Systematic review of severe fever with thrombocytopenia syndrome: virology, epidemiology, and clinical characteristics

Factors Associated With the Spatial Distribution of Severe Fever With Thrombocytopenia Syndrome in Zhejiang Province, China: Risk Analysis Based on Maximum Entropy

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease that was first identified in mainland China in 2009 and has been reported in Zhejiang Province, China, since 2011. However, few studies have focused on the association between ticks, host animals, and SFTS.

Objective

In this study, we analyzed the influence of meteorological and environmental factors as well as the influence of ticks and host animals on SFTS. This can serve as a foundational basis for the development of strategic policies aimed at the prevention and control of SFTS.

Methods

Data on SFTS incidence, tick density, cattle density, and meteorological and environmental factors were collected and analyzed using a maximum entropy-based model.

Results

As of December 2019, 463 laboratory-confirmed SFTS cases were reported in Zhejiang Province. We found that the density of ticks, precipitation in the wettest month, average temperature, elevation, and the normalized difference vegetation index were significantly associated with SFTS spatial distribution. The niche model fitted accurately with good performance in predicting the potential risk areas of SFTS (the average test area under the receiver operating characteristic curve for the replicate runs was 0.803 and the SD was 0.013). The risk of SFTS occurrence increased with an increase in tick density, and the response curve indicated that the risk was greater than 0.5 when tick density exceeded 1.4. The risk of SFTS occurrence decreased with increased precipitation in the wettest month, and the risk was less than 0.5 when precipitation exceeded 224.4 mm. The relationship between elevation and SFTS occurrence showed a reverse V shape, and the risk peaked at approximately 400 m.

Conclusions

Tick density, precipitation, and elevation were dominant influencing factors for SFTS, and comprehensive intervention measures should be adjusted according to these factors to reduce SFTS incidence in Zhejiang Province.

Prevalence, Isolation, and Molecular Characterizationof Severe Fever with Thrombocytopenia Syndrome Virus in Cattle from the Republic of Korea

Background: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne disease caused by Bandavirus dabieense. Initially identified in China, this disease has spread throughout Asian countries via tick bites and animal-to-human transmission. However, reports of the prevalence of SFTS virus (SFTSV) in cattle in Korea are lacking. This study aimed to investigate SFTSV infections in grazing cattle in the Republic of Korea (ROK). Materials and Methods: In total, 845 grazing cattle serum samples were collected over 2 years (2019 and 2020) in the ROK, and viral RNA was extracted using a kit. One-step RT-nested PCR was performed to amplify the S-segment of SFTSV. Positive serum samples were used to isolate SFTSV in Vero E6 cells, and the full sequences were analyzed. A phylogenetic tree was constructed using the maximum-likelihood method with MEGA X. In addition, immunoglobulin G antibodies against SFTSV were investigated using an enzyme-linked immunosorbent assay. Results: Here, 4.0% of serum samples (34/845) were positive for SFTSV S-segments, and one virus isolate was cultured in Vero E6 cells. Phylogenetic analysis based on the partial S-segment classified 4 SFTSV isolates as the B-2 genotype, 9 as the B-3 genotype, 18 as an unclassified B genotype, and 3 as the D genotype. One cultured virus was classified as the B-2 genotype based on SFTSV L-, M-, and S-segments. Antibody detection results showed that 21.1% of serum samples (161/763) were positive for SFTSV. Conclusion: To the best of our knowledge, this is the first study performed to identify the prevalence of SFTSV in grazing cattle in the ROK. Our findings indicate the necessity for more intensive and continuous SFTSV monitoring, not only in cattle but also in other animals, to comprehend the genetic diversity of the virus and its potential eco-epidemiological impact on human health.

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.

Bunyavirus SFTSV NSs utilizes autophagy to escape the antiviral innate immune response

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

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.

Seroprevalence for severe fever with thrombocytopenia syndrome virus among the residents of Miyazaki, Japan: An epidemiological study

INTRODUCTION

Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne infectious disease caused by the SFTS virus (SFTSV). The Miyazaki Prefecture has the highest number of SFTS cases in Japan and requires countermeasures for prevention. In this study, we aimed to conduct an epidemiological survey in Miyazaki Prefecture to determine the exposure conditions of SFTSV by measuring the seroprevalence among residents of Miyazaki and to evaluate the factors that influence the endemicity of SFTS.

METHODS

The survey was conducted between June 2014 and April 2019 in all 26 municipalities in Miyazaki Prefecture. SFTSV antibodies were detected using an enzyme-linked immunosorbent assay in the blood samples of 6013 residents (3184 men and 2829 women). A questionnaire-based survey of the living environment was also conducted.

RESULTS

Multiple logistic regression analysis revealed that age and occupation were significant factors related to the proportion of participants with an optical density (OD) value > 0.2 and a seroprevalence of 0.9 % (54/6013). Seven seropositive individuals (0.1 %) with an OD value of >0.4 were identified (three men and four women, aged 54-69 years), and all were asymptomatic. One participant had a higher OD than the positive control.

CONCLUSION

Although SFTS is endemic in Miyazaki Prefecture, Japan, its seroprevalence is relatively low. Since some risk areas in Miyazaki prefecture have been identified, it is important to enhance awareness of SFTS in residences and reduce contact with ticks, especially in high-risk areas.

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.

Correlation between the Cycle Threshold Values in Detection of Severe Fever with Thrombocytopenia Syndrome Virus Using PowerChekTM SFTSV Real-Time PCR Kit and Viral Load: Prognostic Implications

BACKGROUND

This study aimed to analyze the correlation between the cycle threshold (Ct) values of severe fever with thrombocytopenia syndrome (SFTS) virus small (S) and middle (M) segments and the SFTS viral load, aiming to estimate the initial viral load and predict prognosis in the early clinical course.

METHOD

A retrospective study was conducted with confirmed SFTS patients at Jeju National University Hospital (2016-2022). Patients were categorized into non-fatal and fatal groups.

RESULTS

This study included 49 patients with confirmed SFTS (non-fatal group, n = 42; fatal group, n = 7). A significant negative correlation (-0.783) was observed between the log SFTS viral load and Ct values (p < 0.001). This negative correlation was notably stronger in the fatal group (correlation coefficient -0.940) than in the non-fatal group (correlation coefficient -0.345).

CONCLUSION

In this study, we established a correlation between SFTS viral load and Ct values for estimating the initial viral load and early predicting prognosis. These results are expected to offer valuable insights for SFTS patient treatment and prognosis prediction.

Antiviral immunity of severe fever with thrombocytopenia syndrome: current understanding and implications for clinical treatment

Dabie Banda virus (DBV), a tick-borne pathogen, was first identified in China in 2009 and causes profound symptoms including fever, leukopenia, thrombocytopenia and multi-organ dysfunction, which is known as severe fever with thrombocytopenia syndrome (SFTS). In the last decade, global incidence and mortality of SFTS increased significantly, especially in East Asia. Though previous studies provide understandings of clinical and immunological characteristics of SFTS development, comprehensive insight of antiviral immunity response is still lacking. Here, we intensively discuss the antiviral immune response after DBV infection by integrating previous ex- and in-vivo studies, including innate and adaptive immune responses, anti-viral immune responses and long-term immune characters. A comprehensive overview of potential immune targets for clinical trials is provided as well. However, development of novel strategies for improving the prognosis of the disease remains on challenge. The current review may shed light on the establishment of immunological interventions for the critical disease SFTS.

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

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

Tick Diversity and Pathogen Transmission in Daejeon, Korea: Implications from Companion Animals and Walking Trails

With the ongoing global warming-induced climate change, there has been a surge in vector-borne diseases, particularly tick-borne diseases (TBDs). As the population of companion animals grows, there is growing concern from a One Health perspective about the potential for these animals to spread TBDs. In this study, ticks were collected from companion animals and the surrounding environment in Daejeon Metropolitan City, Korea, using flagging and dragging, and CO2 trap methods. These ticks were then subjected to conventional (nested) PCR for severe fever with thrombocytopenia syndrome virus (SFTSV), Anaplasma spp., Ehrlichia spp., and Borrelia spp. We identified a total of 29,176 ticks, consisting of three genera and four species: H. longicornis, H. flava, I. nipponensis, and A. testudinarium. Notably, H. longicornis was the predominant species. The presence of A. testudinarium suggested that the species traditionally found in southern regions are migrating northward, likely as a result of climate change. Our PCR results confirmed the presence of all four pathogens in both companion animals and the surrounding environment, underscoring the potential for the indirect transmission of tick-borne pathogens to humans through companion animals. These findings emphasize the importance of the ongoing surveillance of companion animals in the management and control of TBDs.

Characterization of antibodies targeting severe fever with thrombocytopenia syndrome virus glycoprotein Gc

Severe fever with thrombocytopenia syndrome (SFTS) is a hemorrhagic fever caused by SFTS virus (SFTSV), which is primarily found in East Asian countries. Despite its high mortality rate and increasing incidence, no vaccines or therapeutics have yet been approved for use against SFTS. Antibody drugs have shown promise in treating lethal infectious diseases that currently have no established treatments. In the case of SFTS, however, only a limited amount of research has been done on SFTSV-neutralizing antibodies targeting the transmembrane proteins Gn and Gc, which play critical roles in viral infection. This study focuses on the production and characterization of antibodies targeting the SFTSV Gc protein. Monoclonal antibodies against Gc were generated through immunization of mice, and their antiviral activity was evaluated. Three out of four anti-Gc antibody clones from this study demonstrated dose-dependent SFTSV neutralization activity, two of which exhibited a synergistic effect on the neutralization activity of the anti-Gn antibody clone Mab4-5. Further studies are necessary to identify key sites on the SFTSV glycoprotein and to develop novel agents as well as antibodies with diverse mechanisms of action against SFTSV.

A person-to-person transmission cluster of severe fever with thrombocytopenia syndrome characterized by mixed viral infections with familial and nosocomial clustering

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infectious disease with sporadic occurrence and high mortality. Herein, we report an example of the in-hospital transmission of SFTS virus (SFTSV) infections with familial and nosocomial clustering in Zhejiang Province, eastern China, from March to April 2023. The epidemiological investigation and genomic analysis revealed that at least eight suspected cases of SFTS occurred in this cluster, including one death and one asymptomatic case. Our report reemphasizes the risk of familial and nosocomial SFTSV infections in healthcare settings and the urgent need for the long-term systematic surveillance of SFTSV evolution in humans and animals in the eastern coastal regions of China.

Systemic inflammatory response syndrome in patients with severe fever with thrombocytopenia syndrome: prevalence, characteristics, and impact on prognosis

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging zoonosis with a high fatality rate in China. Previous studies have reported that dysregulated inflammatory response is associated with disease pathogenesis and mortality in patients with SFTS. This investigation aimed to evaluate the prevalence and characteristics of systemic inflammatory response syndrome (SIRS), and its impact on prognosis.

METHODS

Data on demographic characteristics, comorbid conditions, clinical manifestations, laboratory parameters, and survival time of patients with SFTS were collected. Patients were divided into the non-SIRS and SIRS groups according to the presence of SIRS, then their clinical data were compared.

RESULTS

A total of 290 patients diagnosed with SFTS were retrospectively enrolled, including 126(43.4%) patients with SIRS. Patients in the non-survivor group had more prevalence of SIRS than patients in the survivor group (P < 0.001), and SIRS (adjusted OR 2.885, 95% CI 1.226-6.786; P = 0.005) was shown as an independent risk factor for prognosis of patients with SFTS. Compared with patients without SIRS, patients with SIRS had lower WBC and neutrophils counts, and fibrinogen levels, but higher AST, LDH, amylase, lipase, CK, CK-MB, troponin I, APTT, thrombin time, D-dimer, CRP, IL-6, SAA levels, and viral load. The cumulative survival rate of patients with SIRS was significantly lower than that of patients without SIRS. Patients with SIRS also showed a higher incidence of bacterial or fungal infections than patients without SIRS.

CONCLUSIONS

SIRS is highly frequent in patients with SFTS, and it is associated with high mortality.

A nanoluciferase SFTSV for rapid screening antivirals and real-time visualization of virus infection in mice

BACKGROUND

Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging tick-borne pathogen that causes severe hemorrhagic fever in humans, but no FDA-approved specific antivirals or vaccines are available to treat or prevent SFTS.

METHODS

The plasmids construction and transfection were performed to generate the recombinant SFTSV harboring the nanoluciferase gene (SFTSV-Nluc). Immunostaining plaque assay was performed to measure viral titers, and DNA electrophoresis and Sanger sequencing were performed to evaluate the genetic stability. Luciferase assay and quantitative RT-PCR were performed to evaluate the efficacy of antivirals in vitro. Bioluminescence imaging, titration of virus from excised organs, hematology, and histopathology and immunohistochemistry were performed to evaluate the efficacy of antivirals in vivo.

FINDINGS

SFTSV-Nluc exhibited high genetic stability and replication kinetics similar to those of wild-type virus (SFTSVwt), then a rapid high-throughput screening system for identifying inhibitors to treat SFTS was developed, and a nucleoside analog, 4-FlU, was identified to effectively inhibit SFTSV in vitro. SFTSV-Nluc mimicked the replication characteristics and localization of SFTSVwt in counterpart model mice. Bioluminescence imaging of SFTSV-Nluc allowed real-time visualization and quantification of SFTSV replication in the mice. 4-FlU was demonstrated to inhibit the replication of SFTSV with more efficiency than T-705 and without obvious adverse effect in vivo.

INTERPRETATION

The high-throughput screening system based on SFTSV-Nluc for use in vitro and in vivo revealed that a safe and effective antiviral nucleoside analog, 4-FlU, may be a basis for the strategic treatment of SFTSV and other bunyavirus infections, paving the way for the discovery of antivirals.

FUNDING

This work was supported by grants from the National Key Research and Development Plan of China (2021YFC2300700 to L. Zhang, 2022YFC2303300 to L. Zhang), Strategic Priority Research Program of Chinese Academy of Sciences (XDB0490000 to L. Zhang), National Natural Science Foundation of China (31970165 to L. Zhang, U22A20379 to G. Xiao), the Science and Technology Commission of Shanghai Municipality (21S11903100 to Y. Xie), Hubei Natural Science Foundation for Distinguished Young Scholars (2022CFA099 to L. Zhang).

Metatranscriptomics Reveals the RNA Virome of Ixodes Persulcatus in the China-North Korea Border, 2017

In recent years, numerous viruses have been identified from ticks, and some have been linked to clinical cases of emerging tick-borne diseases. Chinese northeast frontier is tick infested. However, there is a notable lack of systematic monitoring efforts to assess the viral composition in the area, leaving the ecological landscape of viruses carried by ticks not clear enough. Between April and June 2017, 7101 ticks were collected to perform virus surveillance on the China-North Korea border, specifically in Tonghua, Baishan, and Yanbian. A total of 2127 Ixodes persulcatus were identified. Further investigation revealed the diversity of tick-borne viruses by transcriptome sequencing of Ixodes persulcatus. All ticks tested negative for tick-borne encephalitis virus. Transcriptome sequencing expanded 121 genomic sequence data of 12 different virus species from Ixodes persulcatus. Notably, a new segmented flavivirus, named Baishan Forest Tick Virus, were identified, closely related to Alongshan virus and Harz mountain virus. Therefore, this new virus may pose a potential threat to humans. Furthermore, the study revealed the existence of seven emerging tick-borne viruses dating back to 2017. These previously identified viruses included Mudanjiang phlebovirus, Onega tick phlebovirus, Sara tick phlebovirus, Yichun mivirus, and three unnamed viruses (one belonging to the Peribunyaviridae family and the other two belonging to the Phenuiviridae family). The existence of these emerging tick-borne viruses in tick samples collected in 2017 suggests that their history may extend further than previously recognized. This study provides invaluable insights into the virome of Ixodes persulcatus in the China-North Korea border region, enhancing our ongoing efforts to manage the risks associated with tick-borne viruses.

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

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

Evaluation of reverse transcription loop-mediated isothermal amplification assay for the detection of severe fever with thrombocytopenia syndrome in clinical laboratories: A single-center study

Severe fever with thrombocytopenia syndrome (SFTS) is an acute infectious disease prevalent in East Asia with a high mortality rate (5%-30%). Reverse transcription loop-mediated isothermal amplification (RT-LAMP), a rapid nucleic acid-based diagnostic technique, is a useful alternative for the clinical diagnosis of SFTS, particularly in resource-limited hospitals or rural clinics in SFTS virus-endemic regions. However, the actual clinical sensitivity and specificity of RT-LAMP remain unclear. This study evaluated the field application of RT-LAMP. This prospective field study included 130 patients with laboratory-confirmed SFTS from Yantai, Shandong Province, China. Two sets of RT-LAMP primers were validated, and one set of RT-LAMP assays was optimized for field detection. Nucleic acids of serially collected serum/plasma samples were identified using quantitative reverse transcription polymerase chain reaction (RT-qPCR) and RT-LAMP. In laboratory tests, we optimized the detection time of primer set 2 for the RT-LAMP to 60 min. Notably, the onsite testing of 279 plasma samples from patients with SFTS revealed that the sensitivity and specificity of the test were 81.9% and 96.3%, respectively. We also analyzed samples with different durations of the disease, and our study showed that the sensitivity of RT-LAMP detection at the beginning of admission was 89.92%. Univariate analysis showed that the detection rate of RT-LAMP was similar to that of RT-qPCR in the first 5 days of the disease course and was lower than that of RT-qPCR on Days 6 and 14-15 of the disease course. The positive detection rate in patients aged ≥ 65 years was significantly higher than that in younger age groups. RT-LAMP is a simple, suitable, and rapid clinical detection method of SFTS onsite screening. It is more suitable for screening patients in the early stages of the disease and analyzing samples obtained from patients aged ≥ 65 years before the 6th day of the disease course.

A Case of Severe Fever With Thrombocytopenia Syndrome With Recurrent Shock and Erythema

Severe fever with thrombocytopenia syndrome (SFTS) is a fatal infectious disease often transmitted through tick bites and exposure to fluids from infected individuals. Early diagnosis is critical due to the high mortality rates of the disease; however, it might be challenging if a patient's history of tick contact is unclear. We report a detailed diagnosis of SFTS in a 69-year-old man with atypical symptoms but without identifiable tick bites. The diagnosis was made on the basis of massive diarrhea, recurrent shock, and unusual erythema presentation following hospital admission.

The ecological and etiological investigation of ticks and rodents in China: results from an ongoing surveillance study in Zhejiang Province

OBJECTIVES

This study aimed to analyze the population density of vector ticks and reservoir hosts rodents, and to investigate the relevant pathogen infection in Zhejiang Province, China.

METHODS

In this surveillance study, the data of ticks density were collected with the tick picking method on animal body surface and the drag-flag method, while the rodent density with the night trapping method. The samples of ticks were examined for the severe fever with thrombocytopenia syndrome virus (SFTSV), and blood serum and organs from rodents were subjected for SFTSV, hantavirus, Leptospira, Orientia tsutsugamushi (O. tsutsugamushi) and Yersinia pestis (Y. pestis) screening in the laboratory.

RESULTS

From 2017 to 2022 in Zhejiang Province, 16,230 parasitic ticks were found in 1848 positive animals, with the density of parasitic ticks of 1.29 ticks per host animal, and a total of 5,201 questing ticks were captured from 1,140,910 meters of vegetation distance with the questing tick density of 0.46 ticks/flag·100 m. Haemaphysalis longicornis (H. longicornis) was the major species. A total of 2,187,739 mousetraps were distributed and 12,705 rodents were trapped, with the density of 0.58 per 100 trap-nights. Rattus norvegicus was the major species. For SFTSV screening, two groups nymphal ticks of H. longicornis were tested to be positive. For the rodents samples, the Leptospira had a positive rate of 12.28% (197/1604), the hantavirus was 1.00% (16/1604), and the O. tsutsugamushi was 0.15% (2/1332). No positive results were found with SFTSV and Y. pestis in the rodents samples.

CONCLUSION

Findings from this study indicated that the ticks and rodents were widely distributed in Zhejiang Province. Particularly, the positive detection of SFTSV, Leptospira, hantavirus and O. tsutsugamushi in ticks or rodents from this area suggested that more attention should be paid to the possibilities of relevant vector-borne diseases occurrence.

Prevalence and clinical characteristics of increased pancreatic enzymes in patients with severe fever with thrombocytopenia syndrome

BACKGROUND AND AIM

The increased pancreatic enzymes have recently been reported in patients with severe fever with thrombocytopenia syndrome (SFTS). However, its significance has not been elucidated clearly. The aim of this study was to explore the prevalence, clinical characteristics of elevated pancreatic enzymes (amylase and lipase) and its association with AP in patients with SFTS.

METHODS

Data of demographics, comorbid conditions, clinical symptoms, laboratory parameters and survival time of patients with SFTS were collected. Patients were assigned into the non-AP and AP groups according to the diagnostic criteria of AP. Patients in the non-AP group were divided into the normal (3×ULN) groups according to the serum amylase and lipase levels, and then their clinical data were compared.

RESULTS

A total of 284 patients diagnosed with SFTS were retrospectively enrolled, including 248 patients in the non-AP group and 36 patients in the AP group. Patients in the non-AP group were composed of 48, 116 and 84 patients in the normal, EPE and HPE groups, respectively. Compared with patients in the normal and EPE groups, patients in the HPE group had higher serum levels of laboratory parameters referring to liver, kidney, heart and coagulation system injury, as well as higher viral load. The cumulative survival rate of patients in the HPE group was significantly lower than that of patients in the normal group. In addition, patients in the AP group also had higher serum levels of laboratory variables reflecting liver, heart, coagulation dysfunction and viral load than patients in the HPE group. The cumulative survival rate of patients in the AP group was significantly lower than that of patients in the HPE group.

CONCLUSION

The increased pancreatic enzymes are very common in patients with SFTS, but they are not always associated with AP. Though AP accounts for the majority of deaths for patients with elevated pancreatic enzymes, patients with pancreatic enzymes >3×ULN except for AP also have a high in-hospital mortality rate.

mRNA vaccine encoding Gn provides protection against severe fever with thrombocytopenia syndrome virus in mice

We developed a promising mRNA vaccine against severe fever with thrombocytopenia syndrome (SFTS), an infectious disease caused by the SFTS virus that is primarily transmitted through tick bites. Administration of lipid nanoparticle-encapsulated mRNA-Gn successfully induced neutralizing antibodies and T-cell responses in mice. The vaccinated mice were protected against a lethal SFTS virus challenge, suggesting that this mRNA vaccine may be an effective and successful SFTS vaccine candidate.

Identification of tanshinone I as cap-dependent endonuclease inhibitor with broad-spectrum antiviral effect

IMPORTANCE

The spread of avian-borne, tick-borne, and rodent-borne pathogens has the potential to pose a serious threat to human health, and candidate vaccines as well as therapeutics for these pathogens are urgently needed. Tanshinones, especially tanshinone I, were identified as a cap-dependent endonuclease inhibitor with broad-spectrum antiviral effects on negative-stranded, segmented RNA viruses including bandavirus, orthomyxovirus, and arenavirus from natural products, implying an important resource of candidate antivirals from the traditional Chinese medicines. This study supplies novel candidate antivirals for the negative-stranded, segmented RNA virus and highlights the endonuclease involved in the cap-snatching process as a reliable broad-spectrum antiviral target.

Clinical characteristics and outcomes of acute kidney injury in patients with severe fever with thrombocytopenia syndrome

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging zoonosis caused by a novel bunyavirus. Until recently, the SFTS related acute kidney injury (AKI) was largely unexplored. This study aimed to investigate the clinical characteristics and outcomes of AKI in patients with SFTS.

Methods

The non-AKI and AKI groups were compared in terms of general characteristics, clinical features, laboratory parameters and cumulative survival rate. The independent risk factors for in-hospital mortality in patients with SFTS were analyzed by multivariate logistic regression to identify the population with poor prognosis.

Results

A total of 208 consecutive patients diagnosed with SFTS were enrolled, including 153 (73.6%) patients in the non-AKI group and 55 (26.4%) patients in the AKI group. Compared with patients without AKI, patients with AKI were older and had a higher frequency of diabetes. Among these laboratory parameters, platelet count, albumin and fibrinogen levels of patients with AKI were identified to be significantly lower than those of patients without AKI, while ALT, AST, ALP, triglyceride, LDH, BUN, uric acid, creatine, Cys-C, β2-MG, potassium, AMY, lipase, CK-MB, TnI, BNP, APTT, thrombin time, D-dimer, CRP, IL-6, PCT and ESR levels were significantly higher in patients with AKI. A higher SFTS viral load was also detected in the AKI patients than in the non-AKI patients. The cumulative survival rates of patients at AKI stage 2 or 3 were significantly lower than those of patients without AKI or at AKI stage 1. However, there was no significant difference in the cumulative survival rates between patients without AKI and those with stage 1 AKI. Univariate and multivariate binary logistic regression analyses demonstrated that stage 2 or 3 AKI was an independent risk factor for in-hospital mortality in patients with SFTS.

Conclusion

AKI is associated with poor outcomes in patients with SFTS, especially patients at AKI stage 2 or 3, who generally have high mortality. Our findings support the importance of early identification and timely treatment of AKI in patients with SFTS.

Metagenomic next-generation sequencing for diagnosis and efficacy evaluation of a critical case of SFTS complicated by invasive pulmonary aspergillosis

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by SFTS virus (SFTSV). SFTS patients were prone to invasive pulmonary aspergillosis (IPA), which was directly related to increased mortality. Here, we present a critical case of SFTS complicated by IPA in a previously healthy 58-year-old woman. On day 1, SFTSV and three different Aspergillus species were both detected in the patient's bronchoalveolar lavage fluid and blood through metagenomic next-generation sequencing (mNGS). After 17 days of treatment, the patient was still in poor condition and A. fumigatus was once again detected in her blood through mNGS. Then her family decided to give up treatment because of financial problems and grave prognosis. She was discharged home and died the next day. Medical personnel should be alter to the possibility of IPA in SFTS patients due to its high mortality. mNGS may be used as an auxiliary diagnostic tool and efficacy-monitoring method for suspected SFTS complicated by IPA.

Risk Factors for Death in Patients with Severe Fever with Thrombocytopenia Syndrome

To establish a Cox regression model predicting risk factors for mortality in patients with severe fever with thrombocytopenia syndrome (SFTS), a total of 109 SFTS patients treated at The Second Hospital of Nanjing between June 2016 and October 2020 were included in this study. The patients were categorized into survival (n = 82) and death (n = 27) groups, and the clinical manifestations on admission and laboratory examination were collected. The factors associated with the mortality risk of SFTS patients were explored by univariate and binary logistic regression analyses. The receiver operating characteristic curve was used to evaluate the predictive value of independent influencing factors and the STFS scoring system. Univariate screening showed that the putative influencing factors were age, Acute Physiology and Chronic Health Evaluation II (APACHE II) score, invasive mechanical ventilation, continuous renal replacement therapy, application of vasoactive medications, absolute count of lymphocytes, count of platelets, and levels of albumin and D-dimer (P < 0.05). Binary logistic regression showed that age (P = 0.042), APACHE II score (P = 0.030), and vasoactive medications (P = 0.035) were independent risk factors in SFTS patients. The combined prediction equation for the mortality risk of SFTS patients was "Combined predictor = age + 3.162 × APACHE II score + 22.306 × vasoactive medications," and the predictive value of combined predictor was greater than that of age (P = 0.004) or APACHE II score (P < 0.001). The combination of age, APACHE II score, and vasoactive medications had the highest ability to predict the risk of death. The STFS scoring system could make the clinical application of independent risk factors feasible.

Risk factors associated with death due to severe fever with thrombocytopenia syndrome in hospitalized Korean patients (2018-2022)

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) has no vaccine or treatment and an extremely high fatality rate. We aimed to analyze and evaluate the risk factors for death associated with SFTS.

METHODS

Among reports from 2018 to 2022, we compared and analyzed 1,034 inpatients aged 18 years or older with laboratory-confirmed SFTS who underwent complete epidemiological investigations.

RESULTS

Most of the inpatients with SFTS were aged 50 years or older (average age, 67.6 years). The median time from symptom onset to death was 9 days, and the average case fatality rate was 18.5%. Risk factors for death included age of 70 years or older (odds ratio [OR], 4.82); agriculture-related occupation (OR, 2.01); underlying disease (OR, 7.20); delayed diagnosis (OR, 1.28 per day); decreased level of consciousness (OR, 5.53); fever/chills (OR, 20.52); prolonged activated partial thromboplastin time (OR, 4.19); and elevated levels of aspartate aminotransferase (OR, 2.91), blood urea nitrogen (OR, 2.62), and creatine (OR, 3.21).

CONCLUSION

The risk factors for death in patients with SFTS were old age; agriculture-related occupation; underlying disease; delayed clinical suspicion; fever/chills; decreased level of consciousness; and elevated activated partial thromboplastin time, aspartate aminotransferase, blood urea nitrogen, and creatine levels.

Heterologous vaccination utilizing viral vector and protein platforms confers complete protection against SFTSV

Severe fever with thrombocytopenia syndrome virus was first discovered in 2009 as the causative agent of severe fever with thrombocytopenia syndrome. Despite its potential threat to public health, no prophylactic vaccine is yet available. This study developed a heterologous prime-boost strategy comprising priming with recombinant replication-deficient human adenovirus type 5 (rAd5) expressing the surface glycoprotein, Gn, and boosting with Gn protein. This vaccination regimen induced balanced Th1/Th2 immune responses and resulted in potent humoral and T cell-mediated responses in mice. It elicited high neutralizing antibody titers in both mice and non-human primates. Transcriptome analysis revealed that rAd5 and Gn proteins induced adaptive and innate immune pathways, respectively. This study provides immunological and mechanistic insight into this heterologous regimen and paves the way for future strategies against emerging infectious diseases.

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

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

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

Introduction

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

Methods

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

Results

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

Discussion

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

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

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

A new model for predicting the outcome and effectiveness of drug therapy in patients with severe fever with thrombocytopenia syndrome: A multicenter Chinese study

BACKGROUND

There are a few models for predicting the outcomes of patients with severe fever with thrombocytopenia syndrome (SFTS) based on single-center data, but clinicians need more reliable models based on multicenter data to predict the clinical outcomes and effectiveness of drug therapy.

METHODOLOGY/PRINCIPAL FINDINGS

This retrospective multicenter study analyzed data from 377 patients with SFTS, including a modeling group and a validation group. In the modeling group, the presence of neurologic symptoms was a strong predictor of mortality (odds ratio: 168). Based on neurologic symptoms and the joint indices score, which included age, gastrointestinal bleeding, and the SFTS virus viral load, patients were divided into double-positive, single-positive, and double-negative groups, which had mortality rates of 79.3%, 6.8%, and 0%, respectively. Validation using data on 216 cases from two other hospitals yielded similar results. A subgroup analysis revealed that ribavirin had a significant effect on mortality in the single-positive group (P = 0.006), but not in the double-positive or double-negative group. In the single-positive group, prompt antibiotic use was associated with reduced mortality (7.2% vs 47.4%, P < 0.001), even in individuals without significant granulocytopenia and infection, and early prophylaxis was associated with reduced mortality (9.0% vs. 22.8%, P = 0.008). The infected group included SFTS patients with pneumonia or sepsis, while the noninfected group included patients with no signs of infection. The white blood cell count and levels of C-reactive protein and procalcitonin differed significantly between the infection and non-infection groups (P = 0.020, P = 0.011, and P = 0.003, respectively), although the absolute difference in the medians were small.

CONCLUSIONS/SIGNIFICANCE

We developed a simple model to predict mortality in patients with SFTS. Our model may help to evaluate the effectiveness of drugs in these patients. In patients with severe SFTS, ribavirin and antibiotics may reduce mortality.

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

Background

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

Methods

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

Results

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

Conclusions

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

Pathogenic Interleukin-10 Receptor Alpha Variants in Humans - Balancing Natural Selection and Clinical Implications

Balancing natural selection is a process by which genetic variants arise in populations that are beneficial to heterozygous carriers, but pathogenic when homozygous. We systematically investigated the prevalence, structural, and functional consequences of pathogenic IL10RA variants that are associated with monogenic inflammatory bowel disease. We identify 36 non-synonymous and non-sense variants in the IL10RA gene. Since the majority of these IL10RA variants have not been functionally characterized, we performed a systematic screening of their impact on STAT3 phosphorylation upon IL-10 stimulation. Based on the geographic accumulation of confirmed pathogenic IL10RA variants in East Asia and in Northeast China, the distribution of infectious disorders worldwide, and the functional evidence of IL-10 signaling in the pathogenesis, we identify Schistosoma japonicum infection as plausible selection pressure driving variation in IL10RA. Consistent with this is a partially augmented IL-10 response in peripheral blood mononuclear cells from heterozygous variant carriers. A parasite-driven heterozygote advantage through reduced IL-10 signaling has implications for health care utilization in regions with high allele frequencies and potentially indicates pathogen eradication strategies that target IL-10 signaling.

The Threat of Climate Change on Tick-Borne Infections: Rising Trend of Infections and Geographic Distribution of Climate Risk Factors Associated With Ticks

Ticks transmit a wide range of pathogens. The spread of tick-borne infections is an emerging, yet often overlooked, threat in the context of climate change. The infections have rapidly increased over the past few years in South Korea despite no significant changes in socioeconomic circumstances. We investigated the impact of climate change on the surge of tick-borne infections and identified potential disease hot spots at a resolution of 5 km by 5 km. A composite index was constructed based on multiple climate and environmental indicators and compared with the observed tick-borne infections. The surge of tick-borne episodes corresponded to the rising trend of the index over time. High-risk areas identified by the index can be used to prioritize locations for disease prevention activities. Monitoring climate risk factors may provide an opportunity to predict the spread of the infections in advance.

Longitudinal analysis of immunocyte responses and inflammatory cytokine profiles in SFTSV-infected rhesus macaques

Severe fever with thrombocytopenia syndrome virus (SFTSV), an emerging bunyavirus, causes severe fever with thrombocytopenia syndrome (SFTS), with a high fatality rate of 20%-30%. At present, however, the pathogenesis of SFTSV remains largely unclear and no specific therapeutics or vaccines against its infection are currently available. Therefore, animal models that can faithfully recapitulate human disease are important to help understand and treat SFTSV infection. Here, we infected seven Chinese rhesus macaques (Macaca mulatta) with SFTSV. Virological and immunological changes were monitored over 28 days post-infection. Results showed that mild symptoms appeared in the macaques, including slight fever, thrombocytopenia, leukocytopenia, increased aspartate aminotransferase (AST) and creatine kinase (CK) in the blood. Viral replication was persistently detectable in lymphoid tissues and bone marrow even after viremia disappeared. Immunocyte detection showed that the number of T cells (mainly CD8⁺ T cells), B cells, natural killer (NK) cells, and monocytes decreased during infection. In detail, effector memory CD8⁺ T cells declined but showed increased activation, while both the number and activation of effector memory CD4⁺ T cells increased significantly. Furthermore, activated memory B cells decreased, while CD80⁺/CD86⁺ B cells and resting memory B cells (CD27⁺CD21⁺) increased significantly. Intermediate monocytes (CD14⁺CD16⁺) increased, while myeloid dendritic cells (mDCs) rather than plasmacytoid dendritic cells (pDCs) markedly declined during early infection. Cytokines, including interleukin-6 (IL-6), interferon-inducible protein-10 (IP-10), and macrophage inflammatory protein 1 (MCP-1), were substantially elevated in blood and were correlated with activated CD4⁺ T cells, B cells, CD16⁺CD56⁺ NK cells, CD14⁺CD16⁺ monocytes during infection. Thus, this study demonstrates that Chinese rhesus macaques infected with SFTSV resemble mild clinical symptoms of human SFTS and provides detailed virological and immunological parameters in macaques for understanding the pathogenesis of SFTSV infection.

Hedgehogs as Amplifying Hosts of Severe Fever with Thrombocytopenia Syndrome Virus, China

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tickborne bandavirus mainly transmitted by Haemaphysalis longicornis ticks in East Asia, mostly in rural areas. As of April 2022, the amplifying host involved in the natural transmission of SFTSV remained unidentified. Our epidemiologic field survey conducted in endemic areas in China showed that hedgehogs were widely distributed, had heavy tick infestations, and had high SFTSV seroprevalence and RNA prevalence. After experimental infection of Erinaceus amurensis and Atelerix albiventris hedgehogs with SFTSV, we detected robust but transitory viremias that lasted for 9-11 days. We completed the SFTSV transmission cycle between hedgehogs and nymph and adult H. longicornis ticks under laboratory conditions with 100% efficiency. Furthermore, naive H. longicornis ticks could be infected by SFTSV-positive ticks co-feeding on naive hedgehogs; we confirmed transstadial transmission of SFTSV. Our study suggests that the hedgehogs are a notable wildlife amplifying host of SFTSV in China.

Risk factors of severe fever with thrombocytopenia syndrome combined with central neurological complications: A five-year retrospective case-control study

OBJECTIVE

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with high mortality rate, especially SFTS combined with central neurological complications. The purpose of this study was to explore risk factors of central neurological complications in SFTS patients.

METHODS

In this retrospective study, SFTS patients admitted to the First Affiliated Hospital of Nanjing Medical University between January 2017 and December 2021 were enrolled. Based on the presence or absence of central neurological complications, SFTS patients were divided into case group and control group. The patients' laboratory parameters and clinical data were collected for statistical analysis. Receiver operating characteristic (ROC) curve analysis was used to evaluate the prediction accuracy of independent risk factors in identifying SFTS patients with central neurological complications.

RESULTS

In total, 198 hospitalized SFTS patients with complete medical records, clear etiological diagnosis and clinical outcomes were enrolled in this study. Of these, 74 (37.4%) cases were diagnosed with SFTS with central neurological complications, 29 (39.2%) cases died, and no death occurred in the control group. Multivariate logistic regression analysis revealed pulmonary rales, atrial fibrillation, and high serum SFTSV RNA, lactate dehydrogenase level during the fever stage as independent risk factors for the development of central neurological complications in SFTS patients. ROC curve analysis showed that the area under the ROC curve (AUC) of serum SFTSV RNA and lactate dehydrogenase levels were 0.748 (95%CI: 0.673-0.823, p < 0.001) and 0.864 (95%CI: 0.815-0.914, p < 0.001), respectively, in central neurological complications predicted in SFTS patients.

CONCLUSION

Severe fever with thrombocytopenia syndrome (SFTS) combined with central neurological complications has high morbidity and mortality and diverse clinical manifestations. Early monitoring of lung signs, electrocardiogram, blood SFTSV RNA, and lactate dehydrogenase levels in SFTS patients may be useful in predicting the occurrence of central neurological complications.

High levels of C-reactive protein-to-albumin ratio (CAR) are associated with a poor prognosis in patients with severe fever with thrombocytopenia syndrome in early stage

C-reactive protein-to-albumin ratio (CAR) can be used to assess the prognosis of various diseases. This study aimed to evaluate the relationship between CAR on the prognosis of patients with severe fever with thrombocytopenia syndrome (SFTS). This study included 155 SFTS patients from the Public Health Clinical Center of Dalian from January to December 2021. They were divided into survival and deceased groups based on the clinical prognosis. The independent risk factors for poor prognosis of SFTS patients at an early stage were determined by Cox regression. The efficacy of CAR prediction was assessed by the receiver operating characteristic (ROC) curve. A total of 155 patients were included in this study, with an average age of 61.98± 11.70 years, including 77 males and 65 females. The mortality rate of the patients enrolled in this study was 14.19%. Multivariate Cox regression indicated that CAR (hazard ratio = 2.585, 95% confidence interval [CI] 1.405-4.753, p = 0.002) could be an independent predictor for prognosis in SFTS patients at an early stage. CAR had an AUC of 0.781 (95% CI, 0.665-0.898, p = 0.000), a cutoff value of 0.57, a sensitivity of 0.77, and a specificity of 0.80, with better predictive efficacy, compared to neutrophil-to-lymphocyte ratio (NLR). High levels of CAR are associated with poor prognosis in SFTS patients, and CAR can be used as an independent predictor for SFTS patients.

Evaluation of a community intervention program on knowledge, attitudes, and practices regarding severe fever with thrombocytopenia syndrome in Anhui Province, China

Background

Severe fever with thrombocytopenia syndrome (SFTS) is a novel infectious disease with no specific therapeutics and vaccines. We hypothesize that health education in vulnerable people would ameliorate their knowledge, attitudes and practices (KAP) regarding SFTS and reduce its prevalence.

Methods

A four-stage cluster cross-section study in sixteen community units was performed. Sixteen groups were allocated to the intervention or control groups. A 6 months education program was administrated. The primary outcome was KAP scores 6 months after intervention. Predictors of KAP score changes were also analyzed.

Results

Eight hundred and fifteen valid questionnaires pre-intervention and 767 ones post-intervention were retreated. No significant differences were found in demographic characteristics and KAP scores before intervention. A significant improvement in KAP score (16.8 ± 4.7 vs. 22.0 ± 4.2, p < 0.001) in the intervention group was observed compare with the controls. Educational level and intervention program were the common predictors of KAP score changes.

Conclusions

Education improved KAP scores in SFTS vulnerable people which may contribute to the control of the disease.

Serological Evidence of Severe Fever with Thrombocytopenia Syndrome Virus and IgM Positivity Were Identified in Healthy Residents in Vietnam

Severe fever with thrombocytopenia syndrome (SFTS), an emerging tick-borne viral disease, is prevalent in East Asia and has also been reported in Southeast Asia since 2019. SFTS patients in Vietnam were first reported in 2019. However, the seroprevalence of severe fever with thrombocytopenia syndrome virus (SFTSV) in Vietnam has not been reported. To investigate the seroprevalence of SFTSV in Vietnam, we collected serum samples from 714 healthy residents in Thua Thien Hue and Quang Nam Province, Vietnam, and the seroprevalence of SFTSV was assessed using immunofluorescence antibody assay (IFA), Enzyme-Linked Immunosorbent Assays (ELISAs) and the 50% focus reduction neutralization test (FRNT50) assay. The seroprevalence of anti-SFTSV IgM or IgG was observed to be 3.64% (26/714), high IgM positivity was >80 (0.28%, 2/714) and the titer of neutralizing antibodies against SFTSV ranged from 15.5 to 55.9. In Pakistan, SFTSV infection confirmed using a microneutralization test (MNT) assay (prevalence is 2.5%) and ELISAs showed a high seroprevalence (46.7%) of SFTSV. Hence, the seroprevalence rate in Vietnam is similar to that in Pakistan and the number of SFTS patients could increase in Vietnam.

Whole-genome sequencing and genetic diversity of severe fever with thrombocytopenia syndrome virus using multiplex PCR-based nanopore sequencing, Republic of Korea

Background

Whole-genome sequencing plays a critical role in the genomic epidemiology intended to improve understanding the spread of emerging viruses. Dabie bandavirus, causing severe fever with thrombocytopenia syndrome (SFTS), is a zoonotic tick-borne virus that poses a significant public health threat. We aimed to evaluate a novel amplicon-based nanopore sequencing tool to obtain whole-genome sequences of Dabie bandavirus, also known as SFTS virus (SFTSV), and investigate the molecular prevalence in wild ticks, Republic of Korea (ROK).

Principal findings

A total of 6,593 ticks were collected from Gyeonggi and Gangwon Provinces, ROK in 2019 and 2020. Quantitative polymerase chain reaction revealed the presence of SFSTV RNA in three Haemaphysalis longicornis ticks. Two SFTSV strains were isolated from H. longicornis captured from Pocheon and Cheorwon. Multiplex polymerase chain reaction-based nanopore sequencing provided nearly full-length tripartite genome sequences of SFTSV within one hour running. Phylogenetic and reassortment analyses were performed to infer evolutionary relationships among SFTSVs. Phylogenetic analysis grouped SFTSV Hl19-31-4 and Hl19-31-13 from Pocheon with sub-genotype B-1 in all segments. SFTSV Hl20-8 was found to be a genomic organization compatible with B-1 (for L segment) and B-2 (for M and S segments) sub-genotypes, indicating a natural reassortment between sub-genotypes.

Conclusion/Significance

Amplicon-based next-generation sequencing is a robust tool for whole-genome sequencing of SFTSV using the nanopore platform. The molecular prevalence and geographical distribution of SFTSV enhanced the phylogeographic map at high resolution for sophisticated prevention of emerging SFTS in endemic areas. Our findings provide important insights into the rapid whole-genome sequencing and genetic diversity for the genome-based diagnosis of SFTSV in the endemic outbreak.

The Endless Wars: Severe Fever With Thrombocytopenia Syndrome Virus, Host Immune and Genetic Factors

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging arboviral infectious disease with a high rate of lethality in susceptible humans and caused by severe fever with thrombocytopenia syndrome bunyavirus (SFTSV). Currently, neither vaccine nor specific antiviral drugs are available. In recent years, given the fact that both the number of SFTS cases and epidemic regions are increasing year by year, SFTS has become a public health problem. SFTSV can be internalized into host cells through the interaction between SFTSV glycoproteins and cell receptors and can activate the host immune system to trigger antiviral immune response. However, SFTSV has evolved multiple strategies to manipulate host factors to create an optimal environment for itself. Not to be discounted, host genetic factors may be operative also in the never-ending winning or losing wars. Therefore, the identifications of SFTSV, host immune and genetic factors, and their interactions are critical for understanding the pathogenic mechanisms of SFTSV infection. This review summarizes the updated pathogenesis of SFTS with regard to virus, host immune response, and host genetic factors to provide some novel perspectives of the prevention, treatment, as well as drug and vaccine developments.

Animal Model of Severe Fever With Thrombocytopenia Syndrome Virus Infection

Severe fever with thrombocytopenia syndrome (SFTS), an emerging life-threatening infectious disease caused by SFTS bunyavirus (SFTSV; genus Bandavirus, family Phenuiviridae, order Bunyavirales), has been a significant medical problem. Currently, there are no licensed vaccines or specific therapeutic agents available and the viral pathogenesis remains largely unclear. Developing appropriate animal models capable of recapitulating SFTSV infection in humans is crucial for both the study of the viral pathogenic processes and the development of treatment and prevention strategies. Here, we review the current progress in animal models for SFTSV infection by summarizing susceptibility of various potential animal models to SFTSV challenge and the clinical manifestations and histopathological changes in these models. Together with exemplification of studies on SFTSV molecular mechanisms, vaccine candidates, and antiviral drugs, in which animal infection models are utilized, the strengths and limitations of the existing SFTSV animal models and some important directions for future research are also discussed. Further exploration and optimization of SFTSV animal models and the corresponding experimental methods will be undoubtedly valuable for elucidating the viral infection and pathogenesis and evaluating vaccines and antiviral therapies.

Acute Myocarditis with Severe Fever and Thrombocytopenia Syndrome

A 67-year-old man, hospitalized with fever and pancytopenia, experienced cardiogenic shock on the 3rd day of hospitalization. He complained of chest pain and exhibited cardiac dysfunction, upregulated serum troponin levels, and an ST elevation on electrocardiogram. Severe fever with thrombocytopenia syndrome (SFTS) was suspected based on the symptom course after a tick bite and was definitively diagnosed using the serum polymerase chain reaction (PCR) test. An endomyocardial biopsy performed in the convalescent phase revealed a sign of myocardial inflammation with increases in CD3- and CD68-positive cells. We herein report the first case of acute myocarditis complicated with SFTS.

Bunyavirus SFTSV exploits autophagic flux for viral assembly and egress

Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging negatively stranded enveloped RNA bunyavirus that causes SFTS with a high case fatality rate of up to 30%. Macroautophagy/autophagy is an evolutionarily conserved process involved in the maintenance of host homeostasis, which exhibits anti-viral or pro-viral responses in reaction to different viral challenges. However, the interaction between the bunyavirus SFTSV and the autophagic process is still largely unclear. By establishing various autophagy-deficient cell lines, we found that SFTSV triggered RB1CC1/FIP200-BECN1-ATG5-dependent classical autophagy flux. SFTSV nucleoprotein induced BECN1-dependent autophagy by disrupting the BECN1-BCL2 association. Importantly, SFTSV utilized autophagy for the viral life cycle, which not only assembled in autophagosomes derived from the ERGIC and Golgi complex, but also utilized autophagic vesicles for exocytosis. Taken together, our results suggest a novel virus-autophagy interaction model in which bunyavirus SFTSV induces classical autophagy flux for viral assembly and egress processes, suggesting that autophagy inhibition may be a novel therapy for treating or releasing SFTS.

Severe fever with thrombocytopenia syndrome virus (SFTSV)-host interactome screen identifies viral nucleoprotein-associated host factors as potential antiviral targets

Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging tick-borne virus that causes severe infection in humans characterized by an acute febrile illness with thrombocytopenia and hemorrhagic complications, and a mortality rate of up to 30%. Understanding on virus-host protein interactions may facilitate the identification of druggable antiviral targets. Herein, we utilized liquid chromatography-tandem mass spectrometry to characterize the SFTSV interactome in human embryonic kidney-derived permanent culture (HEK-293T) cells. We identified 445 host proteins that co-precipitated with the viral glycoprotein N, glycoprotein C, nucleoprotein, or nonstructural protein. A network of SFTSV-host protein interactions based on reduced viral fitness affected upon host factor down-regulation was then generated. Screening of the DrugBank database revealed numerous drug compounds that inhibited the prioritized host factors in this SFTSV interactome. Among these drug compounds, the clinically approved artenimol (an antimalarial) and omacetaxine mepesuccinate (a cephalotaxine) were found to exhibit anti-SFTSV activity in vitro. The higher selectivity of artenimol (71.83) than omacetaxine mepesuccinate (8.00) highlights artenimol’s potential for further antiviral development. Mechanistic evaluation showed that artenimol interfered with the interaction between the SFTSV nucleoprotein and the host glucose-6-phosphate isomerase (GPI), and that omacetaxine mepesuccinate interfered with the interaction between the viral nucleoprotein with the host ribosomal protein L3 (RPL3). In summary, the novel interactomic data in this study revealed the virus-host protein interactions in SFTSV infection and facilitated the discovery of potential anti-SFTSV treatments.

In Silico Structure-Based Design of Antiviral Peptides Targeting the Severe Fever with Thrombocytopenia Syndrome Virus Glycoprotein Gn

Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging tick-borne bunyavirus in Asia that causes severe disease. Despite its clinical importance, treatment options for SFTSV infection remains limited. The SFTSV glycoprotein Gn plays a major role in mediating virus entry into host cells and is therefore a potential antiviral target. In this study, we employed an in silico structure-based strategy to design novel cyclic antiviral peptides that target the SFTSV glycoprotein Gn. Among the cyclic peptides, HKU-P1 potently neutralizes the SFTSV virion. Combinatorial treatment with HKU-P1 and the broad-spectrum viral RNA-dependent RNA polymerase inhibitor favipiravir exhibited synergistic antiviral effects in vitro. The in silico peptide design platform in this study may facilitate the generation of novel antiviral peptides for other emerging viruses.

Novel viruses in hard ticks collected in the Republic of Korea unveiled by metagenomic high-throughput sequencing analysis

Ticks are vectors of a wide range of zoonotic viruses of medical and veterinary importance. Recently, metagenomics studies demonstrated that they are also the source of potentially pathogenic novel viruses. During the period from 2015 to 2017, questing ticks were collected by dragging the vegetation from geographically distant locations in the Republic of Korea (ROK) and a target-independent high-throughput sequencing method was utilized to study their virome. A total of seven viruses, including six putative novel viral entities, were identified. Genomic analysis showed that the novel viruses were most closely related to members in the orders Jingchuvirales and Bunyavirales. Phylogenetic reconstruction showed that the Bunyavirales-like viruses grouped in the same clade with other viruses within the Nairovirus and Phlebovirus genera, while the novel Jingchuvirales-like virus grouped together with other viruses within the family Chuviridae. Real-time RT-PCR was used to determine the geographic distribution and prevalence of these viruses in adult ticks. These novel viruses have a wide geographic distribution in the ROK with prevalences ranging from 2% to 18%. Our study expands the knowledge about the composition of the tick virome and highlights the wide diversity of viruses they harbor in the ROK. The discovery of novel viruses associated with ticks in the ROK highlights the need for an active tick-borne disease surveillance program to identify possible reservoirs of putative novel human pathogens.