Severe fever with thrombocytopenia syndrome and its pathogen SFTSV

Risk Factors for Co-Infections in Patients With Severe Fever With Thrombocytopenia Syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging viral hemorrhagic fever with a high fatality rate and notable public health impact, caused by a novel phlebovirus, primarily transmitted through infected tick bites. This study aimed to assess the prevalence of co-infections among hospitalized patients with SFTS, characterize isolated pathogens, and evaluate demographics, clinical features, and laboratory variations to identify potential risk factors for co-infections. In a cohort of 78 SFTS patients categorized into co-infection and non-co-infection groups, 44.9% (35/78) experienced co-infections, with a 25.7% mortality rate in that subgroup. Pulmonary and bloodstream infections, particularly fungal infections, were most common, and earlier onset of co-infections correlated with higher fatality. Univariable logistic regression identified significant risk factors, followed by multivariable analysis to determine independent predictors. Changes in mental status, hemorrhage, deep venous or arterial catheterization, mechanical ventilation, activated partial thromboplastin time (APTT) > 55 s, albumin < 37.5 g/L, interleukin-6 > 18.700 pg/mL, and interleukin-10 > 21.300 pg/mL emerged as significant risk factors, with hemorrhagic symptoms and low albumin remaining independent predictors. Internal validation through bootstrap resampling yielded a mean area under the receiver operating characteristic curve of 0.795 (95% CI: 0.706-0.868). These findings suggest that early recognition of these predictors may improve co-infection management in SFTS patients, leading to better clinical outcomes and more informed clinical decisions.

Two amino acid pairs in the Gc glycoprotein of severe fever with thrombocytopenia syndrome virus responsible for the enhanced virulence

Severe fever with thrombocytopenia syndrome (SFTS) is a significant public health concern, with a high fatality rate in humans and cats. In this study, we explored the genetic determinants that contribute to the different virulence of SFTS virus (SFTSV) based on Tk-F123 and Ng-F264 strains isolated from cats. Tk-F123 was 100% lethal in type I interferon receptor-knockout mice, whereas Ng-F264 exhibited no fatality. We identified a pair of amino acid residues in the Gc protein, glycine and serine, at residues 581 and 934, respectively, derived from Tk-F123, leading to a fatal infection. Those in Ng-F264 were arginine and asparagine. These results suggest that this pair of residues affects the Gc protein function and regulates SFTSV virulence. Our findings provide useful clues for the elucidation of viral pathogenicity and the development of effective live-attenuated vaccines and antiviral strategies.

MβCD inhibits SFTSV entry by disrupting lipid raft structure of the host cells

Severe fever with thrombocytopenia syndrome virus (SFTSV), recently named as Dabie bandavirus, belongs to the family Phenuiviridae of the order Bunyavirales, is a newly-identified bunyavirus with a case fatality rate of up to 30%, posing a serious threat to public health. Lipid rafts on plasm membranes are important for the entry of enveloped viruses; however, the role of lipid rafts in bunyavirus entry remains unclear. In this study, we found that methyl-beta-cyclodextrin (MβCD), a drug that disrupts cholesterol in lipid rafts of cell membranes, inhibits SFTSV infection. Additionally, there is a back-complementary effect of SFTSV infection upon the addition of cholesterol. Moreover, the concentration of SFTSV particles in lipid rafts during entry directly indicated the role of lipid rafts as a gateway, whereas MβCD could inhibit SFTSV entry by affecting the structure of lipid rafts. In an in vivo study, MβCD also reduced the susceptibility of mice to SFTSV infection. Our results suggest that SFTSV can interact with Talin1 proteins on lipid rafts to enter host cells by endocytosis of lipid rafts and reveal the potential therapeutic value of MβCD for SFTSV infection.

Adenovirus type 5-expressing Gn induces better protective immunity than Gc against SFTSV infection in mice

Severe fever with thrombocytopenia syndrome (SFTS) is caused by the SFTS virus (SFTSV) with high morbidity and mortality. The major immunodominant region of SFTSV surface glycoprotein (G) remains unclear. In this study, we constructed adenovirus type 5 (Ad5) vectored vaccine candidates expressing different regions of SFTSV G (Gn, Gc and Gn-Gc) and evaluated their immunogenicity and protective efficacy in mice. In wild-type mice, compared with Ad5-Gc or Ad5-Gn-Gc, Ad5-Gn recruited/activated more dendritic cells and B cells in lymph nodes or peripheral blood, causing Th1-/Th2-mediated responses in splenocytes and triggered a greater level of SFTSV-neutralizing antibodies. In IFNAR Ab-treated mice, immunization of Ad5-Gn exhibited better protection against SFTSV challenge than Ad5-Gc or Ad5-Gn-Gc. Furthermore, passive immunization revealed complete protective immunity of Gn-specific serum rather than Gc. Collectively, our data demonstrated that Gn is the immunodominant fragment of SFTSV G and could be a potential candidate for SFTSV vaccine development.

A nomogram and heat map based on LASSO-Cox regression for predicting the risk of early-stage severe fever with thrombocytopenia syndrome patients developing into critical illness at 7-day and 14-day

Severe fever with thrombocytopenia syndrome (SFTS) represents an emerging infectious disease characterized by a substantial mortality risk. Early identification of patients is crucial for effective risk assessment and timely interventions. In the present study, least absolute shrinkage and selection operator (LASSO)-Cox regression analysis was conducted to identify key risk factors associated with progression to critical illness at 7-day and 14-day. A nomogram was constructed and subsequently assessed for its predictive accuracy through evaluation and validation processes. The risk stratification of patients was performed using X-tile software. The performance of this risk stratification system was assessed using the Kaplan-Meier method. Additionally, a heat map was generated to visualize the results of these analyses. A total of 262 SFTS patients were included in this study, and four predictive factors were included in the nomogram, namely viral copies, aspartate aminotransferase (AST) level, C-reactive protein (CRP), and neurological symptoms. The AUCs for 7-day and 14-day were 0.802 [95% confidence interval (CI): 0.707-0.897] and 0.859 (95% CI: 0.794-0.925), respectively. The nomogram demonstrated good discrimination among low, moderate, and high-risk groups. The heat map effectively illustrated the relationships between risk groups and predictive factors, providing valuable insights with high predictive and practical significance.

The differences in cytokine signatures between severe fever with thrombocytopenia syndrome (SFTS) and hemorrhagic fever with renal syndrome (HFRS)

Severe fever with thrombocytopenia syndrome (SFTS) virus and hantavirus are categorized under the Bunyavirales order. The severe disease progression in both SFTS and hemorrhagic fever with renal syndrome (HFRS) is associated with cytokine storms. This study aimed to explore the differences in cytokine profiles and immune responses between the two diseases. A cross-sectional, single-center study involved 100 participants, comprising 46 SFTS patients, 48 HFRS patients, and 6 healthy controls. The study employed the Luminex cytokine detection platform to measure 48 cytokines. The differences in cytokine profiles and immune characteristics between the two diseases were further analyzed using multiple linear regression, principal component analysis, and random forest method. Among the 48 cytokines tested, 30 showed elevated levels in SFTS and/or HFRS compared to the healthy control group. Furthermore, there were 19 cytokines that exhibited significant differences between SFTS and HFRS. Random forest analysis suggested that TRAIL and CTACK were predictive of SFTS, while IL2Ralpha, MIG, IL-8, IFNalpha2, HGF, SCF, MCP-3, and PDGFBB were more common with HFRS. It was further verified by the receiver operating characteristic with area under the curve >0.8 and P-values <0.05, except for TRAIL. Significant differences were observed in the cytokine profiles of SFTS and HFRS, with TRAIL, IL2Ralpha, MIG, and IL-8 being the top 4 cytokines that most clearly distinguished the two diseases.

IMPORTANCE

SFTS and HFRS differ in terms of cytokine immune characteristics. TRAIL, IL-2Ralpha, MIG, and IL-8 were the top 4 that differed markedly between SFTS and HFRS.

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.

High CRP/PNI levels predict an unfavorable prognosis in severe fever with thrombocytopenia syndrome: A propensity score matching study

BACKGROUND

This study aimed to identify a novel inflammatory index and construct a nomogram for predicting in-hospital mortality due to severe fever with thrombocytopenia syndrome (SFTS).

METHODS

This cohort included 610 patients with SFTS hospitalized in Wuhan Union Hospital between March 2017 and November 2022. The ratio of C-reactive protein (CRP) to the prognostic nutritional index (PNI) was calculated and used to reflect patients' inflammatory status. Propensity score matching (PSM) was utilized to balance confounding factors between the low- and high-CRP/PNI groups. SFTS individuals from Jinyinhu Hospital were used as the validation cohort.

RESULTS

Patients with SFTS and high CRP/PNI were significantly correlated with a higher percentage of severe and critical SFTS types and higher in-hospital mortality rates than those with low CRP/PNI. CRP/PNI was the potent risk indicator for in-hospital mortality in individuals with SFTS. The CRP/PNI nomogram showed a good predictive value for in-hospital mortality in patients with SFTS. After PSM, the predictive performance of CRP/PNI for 28-day mortality was excellent. Finally, the CRP/PNI could still assess patients with SFTS at different risks based on SFTS data from another medical center.

CONCLUSION

The CPR/PNI ratio exhibited a strong positive correlation with the SFTS disease type and could predict in-hospital mortality in the early stages of SFTS. The CPR/PNI ratio could substantially help clinicians facilitate the early identification of patients with high-risk SFTS and the timely initiation of intensive therapy.

Dabie bandavirus infection induces macrophagic pyroptosis and this process is attenuated by platelets

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infection with a high mortality rate in humans, which is caused by Dabie bandavirus (DBV), formerly known as SFTS virus. Clinical manifestations of SFTS are characterized by high fever, thrombocytopenia, leukopenia, hemorrhage, gastrointestinal symptoms, myalgia and local lymph node enlargement with up to 30% case fatality rates in human. Macrophage depletion in secondary lymphoid organs have important roles in the pathogenic process of fatal SFTS, but its exact cell death mechanism remains largely unknown. Here, we showed for the first time that DBV infection induced macrophagic pyroptosis, as evidenced by swollen cells, pore-forming structures, accumulation of gasdermin D N-terminal (GSDMD-NT) as well as the release of lactate dehydrogenase (LDH) and IL-1β in human macrophages. In addition to the upregulation of pyronecrosis genes, the expressions of pyroptosis-related proteins (GSDMD, caspase-1 and IL-1β) were also elevated. To be noted, platelets were found to play a protective role in DBV-derived pyroptosis. Transcriptome analysis and in vitro studies demonstrated that platelets significantly reduced the gene expressions and protein production of pro-pyroptotic markers and inflammatory cytokines in macrophages, whereas platelets conferred a propagation advantage for DBV. Collectively, this study demonstrates a novel mechanism by which DBV invasion triggers pyroptosis as a host defense to remove replication niches in human macrophages and platelets provide an additional layer to reduce cellular death. These findings may have important implications to the pathogenesis of lethal DBV, and provide new ideas for developing novel therapeutics to combat its infection.

Tick-borne encephalitis

PURPOSE OF REVIEW

Tick-borne encephalitis continues to be one of the most significant causes of viral encephalitis in Europe and Asia. This review will focus on recent developments in the epidemiology, pathogenesis and therapeutic approaches related to infection with tick-borne encephalitis virus.

RECENT FINDINGS

There is a growing consensus that tick-borne encephalitis viruses are increasing in geographical range, with countries previously free of disease reporting detection of both human cases and presence of virus within indigenous tick populations. The drivers for this are multifactorial but underpinned by human-mediated climate change. Recent developments in pathogenesis have focussed on the intracellular response to infection, particularly in different cell types within the central nervous system (CNS) that are revealing the array of cellular networks triggered by infection. This in turn highlights the need for small molecule therapeutics, such as nucleoside analogues, that can enter the CNS, and the intracellular environment, to inhibit virus replication following neuroinvasion.

SUMMARY

Based on continued epidemiological surveillance, tick-borne encephalitis viruses will increasingly affect human populations in Europe and Asia. Much of the research highlighted in this review demonstrates incremental advances in our understanding of these viruses. However, more is required if effective prevention and treatment of this devastating encephalitic viruses are to be realized.

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

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

Analysis of spatial-temporal distribution characteristics and natural infection status of SFTS cases in Hefei from 2015 to 2021

BACKGROUND

To analyze the prevalence and spatial-temporal characteristics of severe fever with thrombocytopenia syndrome (SFTS), clustering mode of transmission, and the serological dynamic detection results in multiple areas in Hefei from 2015 to 2021, and to provide the basis for SFTS prevention and control.

METHOD

Case data were obtained from the Chinese Disease Control and Prevention Information System. Information on the clustering outbreak was obtained from the outbreak investigation and disposal report. Population latent infection rate information was obtained from field sampling in multiple-incidence counties in 2016 and 2021 by multi-stage random sampling. Epi data3.2 and SPSS 16.0 softwares were used to perform a statistical analysis of the data on SFTS cases, and QGIS 3.26 software was used to draw the incidence map with township (street) as unit.

RESULTS

The an average annual reported incidence rate of SFTS in Hefei from 2015 to 2021 was 0.65/100,000, and the case fatality rate was 9.73%. The overall prevalence of SFTS epidemics in Hefei City showed a fluctuating upward trend from 2015 to 2021 (χ2trends = 103.353, P < 0.001). Chaohu City, Feixi County, Feidong County and Lujiang County ranked the top 4 in the city in terms of average annual incidence rate. The number of epidemic-involved towns (streets) kept increasing ((χ2trend = 47.640, P = 0.000)). Co-exposure to ticks accounted for the majority of clustered outbreaks and also human-to-human outbreaks. Population-based latent infection rate surveys were conducted in four SFTS multi-incidence counties, with 385 people surveyed in 2016 and 403 people surveyed in 2021, increasing the population-based latent infection rate from 6.75% to 10.91%, just as the incidence rate increased.

CONCLUSIONS

The incidence rate of SFTS in Hefei is obviously regional, with an expanding trend in the extent of the epidemic involved. Co-exposure to ticks accounted for the majority of clustered outbreaks and the latent infection rate cannot be ignored.

Pseudotyped Virus for Bandavirus

The genus Bandavirus, belonging to family Phenuiviridae, order Bunyavirales, consists of eight tick-borne bunyaviruses. The Dabie bandavirus, formerly known as severe fever with thrombocytopenia virus (SFTSV), belongs to the genus Bandavirus. This emerging pathogen was first identified in central China in 2009. In recent years, the disease has been reported to cause several outbreaks in eastern Asia areas, including China, Japan, Korea, and Vietnam. Tick-to-human transmission is the main route of infection in humans, and transmission via the contact of body fluids from person-to-person was also reported. Despite its high fatality rate, there is currently no vaccine or antiviral therapy available. The therapeutic efficacies of several antiviral agents against Dabie bandavirus are still being evaluated. However, the virus is a potent pathogen with high biosafety experimental conditions. Therefore, replication-incompetent pseudotyped viruses play an important role. In this chapter, we succinctly summarize the basic features concerning Dabie bandavirus, including virion structure, genome characteristics, especially the characteristics of glycoprotein, and probable pathogenic mechanism. And, we put an important part in expounding the construction of pseudoviruses and its application.

Clinical characteristics and risk factors of 267 patients having severe fever with thrombocytopenia syndrome-new epidemiological characteristics of fever with thrombocytopenia syndrome: Epidemiological characteristics of SFTS

OBJECTIVE

To analyze the epidemiological distribution, clinical characteristics, and prognostic risk factors of patients having severe fever with thrombocytopenia syndrome (SFTS).

METHODS

We enrolled 790 patients with SFTS divided into the ordinary group and the severe group, analyzed the clinical characteristics, and screened the risk factors of severious patients by univariate logistic regression analysis.

RESULTS

Most of the 790 patients (SFTS) are farmers (84.56%). The proportion of patients with fieldwork history was 72.41%, of which 21.27% had a clear history of a tick bite and 98.61% were sporadic cases. The annual peak season is from April to November. 16.33% patients were not accompanied by fever. The incidence of severe thrombocytopenia was 47.59%. They were statistically significant between the 2 groups in indicators such as age, hypertension, coronary heart disease, diabetes mellitus, bunyavirus nucleic acid load and mean platelet count (P < .05). Multivariate non conditional Logistic regression analysis showed that the risk factors of the mild patients deteriorating severe disease were age (OR = 1.985, P  ≤ .003), diabetes mellitus (OR = 1.702, P  ≤ .001), coronary heart disease (OR = 1.381, P ≤ .003), platelet count (OR = 2.592, P  ≤ .001), viral nucleic acid loading (OR = 3.908, P  ≤ .001).

CONCLUSION

The incidence population and seasonal distribution characteristics of patients with SFTS are obvious. The risk factors for poor prognosis of severe patients are old age, multiple basic medical histories, high viral load, a serious decrease of mean platelet count, and delay of treatment time.

Development of functional anti-Gn nanobodies specific for SFTSV based on next-generation sequencing and proteomics

Severe fever with thrombocytopenia syndrome (SFTS) is an acute infectious disease caused by novel bunyavirus (SFTSV), with a mortality rate of 6.3% ~ 30%. To date, there is no specific treatment for SFTS. Previously, we demonstrated that SFTSV surface glycoprotein (Glycoprotein N, Gn) was a potential target for the development of SFTS vaccine or therapeutic antibodies, and anti-Gn neutralizing antibodies played a protective role in SFTS infection. Compared with traditional antibodies, nanobodies from camelids have various advantages, including small molecular weight, high affinity, low immunogenicity, convenient production by gene engineering, etc. In this study, we combined next-generation sequencing (NGS) with proteomics technology based on affinity purification-mass spectrometry (AP-MS) and bioinformatics analysis to high-throughput screen monoclonal anti-Gn nanobodies from camel immunized with Gn protein. We identified 19 anti-Gn monoclonal nanobody sequences, of which six sequences were selected for recombinant protein expression and purification. Among these six anti-Gn nanobodies, nanobody 57,493 was validated to be highly specific for Gn. The innovative high-throughput technical route developed in this study could also be expanded to the production of nanobodies specific for other viruses like SARS-CoV-2.

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

Severe fever with thrombocytopenia syndrome (SFTS) has been acknowledged as an emerging infectious disease that is caused by the SFTS virus (SFTSV). The main clinical features of SFTS on presentation include fever, thrombocytopenia, leukocytopenia and gastrointestinal symptoms. The mortality rate is estimated to range between 5-30% in East Asia. However, SFTSV infection is increasing on an annual basis globally and is becoming a public health problem. The transmission cycle of SFTSV remains poorly understood, which is compounded by the pathogenesis of SFTS not being fully elucidated. Since the mechanism underlying the host immune response towards SFTSV is also unclear, there are no effective vaccines or specific therapeutic agents against SFTS, with supportive care being the only realistic option. Therefore, it is now crucial to understand all aspects of the host-virus interaction following SFTSV infection, including the antiviral states and viral evasion mechanisms. In the present review, recent research progress into the possible host immune responses against SFTSV was summarized, which may be useful in designing novel therapeutics against SFTS.

Factors Associated With Severe Fever With Thrombocytopenia Syndrome in Endemic Areas of China

Objective

To explore the influence of climatic, environmental and socioeconomic factors on SFTS occurrence in Shandong Province, China.

Methods

We used generalized additive model to estimate the association between SFTS cases and climatic factors, environmental factors and socioeconomic factors, including annual average temperature, precipitation, land cover, normalized difference vegetation index, altitude, population density, meat production, milk production, and gross domestic product (GDP).

Results

There were a total of 4,830 cases reported in 100 (70.9%) counties and districts in Shandong Province from 2010 to 2020. The results showed that the annual average temperature, precipitation, forest and grassland coverage rate, altitude and meat production (square root transform) had a reversed “V” relationship with SFTS occurrence, with the inflection points around 12.5–13.0°C in temperature, around 650 mm in precipitation, around 0.3 in forest and grassland coverage rate, around 300 m in altitude, and around 200–300 tons in meat production (square root transform), respectively. SFTS occurrence had a “V” relationship with milk production (square root transform) and GDP (square root transform), with the inflection points around 100–200 tons in milk production (square root transform), and around 150,000–200,000 yuan in GDP (square root transform), respectively.

Conclusions

Climatic, environmental, and socioeconomic factors contributed to the heterogeneous distribution of SFTS in Shandong Province, and the influence of these factors on SFTS occurrence was nonlinear.

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.

Predictive Value of Triglyceride-Glucose Index for In-hospital Mortality in Patients With Severe Fever With Thrombocytopenia Syndrome: A Multi-Center Observational Study

Background: Triglyceride-glucose (TyG) index has been proposed as a reliable indicator for insulin resistance and proved to be closely associated with the severity and mortality risk of infectious diseases. It remains indistinct whether TyG index performs an important role in predicting in-hospital mortality in patients with severe fever with thrombocytopenia syndrome (SFTS).

Methods: The current study retrospectively recruited patients who were admitted for SFTS from January to December 2019 at five medical centers. TyG index was calculated in accordance with the description of previous study: Ln [fasting triglyceride (TG) (mg/dl) × fasting blood glucose (FBG) (mg/dl)/2]. The observational endpoint of the present study was defined as the in-hospital death.

Results: In total, 79 patients (64.9 ± 10.5 years, 39.2% female) who met the enrollment criteria were enrolled in the current study. During the hospitalization period, 17 (21.5%) patients died in the hospital. TyG index remained a significant and independent predictor for in-hospital death despite being fully adjusted for confounders, either being taken as a nominal [hazard ratio (HR) 5.923, 95% CI 1.208–29.036, P = 0.028] or continuous (HR 7.309, 95% CI 1.854–28.818, P = 0.004) variate. TyG index exhibited a moderate-to-high strength in predicting in-hospital death, with an area under the receiver operating characteristic curve (AUC) of 0.821 (95% CI 0.712–0.929, P < 0.001). The addition of TyG index displayed significant enhancement on the predictive value for in-hospital death beyond a baseline model, manifested as increased AUC (baseline model: 0.788, 95% CI 0.676–0.901 vs. + TyG index 0.866, 95% CI 0.783–0.950, P for comparison = 0.041), increased Harrell's C-index (baseline model: 0.762, 95% CI 0.645–0.880 vs. + TyG index 0.813, 95% CI 0.724–0.903, P for comparison = 0.035), significant continuous net reclassification improvement (NRI) (0.310, 95% CI 0.092–0.714, P = 0.013), and significant integrated discrimination improvement (0.111, 95% CI 0.008–0.254, P = 0.040).

Conclusion: Triglyceride-glucose index, a novel indicator simply calculated from fasting TG and FBG, is strongly and independently associated with the risk of in-hospital death in patients with SFTS.

Antiviral RNA interference in disease vector (Asian longhorned) ticks

Disease vectors such as mosquitoes and ticks play a major role in the emergence and re-emergence of human and animal viral pathogens. Compared to mosquitoes, however, much less is known about the antiviral responses of ticks. Here we showed that Asian longhorned ticks (Haemaphysalis longicornis) produced predominantly 22-nucleotide virus-derived siRNAs (vsiRNAs) in response to severe fever with thrombocytopenia syndrome virus (SFTSV, an emerging tick-borne virus), Nodamura virus (NoV), or Sindbis virus (SINV) acquired by blood feeding. Notably, experimental acquisition of NoV and SINV by intrathoracic injection also initiated viral replication and triggered the production of vsiRNAs in H. longicornis. We demonstrated that a mutant NoV deficient in expressing its viral suppressor of RNAi (VSR) replicated to significantly lower levels than wildtype NoV in H. longicornis, but accumulated to higher levels after knockdown of the tick Dicer2-like protein identified by phylogeny comparison. Moreover, the expression of a panel of known animal VSRs in cis from the genome of SINV drastically enhanced the accumulation of the recombinant viruses. This study establishes a novel model for virus-vector-mouse experiments with longhorned ticks and provides the first in vivo evidence for an antiviral function of the RNAi response in ticks. Interestingly, comparing the accumulation levels of SINV recombinants expressing green fluorescent protein or SFTSV proteins identified the viral non-structural protein as a putative VSR. Elucidating the function of ticks’ antiviral RNAi pathway in vivo is critical to understand the virus-host interaction and the control of tick-borne viral pathogens.

Tick-borne diseases (TBDs) are the most common illnesses transmitted by ticks, and the annual number of reported TBD cases continues to increase. The Asian longhorned tick, a vector associated with at least 30 human pathogens, is native to eastern Asia and recently reached the USA as an emerging disease threat. Newly identified tick-transmitted pathogens continue to be reported, raising concerns about how TBDs occur. Interestingly, tick can harbor pathogens without being affected themselves. For viral infections, ticks have their own immune systems that protect them from infection. Meanwhile, tick-borne viruses have evolved to avoid these defenses as they establish themselves within the vector. Here, we show in detail that infecting longhorned ticks with distinct arthropod-borne RNA viruses through two approaches natural blood feeding and injection, all induce the production of vsiRNAs. Dicer2-like homolog plays a role in regulating antiviral RNAi responses as knocking down of this gene enhanced viral replication. Furthermore, we demonstrate that tick antiviral RNAi responses are inhibited through expression heterologous VSR proteins in recombinant SINV. We identify both the virus and tick factors are critical components to understanding TBDs. Importantly, our study introduces a novel, in vivo virus-vector-mouse model system for exploring TBDs in the future.

Single-cell landscape of peripheral immune responses to fatal SFTS

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with high fatality. Poor prognosis of SFTS has been associated with dysregulated host immunity; however, the immune patterns associated with pathophysiology involving SFTS exacerbation remain unclear. Here, we show that the single-cell landscape of peripheral immune responses is reprogrammed in SFTS and characterized by monocyte shift to an intermediate type along with complement activation, perturbation of plasmablast composition, and highly exhausted T cells, all correlated with lethal consequences. We identify the overexpression of interferon (IFN)-stimulated genes across most immune cell types after SFTSV infection, which are simultaneously related to older age, high viremia, and a hyperinflammatory response. A retrospective clinical study reveals no efficiency of IFN-α in treating SFTS. These data collectively support the intermediate monocytes and IFN-I-inducible plasmablasts to be major targets for SFTS virus infection, and they indicate the pivotal role of the IFN-I response in exacerbating hyperinflammation and lethal SFTS.

A longitudinal sampling study of transcriptomic and epigenetic profiles in patients with thrombocytopenia syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is a novel tick-borne infectious disease caused by a new type of SFTS virus (SFTSV). Here, a longitudinal sampling study is conducted to explore the differences in transcript levels after SFTSV infection, and to characterize the transcriptomic and epigenetic profiles of hospitalized patients. The results reveal significant changes in the mRNA expression of certain genes from onset to recovery. Moreover, m⁶A-seq reveals that certain genes related with immune regulation may be regulated by m⁶A. Besides the routine tests such as platelet counts, serum ALT and AST levels testing, distinct changes in myocardial enzymes, coagulation function, and inflammation are well correlated with the clinical data and sequencing data, suggesting that clinical practitioners should monitor the above indicators to track disease progression and guide personalized treatment. In this study, the transcript changes and RNA modification may lend a fresh perspective to our understanding of the SFTSV and play a significant role in the discovery of drugs for effective treatment of this disease.

Non-structural Proteins of Severe Fever With Thrombocytopenia Syndrome Virus Suppress RNA Synthesis in a Transcriptionally Active cDNA-Derived Viral RNA Synthesis System

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by the tick-borne SFTS bunyavirus (SFTSV) resulting in a high fatality rate up to 30%. SFTSV is a negative-strand RNA virus containing three single-stranded RNA genome segments designated as L, M, and S, which respectively, encode the RNA-dependent RNA polymerase (RdRp), glycoproteins Gn and Gc, and nucleoprotein (N) and non-structural proteins (NSs). NSs can form inclusion bodies (IBs) in infected and transfected cells. A previous study has provided a clue that SFTSV NSs may be involved in virus-like or viral RNA synthesis; however, the details remain unclear. Our work described here reveals that SFTSV NSs can downregulate virus-like RNA synthesis in a dose-dependent manner within a cDNA-derived viral RNA synthesis system, i.e., minigenome (−) and minigenome (+) systems based on transfection, superinfection, and luciferase reporter activity determination; meanwhile, NSs also show a weak inhibitory effect on virus replication. By using co-immunoprecipitation (Co-IP) and RT-PCR combined with site-directed mutagenesis, we found that NSs suppress virus-like RNA or virus replication through interacting with N but not with RdRp, and the negative regulatory effect correlates closely with the IB structure it formed but is not associated with its role of antagonizing host innate immune responses. When the cytoplasmic structure of IB formed by SFTSV NSs was deprived, the inhibitory effect of NSs on virus-like RNA synthesis would weaken and even disappear. Similarly, we also evaluated other bandavirus NSs that cannot form IB in neither infected nor transfected cells, and the results showed that the NSs of Heartland bandavirus (HRTV) did not show a significant inhibitory effect on virus-like RNA synthesis within a minigenome system. Our findings provide experimental evidence that SFTSV NSs participate in regulating virus-like or viral RNA synthesis and the negative effect may be due to the NSs–N interaction.

Epidemiological and clinical characteristics of severe fever with thrombocytopenia syndrome in southern Anhui Province, 2011-2020

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging hemorrhagic fever, and the causative pathogen, the SFTS virus (SFTSV), was first discovered in China in 2010. In this study, a retrospective analysis of 86 patients that diagnosed with SFTS from two five-year periods (2011-2015 and 2016-2020) that was performed to explore the changes in epidemiology, clinical characteristics, laboratory parameters and prognosis between those two periods. The results showed that there were significant differences in age, the proportion of farmers, geographical distribution, the incidence of multiple organ dysfunction, the decrease in thrombocyte count, and the elevations of serum AST and lipase levels between the two groups (p<0.05). Additionally, the case-fatality rate in the 2016-2020 group (16.7%) was higher than that in the 2011-2015 group (6.25%), although the difference was not significant. Our study shows that SFTS is broadly distributed across Anhui Province. The mortality rate is high. May to July was the peak of the epidemic, and farmers constituted a high-risk group. In recent years, thrombocytopenia has become more serious, and multiple organ dysfunction is more common. Clinicians need to further strengthen their knowledge of the changing epidemiological and clinical characteristics of this disease.

The associations between fasting blood glucose levels and mortality of SFTS in patients

Objective

To identify the correlation between the level of at-admission fasting blood glucose (FBG) with poor outcomes in hospitalized patients suffering from severe fever with thrombocytopenia syndrome (SFTS).

Methods

Between April 1 and December 1, 2020, the list of hospitalized patients affected with SFTS infection was provided by the Infectious Disease Department at First Affiliated Hospital of Anhui Medical University, followed by the collection of information I.e., gender, age, diabetic history and the level of FBG on admission.

Results

In this study, a total of 77 patients were included and were categorized into three groups (< 5.6, 5.6–6.9, and ≥ 7.0 mmol/l) on the basis of their glucose level in the blood. The obtained results revealed that among three groups considerable variations were observed in leukocytes, FBG, D-Dimer, aspartate aminotransferase (AST), tumor necrosis factor-α (TNF-α), fibrin degradation products (FDP), and interleukin (IL)-10 level. Correlation analysis indicated a linear negative correlation between PLT and FBG (r = − 0.28, P = 0.01), however, a linear positive correlation was observed between AST, IL10, D-Dimer, and FDP levels and FBG (P-value < 0.05). Multivariate statistical analysis results shown that there was significant difference between group comparison (F = 17.01, P < 0.001) and interaction between group and time (F = 8.48, P < 0.05); but there was no significant difference between time point comparison (F = 0.04, P = 0.96). With the prolongation of time, the changes of FBG were different between survivor group and non-survivor group. The FBG in survival group shown a downward trend; The non-survivor group shown an upward trend.

Conclusions

Elevated level of FBG has been correlated with hypercoagulability, inflammation, and lower PLT in SFTS patients. The measurement of FBG level can help in evaluating the inflammatory process, hypercoagulability, and prognosis of patients suffering from SFTS. FBG can predict the prognosis of SFTS. It is necessary to pay attention to the role of FBG in the process of treatment in patients with SFTS.

Discovery and Surveillance of Tick-Borne Pathogens

Within the past 30 yr molecular assays have largely supplanted classical methods for detection of tick-borne agents. Enhancements provided by molecular assays, including speed, throughput, sensitivity, and specificity, have resulted in a rapid increase in the number of newly characterized tick-borne agents. The use of unbiased high throughput sequencing has enabled the prompt identification of new pathogens and the examination of tick microbiomes. These efforts have led to the identification of hundreds of new tick-borne agents in the last decade alone. However, little is currently known about the majority of these agents beyond their phylogenetic classification. Our article outlines the primary methods involved in tick-borne agent discovery and the current status of our understanding of tick-borne agent diversity.

shRNA targeting nonstructural protein inhibits the replication of severe fever with thrombocytopenia syndrome virus

Aim: To explore whether shRNA targeting nonstructural protein (NSs) of severe fever with thrombocytopenia syndrome virus (SFTSV) could inhibit SFTSV replication in Vero cells. Materials & methods: SFTSV used in this experiment was propagated in Vero cells and stored at -20°C. shRNA plasmid against NSs of SFTSV was transfected to Vero cells and infected with SFTSV, after which western blotting and tissue culture infective dose (TCID50) were used to measure the virus titers. Results: shRNA against NSs protein decreased the expression of NSs and inhibited the replication of SFTSV. Conclusion: The constructed SFTSV NSs-shRNA plasmid could inhibit the replication of SFTSV. It was concluded that SFTSV NSs-shRNA could inhibit virus replication for at least 72 h. shRNA-mediated antiviral effects were dose-dependent.

Development and evaluation of two different double-antibody sandwich ELISAs for detecting severe fever with thrombocytopenia syndrome virus infection

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a newly emerging tick-borne virus with a case fatality rate between 12% and 50%. Currently, effective vaccines or antiviral drugs are not available, and a diagnostic method for detecting SFTSV is urgently needed. The monoclonal (MAb) and polyclonal antibodies (PAb) against SFTSV were prepared by immunizing animals with SFTSV nucleocapsid protein (NP), and using both monoclonal and polyclonal antibodies as capture antibodies against NP, we developed two different double-antibody sandwich enzyme-linked immunosorbent assays (DAS-ELISAs) for detecting the NP of SFTSV. Both methods were applicable for the diagnosis of SFTSV-infected patients, as confirmed by quantitative polymerase chain reaction. Furthermore, the sensitivity and specificity of two assays for diagnosing SFTS were both 100%, and had no reaction to recombinant Dabieshan NP or recombinant Dengue virus NS1 subtype 1 and 2 proteins. In addition, two standard curves were established for quantitative detection of the NP, and the monoclonal antibody-based ELISA (MAb-based ELISA) test had a lower limit of detection than the polyclonal-based ELISA (PAb-based ELISA) test. Therefore, the MAb-based ELISA could be employed for detecting SFTSV in a convenient and effective way.

Hedgehogs as a Potential Source of Zoonotic Pathogens-A Review and an Update of Knowledge

Simple Summary

Up to date studies indicate that wild hedgehogs may act as carriers and/or hosts for bacterial, viral, and fungal pathogens with zoonotic potential, posing a significant threat to humans. The same applies to domestic hedgehogs, which are increasingly kept as pets. Considering the potential risk of infection to humans through close contact with hedgehogs or the contaminated environment they inhabit, current data on the prevalence of various zoonotic pathogens in these animals is desirable.

Abstract

Hedgehogs are small insectivorous mammals common across Europe, Asia, and Africa. The increased encroachment of humans into hedgehog habitats has disrupted the human-animal-environment interface. With growing interest in the zoonotic diseases of wildlife species, more studies have been devoted to this subject in the last few years. These papers provide information about known and new emerging diseases. Here we review the current knowledge regarding bacterial, viral, protozoic, and mycotic pathogens with zoonotic potential and assess the importance of hedgehogs as their carriers. Both wild and pet hedgehogs were included in the review. Data from several countries and various hedgehog species were included. The study shows the importance of hedgehogs as carriers of zoonotic diseases and reservoirs of zoonotic pathogens in varied habitats.

Severe fever with thrombocytopenia syndrome in Hefei: Clinical features, risk factors, and ribavirin therapeutic efficacy

OBJECTIVES

This study described the clinical features, risk factors, factors affecting the outcome of this disease, and ribavirin therapeutic efficacy for severe fever with thrombocytopenia syndrome (SFTS) patients in Hefei.

METHODS

Between April 2020 and July 2020, 62 cases admitted to the First Affiliated Hospital of Anhui Medical University were included in this study. Serum samples were collected from all patients, after which diagnosis was made via reverse transcription-polymerase chain reaction and via the use of a colloidal gold immunochromatography assay approach.

RESULTS

In multivariate analysis, the following factors were determined as risk factors for SFTS: Being a farmer (odds ratio [OR], 3.033), working in areas with weeds and shrubs (OR, 2.807), and being bitten by a tick (OR, 6.64). The rates of confusion, neck stiffness, viral encephalopathy, and the presence of liver damage were higher in the patients who died than that in the surviving ones. Additionally, the median of alanine aminotransferase, aspartate aminotransferase, lactate dehydrogenase, creatine phosphokinase, activated partial thromboplastin time, D-dimer, fibrinogen degradation products, creatinine, and urea was also higher in the patients who died. One of the 15 patients treated with ribavirin in the early stage could not survive (6.7%), whereas 11 of the 35 patients treated with ribavirin in the late stage could not survive (31.4%); this difference was statistically significant. However, there was no significant difference in mortality between the untreated group and the other two groups (i.e., patients who started antiviral treatment <5 days from the onset and those who started antiviral treatment ≥5 days from the onset). Moreover, there was no positive effect determined on clinical or laboratory parameters in SFTS patients treated with ribavirin. Also, it was observed that leukocyte levels and platelet levels took longer to return to normal.

CONCLUSIONS

In Hefei, clinical features, prognostic factors, and risk factors associated with SFTS are similar to those in other areas. Patients who were given ribavirin did not have better survival rates than patients who were not given ribavirin.

The antiviral immunity of ticks against transmitted viral pathogens

Ticks, being obligate hematophagous arthropods, are exposed to various blood-borne pathogens, including arboviruses. Consequently, their feeding behavior can readily transmit economically important viral pathogens to humans and animals. With this tightly knit vector and pathogen interaction, the replication and transmission of tick-borne viruses (TBVs) must be highly regulated by their respective tick vectors to avoid any adverse effect on the ticks' biological development and viability. Knowledge about the tick-virus interface, although gaining relevant advances in recent years, is advancing at a slower pace than the scientific developments related to mosquito-virus interactions. The unique and complicated feeding behavior of ticks, compared to that of other blood-feeding arthropods, also limits the studies that would further elaborate the antiviral immunity of ticks against TBVs. Hence, knowledge of molecular and cellular immune mechanisms at the tick-virus interface, will further elucidate the successful viral replication of TBVs in ticks and their effective transmission to human and animal hosts.

A new emerging pandemic of severe fever with thrombocytopenia syndrome (SFTS)

The aim of this study is to make aware every one of the deadliest diseases named severe fever with thrombocytopenia syndrome (SFTS). It has become the worldwide pandemic in recent few years. It is a kind of haemorrhagic fever, caused by SFTS virus (SFTSV), a novel phlebovirus of family Bunyaviridae. This syndrome is also a tick-borne zoonosis that means the virus transmitted from tick bite (having virus) into human body, i.e. infection spread from animals to humans and also transmitted from human to human. Epidemiological data of SFTS was collected to know the nature/symptoms of SFTSV. First case of this disease has been reported in China, followed by Japan, South korea, Taiwan, USA and many other countries. Vertebrates are the host of this disease and tick functions as a vector, where the virus can undergo brisk changes using gene mutation, homologous recombination and reassortments. The major symptoms of hemorrhagic fever are fever, thrombocytopenia, leucopenia and gastrointestinal abnormalities. Sometimes in very severe cases, full body organ failure may also take place and average death rate in humans is nearly 10 %. Old aged peoples are more prone to SFTSV infection. Apart from the fact of increasing SFTSV related health problems to humans, the pathogenesis of SFTS virus in human is not entirely understood and no treatment to this virus is still available. The simplest way to protect our self from this infection is to refrain from tick bite. Therefore, this disease has evolved to produce serious health issues to humans in various countries of world including china. This review discussing about causative agent, epidemiology, pathogenesis, diagnosis and treatment of SFTS. In order to control the spread of SFTSV, we have to stop the viral transmission or to protect the easily vulnerable population from tick bites, avoiding direct contact of infectious and also to use personal protective devices for SFTS patients. So, the weather conditions, mode of transmission and creation of new therapeutics like vaccines and drugs are the main areas of forthcoming research.

Fine mapping epitope on Glycoprotein-Gn from Severe Fever with Thrombocytopenia Syndrome Virus

Severe Fever with Thrombocytopenia Syndrome Virus (SFTSV) was recently identified as a tick-borne pathogen that threat to human health. Since 2010, many countries including China, South Korea, and Japan have reported Human SFTS caused by SFTSV infection. The glycoprotein encoded by the SFTSV M gene is the major antigenic component on the viral surface, and responsible for the viral entry, which makes it an important viral antigen and a clinical diagnostic target. The present study aimed to map linear B cell epitopes (BCEs) on the N-terminal glycoprotein (Gn) from SFTSV strain WCH/97/HN/China/2011 using the modified biosynthetic peptide method. Five fine epitopes (E1, 196FSQSEFPD203; E2, 232GHSHKII238; E3, 256VCYKEGTGPC265; E4, 285FCKVAG290, and E5, 316SYGGM320) were identified using the rabbit antisera. Western blot analysis showed that all the five epitopes interacted with the positive serum of sheep that had been naturally infected with SFTSV. Three-dimensional structural modeling analysis showed that all identified BCEs were located on the surface of the SFTSV-Gn and contained flexible loops. The sequence alignment revealed high conservation of the identified BCEs among 13 SFTSV strains from different lineage. These mapped epitopes will escalate the understanding of the epitope distribution and pathogenic mechanism of SFTSV, and could provide a basis for the development of a SFTSV multi-epitope detection antigen.

Research Progress of [68Ga]Citrate PET's Utility in Infection and Inflammation Imaging: a Review

Imaging diagnosis of infection and inflammation has been challenging for many years. Infection imaging agents commonly used in nuclear medicine, such as [⁶⁷Ga]citrate, 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG), and radionuclide-labeled leukocytes, have their own shortcomings. Identification of a tracer with considerable economic benefit, high specificity, and low radiation dose has become clinically urgent. In the twenty-first century, with the increasing availability of positron emission tomography (PET) devices and the commercialization of Ge-68/Ga-68 generators, the study of [⁶⁸Ga]citrate applications for infection and inflammation has increased and shown good potential. In this report, the research progress that supports [⁶⁸Ga]citrate PET's applications various infectious diseases and inflammation is reviewed.

Correlation between thrombocytopenia and host response in severe fever with thrombocytopenia syndrome

Severe Fever with Thrombocytopenia Syndrome (SFTS) is an emerging infectious disease caused by a novel bunyavirus, SFTS virus (SFTSV), with fatal outcome developed in approximately 17% of the cases. Thrombocytopenia is a hallmark feature of SFTS, and associated with a higher risk of fatal outcome, however, the pathophysiological involvement of platelet in the clinical outcome of SFTS remained under-investigated. In the current study, by retrospectively analyzing 1538 confirmed SFTS patients, we observed that thrombocytopenia was associated with enhanced activation of the cytokine network and the vascular endothelium, also with a disturbed coagulation response. The platelet phenotypes were also extensively altered in the process of thrombocytopenia development of SFTS patients. More importantly, all these disturbed host responses were related to the severity of thrombocytopenia, thus were considered to play in a synergistic way to influence the disease outcome. Moreover, the clinical effect of platelet transfusion was assessed by comparing two groups of patients with or without receiving this therapy. As a result, we observed no therapy effect in altering frequencies of fatal outcome, clinical bleeding development, or dynamic change of platelet count during the hospitalization. It’s suggested that platelet supplementation alone acted a minor role in improving disease outcome, therefore new therapeutic intervention to regulate host response should be proposed. The current results revealed some evidence of interrelationship between platelet count and clinical outcome of SFTS disease from the perspective of activation of the cytokine network, the vascular endothelium, and the coagulation/fibrinolysis system. These evaluations might help to attain a better understanding of the pathogenesis and therapy choice in SFTS.

Thrombocytopenia in SFTSV is a multifactor-process involving a combination of platelet size or morphology alterations, fibrinolysis activation and coagulation abnormalities, increased inflammatory response and endothelial injury. Platelet supplementation alone shows minor role in improving disease, therefore new therapeutic intervention to regulate host response should be proposed.

Severe Fever with Thrombocytopenia Syndrome: Japan under Threat from Life-threatening Emerging Tick-borne Disease

Japan, like many other parts of the world, is under threat from newly emerging, potentially fatal diseases. Severe fever with thrombocytopenia syndrome (SFTS), first clinically identified in 2009, is an emerging tick-borne hemorrhagic viral disease, currently limited in distribution to East Asia. Relatively little is known about the disease with an initial Case Fatality Rate ranging from 5% to 40%. It primarily affects the elderly living in rural areas, which is particularly troublesome given Japan’s rapidly aging population. Control efforts are severely hampered by lack of specific knowledge of the disease and its means of transmission, coupled with the absence of both a vaccine and an effective treatment regime, although some antiviral drugs and blood transfusions are successful in treating the disease. Despite both the causative virus and vector ticks being commonly found throughout Japan, the disease shows a very specific, limited geographical distribution for as yet unknown reasons.

The Nonstructural Protein of Guertu Virus Disrupts Host Defenses by Blocking Antiviral Interferon Induction and Action

Guertu virus (GTV) is a potentially highly pathogenic bunyavirus newly isolated in China, which is genetically related to the severe fever with thrombocytopenia syndrome virus (SFTSV) and Heartland virus (HRTV), two other emerging life-threatening bunyaviruses. Previous studies suggested that SFTSV and HRTV antagonize the interferon (IFN) system by targeting antiviral signaling proteins in different ways. However, whether and how GTV counteracts the host innate immunity are unclear. Here, we found that GTV strongly inhibits both IFN induction and action through its nonstructural protein (NSs). Different from the NSs of SFTSV and HRTV, GTV NSs (G-NSs) induced the formation of two distinctive cytoplasmic structures, compact inclusion bodies (IBs) and extended filamentous structures (FSs). Protein interaction and colocalization analyses demonstrated that G-NSs interacts with TBK1 (TANK binding kinase-1, the pivotal kinase for IFN induction) and STAT2 (signal transducer and activator of transcription 2, the essential transcription factor for IFN action) and irreversibly sequesters the host proteins into the viral IBs and FSs. Consistently, G-NSs thus inhibited phosphorylation/activation and nuclear translocation of IFN-regulatory factor 3 (IRF3, the substrate of TBK1), diminishing the IFN induction. Furthermore, G-NSs sequestration of STAT2 blocked phosphorylation/activation and nuclear translocation of STAT2, disabling IFN action and host antiviral state establishment. Collectively, this study shows the robust subversion of the two phases of the IFN antiviral system by GTV and unravels the respective molecular mechanisms, exhibiting some notable differences from those employed by SFTSV and HRTV, providing insights into the virus-host interactions and pathogenesis, and probably also benefiting the prevention and treatment of the related infectious diseases in the future.

The Severe Fever with Thrombocytopenia Syndrome Virus NSs Protein Interacts with CDK1 To Induce G2 Cell Cycle Arrest and Positively Regulate Viral Replication

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a newly identified phlebovirus associated with severe hemorrhagic fever in humans. While many viruses subvert the host cell cycle to promote viral growth, it is unknown whether this is a strategy employed by SFTSV. In this study, we investigated how SFTSV manipulates the cell cycle and the effect of the host cell cycle on SFTSV replication. Our results suggest that cells arrest at the G₂/M transition following infection with SFTSV. The accumulation of cells at the G₂/M transition did not affect virus adsorption and entry but did facilitate viral replication. In addition, we found that SFTSV NSs, a nonstructural protein that forms viroplasm-like structures in the cytoplasm of infected cells and promotes virulence by modulating the interferon response, induces a large number of cells to arrest at the G₂/M transition by interacting with CDK1. The interaction between NSs and CDK1, which is inclusion body dependent, inhibits formation and nuclear import of the cyclin B1-CDK1 complex, thereby leading to cell cycle arrest. Expression of a CDK1 loss-of-function mutant reversed the inhibitive effect of NSs on the cell cycle, suggesting that this protein is a potential antiviral target. Our study provides new insight into the role of a specific viral protein in SFTSV replication, indicating that NSs induces G₂/M arrest of SFTSV-infected cells, which promotes viral replication.IMPORTANCE Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne pathogen that causes severe hemorrhagic fever. Although SFTSV poses a serious threat to public health and was recently isolated, its pathogenesis remains unclear. In particular, the relationship between SFTSV infection and the host cell cycle has not been described. Here, we show for the first time that both asynchronized and synchronized SFTSV-susceptible cells arrest at the G₂/M checkpoint following SFTSV infection and that the accumulation of cells at this checkpoint facilitates viral replication. We also identify a key mechanism underlying SFTSV-induced G₂/M arrest, in which SFTSV NSs interacts with CDK1 to inhibit formation and nuclear import of the cyclin B1-CDK1 complex, thus preventing it from regulating cell cycle progression. Our study highlights the key role that NSs plays in SFTSV-induced G₂/M arrest.

The Cap-Snatching SFTSV Endonuclease Domain Is an Antiviral Target

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne virus with 12%-30% case mortality rates and is related to the Heartland virus (HRTV) identified in the United States. Together, SFTSV and HRTV are emerging segmented, negative-sense RNA viral (sNSV) pathogens with potential global health impact. Here, we characterize the amino-terminal cap-snatching endonuclease domain of SFTSV polymerase (L) and solve a 2.4-Å X-ray crystal structure. While the overall structure is similar to those of other cap-snatching sNSV endonucleases, differences near the C terminus of the SFTSV endonuclease suggest divergence in regulation. Influenza virus endonuclease inhibitors, including the US Food and Drug Administration (FDA) approved Baloxavir (BXA), inhibit the endonuclease activity in in vitro enzymatic assays and in cell-based studies. BXA displays potent activity with a half maximal inhibitory concentration (IC50) of ∼100 nM in enzyme inhibition and an EC50 value of ∼250 nM against SFTSV and HRTV in plaque assays. Together, our data support sNSV endonucleases as an antiviral target.

Basic Science of PET Imaging for Inflammatory Diseases

FDG-PET/CT has recently emerged as a useful tool for the evaluation of inflammatory diseases too, in addition to that of malignant diseases. The imaging is based on active glucose utilization by inflammatory tissue. Autoradiography studies have demonstrated high FDG uptake in macrophages, granulocytes, fibroblasts, and granulation tissue. Especially, activated macrophages are responsible for the elevated FDG uptake in some types of inflammation. According to one study, after activation by lipopolysaccharide of cultured macrophages, the [¹⁴C]2DG uptake by the cells doubled, reaching the level seen in glioblastoma cells. In activated macrophages, increase in the expression of total GLUT1 and redistributions from the intracellular compartments toward the cell surface have been reported. In one rheumatoid arthritis model, following stimulation by hypoxia or TNF-α, the highest elevation of the [³H]FDG uptake was observed in the fibroblasts, followed by that in macrophages and neutrophils. As the fundamental mechanism of elevated glucose uptake in both cancer cells and inflammatory cells, activation of glucose metabolism as an adaptive response to a hypoxic environment has been reported, with transcription factor HIF-1α playing a key role. Inflammatory cells and cancer cells seem to share the same molecular mechanism of elevated glucose metabolism, lending support to the notion of usefulness of FDGPET/CT for the evaluation of inflammatory diseases, besides cancer.

Patient with severe fever with thrombocytopenia syndrome virus infection and central nervous system disturbance in Dongyang, Zhejiang Province, China, 2017

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging hemorrhagic fever that was first described in China in 2011. We report a patient who died of Severe fever with thrombocytopenia syndrome virus (SFTSV) infection, with a rapidly progressive central nervous system (CNS) disturbance, in Dongyang, Zhejiang Province, China, in 2017.

Case presentation

A 64-year-old man was admitted to hospital after 4 days of fever. SFTSV was detected 1 day after the patient was admitted to hospital. The patient presented with CNS disturbance and died 4 days after admission. Detailed clinical and epidemiological investigations and laboratory tests were conducted. Reduced platelet, white blood cell, lymphocyte, and neutrophil counts, elevated lactate dehydrogenase, creatine kinase, aspartate aminotransferaseand alanine aminotransferase concentrations, and an increased activated partial thromboplastin time were observed. In a phylogenetic analysis, the isolate clustered close to a strain derived from South Korea.

Conclusions: This is the first case of SFTSV infection with CNS disturbance in Dongyang, Zhejiang Province, China. The surveillance of suspected cases of SFTS is important in SFTSV endemic regions.

Development of DNA Aptamers against the Nucleocapsid Protein of Severe Fever with Thrombocytopenia Syndrome Virus for Diagnostic Application: Catalytic Signal Amplification using Replication Protein A-Conjugated Liposomes

Most prevalent infectious diseases worldwide are caused by mediators such as insects and characterized by high mortality and morbidity, thereby creating a global public health concern. Therefore, a sensitive, selective detection platform for diagnosing diseases in the early stages of infection is needed to prevent disease spread and to protect public health. Here, we developed novel DNA aptamers specific to the nucleocapsid protein (NP) of the severe fever with thrombocytopenia syndrome (SFTS) virus and synthesized ssDNA-binding protein-conjugated liposomes encapsulated with horseradish peroxidase (HRP) for application in a simple and universal platform. This platform achieved highly sensitive detection of the NP by measuring the colorimetric signal following lysis of the HRP encapsulated liposomes, mediated by a mixture of 3,3',5,5'-tetramethylbenzidine and H₂O₂ solution. The limit of detection was 0.009 ng·mL^-1, and NP was successfully detected in diluted human serum with a high recovery rate. Moreover, this method was specific and did not exhibit cross-reactivity among NPs of other virus types. These results demonstrated the efficacy of the proposed method as a highly sensitive, specific, and universal diagnostic tool for potential application in monitoring of the early stages of infectious diseases.

Proteasome Inhibitor PS-341 Effectively Blocks Infection by the Severe Fever with Thrombocytopenia Syndrome Virus

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging hemorrhagic fever disease caused by SFTSV, a newly discovered phlebovirus that is named after the disease. Currently, no effective vaccines or drugs are available for use against SFTSV infection, as our understanding of the viral pathogenesis is limited. Bortezomib (PS-341), a dipeptide-boronic acid analog, is the first clinically approved proteasome inhibitor for use in humans. In this study, the antiviral efficacy of PS-341 against SFTSV infection was tested in human embryonic kidney HEK293T (293T) cells. We employed four different assays to analyze the antiviral ability of PS-341 and determined that PS-341 inhibited the proliferation of SFTSV in 293T cells under various treatment conditions. Although PS-341 did not affect the virus absorption, PS-341 treatment within a non-toxic concentration range resulted in a significant reduction of progeny viral titers in infected cells. Dual-luciferase reporter assays and Western blot analysis revealed that PS-341 could reverse the SFTSV-encoded non-structural protein (NS) mediated degradation of retinoic acid-inducible gene-1 (RIG-I), thereby antagonizing the inhibitory effect of NSs on interferons and blocking virus replication. In addition, we observed that inhibition of apoptosis promotes virus replication. These results indicate that targeting of cellular interferon pathways and apoptosis during acute infection might serve as the bases of future therapeutics for the treatment of SFTSV infections.

Development of a SFTSV DNA vaccine that confers complete protection against lethal infection in ferrets

Although the incidence of severe fever with thrombocytopenia syndrome virus (SFTSV) infection has increased from its discovery with a mortality rate of 10-20%, no effective vaccines are currently available. Here we describe the development of a SFTSV DNA vaccine, its immunogenicity, and its protective efficacy. Vaccine candidates induce both a neutralizing antibody response and multifunctional SFTSV-specific T cell response in mice and ferrets. When the vaccine efficacy is investigated in aged-ferrets that recapitulate fatal clinical symptoms, vaccinated ferrets are completely protected from lethal SFTSV challenge without developing any clinical signs. A serum transfer study reveals that anti-envelope antibodies play an important role in protective immunity. Our results suggest that Gn/Gc may be the most effective antigens for inducing protective immunity and non-envelope-specific T cell responses also can contribute to protection against SFTSV infection. This study provides important insights into the development of an effective vaccine, as well as corresponding immune parameters, to control SFTSV infection.

Cutaneous histopathology of the tick-bite region in severe fever with thrombocytopenia syndrome

A case of severe fever with thrombocytopenia syndrome (SFTS) in which a skin biopsy from the tick-bite region was analyzed is reported. The patient was a 72-year-old woman who developed fever and thrombocytopenia after a tick bite. SFTS was diagnosed from polymerase chain reaction (PCR) analysis of a blood sample. Histopathological analysis of a skin biopsy specimen from the tick-bite region showed CD20-positive perivascular and interstitial immunoblastic cells, which were positive to anti-SFTS virus (SFTSV) nucleoprotein antibody. In addition, SFTSV RNA was detected by real-time PCR from this biopsy specimen. Moreover, hemophagocytosis was also found in the tick-bite region. To the best of our knowledge, this is the first report to analyze the details of the tick-bite region of skin in SFTS, and the first to detect virus-infected cells in the skin. The present findings may help elucidate the mechanisms of entry of SFTSV.

Rapid Detection of Severe Fever with Thrombocytopenia Syndrome Virus via Colloidal Gold Immunochromatography Assay

To develop the point-of-care testing method to facilitate the clinical detection of severe fever with thrombocytopenia syndrome virus (SFTSV), colloidal gold paper-based lateral flow immunochromatography test strips (LFITSs) have been fabricated for the rapid detection for the first time. The pH value and the amount of monoclonal antibody to prepare colloidal gold nanoparticle-labeled monoclonal antibody bioconjugates were optimized. In addition, 0.4% bovine serum albumin was considered to be the best concentration for blocking nitrocellulose membranes. Under optimal conditions, the limit of detection for SFTSV was as low as 1 ng/mL depending on a visual line. Meanwhile, the entire detection process required no more than 10 min with a volume of only 50 μL of the analyte solution. Moreover, paper-based LFITSs were evaluated in real samples of human serum of patients with satisfactory results. In addition, all strips were of high stability and specificity. In the light of advantages such as simple, portable, rapid, and low cost, the developed LFITSs will extensively come into service, especially in remote areas.

Therapeutic effects of favipiravir against severe fever with thrombocytopenia syndrome virus infection in a lethal mouse model: Dose-efficacy studies upon oral administration

Severe fever with thrombocytopenia syndrome (SFTS), caused by SFTS virus (SFTSV), is a viral hemorrhagic fever with a high case fatality rate. Favipiravir was reported to be effective in the treatment of SFTSV infection in vivo in type I interferon receptor knockout (IFNAR-/-) mice at treatment dosages of both 60 mg/kg/day and 300 mg/kg/day for a duration of 5 days. In this study, the efficacy of favipiravir at dosages of 120 mg/kg/day and 200 mg/kg/day against SFTSV infection in an IFNAR-/- mouse infection model was investigated. IFNAR-/- mice were subcutaneously infected with SFTSV at a 1.0 × 10(6) 50% tissue culture infectious dose followed by twice daily administration of favipiravir, comprising a total dose of either 120 mg/kg/day or 200 mg/kg/day. The treatment was initiated either immediately post infection or at predesignated time points post infection. Neutralizing antibodies in the convalescent-phase mouse sera was examined by the pseudotyped VSV system. All mice treated with favipiravir at dosages of 120 mg/kg/day or 200 mg/kg/day survived when the treatment was initiated at no later than 4 days post infection. A decrease in body weight of mice was observed when the treatment was initiated at 3-4 days post infection. Furthermore, all control mice died. The body weight of mice did not decrease when treatment with favipiravir was initiated immediately post infection at dosages of 120 mg/kg/day and 200 mg/kg/day. Neutralizing antibodies were detected in the convalescent-phase mouse sera. Similar to the literature-reported peritoneal administration of favipiravir at 300 mg/kg/day, the oral administration of favipiravir at dosages of 120 mg/kg/day and 200 mg/kg/day to IFNAR-/- mice infected with SFTSV was effective.

Laboratory detection and molecular phylogenetic analysis of severe fever with thrombocytopenia syndrome virus in Hubei Province, central China

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by the SFTS virus (SFTSV). Hubei Province is a major epidemic area for SFTS in China. In this study, quantitative reverse-transcription polymerase chain reaction (qRT-PCR) and serological testing (IgM) were used simultaneously for laboratory detection of SFTS; however, testing results showed poor consistency between these two methods. Further analysis revealed that time post-onset was the main factor leading to inconsistent results. Thus, qRT-PCR is unable to detect all SFTS cases, and serological testing is essential. Here, 15 strains of SFTSV were successfully isolated from serum samples of acute SFTSV infection and their complete genomes were sequenced and submitted to GenBank. Phylogenetic analysis showed that the 15 SFTS virus strains clustered into four independent genotypes (A, B, D, and E), demonstrating that at least four genotypes of SFTSV have been co-circulating in Hubei Province. Furthermore, four strains of our isolates (HB2014-31, HB2014-35, HB2014-36, and HB2014-37) clustered in genotype E, which was the predominant genotype in Japan and South Korea. In this study, we identified multiple co-prevalent genotypes and confirmed the existence of genotype E viruses circulating in the Dabie Mountains of Hubei, central China. We concluded that SFTSV strains from Hubei exhibit most of the genetic diversity found in China.

A metagenomic survey identifies Tamdy orthonairovirus as well as divergent phlebo-, rhabdo-, chu- and flavi-like viruses in Anatolia, Turkey

We employed a direct metagenomic approach via next-generation sequencing for a cross-sectional investigation of viruses in 10 tick pools, collected from Aegean, Mediterranean and central Anatolian locations in Turkey. Sequences from all genome segments of Tamdy orthonairovirus (family Nairoviridae) were characterized in ticks collected from a Meriones tristrami. We further obtained near-complete L and partial S segments of several tick-associated phleboviruses (family Phenuiviridae), including Tacheng tick virus 2 and a novel virus, tentatively named as the tick phlebovirus Anatolia. Partial NS5-coding region of recently-described flavi-like virus (Tacheng tick virus 8) was further detected. Moreover, near-complete and polymerase-coding regions of arthropod-associated rhabdoviruses as well as sequences closely-related to the members of the newly-proposed virus family, the Chuviridae, were characterized. Despite origins of the viral sequences could not be fully elucidated, the findings suggest the circulation of diverse arthropod and tick-associated viruses in Anatolia. Occurrence and outcome of vertebrate exposure and probable health impact of these viruses require further investigation. We also report the initial detection of Tamdy orthonairovirus, an established human pathogen, which should be included in the diagnostic workup of infections with unknown etiology.