Severe fever with thrombocytopenia syndrome virus: emerging novel phlebovirus and their control strategy

Development of a candidate vaccine against severe fever with thrombocytopenia syndrome virus using Gn/Gc glycoprotein via multiple expression vectors delivered by attenuated Salmonella confers effective protection in hDC-SIGN transduced mice

In this study, we developed two plasmid constructs, pJHL270 and pJHL305, for the dual expression of Severe Fever with Thrombocytopenia Syndrome Virus (SFTSV) Gn and Gc glycoproteins in both prokaryotic and eukaryotic systems. The constructs feature a prokaryotic expression controlled by the Ptrc promoter and a eukaryotic expression driven by the cytomegalovirus promoter and Semliki Forest Virus RNA-dependent RNA polymerase. The Gn/Gc antigenic epitope was derived from consensus sequences of 12 SFTSV M segments collected in South Korea and designed for optimal antigen expression. The full antigen was expressed eukaryotically for post-translational modifications, while the epitope construct was expressed prokaryotically. These constructs were electroporated into an attenuated Salmonella Typhimurium strain (JOL2500) for plasmid delivery, resulting in JOL3042 and JOL3045. Successful expression was confirmed via qRT-PCR and western blot analysis. Mice immunized with JOL3042 showed antibody responses as early as two weeks, while JOL3045 elicited responses at six weeks, skewed toward a Th1 response initially, later balancing with Th2. Flow cytometry revealed significant CD3+CD4+ and CD3+CD8+ T-cell responses. Both constructs generated neutralizing antibodies, and a challenge study indicated significant reductions in viral loads in the serum, liver, and spleen of vaccinated mice, demonstrating the effectiveness of the Salmonella-mediated delivery system against SFTSV infection. The outcome of the current study may pave the way to develop a safer and more effective Salmonella-mediated vaccine against lethal SFTSV infection in vulnerable populations.

Establishment of an Early Prediction Model for Severe Fever With Thrombocytopenia Syndrome-Associated Encephalitis

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease primarily transmitted by ticks. The development of encephalitis in SFTS patients significantly increases the risk of adverse outcomes. However, the understanding of SFTS-associated encephalitis (SFTSAE) is still limited. This study aimed to identify the clinical characteristics of SFTSAE and develop a predictive model for early detection.

METHODS

We retrospectively collected data from 220 SFTS patients admitted to Nanjing Drum Tower Hospital between May 2019 and January 2024. The patients were first randomly divided into a training set (154 people, 70%) and a validation set (66 people, 30%). The patients in the training set were divided into SFTSAE and non-SFTSAE groups according to the presence of encephalitis. A prediction model was constructed using the training set: important clinical parameters were selected using univariate logistic regression, and then multivariate logistic regression was performed to determine the independent risk factors for SFTSAE. A prediction model was constructed using these independent risk factors. Finally, the validation set was used to verify the predictive ability of the model.

RESULTS

Age, C-reactive protein, d-dimer, and viral load were independent risk factors for SFTSAE (p < 0.05). A nomogram containing these four indicators was constructed, and the predictive performance of the nomogram was evaluated using the ROC curve. The AUC of the model was 0.846 (95% confidence interval [CI]: 0.770-0.921), which had good predictive ability for SFTSAE.

CONCLUSION

Conclusion: The overall mortality rate of SFTS patients was 17.53%, and the mortality rate of encephalitis patients was 50%. Old age, high C-reactive protein, elevated d-dimer, and high viral load were independent risk factors for SFTSAE. The nomogram constructed based on these four indicators had good predictive ability and could be used as an evaluation tool for clinical treatment.

Insights into the virome of Hyalomma marginatum in the Danube Delta: a major vector of Crimean-Congo hemorrhagic fever virus in Eastern Europe

BACKGROUND

Ticks are significant vectors of pathogens, including viruses, bacteria, and protozoa. With approximately 900 tick species worldwide, many are expanding their geographical range due to changing socioeconomic and climate factors. The Danube Delta, one of Europe's largest wetlands, is an ecosystem that, despite its ecological importance, remains understudied concerning the risk of introducing new tick-borne viruses. This region serves as a critical habitat for migratory birds, which can carry ticks over long distances, potentially introducing exotic tick species and their pathogens into the local ecosystem. Hyalomma marginatum ticks, the primary vector of Crimean-Congo hemorrhagic fever virus (CCHFV), are of particular concern due to their expanding presence in Europe and potential to spread other arboviruses. In addition to being the primary vector for CCHFV, Hyalomma sp. ticks are capable of transmitting other pathogens of medical and veterinary importance, including Dugbe virus, West Nile virus, African horse sickness virus, and Kyasanur forest disease virus. Therefore, it is essential to monitor the presence of Hyalomma sp. ticks while simultaneously surveilling arbovirus circulation in tick populations to mitigate the risk of arboviral outbreaks.

METHODS

In this work, we used an RNA sequencing technique to analyze the virome of H. marginatum ticks collected from the Danube Delta Biosphere Reserve, Romania, one of the major bird migration hubs from Africa to Europe.

RESULTS

Among the viral taxa detected in H. marginatum ticks, sequences belonging to Volzhskoe tick virus (VTV), Balambala tick virus (BMTV) and Bole tick virus 4 (BTV4) were identified. In addition, we report the first identification of a novel Rhabdoviridae-related virus, Hyalomma marginatum rhabdovirus (HMRV). No CCHFV or any CCHFV-related nairovirus were detected in this study.

CONCLUSIONS

To summarize, detecting new viruses is essential for monitoring potential viral outbreaks. Our research expands the understanding of virus diversity in Eastern Europe, including the identification of novel viruses. This insight is crucial for monitoring viruses that may pose risks to both animal and human health, such as CCHFV.

Pathogen isolation and traceability analysis of a fatal case of severe fever with thrombocytopenia syndrome virus (SFTSV) infectious encephalitis in China

BACKGROUND

The initial clinical symptoms of severe fever with thrombocytopenia syndrome (SFTS) mainly include high fever, thrombocytopenia and gastrointestinal symptoms, and severe patients may suffer from severe complications such as multiple organ failure, which can lead to death. Studies have shown that central nervous system symptoms are associated with severe adverse outcomes of SFTS, but there are few reports on confirmed cases of SFTS encephalitis. This is a special case in which her initial SFTS symptoms were atypical, while the disease deteriorated rapidly after the appearance of encephalitis. The purpose of this study was to report the clinical and epidemiological features of this case, isolate and trace the SFTS virus (SFTSV) strain, identify the genotype of the strain, and speculate on the infection route to provide an important reference for the diagnosis and control of SFTSV.

METHODS

Cerebrospinal fluid and serum samples were collected, multipathogen detection was performed via next-generation sequencing (NGS), and SFTSV virus isolation was performed via inoculation of the samples with Vero cells. The serum of key populations closed to patients, parasitic ticks on the surface of domestic animal bodies and environmentally free ticks were collected for SFTSV monitoring. The whole genomes of the virus strains and positive nucleic acid samples were sequenced and compared with the GenBank reference sequence to construct a phylogenetic analysis tree.

RESULTS

This patient was diagnosed with SFTSV encephalitis, and the viral strain was successfully isolated. The SFTSV strain is closely related to the Hubei strain HB2017-02, and the SFTSV M and L fragments belong to the B genotype, whereas the M fragments belong to the F genotype. In addition, the similarities of coding sequences of case strain to those of tick-carried SFTSV strain in the residence were more than 99.9%.

CONCLUSIONS

The patient was confirmed to have SFTSV-infected encephalitis and died rapidly. The SFTSV strain was of Chinese local origin, and tick bites were the most likely route of infection.

Transcriptome Profiles Characteristics of the Peripheral Immune in Patients with Severe Fever with Thrombocytopenia Syndrome

Purpose

Severe fever with thrombocytopenia syndrome (SFTS) is an acute viral infection disease with a high mortality, but there are no specific effective drugs or vaccines available for use. To develop effective treatment methods, more basic researches are urgently needed to elucidate the response mechanisms of patients.

Patients and Methods

Here, we conducted the transcriptomic analysis of peripheral immunity in 14 SFTS patients, ranging from moderate infection to severe and fatal disease.

Results

The results showed orderly cytokine signaling pathway modulation in moderate patients, cellular immunosuppression in severe patients, and significant dysregulation of the inflammatory response and coagulation dysfunction characteristic of deceased patients. In addition, WGCNA further showed a significant positive correlation between fatal outcomes and B cell and immunoglobulin mediated immune function modules, as well as a significant negative correlation with coagulation function modules.

Conclusion

Overall, our research findings systematically observed potential immune mechanisms underlying clinical symptom heterogeneity and noteworthily revealed multiple signaling pathways leading to coagulation dysfunction in fatal outcomes, not just related to decreased platelet count, which can further elucidate the interaction between viruses and hosts and contribute to clinical treatment.

Transmission of Severe Fever with Thrombocytopenia Syndrome Virus to Human from Nonindigenous Tick Host, Japan

We report a human case of severe fever with thrombocytopenia syndrome virus infection transmitted by a tick, confirmed by viral identification. Haemaphysalis aborensis, a tick species not native to Japan that has been observed to transmit the virus to humans, is now recognized as a potential vector of this virus in Japan.

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.

Ultra-rapid detection of nuclear protein of severe fever with thrombocytopenia syndrome virus by colloidal gold immunochromatography assay

In 2009, severe fever with thrombocytopenia syndrome virus (SFTSV), also known as the Dabie bandavirus (DBV), was first discovered in Henan, China. It is a tick-borne zoonotic virus with a fatality rate ranging from 6% to 30%. Currently, we lack safe and effective vaccines or antiviral drugs to treat SFTSV infection. Therefore, the development of a specific, sensitive, and cost-effective detection method is crucial. Using inactivated SFTSV and recombinant SFTSV nucleocapsid protein (SFTSV-NP), we repeatedly immunized mice with different adjuvants and obtained two monoclonal antibodies against SFTSV-NP, which were used to develop a colloidal gold immunochromatographic assay (ICA) rapid test kit for SFTSV. Compared with nucleic acid testing (gold standard), the ICA test strips are 97.67% accurate in testing clinical serum samples (36 cases of clinical serum samples and seven cases of whole blood samples). The test kit was 100% accurate in detecting different SFTSV strains. No false-positive results were generated when detecting other arboviruses. Therefore, our developed SFTSV test kit conveniently, rapidly, and effectively detects SFTSV.

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.

Severe fever with thrombocytopenia syndrome (SFTS) in Thailand: using a one health approach to respond to novel zoonosis and its implications in clinical practice

Severe fever with thrombocytopenia syndrome (SFTS), a tick-borne disease caused by Dabie bandavirus (SFTSV) is an emerging infectious disease of substantial concern in East Asia. In 2019, Ongkittikul S et al. reported the first case of SFTS in Thailand. Our report describes a One Health investigation of SFTS zoonosis examining the index case and suspected animal reservoirs using real-time RT-PCR and immunoassays. We add to the report on the first confirmed case of SFTSV infection in a human in Thailand by conducting a limited but informative One Health surveillance study. Dogs and cats tested positive for SFTSV antibody using IgG ELISA. We conclude that domestic dogs and cats might serve as potential reservoirs for SFTSV spread due to their closer proximity to the index case than other non-domestic animals. Notably, we did not detect SFTSV in synanthropic cats or dogs-nor did we detect SFTSV in Rhipicephalus sanguineus ticks-using RT-PCR. We propose that One Health investigations coupling genomic and serologic assays in response to new SFTS cases could play a pivotal role in preventing and managing SFTS among humans and animals in East Asia. As such, we are establishing a collaborative response to SFTS in Thailand through human outbreak investigations that align with principles of One Health, through environmental surveys and animal RT-PCR and immunoassays. Our investigation highlights the importance of coupling RT-PCR with seroprevalence assays as principal elements of One Health surveillance for SFTS in order to shed light on potential animal reservoirs and track emerging zoonosis.

Detection and prevalence of a novel Bandavirus related to Guertu virus in Amblyomma gemma ticks and human populations in Isiolo County, Kenya

INTRODUCTION

Emerging tick-borne viruses of medical and veterinary importance are increasingly being reported globally. This resurgence emphasizes the need for sustained surveillance to provide insights into tick-borne viral diversity and associated potential public health risks. We report on a virus tentatively designated Kinna virus (KIV) in the family Phenuiviridae and genus Bandavirus. The virus was isolated from a pool of Amblyomma gemma ticks from Kinna in Isiolo County, Kenya. High throughput sequencing of the virus isolate revealed close relatedness to the Guertu virus. The virus genome is consistent with the described genomes of other members of the genus Bandavirus, with nucleotides lengths of 6403, 3332 and 1752 in the Large (L), Medium (M) and Small (S) segments respectively. Phylogenetic analysis showed that the virus clustered with Guertu virus although it formed a distinct and well supported branch. The RdRp amino acid sequence had a 93.3% identity to that of Guertu virus, an indication that the virus is possibly novel. Neutralizing antibodies were detected in 125 (38.6%, 95% CI 33.3-44.1%) of the human sera from the communities in this region. In vivo experiments showed that the virus was lethal to mice with death occurring 6-9 days post-infection. The virus infected mammalian cells (Vero cells) but had reduced infectivity in the mosquito cell line (C636) tested.

CONCLUSION

Isolation of this novel virus with the potential to cause disease in human and animal populations necessitates the need to evaluate its public health significance and contribution to disease burden in the affected regions. This also points to the need for continuous monitoring of vector and human populations in high-risk ecosystems to update pathogen diversity.

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.

Machine learning for identifying risk of death in patients with severe fever with thrombocytopenia syndrome

Background

Severe fever with thrombocytopenia syndrome (SFTS) has attracted attention due to the rising incidence and high severity and mortality rates. This study aims to construct a machine learning (ML) model to identify SFTS patients at high risk of death early in hospital admission, and to provide early intensive intervention with a view to reducing the risk of death.

Methods

Data of patients hospitalized for SFTS in two hospitals were collected as training and validation sets, respectively, and six ML methods were used to construct the models using the screened variables as features. The performance of the models was comprehensively evaluated and the best model was selected for interpretation and development of an online web calculator for application.

Results

A total of 483 participants were enrolled in the study and 96 (19.88%) patients died due to SFTS. After a comprehensive evaluation, the XGBoost-based model performs best: the AUC scores for the training and validation sets are 0.962 and 0.997.

Conclusion

Using ML can be a good way to identify high risk individuals in SFTS patients. We can use this model to identify patients at high risk of death early in their admission and manage them intensively at an early stage.

Severe Fever with Thrombocytopenia Syndrome in South Korea, 2016-2021: Clinical Features of Severe Progression and Complications

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infection with a high case fatality rate. The serious clinical features need to be further defined. We performed a retrospective analysis among SFTS patients in South Korea during 2016-2021 to update the current status. The basic epidemiology of all reported cases was analyzed, and the detailed clinical data of the subjects were further collected from study hospitals selected in terms of their geographic location and capability of SFTS care. Cases of SFTS were reported across the country and were greatly increased since the initial endemic phase, even under the passive surveillance system. The case fatality rate remained at approximately 16.8%. Coinfections at admission were present in 7.8% of the patients. Major complications included bleeding (15.2%), hemophagocytic lymphohistiocytosis (6.7%), bacteremia or candidemia (4.0%), and invasive pulmonary aspergillosis (1.7%). It took a median 4 days from the onset of illness to hospital admission. Rapid clinical deterioration was observed with a median 1 day for intensive care unit admission, 3 days for mechanical ventilation, 4 days for renal replacement therapy, and 5 days for death, all after the hospitalization. Multivariate analysis showed that the fatality was associated with older age, bacteremia, or candidemia during hospitalization, and the presence of several variables at admission such as fever, altered mentality, aspartate aminotransferase >200 IU/L, serum creatinine level >1.2 mg/dL, and prolonged prothrombin time and activated partial thromboplastin time. Treatment options to improve clinical outcomes are limited, despite best supportive care. Specific treatment is urgently needed to change the fatal course.

Phenology and habitat associations of the invasive Asian longhorned tick from Ohio, USA

Geographically expanding and invading ticks are a global concern. The Asian longhorned tick (ALT, Haemaphysalis longicornis) was introduced to the mid-Atlantic US between 2010 and 2017 and recently invaded Ohio, an inland state. To date, ALTs in the US have been associated with livestock exsanguination and transmission of the agent of bovine theileriosis. To inform management, studies describing tick ecology and epidemiology of associated disease agents are critical. In this study, we described phenology, habitat and host associations, and tested for agents of medical and veterinary concern at the site of the first known established ALT population in Ohio, where pesticide treatment was applied in early fall 2021. In spring-fall 2022, we sampled wildlife (small mammals) and collected ticks from forest, edge, and grassland habitats. We also opportunistically sampled harvested white-tailed deer at nearby processing stations and fresh wildlife carcasses found near roads. Field-collected ALTs were tested for five agents using real-time PCR. We found that ALT nymphs emerged in June, followed by adults, and concluded with larvae in the fall. ALTs were detected in all habitats but not in wildlife. We also found a 4.88% (2/41) prevalence of Anaplasma phagocytophilum across ALT adults and nymphs. Host and habitat associations were similar to other studies in the eastern United States, but two potential differences in phenology were identified. Whether ALTs will acquire more endemic disease agents requires further investigations. Our findings provide the first evidence regarding ALT life history from the Midwest region of the United States and can inform exposure risk and guide integrated management.

Molecular mechanism and structure-guided humanization of a broadly neutralizing antibody against SFTSV

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a novel tick-borne bunyavirus that causes severe fever with thrombocytopenia syndrome (SFTS), with a high mortality rate of up to 30%. The envelope glycoproteins of SFTSV, glycoprotein N (Gn) and glycoprotein C (Gc), facilitate the recognition of host receptors and the process of membrane fusion, allowing the virus to enter host cells. We previously reported a monoclonal antibody, mAb 40C10, capable of neutralizing different genotypes of SFTSV and SFTSV-related viruses. However, the specific neutralization mechanism is poorly understood. In this study, we elucidated the high-resolution structure of the SFTSV Gn head domain in complex with mAb 40C10, confirming that the binding epitope in the domain I region of SFTSV Gn, and it represented that a novel binding epitope of SFTSV Gn was identified. Through in-depth structural and sequence analyses, we found that the binding sites of mAb 40C10 are relatively conserved among different genotypes of SFTSV and SFTSV-related Heartland virus and Guertu virus, elucidating the molecular mechanism underlying the broad-spectrum neutralizing activity of mAb 40C10. Furthermore, we humanized of mAb 40C10, which is originally of murine origin, to reduce its immunogenicity. The resulting nine humanized antibodies maintained potent affinity and neutralizing activity. One of the humanized antibodies exhibited neutralizing activity at picomolar IC50 values and demonstrated effective therapeutic and protective effects in a mouse infection model. These findings provide a novel target for the future development of SFTSV vaccines or drugs and establish a foundation for the research and development of antibody therapeutics for clinical applications.

First detection of Bandavirus dabieense in ticks collected from migratory birds in the Republic of Korea

The causative agent of severe fever with thrombocytopenia syndrome (SFTS) is Bandavirus dabieense, an emerging tick-borne zoonotic pathogen. Migratory birds have often been suggested as potential carriers of ticks that can transmit Bandavirus dabieense; however, their role remains unclear. The Republic of Korea (ROK) holds an important position as a stopover on the East Asian-Australasian Flyway. The present study aimed to investigate the potential involvement of migratory birds in the transmission of the SFTS virus (SFTSV) in the ROK. A total of 4,497 ticks were collected across various regions, including Heuksando and Daecheongdo, in the ROK, from bird migration seasons in 2022 and 2023. Genetic analysis of the SFTSV was performed for 96 ticks collected from 20 different species of migratory birds. Polymerase chain reaction (PCR) fragments of SFTSV were detected in one Haemaphysalis concinna nymph collected from a Black-faced Bunting (Emberiza spodocephala) and one Ixodes turdus nymph collected from an Olive-backed Pipit (Anthus hodgsoni) on Daecheongdo and Heuksando, respectively, during their northward migration in two spring seasons. This finding suggests that migratory birds can be considered as possible carriers and long-distance dispersers of ticks and associated tick-borne diseases. This study highlights the importance of clarifying the role and impact of migratory birds in the rapid expansion of tick-borne diseases, facilitating enhanced preparedness and the development of mitigation measures against emerging SFTS across and beyond East Asia.

Clinical and etiological characteristics of severe hemorrhagic fever caused by coinfection of hantaan orthohantavirus and severe fever with thrombocytopenia syndrome virus

Severe fever with thrombocytopenia syndrome (SFTS) and hemorrhagic fever with renal syndrome (HFRS) usually have different infection routes, and coinfection is relatively rare. This study examines the clinical and etiological characteristics of coinfection by these two pathogens to provide important references for clinical diagnosis and treatment. Blood samples from 22 clinically diagnosed patients with HFRS were collected for molecular detection of HFRS and common tick and mouse borne diseases. Inoculate the blood of six severe and critically patients into cells to isolate and proliferate potential viruses, and retest the cell culture to determine the pathogen. In addition, complete data were collected from these 22 HFRS and concurrent SFTS patients, and white blood cells (WBCs), platelet (PLT), blood urea nitrogen (BUN), creatinine (Cr) and other data were compared and analyzed. A total of 31 febrile patients, including 22 HFRS patients and 9 SFTS patients, were collected from September 2021 to October 2022. Among these HFRS patients, 11 were severe or critical. Severe and critical HFRS patients were characterized by rodent exposure history, pharyngeal and conjunctival hyperemia, abnormal WBC and PLT counts, and elevated BUN and Cr values. Virus isolation and molecular detection on blood samples from 6 patients showed that three of the six severe patients were positive for hantaan virus (HTNV), and two of the three HTNV positives were also positive for SFTS bunyavirus (SFTSV). The two coinfected patients exhibited different clinical and laboratory characteristics compared to those infected by either virus alone. Coinfection of HTNV and SFTSV leads to severe and complex hemorrhagic fever. Laboratory characteristics, such as the indicators of WBC, PLT, BUN, and Cr, may differ between HFRS and SFTS. These findings have implications and provide references for the diagnosis and treatment of coinfected cases.

Characterization of high-affinity antibodies against the surface Gc protein of Dabie bandavirus / severe fever with thrombocytopenia syndrome virus

Severe fever with thrombocytopenia syndrome virus (SFTSV) or Dabie bandavirus is an emerging pathogen responsible for SFTS. It is considered a novel threat to human health, given the high associated fatality. SFTSV is a segmented negative-strand RNA virus containing three single-stranded RNAs, with the M segment encoding the glycoproteins Gn and Gc. Gc is vital for viral entry into the host cell surface, along with the Gn protein. As the Gc is the surface-exposable antigen from virions, it is a critical diagnostic marker of infection. Although various SFTSV Gn or N protein-based sero-diagnostic methods have been developed, there are no commercially available sero-diagnostic kits. Therefore, we generated monoclonal antibodies (mAbs) against SFTSV Gc and explored their application in serum diagnostic tests to develop sensitive serodiagnostic tools covering broad-range genotypes (A to F). First, 10 SFTSV Gc antibody-binding fragments (Fabs) were isolated using a phage display system and converted into human IgGs. Enzyme-linked immunosorbent assays (ELISA) of the SFTSV and Rift Valley fever virus (RVFV: same genus as SFTSV) Gc antigens showed that all antibodies attached to the SFTSV Gc protein had high affinity. An immunofluorescence assay (IFA), to verify the cross-reactivity of seven antibodies with high affinities for various SFTSV genotypes (A, B2, B3, D, and F) and detect mAb binding with intact Gc proteins, revealed that five IgG type mAbs were bound to intact Gc proteins of various genotypes. Six high-affinity antibodies were selected using ELISA and IFA. The binding capacity of the six antibodies against the SFTSV Gc antigen was measured using surface plasmon resonance. All antibodies had high binding capacity. Consequently, these antibodies serve as valuable markers in the serological diagnosis of SFTSV.

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.

Rapid Detection of Severe Fever with Thrombocytopenia Syndrome Virus in the Acute Phase of Infection by Direct Real-Time Reverse Transcription without RNA Extraction

No specific treatment has been developed for severe fever with thrombocytopenia syndrome (SFTS). However, the prognosis can improve with early plasma exchange. Therefore, rapid and accurate detection of SFTS virus is important for diagnosis and prognosis. Direct real-time reverse transcription polymerase chain reaction (RT-PCR) testing is easier and more time-efficient than conventional real-time RT-PCR. Our study compared direct real-time RT-PCR efficiency without the RNA extraction and purification of conventional real-time RT-PCR. Samples were collected from 18 patients with SFTS and five without SFTS. A strong correlation (r = 0.774, 95% CI: 0.652-0.857, P <0.01) was found between conventional and direct real-time RT-PCR assays. Direct real-time RT-PCR showed 84.4% sensitivity and 92.0% specificity for viral detection. Direct real-time RT-PCR is an effective diagnostic tool for patients with acute phase SFTS, but further optimization is required for viral detection.

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.

Intra- and inter-host origin, evolution dynamics and spatial-temporal transmission characteristics of circoviruses

Introduction

Since their identification in 1974, circoviruses have caused clinicopathological diseases in various animal species, including humans. However, their origin, transmission, and genetic evolution remain poorly understood.

Methods

In this study, the genome sequences of circovirus were obtained from GenBank, and the Bayesian stochastic search variable selection algorithm was employed to analyzed the evolution and origin of circovirus.

Results

Here, the evolutionary origin, mode of transmission, and genetic recombination of the circovirus were determined based on the available circovirus genome sequences. The origin of circoviruses can be traced back to fish circovirus, which might derive from fish genome, and human contributes to transmission of fish circovirus to other species. Furthermore, mosquitos, ticks, bats, and/or rodents might play a role as intermediate hosts in circovirus intra- and inter-species transmission. Two major lineages (A and B) of circoviruses are identified, and frequent recombination events accelerate their variation and spread. The time to the most recent common ancestor of circoviruses can be traced back to around A.D. 600 and has been evolving at a rate of 10-4 substitutions site-1 year-1 for a long time.

Discussion

These comprehensive findings shed light on the evolutionary origin, population dynamics, transmission model, and genetic recombination of the circovirus providing valuable insights for the development of prevention and control strategies against circovirus infections.

Ecological Changes Exacerbating the Spread of Invasive Ticks has Driven the Dispersal of Severe Fever with Thrombocytopenia Syndrome Virus Throughout Southeast Asia

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne virus recognized by the World Health Organization as an emerging infectious disease of growing concern. Utilizing phylodynamic and phylogeographic methods, we have reconstructed the origin and transmission patterns of SFTSV lineages and the roles demographic, ecological, and climatic factors have played in shaping its emergence and spread throughout Asia. Environmental changes and fluctuations in tick populations, exacerbated by the widespread use of pesticides, have contributed significantly to its geographic expansion. The increased adaptability of Lineage L2 strains to the Haemaphysalis longicornis vector has facilitated the dispersal of SFTSV through Southeast Asia. Increased surveillance and proactive measures are needed to prevent further spread to Australia, Indonesia, and North America.

Analysis of early warning indicators of death in patients with severe fever with thrombocytopenia syndrome

BACKGROUND

Since its discovery, severe fever with thrombocytopenia syndrome (SFTS) has been characterized by rapid progression and poor prognosis, and no specific treatment is available. The aim of this study was to investigate the early warning indicators of mortality in SFTS patients.

METHODS

This is a retrospective cross-sectional study. The study subjects were patients who were admitted to the hospital with a confirmed diagnosis of SFTS from January 2023 to October 2023, and their clinical symptoms and signs at the time of admission, as well as the laboratory indexes of the first blood collection after admission were collected, grouped according to the prognosis, and statistically analyzed.

RESULTS

A total of 141 patients were collected, of which 27 patients died and 114 patients were in the survival group. Through statistical analysis, patients with combined hemorrhagic manifestations, disturbance of consciousness, lymphopenia, elevated lipase, and prolonged thrombin time on admission were independent risk factors for patients' death. By plotting the working characteristic curve of the subjects, as well as calculating the area under the curve, the results showed that the AUC of lymphopenia count was 0.670, 95% CI (0.563-0.776), P = 0.006; the AUC of elevated serum lipase index was 0.789, 95% CI (0.699-0.878), p < 0.001; the AUC of prolonged thrombin time was 0.749, 95% CI (0.645-0.854), p < 0.001.

CONCLUSION

Patients with hemorrhagic manifestations, disturbance of consciousness, lymphocyte reduction, elevated serum lipase, and prolonged thrombin time on admission are more worthy of the clinician's attention, and require early and effective interventions to avoid further disease progression.

Knowledge mapping of severe fever with thrombocytopenia syndrome: a bibliometric analysis

Background

Severe fever with thrombocytopenia syndrome (SFTS), caused by the Dabie bandavirus (DBV), formerly known as the SFTS virus (SFTSV), is characterized by rapid progression, high morbidity, and mortality. This study aims to analyze the current research status, hotspots, and trends of SFTS since 2009 through bibliometrics, focusing on original research and providing valuable references and inspirations for future basic research, prevention and control of SFTS.

Methods

The Web of Science Core Collection (WOSCC) was used to extract global papers on SFTS from 2009 to 2024. VOSviewer and CiteSpace software were also used to process and visualize results.

Results

A total of 760 publications relevant to SFTS were reviewed. Among these publications, the most active country, author, and publication type included China, Liu Wei, and original articles, respectively. Among the institutions, the National Institute of Infectious Diseases emerged as the top publisher. The most frequently used keywords were "China," "Bunyavirus," and "person-to-person transmission." The bibliometric analysis reviewed and summarized the research results in the field of SFTS and demonstrated the research trends in the field. In addition, the study revealed the current research hotspots and predicted the future research frontiers and potential challenges in the field of SFTS, which will provide references for further exploring and investigating the SFTS-related mechanisms and inspire new therapeutic strategies.

Conclusion

Bibliometric visualization provides an overview of research advances, hotspots, and trends regarding SFTS and consolidates existing knowledge. SFTS research is in a phase of rapid development, and the number of annual publications in the field is growing steadily and rapidly. This is laying the groundwork for further research and providing new ideas for clinicians engaged in SFTS-related therapies and researchers working to improve public health. Currently, researchers are focused on elucidating the biology of SFTS, exploring antibodies, delving into pathogenesis, and investigating specific therapies.

Deciphering the evolutionary landscape of severe fever with thrombocytopenia syndrome virus across East Asia

Severe fever with thrombocytopenia syndrome virus (SFTSV) poses a significant public health challenge in East Asia, necessitating a deeper understanding of its evolutionary dynamics to effectively manage its spread and pathogenicity. This study provides a comprehensive analysis of the genetic diversity, recombination patterns, and selection pressures across the SFTSV genome, utilizing an extensive dataset of 2041 sequences from various hosts and regions up to November 2023. Employing maximum likelihood and Bayesian evolutionary analysis by sampling trees (BEAST), we elucidated the phylogenetic relationships among nine distinct SFTSV genotypes (A, B1, B2, B3, B4, C, D, E, and F), revealing intricate patterns of viral evolution and genotype distribution across China, South Korea, and Japan. Furthermore, our analysis identified 34 potential reassortments, underscoring a dynamic genetic interplay among SFTSV strains. Genetic recombination was observed most frequently in the large segment and least in the small segment, with notable recombination hotspots characterized by stem-loop hairpin structures, indicative of a structural propensity for genetic recombination. Additionally, selection pressure analysis on critical viral genes indicated a predominant trend of negative selection, with specific sites within the RNA-dependent RNA polymerase and glycoprotein genes showing positive selection. These sites suggest evolutionary adaptations to host immune responses and environmental pressures. This study sheds light on the intricate evolutionary mechanisms shaping SFTSV, offering insights into its adaptive strategies and potential implications for vaccine development and therapeutic interventions.

Potential mechanisms implied in tick infection by arboviruses and their transmission to vertebrate hosts

Ticks can transmit many pathogens, including arboviruses, to their vertebrate hosts. Arboviruses must overcome or evade defense mechanisms during their passage from the tick gut to the hemolymph, salivary glands, and the feeding site in the host skin. This review summarizes current knowledge of defense mechanisms in specific tick tissues and at the feeding site in the host skin. We discuss the possible roles of these defense mechanisms in viral infection and transmission. The responses of tick salivary proteins to arbovirus infection are also discussed. This review provides information that may help accelerate research on virus-tick interactions.

Characterization and arbovirus susceptibility of cultured CERNI cells derived from sika deer (Cervus nippon)

Cervus nippon (sika deer) are widely distributed throughout eastern Asia. Deer possess a variety of antibodies against several zoonotic pathogens, indicating that they act as reservoir of zoonoses. In this study, we reported the characterization of cultured cells derived from sika deer and evaluated their susceptibility to arthropod-borne viruses to clarify their usefulness in virological studies. Cells derived from testicular tissue in Dulbecco's modified eagle medium with 16% fetal bovine serum started growing as primary cultured cells. The diploid cells consisted of 68 chromosomes, consistent with those of Japanese sika deer previously reported. The phylogenetic analysis showed the cells formed a robust clade with Japanese population of C. nippon, indicating that the cultured cells established in this study were originated from the Japanese sika deer. The cells immortalized by the simian virus 40 T-antigen were predominantly spindle-shaped cells exhibiting adhesive properties, and cultivated at 37°C and 5% CO2, which are common culture conditions for many mammalian cell lines. Western blotting analysis indicated that the cultured cells were multiple types of cells that coexist, including at least epithelial, fibroblast, and also Leydig cells. We confirmed that the cells have susceptibility to several arboviruses distributed in Japan: Getah virus, Japanese encephalitis virus, Oz virus, and severe fever with thrombocytopenia syndrome virus, but not to Tarumiz tick virus. From these results, the cells contribute to clarify the role of sika deer as a reservoir of zoonoses in nature and deer-associated experimental research at the cellular and molecular levels.

Global epidemiology of severe fever with thrombocytopenia syndrome virus in human and animals: a systematic review and meta-analysis

Background

Since the initial identification of the Severe Fever with Thrombocytopenia Syndrome (SFTS) in ticks in rural areas of China in 2009, the virus has been increasingly isolated from a diverse array of hosts globally, exhibiting a rising trend in incidence. This study aims to conduct a systematic analysis of the temporal and spatial distribution of SFTS cases, alongside an examination of the infection rates across various hosts, with the objective of addressing public concerns regarding the spread and impact of the disease.

Methods

In this systematic review and meta-analysis, an exhaustive search was conducted across multiple databases, including PubMed, Web of Science, Embase, and Medline, CNKI, WanFang, and CQVIP. The literature search was confined to publications released between January 1, 2009, and May 29, 2023. The study focused on collating data pertaining to animal infections under natural conditions and human infection cases reported. Additionally, species names were unified using the National Center for Biotechnology Information (NCBI) database. The notification rate, notification death rate, case fatality rate, and infection rates (or MIR) were assessed for each study with available data. The proportions were pooled using a generalized linear mixed-effects model (GLMM). Meta-regressions were conducted for subgroup analysis. This research has been duly registered with PROSPERO, bearing the registration number CRD42023431010.

Findings

We identified 5492 studies from database searches and assessed 238 full-text studies for eligibility, of which 234 studies were included in the meta-analysis. For human infection data, the overall pooled notification rate was 18.93 (95% CI 17.02-21.05) per ten million people, the overall pooled notification deaths rate was 3.49 (95% CI 2.97-4.10) per ten million people, and the overall pooled case fatality rate was 7.80% (95% CI 7.01%-8.69%). There was an increasing trend in notification rate and deaths rate, while the case fatality rate showed a significant decrease globally. Regarding animal infection data, among 94 species tested, 48 species were found to carry positive nucleic acid or antibodies. Out of these, 14 species were classified under Arthropoda, while 34 species fell under Chordata, comprising 27 Mammalia and 7 Aves.

Interpretation

This systematic review and meta-analysis present the latest global report on SFTS. In terms of human infections, notification rates and notification deaths rates are on the rise, while the case fatality rate has significantly decreased. More SFTSV animal hosts have been discovered than before, particularly among birds, indicating a potentially broader transmission range for SFTSV. These findings provide crucial insights for the prevention and control of SFTS on a global scale.

Funding

None.

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.

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.

Increased cTnI Predicts Early Death in Patients with Severe Fever with Thrombocytopenia: A Multicenter Study in North China

Background

Myocardial injury is common in severe fever with thrombocytopenia syndrome (SFTS) patients. Currently, research on the prognostic value of cardiac troponin I (cTnI) for predicting the mortality of SFTS patients, especially death within 7 days is limited.

Methods

Between May 2011 and October 2022, clinical and laboratory data on admission of consecutive SFTS cases were collected from six medical centres in China. The clinical endpoint was in-hospital all-cause death within seven days. Risk factors of myocardial injury and death were analysed using multivariable regression models. Prognostic models were established using Cox regression and performance of indicators was evaluated in terms of calibration, discrimination.

Results

A total of 1379 laboratory-confirmed patients were enrolled, in which 686 subjects were included for analysis. The median age was 66 years, with 48.1% of male. Eighty-seven patients died within seven days and 396 patients diagnosed with myocardial injury during hospitalization. Non-survivors had significant higher levels of cardiac indices than survivors, including cTnI, aspartic transaminase (AST) and lactate dehydrogenase (LDH). Elevated levels of cTnI (HR = 1.058, 95% CI:1.032-1.085), AST (HR = 1.191, 95% CI:1.150-1.234) and LDH (HR = 1.019, 95% CI:1.009-1.029) predicted risk of early in-hospital mortality. cTnI model performed best, with area under curve of 0.850 (0.774-0.926) and concordance index of 0.842, respectively. Statistical differences were found between high and low levels of cTnI for mortality (P<0.001) using 0.35 ng/mL as the optimal cut-off.

Conclusion

The risk of early in-hospital death can be predicted by cTnI. Clinical doctors should remind vigilant concerning the elevation of cardiac enzyme as soon as possible.

Comprehensive meta-analysis of severe fever with thrombocytopenia syndrome virus infections in humans, vertebrate hosts and questing ticks

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne zoonosis caused by the SFTS virus (SFTSV). Understanding the prevalence of SFTSV RNA in humans, vertebrate hosts and ticks is crucial for SFTS control.

METHODS

A systematic review and meta-analysis were conducted to determine the prevalence of SFTSV RNA in humans, vertebrate hosts and questing ticks. Nine electronic databases were searched for relevant publications, and data on SFTSV RNA prevalence were extracted. Pooled prevalence was estimated using a random effects model. Subgroup analysis and multivariable meta-regression were performed to investigate sources of heterogeneity.

RESULTS

The pooled prevalence of SFTSV RNA in humans was 5.59% (95% confidence interval [CI] 2.78-9.15%) in those in close contact (close contacts) with infected individuals (infected cases) and 0.05% (95% CI 0.00-0.65%) in healthy individuals in endemic areas. The SFTSV infection rates in artiodactyls (5.60%; 95% CI 2.95-8.96%) and carnivores (6.34%; 95% CI 3.27-10.23%) were higher than those in rodents (0.45%; 95% CI 0.00-1.50%). Other animals, such as rabbits, hedgehogs and birds, also played significant roles in SFTSV transmission. The genus Haemaphysalis was the primary transmission vector, with members of Ixodes, Dermacentor, and Amblyomma also identified as potential vectors. The highest pooled prevalence was observed in adult ticks (1.03%; 95% CI 0.35-1.96%), followed by nymphs (0.66%; 95% CI 0.11-1.50%) and larvae (0.01%; 95% CI 0.00-0.46%). The pooled prevalence in ticks collected from endemic areas (1.86%; 95% CI 0.86-3.14%) was higher than that in ticks collected in other regions (0.41%; 95% CI 0.12-0.81%).

CONCLUSIONS

Latent SFTSV infections are present in healthy individuals residing in endemic areas, and close contacts with SFTS cases are at a significantly higher risk of infection. The type of animal is linked to infection rates in vertebrate hosts, while infection rates in ticks are associated with the developmental stage. Further research is needed to investigate the impact of various environmental factors on SFTSV prevalence in vertebrate hosts and ticks.

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.

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.

Identification and characterization of three monoclonal antibodies targeting the SFTSV glycoprotein and displaying a broad spectrum recognition of SFTSV-related viruses

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a novel tick-borne viral pathogen that causes severe fever with thrombocytopenia syndrome (SFTS). The disease was initially reported in central and eastern China, then later in Japan and South Korea, with a mortality rate of 13-30%. Currently, no vaccines or effective therapeutics are available for SFTS treatment. In this study, three monoclonal antibodies (mAbs) targeting the SFTSV envelope glycoprotein Gn were obtained using the hybridoma technique. Two mAbs recognized linear epitopes and did not neutralize SFTSV, while the mAb 40C10 can effectively neutralized SFTSV of different genotypes and also the SFTSV-related Guertu virus (GTV) and Heartland virus (HRTV) by targeting a spatial epitope of Gn. Additionally, the mAb 40C10 showed therapeutic effect in mice infected with different genotypes of SFTSV strains against death by preventing the development of lesions and by promoting virus clearance in tissues. The therapeutic effect could still be observed in mice infected with SFTSV which were administered with mAb 40C10 after infection even up to 4 days. These findings enhance our understanding of SFTSV immunogenicity and provide valuable information for designing detection methods and strategies targeting SFTSV antigens. The neutralizing mAb 40C10 possesses the potential to be further developed as a therapeutic monoclonal antibody against SFTSV and SFTSV-related viruses.

Therapeutic plasma exchange combined with ribavirin to rescue critical SFTS patients

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is a zoonotic infectious disease caused by the severe fever with thrombocytopenia syndrome virus (SFTSV). Endemic in East Asia, SFTS is characterized by an exceptionally high mortality rate. Presently, there is no established treatment for SFTS, particularly for patients in critical condition. In this study, we collected and analyzed laboratory and clinical data from 92 critically ill patients with SFTS treated at Weihai Municipal Hospital between 2019 and 2022. We hope that our study will provide some hints for the treatment of critically ill patients with SFTS.

METHODS

A total of 92 critically ill patients with SFTS were included in this study. Of these patients, 45 received treatment with therapeutic plasma exchange (TPE) and ribavirin (referred to as the TPE group), while the remaining patients received only ribavirin (referred to as the non-TPE group). Clinical and laboratory parameters were analyzed retrospectively.

RESULTS

The results showed significant improvements in multiple laboratory parameters following treatment with TPE and ribavirin, including white blood cell and neutrophil count, lactate dehydrogenase, creatine kinase isoenzyme-MB, prothrombin time, activated partial thromboplastin time, D-Dimer, serum sodium and copies of virus genomes. The combination of TPE with ribavirin demonstrated a significant reduction in mortality rates, with a mortality rate of 20.0% in the TPE group compared to 40.4% in the non-TPE group (P = 0.033).

CONCLUSIONS

Our findings suggest that critically ill patients with SFTS who received TPE and ribavirin experienced improvements in both clinical and laboratory parameters. These results indicate that TPE combined with ribavirin may represent a promising novel therapeutic approach for managing critically ill patients with SFTS. However, comparative studies of large sample size or randomized clinical trials are warranted to confirm the effectiveness of this combination therapy in the treatment of severe SFTS cases.

Blood urea nitrogen to albumin ratio is a novel predictor of fatal outcome for patients with severe fever with thrombocytopenia syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is associated with a high death rate and lacks a targeted therapy plan. The ratio of blood urea nitrogen to albumin, known as BAR, is a valuable method for assessing the outlook of various infectious diseases. The objective of this research was to evaluate the effectiveness of BAR in forecasting the outcome of individuals with SFTS. Four hundred and thirty-seven patients with SFTS from two clinical centers were included in this study according to inclusion and exclusion criteria. Clinical characteristics and test parameters of SFTS patients were analyzed between survival and fatal groups. Least absolute shrinkage and selection operator (LASSO) regression and Cox regression suggested that BAR might serve as a standalone prognostic indicator for patients with SFTS in the initial phase (hazard ratio = 18.669, 95% confidence interval [CI]: 8.558-40.725, p < 0.001). And BAR had a better predictive effectiveness in clinical outcomes in patients with SFTS with an AUC of 0.832 (95% CI: 0.788-0.876, p < 0.001), a cutoff value of 0.19, a sensitivity of 0.812, and a specificity of 0.726 compared to C-reactive protein, procalcitonin, and platelet to lymphocyte ratio via receiver operating characteristic curve. KM (Kaplan Meier) curves demonstrated that high level of BAR was associated with poor survival condition in patients with SFTS. Furthermore, the high level of BAR was associated with long hospital stays and test paraments of kidney, liver, and coagulation function in survival patients. So, BAR could be used as a promising early warning biomarker of adverse outcomes in patients with SFTS.

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.

Association of liver function and prognosis in patients with severe fever with thrombocytopenia syndrome

OBJECTIVES

Severe fever with thrombocytopenia syndrome (SFTS) is an epidemic emerging infectious disease with high mortality rate. We investigated the association between liver injury and clinical outcomes in patients with SFTS.

METHODS

A total of 291 hospitalized SFTS patients were retrospectively included. Cox proportional hazards model was adopted to identify risk factors of fatal outcome and Kaplan-Meier curves were used to estimate cumulative risks.

RESULTS

60.1% of patients had liver injury at admission, and the median alanine transaminase, aspartate aminotransferase (AST), alkaline phosphatase (ALP), and total bilirubin (TBil) levels were 76.4 U/L, 152.3 U/L, 69.8 U/L and 9.9 μmol/L, respectively. Compared to survivors, non-survivors had higher levels of AST (253.0 U/L vs. 131.1 U/L, P < 0.001) and ALP (86.2 U/L vs. 67.9 U/L, P = 0.006), higher proportion of elevated ALP (20.0% vs. 4.4%, P < 0.001) and liver injury (78.5% vs. 54.9%, P = 0.001) at admission. The presence of liver injury (HR 2.049, P = 0.033) at admission was an independent risk factor of fatal outcome.

CONCLUSIONS

Liver injury was a common complication and was strongly associated with poor prognosis in SFTS patients. Liver function indicators should be closely monitored for SFTS patients.

Vaccine Development for Severe Fever with Thrombocytopenia Syndrome Virus in Dogs

Severe fever with thrombocytopenia syndrome (SFTS) is a life-threatening viral zoonosis. The causative agent of this disease is the Dabie bandavirus, which is usually known as the SFTS virus (SFTSV). Although the role of vertebrates in SFTSV transmission to humans remains uncertain, some reports have suggested that dogs could potentially transmit SFTSV to humans. Consequently, preventive measures against SFTSV in dogs are urgently needed. In the present study, dogs were immunized three times at two-week intervals with formaldehyde-inactivated SFTSV with two types of adjuvants. SFTSV (KCD46) was injected into all dogs two weeks after the final immunization. Control dogs showed viremia from 2 to 4 days post infection (dpi), and displayed white pulp atrophy in the spleen, along with a high level of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling assay (TUNEL) positive area. However, the inactivated SFTSV vaccine groups exhibited rare pathological changes and significantly reduced TUNEL positive areas in the spleen. Furthermore, SFTSV viral loads were not detected at any of the tested dpi. Our results indicate that both adjuvants can be safely used in combination with an inactivated SFTSV formulation to induce strong neutralizing antibodies. Inactivated SFTSV vaccines effectively prevent pathogenicity and viremia in dogs infected with SFTSV. In conclusion, our study highlighted the potential of inactivated SFTSV vaccination for SFTSV control in dogs.

Towards modelling tick-virus interactions using the weakly pathogenic Sindbis virus: Evidence that ticks are competent vectors

Most tick-borne viruses (TBVs) are highly pathogenic and require high biosecurity, which severely limits their study. We found that Sindbis virus (SINV), predominantly transmitted by mosquitoes, can replicate in ticks and be subsequently transmitted, with the potential to serve as a model for studying tick-virus interactions. We found that both larval and nymphal stages of Rhipicephalus haemaphysaloides can be infected with SINV-wild-type (WT) when feeding on infected mice. SINV replicated in two species of ticks (R. haemaphysaloides and Hyalomma asiaticum) after infecting them by microinjection. Injection of ticks with SINV expressing enhanced Green Fluorescent Protein (eGFP) revealed that SINV-eGFP specifically aggregated in the tick midguts for replication. During blood-feeding, SINV-eGFP migrated from the midguts to the salivary glands and was transmitted to a new host. SINV infection caused changes in expression levels of tick genes related to immune responses, substance transport and metabolism, cell growth and death. SINV mainly induced autophagy during the early stage of infection; with increasing time of infection, the level of autophagy decreased, while the level of apoptosis increased. During the early stages of infection, the transcript levels of immune-related genes were significantly upregulated, and then decreased. In addition, SINV induced changes in the transcription levels of some functional genes that play important roles in the interactions between ticks and tick-borne pathogens. These results confirm that the SINV-based transmission model between ticks, viruses, and mammals can be widely used to unravel the interactions between ticks and viruses.

Pipette-free field-deployable molecular diagnostic kit for bimodal visual detection of infectious RNA viruses

Here, we developed a field-deployable molecular diagnostic kit for the detection of RNA viruses that operates in a pipette-free manner. The kit is composed of acrylic sticks, PCR tubes, and palm-sized three-dimensional(3D)-printed heaters operated by batteries. The kit performs RNA extraction, reverse transcriptase loop-mediated isothermal amplification (RT-LAMP), and visual detection in one kit. An acrylic stick was engraved with one shallow and one deep cylindrical chamber at each end for the insertion of an FTA card and ethidium homodimer-1 (EthD-1), respectively, to perform RNA extraction/purification and bimodal visual detection of the target amplicons. First, an intercalation of EthD-1 into the target DNA initially produces fluorescence upon UV illumination. Next, the addition of a strong oxidant, in this case sodium (meta) periodate (NaIO4 ), produces intense aggregates in the presence of EthD-1-intercalated DNA, realized by electrostatic interaction. In the absence of the target amplicon, no fluorescence or aggregates are observed. Using this kit, two major infectious viruses-severe fever with thrombocytopenia syndrome virus (SFTSV) and severe acute respiratory syndrome coronavirus (SARS-CoV-2)-were successfully detected in 1 h, and the limits of detection (LOD) were approximately 1 virus μL-1 for SFTSV and 103 copies μL-1 for SARS-CoV-2 RNA. The introduced kit is portable, end-user-friendly, and can be operated in a pipette-free manner, paving the way for simple and convenient virus detection in resource-limited settings.

Vimentin cage - A double-edged sword in host anti-infection defense

Vimentin, a type III intermediate filament, reorganizes into what is termed the 'vimentin cage' in response to various pathogenic infections. This cage-like structure provides an envelope to key components of the pathogen's life cycle. In viral infections, the vimentin cage primarily serves as a scaffold and organizer for the replication factory, promoting viral replication. However, it also occasionally contributes to antiviral functions. For bacterial infections, the cage mainly supports bacterial proliferation in most observed cases. These consistent structural alterations in vimentin, induced by a range of viruses and bacteria, highlight the vimentin cage's crucial role. Pathogen-specific factors add complexity to this interaction. In this review, we provide a thorough overview of the functions and mechanisms of the vimentin cage and speculate on vimentin's potential as a novel target for anti-pathogen strategies.

Human Tick-Borne Diseases and Advances in Anti-Tick Vaccine Approaches: A Comprehensive Review

This comprehensive review explores the field of anti-tick vaccines, addressing their significance in combating tick-borne diseases of public health concern. The main objectives are to provide a brief epidemiology of diseases affecting humans and a thorough understanding of tick biology, traditional tick control methods, the development and mechanisms of anti-tick vaccines, their efficacy in field applications, associated challenges, and future prospects. Tick-borne diseases (TBDs) pose a significant and escalating threat to global health and the livestock industries due to the widespread distribution of ticks and the multitude of pathogens they transmit. Traditional tick control methods, such as acaricides and repellents, have limitations, including environmental concerns and the emergence of tick resistance. Anti-tick vaccines offer a promising alternative by targeting specific tick proteins crucial for feeding and pathogen transmission. Developing vaccines with antigens based on these essential proteins is likely to disrupt these processes. Indeed, anti-tick vaccines have shown efficacy in laboratory and field trials successfully implemented in livestock, reducing the prevalence of TBDs. However, some challenges still remain, including vaccine efficacy on different hosts, polymorphisms in ticks of the same species, and the economic considerations of adopting large-scale vaccine strategies. Emerging technologies and approaches hold promise for improving anti-tick vaccine development and expanding their impact on public health and agriculture.

Heartland Virus Disease-An Underreported Emerging Infection

First recognized 15 years ago, Heartland virus disease (Heartland) is a tickborne infection contracted from the transmission of Heartland virus (HRTV) through tick bites from the lone star tick (Amblyomma americanum) and potentially other tick species. Heartland symptoms include a fever <100.4 °F, lethargy, fatigue, headaches, myalgia, a loss of appetite, nausea, diarrhea, weight loss, arthralgia, leukopenia and thrombocytopenia. We reviewed the existing peer-reviewed literature for HRTV and Heartland to more completely characterize this rarely reported, recently discovered illness. The absence of ongoing serosurveys and targeted clinical and tickborne virus investigations specific to HRTV presence and Heartland likely contributes to infection underestimation. While HRTV transmission occurs in southern and midwestern states, the true range of this infection is likely larger than now understood. The disease's proliferation benefits from an expanded tick range due to rising climate temperatures favoring habitat expansion. We recommend HRTV disease be considered in the differential diagnosis for patients with a reported exposure to ticks in areas where HRTV has been previously identified. HRTV testing should be considered early for those matching the Heartland disease profile and nonresponsive to initial broad-spectrum antimicrobial treatment. Despite aggressive supportive therapy, patients deteriorating to sepsis early in the course of the disease have a very grim prognosis.

Current Progress of Severe Fever with Thrombocytopenia Syndrome Virus (SFTSV) Vaccine Development

SFTSV is an emerging tick-borne virus causing hemorrhagic fever with a case fatality rate (CFR) that can reach up to 27%. With endemic infection in East Asia and the recent spread of the vector tick to more than 20 states in the United States, the SFTSV outbreak is a globally growing public health concern. However, there is currently no targeted antiviral therapy or licensed vaccine against SFTSV. Considering the age-dependent SFTS pathogenesis and disease outcome, a sophisticated vaccine development approach is required to safeguard the elderly population from lethal SFTSV infection. Given the recent emergence of SFTSV, the establishment of animal models to study immunogenicity and protection from SFTS symptoms has only occurred recently. The latest research efforts have applied diverse vaccine development approaches-including live-attenuated vaccine, DNA vaccine, whole inactivated virus vaccine, viral vector vaccine, protein subunit vaccine, and mRNA vaccine-in the quest to develop a safe and effective vaccine against SFTSV. This review aims to outline the current progress in SFTSV vaccine development and suggest future directions to enhance the safety and efficacy of these vaccines, ensuring their suitability for clinical application.

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.