Common adverse events associated with ribavirin therapy for Severe Fever with Thrombocytopenia Syndrome

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Severe fever with thrombocytopenia syndrome virus induces platelet activation and apoptosis via a reactive oxygen species-dependent pathway

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infectious disease caused by the SFTS virus (SFTSV) and with a high fatality rate. Thrombocytopenia is a major clinical manifestation observed in SFTS patients, but the underlying mechanism remains largely unclear. Here, we explored the effects of SFTSV infection on platelet function in vivo in severely infected SFTSV IFNar-/- mice and on mouse and human platelet function in vitro. Results showed that SFTSV-induced platelet clearance acceleration may be the main reason for thrombocytopenia. SFTSV-potentiated platelet activation and apoptosis were also observed in infected mice. Further investigation showed that SFTSV infection induced platelet reactive oxygen species (ROS) production and mitochondrial dysfunction. In vitro experiments revealed that administration of SFTSV or SFTSV glycoprotein (Gn) increased activation, apoptosis, ROS production, and mitochondrial dysfunction in separated mouse platelets, which could be effectively ameliorated by the application of antioxidants (NAC (N-acetyl-l-cysteine), SKQ1 (10-(6'-plastoquinonyl) decyltriphenylphosphonium) and resveratrol). In vivo experiments showed that the antioxidants partially rescued SFTSV infection-induced thrombocytopenia by improving excessive ROS production and mitochondrial dysfunction and down-regulating platelet apoptosis and activation. Furthermore, while SFTSV and Gn directly potentiated human platelet activation, it was completely abolished by antioxidants. This study revealed that SFTSV and Gn can directly trigger platelet activation and apoptosis in an ROS-MAPK-dependent manner, which may contribute to thrombocytopenia and hemorrhage during infection, but can be abolished by antioxidants.

Antiviral activity and mechanism of the antifungal drug, anidulafungin, suggesting its potential to promote treatment of viral diseases

BACKGROUND

The severe fever with thrombocytopenia syndrome disease (SFTS), caused by the novel tick-borne SFTS virus (SFTSV), was listed among the top 10 priority infectious disease by World Health Organization due to the high fatality rate of 5-30% and the lack of effective antiviral drugs and vaccines and therefore raised the urgent need to develop effective anti-SFTSV drugs to improve disease treatment.

METHODS

The antiviral drugs to inhibit SFTSV infection were identified by screening the library containing 1340 FDA-approved drugs using the SFTSV infection assays in vitro. The inhibitory effect on virus entry and the process of clathrin-mediated endocytosis under different drug doses was evaluated based on infection assays by qRT-PCR to determine intracellular viral copies, by Western blot to characterize viral protein expression in cells, and by immunofluorescence assays (IFAs) to determine virus infection efficiencies. The therapeutic effect was investigated in type I interferon receptor defective A129 mice in vivo with SFTSV infection, from which lesions and infection in tissues caused by SFTSV infection were assessed by H&E staining and immunohistochemical analysis.

RESULTS

Six drugs were identified as exerting inhibitory effects against SFTSV infection, of which anidulafungin, an antifungal drug of the echinocandin family, has a strong inhibitory effect on SFTSV entry. It suppresses SFTSV internalization by impairing the late endosome maturation and decreasing virus fusion with the membrane. SFTSV-infected A129 mice had relieving symptoms, reduced tissue lesions, and improved disease outcomes following anidulafungin treatment. Moreover, anidulafungin exerts an antiviral effect in inhibiting the entry of other viruses including SARS-CoV-2, SFTSV-related Guertu virus and Heartland virus, Crimean-Congo hemorrhagic fever virus, Zika virus, and Herpes simplex virus 1.

CONCLUSIONS

The results demonstrated that the antifungal drug, anidulafungin, could effectively inhibit virus infection by interfering with virus entry, suggesting it may be utilized for the clinical treatment of infectious viral diseases, in addition to its FDA-approved use as an antifungal. The findings also suggested to further evaluate the anti-viral effects of echinocandins and their clinical importance for patients with infection of viruses, which may promote therapeutic strategies as well as treatments and improve outcomes pertaining to various viral and fungal diseases.

Severe fever with thrombocytopenia syndrome, a viral hemorrhagic fever, endemic to Japan: achievements and directions to the future in the scientific and medical research

A novel infectious disease, severe fever with thrombocytopenia syndrome (SFTS) caused by a novel bunyavirus, with high case fatality rate (CFR) was reported by Chinese scientists in 2011. The causative virus, Dabie bandavirus [former SFTS virus (SFTSV)] belonged to the Bandavirus genus (former Phlebovirus genus) of Phenuiviridae family (former Bunyaviridae family). SFTS was also reported to be endemic to South Korea and Japan in 2013. Humans are infected with SFTSV through bites by ticks such as Haemophysalis longicornis and Amblyomma testidinarium. However, it was reported that domesticated animals such as cats and dogs were also infected with SFTSV probably through tick bites in living environment and show the SFTS-like symptoms with high CFR. Furthermore, there have been the cases of SFTS patients, who were infected with SFTSV through close contacts with sick cats or dogs. The high CFR in patients with SFTS is approximately 30% in Japan. SFTSV is circulating in nature between some species of ticks and animals. There are always the risks of SFTSV infection for human populations living in the endemic areas. Therefore, development of specific therapies and vaccines is an urgent need to reduce the number of fatal SFTS patients.

Clinical feature of severe fever with thrombocytopenia syndrome (SFTS)-associated encephalitis/encephalopathy: a retrospective study

BACKGROUND/OBJECTIVE

Severe fever with thrombocytopenia syndrome (SFTS) cause encephalitis/encephalopathy, but few reports were available. We aimed to investigate the incidence of encephalitis/encephalopathy in SFTS patients and to summarize clinical characteristics, laboratory findings and imaging features.

METHODS

We conducted a retrospective review of all patients with confirmed SFTS admitted to Nanjing Drum Tower Hospital, a tertiary hospital in Nanjing City, China, between January 2016 and July 2020. The patients were divided into two groups according to whether they had encephalitis/encephalopathy: encephalitis/encephalopathy group and non- encephalitis/encephalopathy group. Clinical data, laboratory findings, imaging characteristics, treatments and outcomes of these patients were collected and analyzed.

RESULTS

A total of 109 SFTS patients with were included, of whom 30 (27.5 %) developed encephalitis/encephalopathy. In-hospital mortality (43.3 %) was higher in encephalitis/encephalopathy group than non-encephalitis/encephalopathy group (12.7 %). Univariate logistic regression showed that cough, wheezing, dyspnoea, respiratory failure, vasopressors use, bacteremia, invasive pulmonary aspergillosis (IPA) diagnoses, PCT > 0.5 ug/L, CRP > 8 mg/L, AST > 200 U/L and serum amylase level > 80 U/L were the risk factors for the development of encephalitis/encephalopathy for SFTS patients. Multivariate logistic regression analysis identified bacteremia, PCT > 0.5 mg/L and serum amylase level > 80 U/L as independent predictors of encephalitis/ encephalopathy development for SFTS patients.

CONCLUSIONS

SFTS-associated encephalitis/encephalopathy has high morbidity and mortality. it was necessary to strengthen the screening of CSF testing and brain imaging after admission for SFTS patients who had symptoms of encephalitis/encephalopathy. SFTS patients with bacteremia, PCT > 0.5 ug/L or serum amylase level > 80 U/L should be warned to progress to encephalopathy.

Adverse Cardiovascular Effects of Anti-COVID-19 Drugs

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) or COVID-19 infection is the cause of the ongoing global pandemic. Mortality from COVID-19 infection is particularly high in patients with cardiovascular diseases. In addition, COVID-19 patients with preexisting cardiovascular comorbidities have a higher risk of death. Main cardiovascular complications of COVID-19 are myocardial infarction, myocarditis, acute myocardial injury, arrhythmias, heart failure, stroke, and venous thromboembolism. Therapeutic interventions in terms of drugs for COVID-19 have many cardiac adverse effects. Here, we review the relative therapeutic efficacy and adverse effects of anti-COVID-19 drugs.

Peptides derived from viral glycoprotein Gc Inhibit infection of severe fever with thrombocytopenia syndrome virus

Severe fever with thrombocytopenia syndrome (SFTS) is an acute infectious disease caused by a novel phlebovirus (SFTSV), characterized by fever, thrombocytopenia and leukocytopenia which lead to multiple organ failure with high mortality in severe cases. The SFTSV has spread rapidly in recent years and posed a serious threat to public health in endemic areas. However, specific antiviral therapeutics for SFTSV infection are rare. In this study, we demonstrated that two peptides, SGc1 and SGc8, derived from a hydrophobic region of the SFTSV glycoprotein Gc, could potently inhibit SFTSV replication in a dose-dependent manner without apparent cytotoxicity in various cell lines and with low immunogenicity and good stability. The IC₅₀ (50% inhibition concentration) values for both peptides to inhibit 2 MOI of SFTSV infection were below 10 μM in L02, Vero and BHK21 cells. Mechanistically, SGc1 and SGc8 mainly inhibited viral entry at the early stage of the viral infection. Inhibition of SFTSV replication was specific by both peptides because no inhibitory effect was shown against other viruses including Zika virus and Enterovirus A71. Taken together, our results suggested that viral glycoprotein-derived SGc1 and SGc8 peptides have antiviral potential and warrant further assessment as an SFTSV-specific therapeutic.

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.

Acute pancreatitis in patients with severe fever with thrombocytopenia syndrome virus infection

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS), a novel tick-borne disease caused by SFTS virus (SFTSV), has been reported in China, Japan, South Korea, and Vietnam since 2009. SFTSV infection can cause multiple organ damage, including acute pancreatitis (AP). We summarize the clinical features, treatment and outcome of AP associated with SFTSV.

METHODS

We retrospectively review the clinical manifestations, laboratory tests, treatment, and outcome of AP associated with SFTSV infection from January 2009 to December 2018 in Liaoning Province, China.

RESULTS

A total of 418 SFTS patients were reviewed. Fifteen (3.6%) of 418 met the criteria for AP associated with SFTSV infection. The first reported symptom for all SFTS-AP patients was fever. All the SFTS-AP patients presented with thrombocytopenia, and 13 (86.7%) of them presented with leukopenia on admission. Thirteen (86.7%) of 15 SFTS-AP patients were severe SFTS patients, and 9 (60.0%) patients were diagnosed with multiple organ dysfunction syndrome. One SFTS-AP patient died of multiple organ failure. Six (40%) of 15 SFTS-AP patients were not confirmed with SFTSV infection when AP was diagnosed, and the median delay between SFTSV infection and AP diagnosis was 5 days (range, 2-7 days).

CONCLUSIONS

AP is not a frequent complication of SFTS, and is more frequently seen in severe SFTS patients. Most patients with SFTS-AP have mild or moderate disease, and can recover with conservative management; however, severe SFTS-AP can be fatal. In SFTS endemic areas, clinicians should be alert to the possibility of SFTS when AP patients with tick exposure, thrombocytopenia, and leukopenia have a fever before abdominal pain.

Severe fever with thrombocytopenia syndrome virus: a highly lethal bunyavirus

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a novel bunyavirus. Since 2007, SFTS disease has been reported in China with high fatality rate up to 30%, which drew high attention from Centre for Disease Control and Prevention and government. SFTSV is endemic in the centra l and eastern China, Korea and Japan. There also have been similar cases reported in Vietnam. The number of SFTSV infection cases has a steady growth in these years. As SFTSV could transmitted from person to person, it will expose the public to infectious risk. In 2018 annual review of the Blueprint list of priority diseases, World Health Organisation has listed SFTSV infection as prioritised diseases for research and development in emergency contexts. However, the pathogenesis of SFTSV remains largely unclear. Currently, there are no specific therapeutics or vaccines to combat infections of SFTSV. This review discusses recent findings of epidemiology, transmission pathway, pathogenesis and treatments of SFTS disease.

Antiviral Drugs Against Severe Fever With Thrombocytopenia Syndrome Virus Infection

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infectious disease caused by SFTS virus (SFTSV), which is a novel bunyavirus. SFTSV was first isolated from patients who presented with fever, thrombocytopenia, leukocytopenia, and multiorgan dysfunction in China. Subsequently, it was found to be widely distributed in Southeast Asia (Korea, Japan, and Vietnam). SFTSV can be transmitted not only from ticks but also from domestic animals, companion animals, and humans. Because the case fatality rate of SFTS is high (6–30%), development of specific and effective treatment for SFTS is required. Studies of potential antiviral drugs for SFTS-specific therapy have been conducted on existing or newly discovered agents in vitro and in vivo, with ribavirin and favipiravir being the most promising candidates. While animal experiments and retrospective studies have demonstrated the limited efficacy of ribavirin, it was also speculated that ribavirin would be effective in patients with a viral load <1 × 10⁶ copies/mL. Favipiravir showed higher efficacy than ribavirin against SFTSV in in vitro assays and greater efficacy in animal models, even administrated 3 days after the virus inoculation. Although clinical trials evaluating the efficacy of favipiravir in SFTS patients in Japan are underway, this has yet to be confirmed. Other drugs, including hexachlorophene, calcium channel blockers, 2′-fluoro-2′-deoxycytidine, caffeic acid, amodiaquine, and interferons, have also been evaluated for their inhibitory efficacy against SFTSV. Among them, calcium channel blockers are promising because in addition to their efficacy in vitro and in vivo, retrospective clinical data have indicated that nifedipine, one of the calcium channel blockers, reduced the case fatality rate by >5-fold. Although further research is necessary to develop SFTS-specific therapy, considerable progress has been achieved in this area. Here we summarize and discuss recent advances in antiviral drugs against SFTSV.

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.

Pathophysiology of severe fever with thrombocytopenia syndrome and development of specific antiviral therapy

Severe fever with thrombocytopenia syndrome (SFTS) caused by SFTS virus (SFTSV), a novel phlebovirus, was reported to be endemic to central and northeastern PR China and was also to be endemic to South Korea and western Japan. SFTS is an emerging viral infection, which should be categorized as a viral hemorrhagic fever disease as Crimean-Congo hemorrhagic fever (CCHF) is caused by CCHF virus. SFTS is a tick-borne viral infection. SFTSV is maintained between several species of ticks and wild and domestic animals in nature. Patients with SFTS show symptoms of fever, general fatigue, and gastrointestinal symptoms such as bloody diarrhea. The severely ill SFTS patients usually show gastrointestinal hemorrhage and deteriorated consciousness. The case fatality rate of SFTS ranges from 5 to 40%. Pathological studies on SFTS have revealed that the mechanisms behind the high case fatality rate are virus infection-related hemophagocytic syndrome associated with cytokine storm, coagulopathy due to disseminated intravascular coagulation causing bleeding tendency, and multi-organ failure. Favipiravir was reported to show efficacy in the prevention and treatment of SFTSV infections in an animal model. A clinical study to evaluate the efficacy of favipiravir in the treatment of SFTS patients has been initiated in Japan. SFTSV is circulating in nature in PR China, Korea, and Japan, indicating that we cannot escape from the risk being infected with SFTSV. The development of specific therapy and preventive measures is a pressing issue requiring resolution to reduce the morbidity and mortality of SFTS patients.

Epidemiological and clinical features of laboratory-diagnosed severe fever with thrombocytopenia syndrome in China, 2011-17: a prospective observational study

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with an increasing case number and extensive geographical expansion, raising concerns locally and globally; however, the description of its clinical features needs to be addressed by large studies. We aimed to determine all the clinical features of SFTS in a large population of patients in an endemic area.

METHODS

In this prospective observational study, data were collected on patients admitted to the People's Liberation Army Hospital in Xinyang, Henan Province, China, with laboratory-diagnosed SFTS. Demographic, clinical, laboratory, and treatment data were collected for each patient, and patients were followed up within 2 weeks after discharge or discontinuation of treatment. The association between each demographic, clinical, and laboratory variable with a fatal outcome was assessed. A clinical scoring model was designed for the early prediction of a fatal outcome, and the effect of treatment on outcome was analysed.

FINDINGS

Between April 1, 2011, and Oct 31, 2017, 2096 patients with laboratory-confirmed SFTS were admitted. Mean age at admission was 61·4 years (SD 12·2) and 1239 (59%) patients were female. The case fatality rate (CFR) was 16·2% (95% CI 14·6-17·8). A higher risk was associated with being male (unadjusted odds ratio [OR] 1·45, 95% CI 1·15-1·83; p=0·002), older age (for a 10-year increase, unadjusted OR 1·82, 95% CI 1·62-2·04; p<0·0001), longer delay in admission (for every extra day taken before admission to hospital, unadjusted OR 1·18, 1·12-1·24; p<0·0001), presence of diarrhoea (adjusted OR 1·44, 1·12-1·87; p=0·005) or dyspnoea (adjusted OR 8·35, 5·97-11·69; p<0·0001), and development of haemorrhagic signs (adjusted OR 2·79, 95% CI 2·18-3·57; p<0·0001) or neurological symptoms (adjusted OR 30·26, 21·39-42·81; p<0·0001). Laboratory variables that were associated with death included abnormal concentrations of lactate dehydrogenase, aspartate aminotransferase, and blood urea nitrogen, and abnormal neutrophil percentage, which together with age and neurological symptoms were combined in the clinical scoring system. A total score of more than 8 was the optimal threshold to predict risk of death for patients who were evaluated within 6 days after symptom onset (area under the curve 0·879, 95% CI 0·855-0·902). For all participants, viraemia was a strong predictor of fatal outcome (all p<0·0001). Ribavirin therapy was effective in reducing CFR from 6·25% (15 of 240 participants) to 1·16% (two of 173 participants), but only in patients with a viral load below 1×10⁶ copies per mL (hazard ratio 9·72, 95% CI 1·30-72·87; p=0·027).

INTERPRETATION

The changing epidemiological features and high CFR of SFTS underscore the necessity of continued surveillance. Early prediction of fatal outcome can be attained by monitoring of clinical and laboratory data. Ribavirin should be applied early, with best results achieved before the viral load reaches 1 × 10⁶ copies per mL.

FUNDING

National Natural Science Foundation of China.

Score risk model for predicting severe fever with thrombocytopenia syndrome mortality

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging epidemic infectious disease with high mortality in East Aisa, especially in China. To predict the prognosis of SFTS precisely is important in clinical practice.

Methods

From May 2013 to November 2015, 233 suspected SFTS patients were tested for SFTS virus using RT-PCR. Cox regression model was utilized to comfirm independent risk factors for mortality. A risk score model for mortality was constructed based on regression coefficient of risk factors. Log-rank test was used to evaluate the significance of this model.

Results

One hundred seventy-four patients were confirmed with SFTS, of which 40 patients died (23%). Baseline age, serum aspartate aminotransferase (AST) and serum creatinine (sCr) level were independent risk factors of mortality. The area under ROC curve (AUCs) of these parameters for predicting death were 0.771, 0.797 and 0.764, respectively. And hazard ratio (HR) were 1.128, 1.002 and 1.013, respectively. The cutoff value of the risk model was 10. AUC of the model for predicting mortality was 0.892, with sensitivity and specificity of 82.5 and 86.6%, respectively. Log-rank test indicated strong statistical significance (ײ = 88.35, p < 0.001).

Conclusions

This risk score model may be helpful to predicting the prognosis of SFTS patients.

Efficacy of T-705 (Favipiravir) in the Treatment of Infections with Lethal Severe Fever with Thrombocytopenia Syndrome Virus

Severe fever with thrombocytopenia syndrome virus (SFTSV) is the causative agent of SFTS, an emerging hemorrhagic fever. This disease has a high case fatality rate and is endemic to China, South Korea, and Japan. Because there are currently no effective therapeutics for SFTS, potent and safe antivirals are needed for the treatment of SFTS. The inhibitory effect of T-705 (favipiravir) on the replication of SFTSV in Vero cells was evaluated. Mice lacking the type I interferon receptor (IFNAR(-/-)) were used as an in vivo lethal model for SFTSV infection. T-705, which has been licensed as an anti-influenza drug in Japan, inhibits SFTSV replication both in vitro and in vivo. T-705 inhibited replication of SFTSV in Vero cells by 5 log units, with a 50% inhibitory concentration (IC50) and IC90 of 6.0 µM and 22 µM, respectively. Intraperitoneal or oral administration of T-705 for 5 days to IFNAR(-/-) mice infected with lethal SFTSV significantly improved survival rates (100% survival) without causing body weight loss and reduced the viral load in the serum. Ribavirin also inhibited SFTSV replication. However, it was less effective than T-705 both in vitro and in vivo. A time-of-drug-addition study revealed that therapeutic T-705 treatment of SFTSV infection in IFNAR(-/-) mice was effective. These results suggest that T-705 is a promising candidate for the treatment of SFTS. IMPORTANCE Severe fever with thrombocytopenia syndrome (SFTS), caused by SFTS virus (SFTSV), is a recently identified emerging viral infectious disease. Despite the medical importance of this disease, there are currently neither vaccines nor effective therapeutics for SFTS. T-705, which is a pyrazine derivative, has shown broad antiviral activity against various RNA viruses. The present study demonstrated, for the first time to our knowledge, the efficacy of T-705 in treating SFTSV infection in a mouse lethal model. T-705 showed a high efficacy in the treatment of SFTSV infection in the mouse model, even when treatments were initiated after onset of the disease.