused by SFTS virus (SFTSV), is an emerging tick-borne disease in East Asia. SFTS monitoring has been carried out since 2010 in mainland China, but no confirmed human cases or infected vectors had been reported from the northern regions of Hebei Province. We intensified surveillance in this area by collecting serum samples from patients with fever of unknown origin (FUO) and ticks from local habitats. Subsequently, all collected samples were screened for SFTSV by qRT-PCR. SFTSV RNA was detected in two patient sera from Chengde (2.2%). In six, positive ticks were detected among the Haemaphysalis verticalis (8.6%) collected from Zhangjiakou; no positive ticks were detected among the ticks collected from Chengde. Complete viral genomes were recovered from positive tick samples via next-generation sequencing and subjected to a suite of bioinformatic analyses. Two complete genomes from Haemaphysalis verticalis formed a distinct clade with an Inner Mongolia strain across L/M/S (bootstrap = 1.0) and separate from genotypes A–F; pairwise p-distances to genotypes A–F were >0.11 across L/M/S, supporting designation of a distinct genotype. We designate this lineage as genotype G; no credible recombination was detected. Based on the L segment, molecular-clock analyses dated the genotype G lineage to the late 13th century, predating the crown age of genotypes A–F (~18th century) by more than 400 years. We provide the first evidence of SFTSV circulation in northern Hebei and identify a novel, deeply divergent lineage. This finding confirms the co-circulation of distinct viral lineages (G and F) within the province and provides critical new insights into the virus’s diversity and evolutionary history. These results expand the known range and genetic diversity of SFTSV, underscoring the need for enhanced surveillance and ecological investigation in emerging regions. It is necessary to strengthen public health education, improve the early diagnosis and treatment ability of medical workers, and provide a scientific basis for targeted public health interventions.

Background The Bunyavirales order encompasses hantavirus and severe fever with thrombocytopenia syndrome virus (SFTSV), which could cause hemorrhagic fever with renal syndrome (HFRS) and severe fever with thrombocytopenia syndrome (SFTS), respectively. Both are types of viral hemorrhagic fever (VHF), posing challenges for early differentiation. We focused on identifying predictors for two diseases, assisting clinicians to make diagnosis. Methods We conducted a retrospective analysis of clinical records from patients with SFTS and HFRS patients who were hospitalized at Qingdao No. 6 People’s Hospital and Yantai Qishan Hospital between 2021 and 2023. Independent factors were explored by logistic regression and Lasso regression analysis, following a model was established. The model’s performance was carried out by the receiver operating characteristic curve (ROC) and the area under the curve (AUC), with predictors visualized by nomogram and clinical benefit assessed by decision curve analysis. Results Our study included 129 SFTS patients and 89 HFRS patients. Independent predictors included headache (OR: 0.098, 95% CI: 0.015–0.624, p = 0.014), conjunctival congestion (OR: 0.021, 95% CI: 0.002–0.253, p = 0.002), mucosal hemorrhage (OR: 0.003, 95% CI: 0.000–0.049, p < 0.001), white blood cell count (WBC): 4–10 (OR: 0.019, 95% CI: 0.002–0.186, p = 0.001), WBC > 10 (OR: 0.011, 95% CI: 0.001–0.132, p < 0.001), CD4+ T cells ≥500 (OR: 0.013, 95% CI: 0.001–0.127, p < 0.001). WBC had the strongest predictive power (AUC: 0.916, p < 0.001). The model had optimal predictive ability and clinical net benefit, with an AUC of 0.988. Conclusion Effective predictors were CD4+ T cells, WBC (elevated in HFRS, decreased in SFTS), headache and hemorrhage symptoms.

Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne infectious disease caused by severe fever with thrombocytopenia syndrome virus (SFTSV) which results in a high mortality rate and poses a public health threat. Gene variation of SFTSV is one of the major forces driving its persistence and widespread prevalence. However, how genetic variations affect virus invasion is not yet fully understood. In this study, we evaluated the adaptive advantage of three stable high-frequency substitutions D170N, I323V, and K619R located on the envelope glycoprotein of SFTSV based on 1041M segments of their genomes. The result demonstrated that single mutation of D170N, or K619R reduced infectivity of mutant. However, the combined presence of both D170N, and K619R mutation enhanced infectivity of mutants. Structure model and SPR assay studies indicated that the substitution at the 170 site reduced the binding affinity between Gn glycoprotein and host C-C motif chemokine receptor 2 (CCR2). Additionally, neutralization assay showed I323/K619R mutant exhibited completely resistance to neutralizing antibodies pressure. This study reveals that SFTSV balances its entry ability by gene variation of different loci on its glycoprotein via a trade-off between Gn and Gc. In addition, a weakened invasion strategy facilitated by site mutations benefits its immune evasion. The findings provide mechanistic insights into its prevalence, thereby enabling early warnings for potential future outbreaks.

Abstract Background Severe fever with thrombocytopenia syndrome (SFTS) is a viral hemorrhagic fever caused by the SFTS virus (SFTSV), a tick-borne Phlebovirus. This study investigates the association between viral load and cytokine levels in patients with SFTS. Methods Viral RNA was isolated from plasma collected in EDTA and quantified by real-time reverse transcription-polymerase chain reaction (RT-PCR). Cytokines in the sera of SFTS patients were measured using cytometric bead array (CBA). Results Viral loads ranged from 2.3×10^3 copies/mL to 7.9×10^11 copies/ml. Of the 46 patients, 10 (21.7%) died during treatment. Viral loads were ≥1×10^8 copies/ml in the patients who died. The concentrations of G-CSF, IFN-α, IFN-γ, IL-1β, IL-6, IL-10, MCP-1, and IP-10 were higher in patients with high viral loads. The levels of IFN-α, IFN-γ, IL-6, MCP-1, and IP-10 positively correlated with SFTSV viral load. Conclusion SFTSV RNA load was significantly correlated with the concentration of IFN-α, as well as other cytokines (IFN-γ, IL-6, MIP-1α, and IP-10).

Severe fever with thrombocytopenia syndrome virus (SFTSV), an emerging tick-borne phlebovirus, poses a growing public health threat, with no approved vaccines or targeted therapies. Its genetic diversity and rapid reassortment have hindered the development of broadly effective interventions. Here, we isolated and characterized broadly neutralizing camelid nanobodies generated by a heterologous immunization strategy. These nanobodies exhibited cross-subtype neutralization and conferred protection against disease in humanized and lethal murine models of SFTSV infection. Structural analysis revealed binding to distinct, nonoverlapping epitopes on the viral glycoprotein complex. A rationally designed cocktail leveraging this epitope diversity achieved complete viral inhibition through synergistic mechanisms. In both murine and immunocompetent ferret models, the cocktail enabled efficient viral clearance and full protection against lethal challenge. These results demonstrate the therapeutic potential of nanobody cocktails for SFTSV infection and establish a generalizable framework for nanobody-based countermeasures against genetically variable emerging viruses, including other members of the Bunyavirales order.

Oz virus (OZV) was first isolated from ticks in Japan in 2018, and human infections with OZV were reported in 2023. However, serosurveillance for OZV infections, compared with that for severe fever with thrombocytopenia syndrome (SFTS), is rarely performed among wild animals. We conducted a retrospective study on the epidemiology of SFTS virus and OZV infections in wild animals. Serum samples were collected from 289 deer, 158 raccoons, and 381 wild boars in this study. The positivity rates for the anti-OZV IgG antibody in deer (10.3%), raccoons (12%), and wild boars (12.1%) showed no difference. Both OZV and SFTS virus IgG antibodies were detected in wild animals. Wild animals in Oita Prefecture had anti-OZV antibodies, suggesting that human cases will occur in the future. We recommend educating the public about the tick-borne pathogen risks in this area and implementing tick bite prevention strategies.

ABSTRACT Severe fever with thrombocytopenia syndrome virus (SFTSV) causes severe disease in humans, yet the pathogenesis remains poorly understood. A hallmark of fatal SFTS cases is the marked depletion of T cells. Previous studies on T cell depletion have predominantly focused on alterations in blood and peripheral lymphoid organs, while the thymus, a critical site for T cell development, has remained largely overlooked. In this study, we employed a lethal murine infection model to investigate the impact of SFTSV on thymic function. Our results revealed that SFTSV infected the thymus and induced severe cortical atrophy in type I interferon receptor-deficient (IFNAR−/−) mice, characterized by a dramatic depletion of CD4+CD8+ double-positive (DP) thymocytes. Transcriptomic analysis indicated that thymic damage is likely attributable to impaired thymocyte proliferation and increased apoptosis, which may be a consequence of SFTSV-induced alterations in the thymic microenvironment. We found SFTSV-infected macrophages and dendritic cells in the thymus, which accumulated in the cortex and exhibited elevated secretion of IFN-γ, a cytokine commonly associated with acute thymic atrophy. These results demonstrate thymic atrophy caused by SFTSV infection and suggest potential therapeutic strategies for restoring thymic function and promoting T cell reconstitution.

Introduction: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease of global concern. This case report describes a patient with SFTS-associated encephalopathy complicated by mixed pulmonary infections with Aspergillus fumigatus and Rhizopus microsporus in Ningbo, China — a combination that has not been previously reported. Case Presentation: A forty-five-year-old man with confirmed severe fever with thrombocytopenia syndrome virus (SFTSV) infection developed pulmonary co-infection by Aspergillus and Rhizopus, complicated by massive hemoptysis. He received combined antifungal therapy with liposomal amphotericin B and isavuconazole, as well as bronchoscopy and bronchial artery embolization (BAE). Due to recurrent hemoptysis, a left lower lobectomy was performed, resulting in complete clinical and radiological recovery. Conclusions: This case highlights the importance of early recognition and dynamic reassessment of fungal infections in SFTS patients. Prompt initiation of broad-spectrum antifungal therapy and timely surgical intervention are key to improving survival. Nevertheless, as a single case, the findings should be interpreted cautiously; further studies are needed to determine whether similar dual fungal infections occur more widely in SFTS patients or under specific immunosuppressive conditions.

Haemaphysalis longicornis is a primary vector of severe fever with thrombocytopenia syndrome virus (SFTSV), an emerging virus of public health concern that can cause severe disease and high mortality rates. For zoonotic tick-borne viruses such as SFTSV, it is critical that specific tick-virus pairings are carefully examined to elucidate the intra-tick infection dynamics that enable viral infection, dissemination, and persistence within a particular tick species. This study investigated the intra-tick kinetics of SFTSV acquisition and dissemination in H. longicornis by feeding nymphs on viremic mice. Nymphs were collected and processed at defined time points during and after feeding, as well as post-molting. Viral RNA was detected in nymph bodies within the first 24 hours of feeding, and infectious virus was subsequently detected at 48 hours. The rates of SFTSV acquisition by H. longicornis nymphs were consistently high across all time points. For infected ticks to be capable of transmitting virus during a subsequent blood meal, the virus must disseminate beyond the tick midgut and ultimately infect the salivary glands. Thus, the kinetics of virus dissemination beyond the midgut and into the hemolymph were evaluated by screening nymph legs for the presence of virus. SFTSV was capable of early dissemination beyond the nymph midgut during blood feeding, as well as at time points after the nymphal blood meal was complete. Furthermore, SFTSV RNA was detected in various tissues of molted adults that had acquired virus as nymphs, and these results demonstrated that time post-molting influences the efficiency and level of virus maintained by transstadial transmission. This is the first study using naturally-infected ticks to demonstrate the kinetics of viral dissemination beyond the midgut for any tick-borne virus. These findings offer new insights into tick-virus interactions that can ultimately guide strategies aimed at disrupting virus maintenance and transmission by ticks.

Background: The zoonotic infectious disease, severe fever with thrombocytopenia syndrome (SFTS), caused by the SFTS virus (SFTSV), Bandavirus dabieense, was first identified in China in 2009 and reported in the Republic of Korea in 2013. The primary vector is the tick Haemaphysalis (H.) longicornis, which is endemic to the Asia-Pacific region and has a wide range of hosts. While SFTSV has been studied in various wildlife species, no investigation has focused explicitly on bats, which are ecologically significant in the transmission of zoonotic viruses. Materials and Methods: To investigate the relationship between bats and SFTSV, 1,200 ticks were collected from 12 sites in 6 provinces within 1 km of bat habitats using flagging, and 147 bat sera were collected via cardiac puncture after ether anesthesia between November 2021 and September 2022. Total RNA was extracted from the ticks and bat sera, and nested reverse transcription polymerase chain reaction was performed to amplify the S segment of SFTSV. Bat sera were analyzed for IgG antibodies against SFTSV by enzyme-linked immunosorbent assay (ELISA). Results: Within 1 km of bat habitats, 881 H. longicornis, 209 H. flava, 96 Haemaphysalis spp., and 14 Ixodes (I.) nipponensis were identified. SFTSV was detected in 12.3% (147/1,200) of the ticks. Although no SFTSV RNA was detected in bat sera by nested PCR, 3.4% (5/147) were seropositive by ELISA. Conclusion: While molecular evidence of SFTSV infection was not observed in bats, a few serological positives suggest possible past exposure. The detection of SFTSV in ticks collected from bat habitats suggests potential ecological interactions involving bats, ticks, and other wildlife species. These findings highlight the importance of considering both wildlife reservoirs and the indirect role of bats in the geographical spread of SFTSV.

Gc glycoprotein trimer vaccine elicits robust neutralizing antibodies against severe fever with thrombocytopenia syndrome virus in mice.

Virus envelope glycoprotein targeting bispecific T cell engager protects mice from lethal severe fever with thrombocytopenia virus infection.

Profiling of SFTS virus and host protein interactions by affinity purification-mass spectrometry.