Detection of viral RNA in diverse body fluids in an SFTS patient with encephalopathy, gastrointestinal bleeding and pneumonia: a case report and literature review

Long-Term Detection and Isolation of Severe Fever with Thrombocytopenia Syndrome (SFTS) Virus in Dog Urine

Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne infection caused by the SFTS virus (SFTSV), with a high fatality rate of approximately 30% in humans. In recent years, cases of contact infection with SFTSV via bodily fluids of infected dogs and cats have been reported. In this study, clinical and virological analyses were performed in two dogs in which SFTSV infection was confirmed for the first time in the Toyama prefecture. Both dogs recovered; however, one was severely ill and the other mildly ill. The amount of the SFTSV gene was reduced to almost similar levels in both dogs. In the dogs' sera, the SFTSV gene was detected at a low level but fell below the detection limit approximately 2 weeks after onset. Notably, the SFTSV gene was detected at levels several thousand times higher in urine than in other specimens from both dogs. Furthermore, the gene was detected in the urine for a long period of >2 months. The clinical signs disappeared on days 1 or 6 after onset, but infectious SFTSV was detected in the urine up to 3 weeks later. Therefore, it is necessary to be careful about contact with bodily fluids, especially urine, even after symptoms have disappeared.

Research Progress of Fever with Thrombocytopenia Syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is a new infectious disease first discovered in Ta-pieh Mountains in central China in 2009. It is caused by a novel bunyavirus infection (SFTSV). Since the first discovery of SFTSV, there have been case reports and epidemiological studies on SFTS in several East Asian countries, such as South Korea, Japan, Vietnam and so on. With the rising incidence of SFTS and the rapid spread of the novel bunyavirus around the world, it is clear that the virus has a pandemic potential and may pose a threat to global public health in the future. Early studies have suggested that ticks are an important medium for the transmission of SFTSV to humans; in recent years, it has been reported that there is also human-to-human transmission. In endemic areas, potential hosts include a variety of livestock and wildlife. When people are infected with SFTV, the main clinical manifestations are high fever, thrombocytopenia, leukocytopenia, gastrointestinal symptoms, liver and kidney function damage, and even MODS, with a mortality rate of about 10-30%. This article reviews the latest progress of novel bunyavirus, including virus transmission vector, virus genotypic diversity and epidemiology, pathogenesis, clinical manifestation and treatment.

Severe fever with thrombocytopenia syndrome virus aerosol infection in C57/BL6 mice

Although secondary cases have become infected with the SFTSV after being in the same space without direct contact with the index case, it has not been experimentally determined if the SFTSV can be transmitted through aerosols. Here, this study aimed to verify if the SFTSV could be transmitted by aerosols. Firstly, we demonstrated that the SFTSV can infect BEAS-2B cells, and SFTSV genomes can be isolate from mild patient's sputum, which provided a foundation for the existence of SFTSV aerosol transmission. Then, we evaluated total antibody production in serum and viral load in tissue of mice infected with SFTSV by aerosols. The results showed that the presence of antibodies is related to the dose of virus infection and the SFTSV preferentially replicates in the lungs of mice following an aerosol exposure. Our study will help update the prevention and treatment guidelines for SFTSV and prevent the spread of the SFTSV in hospitals.

Clinical and Pathological Findings in Fatal Cases of Severe Fever With Thrombocytopenia Syndrome With High Viremia in Cats

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging zoonotic disease caused by the SFTS virus (SFTSV). SFTSV causes severe symptoms both in humans and cats. In this study, we report the clinical and pathological findings of 4 fatal cases of cats with high SFTS viremia levels. These cats showed an acute onset of fever, leukopenia, thrombocytopenia, and increased serum amyloid A and pro-inflammatory cytokine levels. A high viral copy number was detected in the blood, oral swabs, rectal swabs, conjunctiva swabs, and urine. Histopathologically, necrotizing lymphadenitis, splenitis with lymphoblastoid cell proliferation, and hemophagocytosis were observed in all 4 cats. Immunohistochemistry revealed the presence of SFTSV antigen on lymphoblastoid B cells. SFTSV-RNA was detected in systemic tissues, including the brain. The present findings provide useful information for understanding the features of fatal SFTS in cats. To elucidate the mechanisms of severe progress of SFTS cats, as well as its role as a source of human infection, further research is needed.

Severe fever with thrombocytopenia syndrome virus replicates in brain tissues and damages neurons in newborn mice

Severe fever with thrombocytopenia syndrome (SFTS) virus (SFTSV) is an emerging tick-borne phlebovirus with a high fatality rate of 12–30%, which has an expanding endemic and caused thousands of infections every year. Central nervous system (CNS) manifestations are an important risk factor of SFTS outcome death. Further understanding of the process of how SFTSV invades the brain is critical for developing effective anti-SFTS encephalitis therapeutics. We obeserved changes of viral load in the brain at different time points after intraperitoneal infection of SFTSV in newborn C57/BL6 mice. The virus invaded the brain at 3 h post-infection (hpi). Notably, the viral load increased exponentially after 24 hpi. In addition, it was found that in addition to macrophages, SFTSV infected neurons and replicated in the brain. These findings provide insights into the CNS manifestations of severe SFTS, which may lead to drug development and encephalitis therapeutics.

Severe fever with thrombocytopenia syndrome virus RNA in ticks from wild mongooses in Okinawa Prefecture, Japan

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging zoonotic tick-borne disease caused by the SFTS virus (SFTSV). SFTSV has a wide spectrum of animal hosts and is thought to circulate in an enzootic tick-vertebrate-tick cycle. A previous seroepidemiological study demonstrated the presence of anti-SFTSV antibodies in wild mongooses (Herpestes auropunctatus) and indicated that outdoor activity is associated with an increased risk of tick bites among Okinawa residents. However, the association of SFTSV between wild mongooses and ticks remains unknown. Thus, to understand the association between ticks and mongooses regarding SFTSV circulation, we investigated the presence of SFTSV RNA in ticks collected from wild mongooses on the main island of Okinawa. A total of 638 ticks, belonging to two genera and three species (Haemaphysalis hystricis, Haemaphysalis formosensis, and Ixodes granulatus), were collected from 22 wild mongooses from 2016 to 2020. SFTSV RNA was detected in two pools of H. hystricis larvae collected from a wild mongoose in the central area of the main island of Okinawa in 2017. Although the prevalence of SFTSV in ticks from wild mongooses is low, endemic circulation of the virus in Okinawa should be carefully monitored in the area to prevent future infections.

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.

Exploration of immunological responses underpinning severe fever with thrombocytopenia syndrome virus infection reveals IL-6 as a therapeutic target in an immunocompromised mouse model

Dabie bandavirus (previously severe fever with thrombocytopenia syndrome virus; SFTSV), is an emerging tick-borne bunyavirus responsible for severe fever with thrombocytopenia syndrome (SFTS), a disease with high case fatality that is characterized by high fever, thrombocytopenia, and potentially lethal hemorrhagic manifestations. Currently, neither effective therapeutic strategies nor approved vaccines exist for SFTS. Therefore, there remains a pressing need to better understand the pathogenesis of the disease and to identify therapeutic strategies to ameliorate SFTS outcomes. Using a type I interferon (IFN)-deficient mouse model, we investigated the viral tropism, disease kinetics, and the role of the virulence factor nonstructural protein (NSs) in SFTS. Ly6C⁺ MHCII⁺ cells in the lymphatic tissues were identified as an important target cell for SFTSV. Advanced SFTS was characterized by significant migration of inflammatory leukocytes, notably neutrophils, into the lymph node and spleen, however, these cells were not required to orchestrate the disease phenotype. The development of SFTS was associated with significant upregulation of proinflammatory cytokines, including high levels of IFN-γ and IL-6 in the serum, lymph node, and spleen. Humoral immunity generated by inoculation with delNSs SFTSV was 100% protective. Importantly, NSs was critical to the inhibition of the host IFNɣ response or downstream IFN-stimulated gene production and allowed for the establishment of severe disease. Finally, therapeutic but not prophylactic use of anti-IL-6 antibodies significantly increased the survival of mice following SFTSV infection and, therefore, this treatment modality presents a novel therapeutic strategy for treating severe SFTS.

Associations between Chest CT Abnormalities and Clinical Features in Patients with the Severe Fever with Thrombocytopenia Syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by the SFTS virus. It involves multiple organ systems, including the lungs. However, the significance of the lung involvement in SFTS remains unclear. In the present study, we aimed to investigate the relationship between the clinical findings and abnormalities noted in the chest computed tomography (CT) of patients with SFTS. The medical records of 22 confirmed SFTS patients hospitalized in five hospitals in Nagasaki, Japan, between April 2013 and September 2019, were reviewed retrospectively. Interstitial septal thickening and ground-glass opacity (GGO) were the most common findings in 15 (68.1%) and 12 (54.5%) patients, respectively, and lung GGOs were associated with fatalities. The SFTS patients with a GGO pattern were elderly, had a disturbance of the conscious and tachycardia, and had higher c-reactive protein levels at admission (p = 0.009, 0.006, 0.002, and 0.038, respectively). These results suggested that the GGO pattern in patients with SFTS displayed disseminated inflammation in multiple organs and that cardiac stress was linked to higher mortality. Chest CT evaluations may be useful for hospitalized patients with SFTS to predict their severity and as early triage for the need of intensive care.

Single-cell landscape of peripheral immune responses to fatal SFTS

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

Predisposing Factors for Person-to-Person Transmission of Severe Fever with Thrombocytopenia Syndrome Bunyavirus

Person-to-person transmission of severe fever with thrombocytopenia syndrome virus (SFTSV) is a new threat to human health. Here we report an outbreak of nosocomial person-to-person transmission of SFTS. Among eight persons with face-to-face contact distance ≤50 centimeters and/or exposure time ≥30 minutes to the index patient, six became were infected. Only one of the 17 persons with exposure distance ≥ 50 centimeters and exposure time ≤ 30 minutes was infected (75% vs. 6.25%, p <0.001). Epidemiological investigation revealed high viral load, bloody secretions and bleeding, exposure time and distance as the key factors in person-to-person transmission.

Clinical effect and antiviral mechanism of T-705 in treating severe fever with thrombocytopenia syndrome

Severe fever with thrombocytopenia syndrome (SFTS) virus (SFTSV) is an emerging tick-borne virus with high fatality and an expanding endemic. Currently, effective anti-SFTSV intervention remains unavailable. Favipiravir (T-705) was recently reported to show in vitro and in animal model antiviral efficacy against SFTSV. Here, we conducted a single-blind, randomized controlled trial to assess the efficacy and safety of T-705 in treating SFTS (Chinese Clinical Trial Registry website, number ChiCTR1900023350). From May to August 2018, laboratory-confirmed SFTS patients were recruited from a designated hospital and randomly assigned to receive oral T-705 in combination with supportive care or supportive care only. Fatal outcome occurred in 9.5% (7/74) of T-705 treated patients and 18.3% (13/71) of controls (odds ratio, 0.466, 95% CI, 0.174-1.247). Cox regression showed a significant reduction in case fatality rate (CFR) with an adjusted hazard ratio of 0.366 (95% CI, 0.142-0.944). Among the low-viral load subgroup (RT-PCR cycle threshold ≥26), T-705 treatment significantly reduced CFR from 11.5 to 1.6% (P = 0.029), while no between-arm difference was observed in the high-viral load subgroup (RT-PCR cycle threshold <26). The T-705-treated group showed shorter viral clearance, lower incidence of hemorrhagic signs, and faster recovery of laboratory abnormities compared with the controls. The in vitro and animal experiments demonstrated that the antiviral efficacies of T-705 were proportionally induced by SFTSV mutation rates, particularly from two transition mutation types. The mutation analyses on T-705-treated serum samples disclosed a partially consistent mutagenesis pattern as those of the in vitro or animal experiments in reducing the SFTSV viral loads, further supporting the anti-SFTSV effect of T-705, especially for the low-viral loads.

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.