The cholesterol, fatty acid and triglyceride synthesis pathways regulated by site 1 protease (S1P) are required for efficient replication of severe fever with thrombocytopenia syndrome virus

The NSs protein of severe fever with thrombocytopenia syndrome virus differentially inhibits the type 1 interferon response among animal species

Severe fever with thrombocytopenia syndrome virus (SFTSV), which has been reported in China, Korea, Japan, Vietnam, and Taiwan, is a causative agent of severe fever thrombocytopenia syndrome (SFTS). This virus has a high mortality and induces thrombocytopenia and leukocytopenia in humans, cats, and aged ferrets, whereas immunocompetent adult mice infected with SFTSV never show symptoms. Anti-SFTSV antibodies have been detected in several animals- including goats, sheep, cattle, and pigs. However, there are no reports of SFTS in these animals. Previous studies have reported that the nonstructural protein NSs of SFTSV inhibits the type I interferon (IFN-I) response through the sequestration of human signal transducer and activator of transcription (STAT) proteins. In this study, comparative analysis of the function of NSs as IFN antagonists in human, cat, dog, ferret, mouse, and pig cells revealed a correlation between pathogenicity of SFTSV and the function of NSs in each animal. Furthermore, we found that the inhibition of IFN-I signaling and phosphorylation of STAT1 and STAT2 by NSs depended on the binding ability of NSs to STAT1 and STAT2. Our results imply that the function of NSs in antagonizing STAT2 determines the species-specific pathogenicity of SFTSV.

A Reservoir Computing with Boosted Topology Model to Predict Encephalitis and Mortality for Patients with Severe Fever with Thrombocytopenia Syndrome: A Retrospective Multicenter Study

INTRODUCTION

Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging tick-borne virus associated with a high rate of mortality, as well as encephalitis. We aim to develop and validate a machine learning model to early predict the potential life-threatening conditions of SFTS.

METHODS

The clinical presentation, demographic information, and laboratory parameters from 327 patients with SFTS at admission in three large tertiary hospitals in Jiangsu, China between 2010 to 2022 are retrieved. We establish a reservoir computing with boosted topology (RC-BT) algorithm to obtain the models' predictions of the encephalitis and mortality of patients with SFTS. The prediction performances of encephalitis and mortality are further tested and validated. Finally, we compare our RC-BT model with the other traditional machine learning algorithms including Lightgbm, support vector machine (SVM), Xgboost, Decision Tree, and Neural Network (NN).

RESULTS

For the prediction of encephalitis among patients with SFTS, nine parameters are selected with equal weight, namely calcium, cholesterol, muscle soreness, dry cough, smoking history, temperature at admission, troponin T, potassium, and thermal peak. The accuracy for the validation cohort by the RC-BT model is 0.897 [95% confidence interval (CI) 0.873-0.921]. The sensitivity and negative predictive value (NPV) of the RC-BT model are 0.855 (95% CI 0.824-0.886) and 0.904 (95% CI 0.863-0.945), respectively. Area under curve of the RC-BT model for the validation cohort is 0.899 (95% CI 0.882-0.916). For the prediction of fatality among patients with SFTS, seven parameters are selected with equal weight, namely calcium, cholesterol, history of drinking, headache, field contact, potassium, and dyspnea. The accuracy of the RC-BT model is 0.903 (95% CI 0.881-0.925). The sensitivity and NPV of the RC-BT model are 0.913 (95% CI 0.902-0.924) and 0.946 (95% CI 0.917-0.975), respectively. The area under curve is 0.917 (95% CI 0.902-0.932). Importantly, the RC-BT models outperform the other artificial intelligence-based algorithms in both prediction tasks.

CONCLUSIONS

Our two RC-BT models of SFTS encephalitis and fatality demonstrate high area under curves, specificity, and NPV, with nine and seven routine clinical parameters, respectively. Our models can not only greatly improve the early prognosis accuracy of SFTS, but can also be widely applied in underdeveloped areas with limited medical resources.

Identification of surfactin as an anti-severe fever with thrombocytopenia syndrome virus multi-target compound extracted from the culture broth of marine microbes

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne virus first identified in China in 2011 and later reported in other Asian countries. Significant efforts have been made to develop anti-SFTSV compounds; however, there are no approved vaccines or antivirals against SFTSV infections. Marine organisms provide nearly unlimited biological resources to produce therapeutic drugs for the treatment and control of disease. In this study, we aimed to identify anti-SFTSV chemical compounds from the culture broth extracts of marine microbes collected from the coasts of the Nagasaki Prefecture, Japan. Of the 80 extracts, two showed an anti-SFTSV effect. One of them, which exhibited low cell toxicity, was used for further characterization. Chemical analysis combined with the anti-SFTSV effect identified surfactin as one of the main components of the selected extract. Our study showed a proof-of-concept to identify novel antiviral compounds from marine microbes against the virus of interest. Further analysis showed that surfactin affected the integrity of the virion membrane and inhibited SFTSV infection-induced membrane fusion at low pH conditions. Furthermore, surfactin inhibits the post-entry step of viral replication in the cell, which is a novel mode of antiviral action of surfactin. These results indicate that surfactin can target multiple steps of SFTSV replication in cells.

Metabolic syndrome and aberrant immune responses to viral infection and vaccination: Insights from small animal models

This review outlines the propensity for metabolic syndrome (MetS) to induce elevated disease severity, higher mortality rates post-infection, and poor vaccination outcomes for viral pathogens. MetS is a cluster of conditions including high blood glucose, an increase in circulating low-density lipoproteins and triglycerides, abdominal obesity, and elevated blood pressure which often overlap in their occurrence. MetS diagnoses are on the rise, as reported cases have increased by greater than 35% since 1988, resulting in one-third of United States adults currently diagnosed as MetS patients. In the aftermath of the 2009 H1N1 pandemic, a link between MetS and disease severity was established. Since then, numerous studies have been conducted to illuminate the impact of MetS on enhancing virally induced morbidity and dysregulation of the host immune response. These correlative studies have emphasized the need for elucidating the mechanisms by which these alterations occur, and animal studies conducted as early as the 1940s have linked the conditions associated with MetS with enhanced viral disease severity and poor vaccine outcomes. In this review, we provide an overview of the importance of considering overall metabolic health in terms of cholesterolemia, glycemia, triglyceridemia, insulin and other metabolic molecules, along with blood pressure levels and obesity when studying the impact of metabolism-related malignancies on immune function. We highlight the novel insights that small animal models have provided for MetS-associated immune dysfunction following viral infection. Such animal models of aberrant metabolism have paved the way for our current understanding of MetS and its impact on viral disease severity, dysregulated immune responses to viral pathogens, poor vaccination outcomes, and contributions to the emergence of viral variants.

Antiviral Treatment Options for Severe Fever with Thrombocytopenia Syndrome Infections

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne virus that produces severe fever with thrombocytopenia syndrome (SFTS). It is widespread in Japan, South Korea, and Central and Eastern China. The epidemic has developed rapidly through China in recent years. SFTS cases have been reported in 25 provinces in China, mainly distributed in rural areas in mountainous and hilly areas. The infection has a high case fatality rate and no specific treatments or vaccinations. Therefore, early diagnosis and treatment of SFTS infection is important to survival and disease control. In this article, we provide an overview on different aspects of SFTS with an emphasis on management, to explore the current treatment and prophylactic measures further.

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.

The novel therapeutic target and inhibitory effects of PF-429242 against Zika virus infection

Zika virus (ZIKV) is a re-emerging mosquito-borne flavivirus of African origin that is transmitted by Aedes mosquitoes. ZIKV was historically limited to Africa and Asia, where mild cases were reported. However, ZIKV has recently been responsible for major global outbreaks associated with a wide range of neurological complications. Since no antiviral therapy exists for ZIKV, drug discovery research for ZIKV is crucial. Intracellular lipids regulated by sterol regulatory element-binding proteins (SREBPs) are important in flavivirus pathogenesis. PF-429242 has been reported to inhibit the activity of site-1 protease (S1P), which regulates the expression of SREBP target genes. Our primary objective in this study is to elucidate the mechanism of the antiviral activity of PF-429242 against the African genotype (ZIKV_MR-766) and Asian genotypes (ZIKV _{H/PF 2013} and ZIKV _PRVABC59) using several primate-derived cell lines. The virus titer was determined via a focus-forming assay; we used flow cytometry to quantify intracellular lipids in ZIKV-infected and mock-treated cells. The PF-429242 molecule effectively suppressed ZIKV infection in neuronal cell lines; T98G, U-87MG, SK-N-SH and primary monocytes cell, indicating that PF-429242 molecule can be used therapeutically. A strong reduction in ZIKV replication was observed at 12 μM and 30 μM in in neuronal cell lines and primary monocytes, respectively. Interestingly, the inhibitory effects of the PF-429242 molecule were observed when it was tested on various ZIKV-lineage infections. Lipid quantification reveals that ZIKV increases lipogenesis in infected cells, while the exogenous addition of cholesterol effectively blocks ZIKV replication. Furthermore, the supplementation of oleic acid increases the ZIKV titer. Fenofibrate, an inhibitor of lipid droplet formation, reduces the ZIKV titer. Collectively, our results demonstrate that the development of antiviral drugs against ZIKV could be based on key regulators of lipid metabolism. In addition, this study reveals that the mechanism of the PF-429242-mediated suppression among flavivirus infections is not entirely identical. Our results warrant further evaluation of PF-429242 as a prospective antiviral drug, given the multiple advantageous properties of this compound, such as its limited toxicity, neuroprotective properties, and broad spectrum of capabilities.

Loperamide Inhibits Replication of Severe Fever with Thrombocytopenia Syndrome Virus

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infectious disease caused by the SFTS virus (SFTSV). SFTS is mainly prevalent in East Asia. It has a mortality rate of up to 30%, and there is no approved treatment against the disease. In this study, we evaluated the effect of loperamide, an antidiarrheal and antihyperalgesic agent, on the propagation of SFTSV in a cell culture system.

METHODS

SFTSV-infected human cell lines were exposed to loperamide, and viral titers were evaluated. To clarify the mode of action of loperamide, several chemical compounds having shared targets with loperamide were used. Calcium imaging was also performed to understand whether loperamide treatment affected calcium influx.

RESULTS

Loperamide inhibited SFTSV propagation in several cell lines. It inhibited SFTSV in the post-entry step and restricted calcium influx into the cell. Furthermore, nifedipine, a calcium channel inhibitor, also blocked post-entry step of SFTSV infection.

CONCLUSIONS

Loperamide inhibits SFTSV propagation mainly by restraining calcium influx into the cytoplasm. This indicates that loperamide, a Food and Drug Administration (FDA)-approved drug, has the potential for being used as a treatment option against SFTS.

Strategy, Progress, and Challenges of Drug Repurposing for Efficient Antiviral Discovery

Emerging or re-emerging viruses are still major threats to public health. Prophylactic vaccines represent the most effective way to prevent virus infection; however, antivirals are more promising for those viruses against which vaccines are not effective enough or contemporarily unavailable. Because of the slow pace of novel antiviral discovery, the high disuse rates, and the substantial cost, repurposing of the well-characterized therapeutics, either approved or under investigation, is becoming an attractive strategy to identify the new directions to treat virus infections. In this review, we described recent progress in identifying broad-spectrum antivirals through drug repurposing. We defined the two major categories of the repurposed antivirals, direct-acting repurposed antivirals (DARA) and host-targeting repurposed antivirals (HTRA). Under each category, we summarized repurposed antivirals with potential broad-spectrum activity against a variety of viruses and discussed the possible mechanisms of action. Finally, we proposed the potential investigative directions of drug repurposing.

Human BST-2/tetherin inhibits Junin virus release from host cells and its inhibition is partially counteracted by viral nucleoprotein

Bone marrow stromal cell antigen-2 (BST-2), also known as tetherin, is an interferon-inducible membrane-associated protein. It effectively targets enveloped viruses at the release step of progeny viruses from host cells, thereby restricting the further spread of viral infection. Junin virus (JUNV) is a member of Arenaviridae, which causes Argentine haemorrhagic fever that is associated with a high rate of mortality. In this study, we examined the effect of human BST-2 on the replication and propagation of JUNV. The production of JUNV Z-mediated virus-like particles (VLPs) was significantly inhibited by over-expression of BST-2. Electron microscopy analysis revealed that BST-2 functions by forming a physical link that directly retains VLPs on the cell surface. Infection using JUNV showed that infectious JUNV production was moderately inhibited by endogenous or exogenous BST-2. We also observed that JUNV infection triggers an intense interferon response, causing an upregulation of BST-2, in infected cells. However, the expression of cell surface BST-2 was reduced upon infection. Furthermore, the expression of JUNV nucleoprotein (NP) partially recovered VLP production from BST-2 restriction, suggesting that the NP functions as an antagonist against antiviral effect of BST-2. We further showed that JUNV NP also rescued the production of Ebola virus VP40-mediated VLP from BST-2 restriction as a broad spectrum BST-2 antagonist. To our knowledge, this is the first report showing that an arenavirus protein counteracts the antiviral function of BST-2.

[Molecular mechanisms of highly pathogenic viruses' replication and their applications for a novel drug discovery]

Productive (lytic) replication of DNA viruses elicits host cell DNA damage responses, which cause both beneficial and detrimental effects on viral replication. Viruses utilize them and selectively cancel the 'noisy' downstream signaling pathways, leading to maintain high S-phase CDK activities required for viral replication. To achieve this fine tuning of cellular environment, herpesviruses encode many (>70) genes in their genome, which are expressed in a strictly regulated temporal cascade (immediate-early, early, and late). Here, I introduce and discuss how Epstein-Barr virus, an oncogenic herpesvirus, hijacks the cellular environment and adapt it for the progeny production.

The clinically licensed antifungal drug itraconazole inhibits influenza virus in vitro and in vivo

Influenza A virus (IAV) is a common pathogen of respiratory disease. The IAV-induced seasonal epidemics and the sporadic pandemics are associated with high morbidity and mortality. Therefore, effective protection and therapy for IAV infections is an important challenge in countering this public health threat. Because vaccinations only protect against known circulating strains, and the currently available antivirals pose the risk of resistance formation, drugs targeting host cell factors needed for viral replication offer a promising therapeutic approach. In this study, we describe the use of the antifungal therapeutics posaconazole and itraconazole in the therapy of IAV. We show that both drugs efficiently inhibit the propagation of IAV in the cell culture model without being cytotoxic. The mode of action is probably based on several targets and includes both a priming of the interferon response and the induced imbalance of cellular cholesterol. The antiviral effect of itraconazole could be confirmed in the mouse model, where the administration of itraconazole led to a drastic reduction in mortality and a significant increase in the survival rate. Thus, our data indicate a promising therapeutic potential of at least itraconazole in influenza therapy.

Species-Specific Pathogenicity of Severe Fever with Thrombocytopenia Syndrome Virus Is Determined by Anti-STAT2 Activity of NSs

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a novel emerging virus that has been identified in China, South Korea, and Japan, and it induces thrombocytopenia and leukocytopenia in humans with a high case fatality rate. SFTSV is pathogenic to humans, while immunocompetent adult mice and golden Syrian hamsters infected with SFTSV never show apparent symptoms. However, mice deficient for the gene encoding the α chain of the alpha- and beta-interferon receptor (Ifnar1-/- mice) and golden Syrian hamsters deficient for the gene encoding signal transducer and activator of transcription 2 (Stat2-/- hamsters) are highly susceptible to SFTSV infection, with infection resulting in death. The nonstructural protein (NSs) of SFTSV has been reported to inhibit the type I IFN response through sequestration of human STAT proteins. Here, we demonstrated that SFTSV induces lethal acute disease in STAT2-deficient mice but not in STAT1-deficient mice. Furthermore, we discovered that NSs cannot inhibit type I IFN signaling in murine cells due to an inability to bind to murine STAT2. Taken together, our results imply that the dysfunction of NSs in antagonizing murine STAT2 can lead to inefficient replication and the loss of pathogenesis of SFTSV in mice.IMPORTANCE Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by SFTSV, which has been reported in China, South Korea, and Japan. Here, we revealed that mice lacking STAT2, which is an important factor for antiviral innate immunity, are highly susceptible to SFTSV infection. We also show that SFTSV NSs cannot exert its anti-innate immunity activity in mice due to the inability of the protein to bind to murine STAT2. Our findings suggest that the dysfunction of SFTSV NSs as an IFN antagonist in murine cells confers a loss of pathogenicity of SFTSV in mice.