Severe fever with thrombocytopenia syndrome virus: a highly lethal bunyavirus

Amodiaquine derivatives as inhibitors of severe fever with thrombocytopenia syndrome virus (SFTSV) replication

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne viral infection caused by a bandavirus in the family of Phenuiviridae, commonly known as SFTS virus (SFTSV). We have previously isolated SFTSV from blood samples of SFTS patients and established an antiviral assay system to identify selective inhibitors of SFTSV in vitro. Using the assay system, the antimalarial agent amodiaquine was identified as a selective inhibitor of SFTSV replication. However, due to its insufficient antiviral activity, 98 amodiaquine derivatives were newly synthesized and examined for their anti-SFTSV activity. Among the derivatives, some compounds showed selective inhibitory effect on SFTSV replication in vitro. The 50% effective concentration (EC₅₀) and cytotoxic concentration (CC₅₀) of the most active compound (C-90) were 2.6 ± 0.6 and >50 μM, respectively. This EC₅₀ value was comparable to or slightly better than that of favipiravir (4.1 ± 0.6 μM). On the other hand, pharmacokinetic studies in vivo revealed that C-90 was poor in its oral bioavailability in mice. Therefore, we further designed and synthesized derivatives and obtained 2 compounds with selective anti-SFTSV activity in vitro and improved pharmacokinetics in vivo.

High C-reactive protein to lymphocyte ratio predicts mortality outcomes of patients with severe fever with thrombocytopenia syndrome: A multicenter study in China

Severe fever with thrombocytopenia syndrome (SFTS) is a life-threatening infectious disease caused by the SFTS virus (SFTSV). This study aimed to evaluate the predictive power of C-reactive protein to lymphocyte ratio (CLR) and establish an early-warning model for SFTS mortality. We retrospectively analyzed hospitalized SFTS patients in six clinical centers from May 2011 to 2022. The efficacy of CLR prediction was evaluated by the receiver operating characteristic (ROC) analysis. A nomogram was established and validated. Eight hundred and eighty-two SFTS patients (median age 64 years, 48.5% male) were enrolled in this study, with a mortality rate of 17.8%. The area under the ROC curve (AUC) of CLR was 0.878 (95% confidence interval [CI]: 0.850-0.903, p < 0.001), which demonstrates high predictive strength. The least absolute shrinkage and selection operator regression selected seven potential predictors. Multivariate logistic regression analysis determined three independent risk factors, including CLR, to construct the nomogram. The performance of the nomogram displayed excellent discrimination and calibration, with significant net benefits in clinical uses. CLR is a brand-new predictor for SFTS mortality. The nomogram based on CLR can serve as a convenient tool for physicians to identify critical SFTS cases in clinical practice.

Analysis of the diversity of tick-borne viruses at the border areas in Liaoning Province, China

Ticks play a significant role in transmitting arboviruses, which pose a risk to human and animal health. The region of Liaoning Province, China, with abundant plant resources with multiple tick populations, has reported several tick-borne diseases. However, there remains a scarcity of research on the composition and evolution of the tick virome. In this study, we conducted the metagenomic analysis of 561 ticks in the border area of Liaoning Province in China and identified viruses related to known diseases in humans and animals, including severe fever with thrombocytopenia syndrome virus (SFTSV) and nairobi sheep disease virus (NSDV). Moreover, the groups of tick viruses were also closely related to the families of Flaviviridae, Parvoviridae, Phenuiviridae, and Rhabdoviridae. Notably, the Dabieshan tick virus (DBTV) of the family Phenuiviridae was prevalent in these ticks, with the minimum infection rate (MIR) of 9.09%, higher than previously reported in numerous provinces in China. In addition, sequences of tick-borne viruses of the family Rhabdoviridae have first been reported from the border area of Liaoning Province, China, after being described from Hubei Province, China. This research furthered the insight into pathogens carried by ticks in the northeastern border areas of China, offering epidemiological information for possible forthcoming outbreaks of infectious diseases. Meanwhile, we provided an essential reference for assessing the risk of tick bite infection in humans and animals, as well as for exploring into the evolution of the virus and the mechanisms of species transmission.

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.

A Patient with Severe Fever with Thrombocytopenia Syndrome, Activated Partial Thromboplastin Time Prolongation, and Transient Antiphospholipid Antibodies

A prolonged activated partial thromboplastin time (APTT) is observed in patients with severe fever with thrombocytopenia syndrome (SFTS) and is one of the risk factors for severe disease. The mechanism underlying a prolonged APTT is largely unknown. The presence of antiphospholipid (aPL) antibodies in various viral infections has been documented but never reported in a patient with SFTS. We herein report the first SFTS patient with APTT prolongation and concurrent transiently positive aPL antibodies (lupus anticoagulants and anticardiolipin antibodies) with no coagulation factor deficiency.

Accuracy of reverse-transcription polymerase chain reaction and loop-mediated isothermal amplification in diagnosing severe fever with thrombocytopenia syndrome: A systematic review and meta-analysis

Nucleic acid molecular diagnostic technology plays an important role in the detection of severe fever with thrombocytopenia syndrome (SFTS). However, no relevant reports have been published on the accuracy of reverse-transcription polymerase chain reaction (RT-PCR) and reverse-transcription loop-mediated isothermal amplification (RT-LAMP) in the diagnosis of SFTS. Thus, we conducted a meta-analysis and systematic review to evaluate the accuracy of the two methods. On June 19, 2022, we comprehensively searched the PubMed, Embase, Cochrane Library, Web of Science, Scoups, Ovid, Proquest, China National Knowledge Infrastructure Database, Wan Fang Data, Traditional Chinese Medicine Database (Sinomed), VIP Database, and Reading Showing Database for articles on nucleic acid diagnostic techniques, such as RT-PCR and RT-LAMP, used to diagnose SFTS. Statistical analysis was performed using STATA 14.0 and Meta-Disc 1.4. Sixteen articles involving 2942 clinical blood samples were included in the analysis. RT-PCR and RT-LAMP were used as index tests, whereas RT-PCR or other detection methods were used as reference standards. The pooled values for the sensitivity, specificity, positive and negative likelihood ratios of the RT-PCR test were 0.97 (95% confidence interval [CI]: 0.92-0.99), 1.00 (95% CI: 0.98-1.00), 483.87 (95% CI: 58.04-4033.76), and 0.03 (95% CI:0.01-0.08), respectively. Those for the RT-LAMP test were 0.95 (95% CI: 0.91-0.97), 0.99 (95% CI: 0.93-1.00), 111.18 (95% CI: 13.96-885.27), and 0.05 (95% CI: 0.03-0.09), respectively. Both RT-PCR and RT-LAMP have high diagnostic value in SFTS and can be applied in different scenarios for laboratory confirmation or on-site screening.

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.

Spatiotemporal analysis of severe fever with thrombocytopenia syndrome in Shandong Province, China, 2014-2018

BACKGROUND

Due to recent emergence, severe fever with thrombocytopenia syndrome (SFTS) is becoming one of the major public health problems in Shandong Province, China. The numbers of reported SFTS cases in general and the area with reported SFTS cases are both continuously increasing in recent years. However, spatiotemporal patterns and clusters of SFTS in Shandong Province have not been investigated yet.

METHODS

The surveillance data of SFTS in Shandong Province, China, during 2014-2018 were extracted from China Information System for Disease Control and Prevention (CISDCP). Geoda software was used to explore spatial autocorrelation analysis, and Satscan software was used to identify spatio-temporal clustering of cases. The results were presented in ArcMap.

RESULTS

The annual average incidence was 0.567/100,000 in Shandong Province during 2014-2018. Results showed that the distribution of SFTS was not random but clustered in space and time. A most likely cluster including 15 counties was observed in the northeastern region of Shandong Province from January 1, 2015 to December 31, 2015 (Relative risk = 5.13, Log likelihood ratio = 361.266, P < 0.001).

CONCLUSIONS

The number of SFTS cases in Shandong Province increased overall. Geographic information system analysis coupled with spatial analysis illustrated regions with SFTS clusters. Our results provide a sound evidence base for future prevention and control programs of SFTS such as allocation of the health resources, surveillance in high-risk regions, health education, improvement of diagnosis and so on.

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.

Analysis of the spatial-temporal components driving transmission of the severe fever with thrombocytopenia syndrome in Shandong Province, China, 2016-2018

Existing models about the spatial-temporal distribution of the severe fever with thrombocytopenia syndrome (SFTS) entirely concentrate on aggregation, which provides limited knowledge to develop effective measures to control the epidemic of SFTS. This study aimed to identify the main spatial-temporal components and heterogeneity in different regions in Shandong Province, China. We applied the spatial-temporal multicomponent model to detect the spatial-temporal component values. A total of 2814 cases were reported from 2016 to 2018 in Shandong Province. The prevalence rate was 0.627 per 100,000, with an overall case fatality rate of 8.99%. SFTS cases were mostly clustered in central and eastern regions of Shandong Province. The total effect values of the autoregressive component, the spatiotemporal component and the endemic component were 0.586, 0.244 and 0.084, respectively, which demonstrated that the autoregressive component was the main factor driving the incidence of SFTS, followed by the spatiotemporal component. Gross domestic product per capita and weekly mean atmospheric pressure contributed to the incidence of SFTS with inverse effects. Obvious heterogeneity across regions for the autoregressive component and the spatiotemporal component was identified. In conclusion, the autoregressive and spatiotemporal components play a key role in driving the transmission of SFTS in Shandong Province. Based on the main component values, targeted measures should be formulated to control SFTS epidemics in different regions.

Metatranscriptomics Reveals the Diversity of the Tick Virome in Northwest China

Blood-sucking ticks are obligate parasites and vectors of a variety of human and animal viruses. Some tick-borne viruses have been identified as pathogens of infectious diseases in humans or animals, potentially imposing significant public health burdens and threats to the husbandry industry. Therefore, identifying the profiles of tick-borne viruses will provide valuable information about the evolution and pathogen ecology of tick-borne viruses. In this study, we investigated the viromes of parasitic ticks collected from the body surfaces of herbivores in Xinjiang Uyghur Autonomous Region and Inner Mongolia Autonomous Region of China, two regions in northwest China. By using a metatranscriptomic approach, 17 RNA viruses with high diversity in genomic organization and evolution were identified. Among them, nine are proposed to be novel species. The classified viruses belonged to six viral families, including Phenuiviridae, Rhabdoviridae, Peribunyaviridae, Lispiviridae, Chuviridae, and Reoviridae, and unclassified viruses were also identified. In addition, although some viruses from different sampling locations shared significant similarities, the abundance and diversity of viruses notably varied among the different collection locations. This study demonstrates the diversity of tick-borne viruses in Xinjiang and Inner Mongolia and provides informative data for further study of the evolution and pathogenicity of these RNA viruses. IMPORTANCE Ticks are widely distributed in pastoral areas in northwestern China and act as vectors that carry and transmit a variety of pathogens, especially viruses. Our study revealed the diversity of tick viruses in Xinjiang and Inner Mongolia and uncovered the phylogenetic relationships of some RNA viruses, especially the important zoonotic tick-borne severe fever with thrombocytopenia syndrome virus in Inner Mongolia. These data suggest a complex and diverse evolutionary history and potential ecological factors associated with pathogenic viruses. The pathogenicity of these tick-borne viruses currently remains unclear. Therefore, future research should focus on evaluating the transmissability and pathogenicity of these tick-borne viruses.

Spectrum and trigger identification of hemophagocytic lymphohistiocytosis in adults: A single-center analysis of 555 cases

Limited data are available about the underlying causes of hemophagocytic lymphohistiocytosis (HLH) in adults. We collected and analyzed the data of 555 cases of adult HLH. HLH in 242 patients were malignancies-related and lymphoid malignancies (42.0%, 233/555) were the most common causes. Aggressive natural killer-cell leukemia, diffuse large B-cell lymphoma, and extranodal natural killer/T-cell lymphoma, nasal type were the most common specified pathological subtypes. Epstein-Barr virus (EBV) (69.0%, 100/145) was the most common pathogen among the cases of infections-related HLH (26.1%, 145/555). Malignancies-related HLH showed male preponderance, more common splenomegaly, more severe anemia and thrombocytopenia, and significantly elevated soluble CD25. In patients with abnormal lymphoid cells in the bone marrow (BM) and increased EBV DNA copy number, 48.9% (45/92) of them were aggressive natural killer-cell leukemia. In patients with abnormal lymphoid cells in the BM and normal EBV DNA copy number, 66.2% (47/71) of them were B-cell non-Hodgkin lymphoma. In patients with elevated EBV DNA copy number but no abnormal lymphoid cells in the BM, 71.0% (98/138) of these cases were EBV infection. In conclusion, lymphoid malignancy is the most common underlying cause of adult HLH, followed by EBV infection. Based on the BM morphology and EBV load, we developed a diagnostic flow for rapid determination of the triggers for HLH.

Immune escape mechanisms of severe fever with thrombocytopenia syndrome virus

Severe fever with thrombocytopenia syndrome (SFTS), which is caused by SFTS virus (SFTSV), poses a serious threat to global public health, with high fatalities and an increasing prevalence. As effective therapies and prevention strategies are limited, there is an urgent need to elucidate the pathogenesis of SFTS. SFTSV has evolved several mechanisms to escape from host immunity. In this review, we summarize the mechanisms through which SFTSV escapes host immune responses, including the inhibition of innate immunity and evasion of adaptive immunity. Understanding the pathogenesis of SFTS will aid in the development of new strategies for the treatment of this disease.

Effects of corticosteroids treatment in patients with Severe Fever with Thrombocytopenia Syndrome:A single-center retrospective cohort study

OBJECTIVES

To evaluate the effect and safety of corticosteroids(CS) treatment in patients with severe fever with thrombocytopenia syndrome(SFTS).

METHODS

Patients with and without CS were retrospectively compared by COX regression and 1:1 propensity score matching analysis to evaluate the effects of CS on mortality and secondary infections in patients with SFTS.

RESULTS

A total of 467 SFTS patients were enrolled in the cohort study, there were 52 fatal cases and 415 nonfatal cases,the overall fatality rate was 11.1%. The mortality were observed in 36/144 (25%) and 16/323 (5%) patients in the CS-treated and non-CS-treated groups,respectively (P<0.001).Multivariate cox regression analysis showed that the difference was not statistically significant for CS treatment in the fatality (P>0.05, aHR 1.003, 95%CI 0.49-2.06).Difference in survival time between CS-treated and non-CS-treated groups after propensity score matching had no statistically significant (Log-Rank test P=0.390),whereas there was a significant difference in secondary infections between the CS-treated and non-CS-treated groups (P=0.007).

CONCLUSIONS

Although the CS treatment had no influence on fatality in patients with SFTS, it increased the risk of secondary infections.Administration of CS in patients with SFTS should be carefully considered and take into account the balance between therapeutic efficacy and adverse effects.

NLR, A Convenient Early-Warning Biomarker of Fatal Outcome in Patients With Severe Fever With Thrombocytopenia Syndrome

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease that greatly threatens public health. This study aimed to examine a convenient early-warning biomarker of fatal outcomes in patients with SFTS to reduce mortality.

Methods

A retrospective cohort study was performed, and patients with confirmed SFTS were enrolled in the top two hospitals in Anhui Province, China from 1 May 2016 to 31 October 2019. The clinical symptoms, laboratory indicators, and treatment data of patients with SFTS were evaluated. All patients with SFTS were followed up till 28 days from the start of admission. The laboratory indicators that could be used to predict the fatal outcome were identified.

Results

A total of 228 patients with SFTS were enrolled, 177 patients were enrolled in the survival group, and 51 patients in the death group. The median age of all 228 patients with SFTS was 63 years. Five laboratory indicators (SFTSV viral load, neutrophil to lymphocyte ratio (NLR), aspartate transaminase (AST)/alanine aminotransferase (ALT), ALT, and blood urea nitrogen (BUN)) were identified as the predicting factors of the fatal outcome of patients with SFTS. The area under the receiver operating characteristic (ROC) curve (AUC) of SFTSV viral load was the highest (0.919), then NLR (0.849), followed by AST/ALT (0.758), AST (0.738), and BUN (0.709). The efficacy of SFTVS viral load and NLR in predicting fatal outcomes was significantly higher than AST/ALT, AST, and BUN. The Kaplan–Meier survival curves show that the case fatality rate was significantly increased in patients whose SFTSV viral load was higher than 500,000 or NLR higher than 2.0. Gamma-globulin treatment showed a significant difference between the survival group and the death group, and the duration of gamma-globulin that had been proposed should not be <3 days.

Conclusion

The SFTSV viral load and NLR showed great efficacy in predicting the fatal outcome of patients with SFTS, and NLR is a convenient and efficient early-warning biomarker that helps healthcare workers focus on patients with high risks of fatal outcomes. The efficacy of gamma-globulin provided a new idea for the treatment of SFTS, which needs further analysis in future studies.

Clinical laboratory parameters and fatality of Severe fever with thrombocytopenia syndrome patients: A systematic review and meta-analysis

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infectious disease with high case fatality rate. Unfortunately, no vaccine or antiviral specifically targeting SFTS virus (SFTSV) are available for the time being. Our objective was to investigate the association between clinical laboratory parameters and fatality of SFTS patients.

Methods

The systematic review was conducted in accordance with The Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 guidelines. We searched (from inception to 24th February 2022) Web of Science, PubMed, National Knowledge Infrastructure databases and Wan Fang Data for relevant researchers on SFTS. Studies were eligible if they reported on laboratory parameters of SFTS patients and were stratified by clinical outcomes. A modified version of Newcastle-Ottawa scale was used to evaluate the quality of included studies. Standardized mean difference (SMD) was used to evaluate the association between laboratory parameters and outcomes. The between-study heterogeneity was evaluated quantitatively by standard Chi-square and the index of heterogeneity (I2). Heterogeneity was explored by subgroup and sensitivity analyses, and univariable meta-regression. Publication bias was determined using funnel plots and Egger’s test.

Results

We identified 34 relevant studies, with over 3300 participants across three countries. The following factors were strongly (SMD>1 or SMD<-0.5) and significantly (P<0.05) associated mortality: thrombin time (TT) (SMD = 1.53), viral load (SMD = 1.47), activated partial-thromboplastin time (APTT) (SMD = 1.37), aspartate aminotransferase (AST) (SMD = 1.19), lactate dehydrogenase (LDH) (SMD = 1.13), platelet count (PLT) (SMD = -0.47), monocyte percentage (MON%) (SMD = -0.47), lymphocyte percentage (LYM%) (SMD = -0.46) and albumin (ALB) (SMD = -0.43). Alanine aminotransferase, AST, creatin phosphokinase, LDH, PLT, partial-thromboplastin time and viral load contributed to the risk of dying of SFTS patients in each subgroup analyses. Sensitivity analysis demonstrated that the results above were robust.

Conclusions/significance

The abnormal levels of viral load, PLT, coagulation function and liver function, significantly increase the risk of SFTS mortality, suggesting that SFTS patients with above symptoms call for special concern.

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.

The Prognostic Significance of C-Reactive Protein to Albumin Ratio in Patients With Severe Fever With Thrombocytopenia Syndrome

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with the high case-fatality rate, lacking effective therapies and vaccines. Inflammation-based indexes have been widely used to predict the prognosis of patients with cancers and some inflammatory diseases. In our study, we aim to explore the predictive value of the inflammation-based indexes in SFTS patients.

Methods

We retrospectively analyzed 82 patients diagnosed with SFTS. The inflammation-based indexes, including neutrophil-to-lymphocyte ratio (NLR), monocyte-to-lymphocyte ratio (MLR), platelet-to-lymphocyte ratio (PLR), systemic immune-inflammation index (SII), systemic inflammation response index (SIRI), aggregate index of systemic inflammation (AISI) and C-reactive protein to albumin ratio (CAR), were compared between the survival and death patients. Receiver operating characteristic (ROC) curves were used to compare the predictive ability of MLR, AISI, and CAR. The survival analysis was based on the Kaplan–Meier (KM) method. Multivariate logistic regression analysis was used to analyze the independent risk factors of poor prognosis in patients with SFTS.

Results

The CAR is higher in the death group while MLR and AISI were higher in the survival group. The ROC curve analysis indicated CAR exhibited more predictive value than the other indexes and the optimal cut-off value of CAR was equal to or greater than 0.14. KM survival curve showed that higher CAR was significantly correlated to the lower overall survival in SFTS patients. Multivariate logistic regression analysis indicated that CAR was an independent risk factor for poor prognosis in patients with SFTS.

Conclusion

The CAR is an independent risk factor for death in patients with SFTS and could predict the poor prognosis of SFTS patients. It could be used as a biomarker to help physicians to monitor and treat patients more aggressively to improve clinical prognosis.

Reverse Genetics System for Heartland Bandavirus: NSs Protein Contributes to Heartland Bandavirus Virulence

Heartland bandavirus (HRTV), which is an emerging tick-borne virus first identified in Missouri in 2009, causes fever, fatigue, decreased appetite, headache, nausea, diarrhea, and muscle or joint pain in humans. HRTV is genetically close to Dabie bandavirus, which is the causative agent of severe fever with thrombocytopenia syndrome (SFTS) in humans and is known as SFTS virus (SFTSV). The generation of infectious HRTV entirely from cloned cDNAs has not yet been reported. The absence of a reverse genetics system for HRTV has delayed efforts to understand its pathogenesis and to generate vaccines and antiviral drugs. Here, we developed a reverse genetics system for HRTV, which employs an RNA polymerase I-mediated expression system. A recombinant nonstructural protein (NSs)-knockout HRTV (rHRTV-NSsKO) was generated. We found that NSs interrupted signaling associated with innate immunity in HRTV-infected cells. The rHRTV-NSsKO was highly attenuated, indicated by the apparent absence of symptoms in a mouse model of HRTV infection. Moreover, mice immunized with rHRTV-NSsKO survived a lethal dose of HRTV. These findings suggest that NSs is a virulence factor of HRTV and that rHRTV-NSsKO could be a vaccine candidate for HRTV. IMPORTANCE Heartland bandavirus (HRTV) is a tick-borne virus identified in the United States in 2009. HRTV causes fever, fatigue, decreased appetite, headache, nausea, diarrhea, and muscle or joint pain in humans. FDA-approved vaccines and antiviral drugs are unavailable. The lack of a reverse genetics system hampers efforts to develop such antiviral therapeutics. Here, we developed a reverse genetics system for HRTV that led to the generation of a recombinant nonstructural protein (NSs)-knockout HRTV (rHRTV-NSsKO). We found that NSs interrupted signaling associated with innate immunity in HRTV-infected cells. Furthermore, rHRTV-NSsKO was highly attenuated and immunogenic in a mouse model. These findings suggest that NSs is a virulence factor of HRTV and that rHRTV-NSsKO could be a vaccine candidate for HRTV.

Virtual screening of phytochemicals from Indian medicinal plants against the endonuclease domain of SFTS virus L polymerase

Severe fever with thrombocytopenia syndrome virus (SFTSV) causes a highly infectious disease with reported mortality in the range 2.8% to 47%. The replication and transcription of the SFTSV genome is performed by L polymerase, which has both an RNA dependent RNA polymerase domain and an N-terminal endonuclease (endoN) domain. Due to its crucial role in the cap-snatching mechanism required for initiation of viral RNA transcription, the endoN domain is an ideal antiviral drug target. In this virtual screening study for the identification of potential inhibitors of the endoN domain of SFTSV L polymerase, we have used molecular docking and molecular dynamics (MD) simulation to explore the natural product space of 14 011 phytochemicals from Indian medicinal plants. After generating a heterogeneous ensemble of endoN domain structures reflecting conformational diversity of the corresponding active site using MD simulations, ensemble docking of the phytochemicals was performed against the endoN domain structures. Apart from the ligand binding energy from docking, our virtual screening workflow imposes additional filters such as drug-likeness, non-covalent interactions with key active site residues, toxicity and chemical similarity with other hits, to identify top 5 potential phytochemical inhibitors of endoN domain of SFTSV L polymerase. Further, the stability of the protein–ligand docked complexes for the top 5 potential inhibitors was analyzed using MD simulations. The potential phytochemical inhibitors, predicted in this study using contemporary computational methods, are expected to serve as lead molecules in future experimental studies towards development of antiviral drugs against SFTSV.

Virtual screening of a large phytochemical library from Indian medicinal plants to identify potential endonuclease inhibitors against emerging virus SFTSV.

CRISPR/Cas12a Technology Combined With RPA for Rapid and Portable SFTSV Detection

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a new tick-borne pathogen that can cause severe hemorrhagic fever. Fever with thrombocytopenia syndrome caused by SFTSV is a new infectious disease that has posed a great threat to public health. Therefore, a fast, sensitive, low-cost, and field-deployable detection method for diagnosing SFTSV is essential for virus surveillance and control. In this study, we developed a rapid, highly sensitive, instrument-flexible SFTSV detection method that utilizes recombinase polymerase amplification and the CRISPR/Cas12a system. We found that three copies of the L gene from the SFTSV genome per reaction were enough to ensure stable detection within 40 min. The assay clearly showed no cross-reactivity with other RNA viruses. Additionally, our method demonstrated 100% agreement with Q-PCR detection results for SFTSV in 46 clinical samples. We simplified the requirements for on-site detection instruments by combining the CRISPR/Cas12a tool and immunochromatographic strips to create a system that can reliably detect one copy/μl sample of the L gene, which showed extremely high sensitivity and specificity for detecting the virus. Taken together, these findings indicate that the new SFTSV detection method is a powerful and effective tool for on-site detection, which can contribute to diagnosing SFTSV quickly and sensitively.

Predictive Value of the Platelet-to-Albumin Ratio (PAR) on the Risk of Death at Admission in Patients Suffering from Severe Fever with Thrombocytopenia Syndrome

Objective

The purpose of this study was to evaluate the predictive value of the platelet-to-albumin ratio (PAR) on the risk of death in patients with severe fever with thrombocytopenia syndrome.

Methods

Between Jan 2019 and June 2021, 127 cases which were admitted to the First Affiliated Hospital of Anhui Medical University have been included in this study. The laboratory data were selected at the time of admission. To identify the potential independent risk factors for severe fever associated with thrombocytopenia syndrome, multivariate logistic regression analysis was performed. Receiver operating characteristic (ROC) curve analysis was used to evaluate the prediction accuracy of PAR in identifying patients exhibiting severe fever with thrombocytopenia syndrome.

Results

Multiple logistic regression analysis showed that PAR could potentially serve as an independent risk factor for the death in patients with SFTS (OR = 4.023, 95% CI 1.204–13.436, P=0.024). The prediction of the risk of death in patients with SFTS was assessed using the AUC. The AUC for the PAR was 0.729 (95% CI, 0.637–0.82, P < 0.001), whereas the optimal cut-off value of PAR was found to be 1.43, with 54.9% sensitivity and 86.1% specificity.

Conclusion

Our study demonstrated for the first time that PAR could act as an independent predictor for mortality in adult patients with SFTS.

Time Course of Severe Fever With Thrombocytopenia Syndrome Virus and Antibodies in Patients by Long-Term Follow-Up Study, China

Objectives: The objective was to describe the changes of severe fever with thrombocytopenia syndrome virus (SFTSV) and antibody in the disease course and explore the relationship between antibody titers and patients’ prognosis.

Methods: The levels of SFTSV, virus-specific immunoglobulin M (IgM), immunoglobulin G (IgG) titers, and cytokines in 37 patients with severe fever with thrombocytopenia syndrome (SFTS) were measured dynamically by real-time PCR and ELISA during the disease course; IgG titers were followed up in 53 cases. The correlation analysis of antibody titers with individual serum cytokines was calculated using the Spearman test.

Results: The average time of SFTSV duration in individual serum was 22.45 ± 7.6 days from onset. We found SFTSV turned negative within the 10th day from the onset in two patients. SFTSV-specific IgM seroconversion occurred as early as within 3 days from the onset, increased gradually within the first 2 months, decreased gradually 3 months later, and disappeared after 6 months in all the patients. The average time of SFTSV-specific IgG antibody seroconversion was at 17 days from onset in the patients; the time was later in severe cases than in mild cases (23 ± 1.4 vs. 14.3 ± 1.0 days, p < 0.0001). IgG titers were maintained at the peak levels during the periods from 6 months to 1 year and decreased from the second year gradually. Severe cases had higher IgG levels than mild cases and also had a slower decreasing trend. During follow-up, only one lost IgG antibody 7 years later; no chronic infection and sequela were found among the 53 patients. None of the patients had SFTSV reinfection even if they were bitten by ticks again. The correlation analysis showed a positive relationship between inflammatory factors and IgG antibody levels.

Conclusion: IgM antibody has important value in early diagnosis of SFTS. A moderate inflammatory response is beneficial for production and duration of IgG antibodies.

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.

Clinical Update of Severe Fever with Thrombocytopenia Syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is an acute febrile illness characterized by fever, leukopenia, thrombocytopenia, and gastrointestinal symptoms such as diarrhea, nausea, and vomiting resulting from infection with the SFTS virus (SFTSV). The SFTSV is transmitted to humans by tick bites, primarily from Haemaphysalis longicornis, Amblyomma testudinarium, Ixodes nipponensis, and Rhipicephalus microplus. Human-to-human transmission has also been reported. Since the first report of an SFTS patient in China, the number of patients has also been increasing. The mortality rate of patients with SFTS remains high because the disease can quickly lead to death through multiple organ failure. In particular, an average fatality rate of approximately 20% has been reported for SFTS patients, and no treatment strategy has been established. Therefore, effective antiviral agents and vaccines are required. Here, we aim to review the epidemiology, clinical manifestations, laboratory diagnosis, and various specific treatments (i.e., antiviral agents, steroids, intravenous immunoglobulin, and plasma exchange) that have been tested to help to cope with the disease.