Computer-aided designing of a novel multi­epitope DNA vaccine against severe fever with thrombocytopenia syndrome virus.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne viral disease caused by the SFTS virus (Dabie bandavirus), which has become a substantial risk to public health. No specific treatment is available now, that calls for an effective vaccine. Given this, we aimed to develop a multi-epitope DNA vaccine through the help of bioinformatics. The final DNA vaccine was inserted into a special plasmid vector pVAX1, consisting of CD8+ T cell epitopes, CD4+ T cell epitopes and B cell epitopes (six epitopes each) screened from four genome-encoded proteins--nuclear protein (NP), glycoprotein (GP), RNA-dependent RNA polymerase (RdRp), as well as nonstructural protein (NSs). To ascertain if the predicted structure would be stable and successful in preventing infection, an immunological simulation was run on it. In conclusion, we designed a multi-epitope DNA vaccine that is expected to be effective against Dabie bandavirus, but in vivo trials are needed to verify this claim.

Direct transmission of severe fever with thrombocytopenia syndrome virus from farm-raised fur animals to workers in Weihai, China.

BACKGROUND: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease. SFTS virus (SFTSV) is transmitted by tick bites and contact with the blood or body fluids of SFTS patients. Animal-to-human transmission of SFTS has been reported in Japan, but not in China. In this study, the possible transmission route of two patients who fed and cared for farm-raised fur animals in a mink farm was explored. METHOD: An epidemiological investigation and a genetic analysis of patients, animals and working environment were carried out. RESULTS: It was found that two patients had not been bitten by ticks and had no contact with patients infected with SFTS virus, but both of them had skinned the dying animals. 54.55% (12/22) of the farm workers were positive for SFTS virus antibody. By analyzing the large, medium and small segments sequences, the viral sequences from the two patients, animals and environments showed 99.9% homology. CONCLUSION: It is suspected that the two patients may be directly infected by farm-raised animals, and that the virus may have been transmitted by aerosols when skinning dying animals. Transmission by direct blood contacts or animal bites cannot be ignored.

Distribution and pathogen prevalence of field-collected ticks from south-western Korea: a study from 2019 to 2022.

Hard ticks are known vectors of various pathogens, including the severe fever with thrombocytopenia syndrome virus, Rickettsia spp., Coxiella burnetii, Borrelia spp., Anaplasma phagocytophilum, and Ehrlichia spp. This study aims to investigate the distribution and prevalence of tick-borne pathogens in southwestern Korea from 2019 to 2022. A total of 13,280 ticks were collected during the study period, with H. longicornis accounting for 86.1% of the collected ticks. H. flava, I. nipponensis and A. testudinarium comprised 9.4%, 3.6%, and 0.8% of the ticks, respectively. Among 983 pools tested, Rickettsia spp. (216 pools, 1.6% MIR) were the most prevalent pathogens across all tick species, with R. japonica and R. monacensis frequently detected in I. nipponensis and Haemaphysalis spp., respectively. Borrelia spp. (28 pools, 0.2% MIR) were predominantly detected in I. nipponensis (27 pools, 13.8% MIR, P < 0.001). Co-infections, mainly involving Rickettsia monacensis and Borrelia afzelii, were detected in I. nipponensis. Notably, this study identified R. monacensis for the first time in A. testudinarium in South Korea. These findings offer valuable insights into the tick population and associated pathogens in the region, underscoring the importance of tick-borne disease surveillance and prevention measures.

Severe fever with thrombocytopenia syndrome with central nervous system symptom onset: a case report and literature review.

BACKGROUND: Severe fever with thrombocytopenia syndrome (SFTS) is a natural focal disease transmitted mainly by tick bites, and the causative agent is SFTS virus (SFTSV). SFTS can rapidly progress to severe disease, with multiple-organ failure (MOF) manifestations such as shock, respiratory failure, disseminated intravascular coagulation (DIC) and death, but cases of SFTS patients with central nervous system (CNS) symptoms onset and marked persistent involuntary shaking of the perioral area and limbs have rarely been reported. CASE PRESENTATION: A 69-year-old woman with fever and persistent involuntary shaking of the perioral area and limbs was diagnosed with SFTS with CNS symptom onset after metagenomic next-generation sequencing (mNGS) of cerebrospinal fluid (CSF) and peripheral blood identified SFTSV. The patient developed a cytokine storm and MOF during the course of the disease, and after aggressive antiviral, glucocorticoid, and gamma globulin treatments, her clinical symptoms improved, her laboratory indices returned to normal, and she had a good prognosis. CONCLUSION: This case gives us great insight that when patients with CNS symptoms similar to those of viral encephalitis combined with thrombocytopenia and leukopenia are encountered in the clinic, it is necessary to consider the possibility of SFTS involving the CNS. Testing for SFTSV nucleic acid in CSF and blood (mNGS or polymerase chain reaction (PCR)) should be carried out, especially in critically ill patients, and treatment should be given accordingly.

Outbreak of Natural Severe Fever with Thrombocytopenia Syndrome Virus Infection in Farmed Minks, China.

We isolated severe fever with thrombocytopenia syndrome virus (SFTSV) from farmed minks in China, providing evidence of natural SFTSV infection in farmed minks. Our findings support the potential role of farmed minks in maintaining SFTSV and are helpful for the development of public health interventions to reduce human infection.

Correlation between the Cycle Threshold Values in Detection of Severe Fever with Thrombocytopenia Syndrome Virus Using PowerChekTM SFTSV Real-Time PCR Kit and Viral Load: Prognostic Implications.

BACKGROUND: This study aimed to analyze the correlation between the cycle threshold (Ct) values of severe fever with thrombocytopenia syndrome (SFTS) virus small (S) and middle (M) segments and the SFTS viral load, aiming to estimate the initial viral load and predict prognosis in the early clinical course. METHOD: A retrospective study was conducted with confirmed SFTS patients at Jeju National University Hospital (2016-2022). Patients were categorized into non-fatal and fatal groups. RESULTS: This study included 49 patients with confirmed SFTS (non-fatal group, n = 42; fatal group, n = 7). A significant negative correlation (-0.783) was observed between the log SFTS viral load and Ct values (p < 0.001). This negative correlation was notably stronger in the fatal group (correlation coefficient -0.940) than in the non-fatal group (correlation coefficient -0.345). CONCLUSION: In this study, we established a correlation between SFTS viral load and Ct values for estimating the initial viral load and early predicting prognosis. These results are expected to offer valuable insights for SFTS patient treatment and prognosis prediction.

SFTSV nucleoprotein mediates DNA sensor cGAS degradation to suppress cGAS-dependent antiviral responses.

Cyclic GMP-AMP synthase (cGAS) is an important DNA pattern recognition receptor that senses double-stranded DNA derived from invading pathogens or self DNA in cytoplasm, leading to an antiviral interferon response. A tick-borne Bunyavirus, severe fever with thrombocytopenia syndrome virus (SFTSV), is an RNA virus that causes a severe emerging viral hemorrhagic fever in Asia with a high case fatality rate of up to 30%. However, it is unclear whether cGAS interacts with SFTSV infection. In this study, we found that SFTSV infection upregulated cGAS RNA transcription and protein expression, indicating that cGAS is an important innate immune response against SFTSV infection. The mechanism of cGAS recognizing SFTSV is by cGAS interacting with misplaced mitochondrial DNA in the cytoplasm. Depletion of mitochondrial DNA significantly inhibited cGAS activation under SFTSV infection. Strikingly, we found that SFTSV nucleoprotein (N) induced cGAS degradation in a dose-dependent manner. Mechanically, N interacted with the 161-382 domain of cGAS and linked the cGAS to LC3. The cGAS-N-LC3 trimer was targeted to N-induced autophagy, and the cGAS was degraded in autolysosome. Taken together, our study discovered a novel antagonistic mechanism of RNA viruses, SFTSV is able to suppress the cGAS-dependent antiviral innate immune responses through N-hijacking cGAS into N-induced autophagy. Our results indicated that SFTSV N is an important virulence factor of SFTSV in mediating host antiviral immune responses. IMPORTANCE: Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne RNA virus that is widespread in East and Southeast Asian countries with a high fatality rate of up to 30%. Up to now, many cytoplasmic pattern recognition receptors, such as RIG-I, MDA5, and SAFA, have been reported to recognize SFTSV genomic RNA and trigger interferon-dependent antiviral responses. However, current knowledge is not clear whether SFTSV can be recognized by DNA sensor cyclic GMP-AMP synthase (cGAS). Our study demonstrated that cGAS could recognize SFTSV infection via ectopic mitochondrial DNA, and the activated cGAS-stimulator of interferon genes signaling pathway could significantly inhibit SFTSV replication. Importantly, we further uncovered a novel mechanism of SFTSV to inhibit innate immune responses by the degradation of cGAS. cGAS was degraded in N-induced autophagy. Collectively, this study illustrated a novel virulence factor of SFTSV to suppress innate immune responses through autophagy-dependent cGAS degradation.

Gn protein expressed in plants for diagnosis of severe fever with thrombocytopenia syndrome virus.

Severe fever with thrombocytopenia syndrome virus (SFTSV) causes the highly fatal disease in humans. To facilitate diagnosis, the native form of subunit glycoprotein (Gn), a prime target for potential vaccines and therapies, was produced in Nicotiana benthamiana using a Bamboo mosaic virus-based vector system. By fusion with secretory signal tags, SSExt, derived from the extension protein, and the (SP)10 motif, the yield of the recombinant Gn (rGn) was remarkably increased to approximately 7 mg/kg infiltrated leaves. Ultimately, an rGn-based ELISA was successfully established for the detection of SFTSV-specific antibodies in serum samples from naturally infected monkeys. As validated with the reference method, the specificity and sensitivity of rGn-ELISA were 94% and 96%, respectively. In conclusion, utilizing well-suited fusion tags facilitates rGn production and purification in substantial quantities while preserving its antigenic properties. The rGn-ELISA, characterized by its commendable sensitivity and specificity could serve as a viable alternative diagnostic method for assessing SFTSV seroprevalence. KEY POINTS: • SFTSV Gn, fused with secretory signal tags, was expressed by the BaMV-based vector. • The plant fusion tags increased expression levels and eased the purification of rGn. • The rGn-ELISA was established and validated; its specificity and sensitivity > 94%.

Comprehensive evaluation of nucleic acid amplification methods widely used for generic detection of sandfly-borne phleboviruses.

Sandfly-borne phleboviruses (SBPs), which cause sandfly fever, aseptic meningitis, encephalitis, and meningoencephalitis, are emerging pathogens of major public health concern. Virus nucleic acid testing is essential for SBP diagnosis, especially in the early stages of infection, and for the discovery of novel SBPs. The efficacy of utilizing generic primers that target conserved nucleotide sequences for the detection of both known and novel SBPs has not been extensively evaluated. We aimed to compare and evaluate the performance of five generic primer sets, widely used to detect S- and L-segments of arthropod-borne phleboviruses and designed as singleplex (n = 3) and nested (n = 2) formats, including both well-known and recently characterized 15 Old World virus strains. Furthermore, we performed in silico analysis to assess the detection capabilities of these generic primer sets. The initial evaluation of previously published generic primer sets for SBP detection yielded two singleplex primer sets with the potential to be adapted for use in real-time or high-throughput detection settings. Studies are ongoing to develop and further optimize a preliminary assay and test various hosts and vectors to assess their capacity to detect known and novel viruses. IMPORTANCE: Virus nucleic acid testing is the primary diagnostic method, particularly in the early stages of illness. Virus-specific or syndromic tests are widely used for this purpose. The use of generic primers has had a considerable impact on the discovery, identification, and detection of Old World sandfly-borne phleboviruses (OWSBP). The study is significant because it is the first to carry out a comparative evaluation of all published OWSBP generic primer sets.

Virome diversity shaped by genetic evolution and ecological landscape of Haemaphysalis longicornis.

BACKGROUND: Haemaphysalis longicornis is drawing attentions for its geographic invasion, extending population, and emerging disease threat. However, there are still substantial gaps in our knowledge of viral composition in relation to genetic diversity of H. longicornis and ecological factors, which are important for us to understand interactions between virus and vector, as well as between vector and ecological elements. RESULTS: We conducted the meta-transcriptomic sequencing of 136 pools of H. longicornis and identified 508 RNA viruses of 48 viral species, 22 of which have never been reported. Phylogenetic analysis of mitochondrion sequences divided the ticks into two genetic clades, each of which was geographically clustered and significantly associated with ecological factors, including altitude, precipitation, and normalized difference vegetation index. The two clades showed significant difference in virome diversity and shared about one fifth number of viral species that might have evolved to "generalists." Notably, Bandavirus dabieense, the pathogen of severe fever with thrombocytopenia syndrome was only detected in ticks of clade 1, and half number of clade 2-specific viruses were aquatic-animal-associated. CONCLUSIONS: These findings highlight that the virome diversity is shaped by internal genetic evolution and external ecological landscape of H. longicornis and provide the new foundation for promoting the studies on virus-vector-ecology interaction and eventually for evaluating the risk of H. longicornis for transmitting the viruses to humans and animals. Video Abstract.

Elucidation of prognostic factors in the acute phase of feline severe fever with thrombocytopenia syndrome virus infection.

Severe fever with thrombocytopenia syndrome (SFTS) is a potentially fatal tick-borne zoonotic disease, endemic to Asian regions, including western Japan. Cats appear to suffer a particularly severe form of the disease; however, feline SFTS is not clinically well characterized. Accordingly, in this study, we investigated the associations of, demographic, hematological and biochemical, immunological, and virological parameters with clinical outcome (fatal cases vs. survivors) in SFTSV-positive cats. Viral genomic analysis was also performed. Viral load in blood, total bilirubin, creatine phosphokinase, serum amyloid A, interleukin-6, tumor necrotic factor-α, and virus-specific IgM and IgG differed significantly between survivors and fatal cases, and thus may have utility as prognosticators. Furthermore, survivor profiling revealed high-level of viremia with multiple parameters (white blood cells, platelet, total bilirubin, glucose, and serum amyloid A) beyond the reference range in the 7-day acute phase, and signs of clinical recovery in the post-acute phase (parameters returning to, or tending toward, the reference range). However, SFTSV was still detectable from some survived cats even 14 days after onset of disease, indicating the risk of infection posed by close-contact exposure may persist through the post-acute phase. This study provides useful information for prognostic assessments of acute feline SFTS, and may contribute to early treatment plans for cats with SFTS. Our findings also alert pet owners and animal health professionals to the need for prolonged vigilance against animal-to-human transmission when handling cats that have been diagnosed with SFTS.

A nanoluciferase SFTSV for rapid screening antivirals and real-time visualization of virus infection in mice.

BACKGROUND: Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging tick-borne pathogen that causes severe hemorrhagic fever in humans, but no FDA-approved specific antivirals or vaccines are available to treat or prevent SFTS. METHODS: The plasmids construction and transfection were performed to generate the recombinant SFTSV harboring the nanoluciferase gene (SFTSV-Nluc). Immunostaining plaque assay was performed to measure viral titers, and DNA electrophoresis and Sanger sequencing were performed to evaluate the genetic stability. Luciferase assay and quantitative RT-PCR were performed to evaluate the efficacy of antivirals in vitro. Bioluminescence imaging, titration of virus from excised organs, hematology, and histopathology and immunohistochemistry were performed to evaluate the efficacy of antivirals in vivo. FINDINGS: SFTSV-Nluc exhibited high genetic stability and replication kinetics similar to those of wild-type virus (SFTSVwt), then a rapid high-throughput screening system for identifying inhibitors to treat SFTS was developed, and a nucleoside analog, 4-FlU, was identified to effectively inhibit SFTSV in vitro. SFTSV-Nluc mimicked the replication characteristics and localization of SFTSVwt in counterpart model mice. Bioluminescence imaging of SFTSV-Nluc allowed real-time visualization and quantification of SFTSV replication in the mice. 4-FlU was demonstrated to inhibit the replication of SFTSV with more efficiency than T-705 and without obvious adverse effect in vivo. INTERPRETATION: The high-throughput screening system based on SFTSV-Nluc for use in vitro and in vivo revealed that a safe and effective antiviral nucleoside analog, 4-FlU, may be a basis for the strategic treatment of SFTSV and other bunyavirus infections, paving the way for the discovery of antivirals. FUNDING: This work was supported by grants from the National Key Research and Development Plan of China (2021YFC2300700 to L. Zhang, 2022YFC2303300 to L. Zhang), Strategic Priority Research Program of Chinese Academy of Sciences (XDB0490000 to L. Zhang), National Natural Science Foundation of China (31970165 to L. Zhang, U22A20379 to G. Xiao), the Science and Technology Commission of Shanghai Municipality (21S11903100 to Y. Xie), Hubei Natural Science Foundation for Distinguished Young Scholars (2022CFA099 to L. Zhang).

Hsp90 ß is critical for the infection of severe fever with thrombocytopenia syndrome virus.

Severe fever with thrombocytopenia syndrome (SFTS) caused by the SFTS virus (SFTSV) is an emerging disease in East Asia with a fatality rate of up to 30%. However, the viral-host interaction of SFTSV remains largely unknown. The heat-shock protein 90 (Hsp90) family consists of highly conserved chaperones that fold and remodel proteins and has a broad impact on the infection of many viruses. Here, we showed that Hsp90 is an important host factor involved in SFTSV infection. Hsp90 inhibitors significantly reduced SFTSV replication, viral protein expression, and the formation of inclusion bodies consisting of nonstructural proteins (NSs). Among viral proteins, NSs appeared to be the most reduced when Hsp90 inhibitors were used, and further analysis showed that their translation was affected. Co-immunoprecipitation of NSs with four isomers of Hsp90 showed that Hsp90 ß specifically interacted with them. Knockdown of Hsp90 ß expression also inhibited replication of SFTSV. These results suggest that Hsp90 ß plays a critical role during SFTSV infection and could be a potential target for the development of drugs against SFTS.

Seroprevalence and transmission of severe fever with thrombocytopenia syndrome virus in a coastal endemic area in Southeastern China.

Severe fever with thrombocytopenia syndrome (SFTS) is a newly emerged tick-borne viral zoonosis and widely prevalent in China, Japan and South Korea. Most reported SFTS cases have been identified in mountainous and hilly areas, with a few in island areas. In this study, we conducted a systematic investigation about natural infection of SFTS virus (SFTSV) among humans, animals and ticks in a coastal endemic prefecture, containing island, plains and mountain settings, in Zhejiang Province, Southeastern China. From July 2020 to June 2021, 1117 participants completed a survey with questionnaire interview and serum testing. Meanwhile, 862 serum samples of domestic animals, 275 spleen tissue samples of wild animals and 829 ticks representing five species (predominantly Haemaphysalis longicornis and Rhipicephalus sanguineus sensu lato) were collected. The seroprevalence of anti-SFTSV total antibody and IgM antibody among the participants was 4.8 % (54/1117) and 0.6 % (7/1117), respectively. Multivariate logistic regression analysis indicated that living in the island area (OR=2.66; 95 %CI: 1.04-6.80; P = 0.041) was significantly associated with seropositivity of total antibody to SFTSV. Furthermore, a higher seroprevalence was observed in domestic animals (36.1 %), while the SFTSV-RNA infection rate was 0.4 % in wild animals and the minimum infection rate (MIR) was 0.8 % for all tick species combined. The only tick species infected with SFTSV was H. longicornis. The prevalence of SFTSV infection in the island area, manifested by anti-SFTSV total antibody (P = 0.012) and IgM antibody (P = 0.004) among humans, anti-SFTSV total antibody (P<0.001) among domestic animals, and SFTSV-RNA among ticks (P = 0.022), was significantly higher than that in the mountainous area and the plain area. Furthermore, phylogenetic analysis showed that SFTSV sequences obtained from ticks in the island area were clustered with reported strains in Japan and South Korea. These results suggest that islands in the study area might be an important natural focus of SFTSV.

Potent immunogenicity and neutralization of recombinant adeno-associated virus expressing the glycoprotein of severe fever with thrombocytopenia virus.

Severe fever with thrombocytopenia syndrome (SFTS) is an infectious disease caused by a tick-borne virus called severe fever with thrombocytopenia syndrome virus (SFTSV). In recent years, human infections through contact with ticks and through contact with the bodily fluids of infected dogs and cats have been reported; however, no vaccine is currently available. SFTSV has two glycoproteins (Gn and Gc) on its envelope, which are vaccine-target antigens involved in immunogenicity. In the present study, we constructed novel SFTS vaccine candidates using an adeno-associated virus (AAV) vector to transport the SFTSV glycoprotein genome. AAV vectors are widely used in gene therapy and their safety has been confirmed in clinical trials. Recently, AAV vectors have been used to develop influenza and SARS-CoV-2 vaccines. Two types of vaccines (AAV9-SFTSV Gn and AAV9-SFTSV Gc) carrying SFTSV Gn and Gc genes were produced. The expression of Gn and Gc proteins in HEK293T cells was confirmed by infection with vaccines. These vaccines were inoculated into mice, and the collected sera produced anti-SFTS antibodies. Furthermore, sera from AAV9-SFTSV Gn infected mice showed a potent neutralizing ability, similar to previously reported SFTS vaccine candidates that protected animals from SFTSV infection. These findings suggest that this vaccine is a promising candidate for a new SFTS vaccine.

High Seroprevalence of Severe Fever with Thrombocytopenia Syndrome Virus Infection among the Dog Population in Thailand.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne zoonotic disease caused by the SFTS virus (SFTSV). In Thailand, three human cases of SFTS were reported in 2019 and 2020, but there was no report of SFTSV infection in animals. Our study revealed that at least 16.6% of dogs in Thailand were seropositive for SFTSV infection, and the SFTSV-positive dogs were found in several districts in Thailand. Additionally, more than 70% of the serum samples collected at one shelter possessed virus-neutralization antibodies against SFTSV and the near-complete genome sequences of the SFTSV were determined from one dog in the shelter. The dog SFTSV was genetically close to those from Thailand and Chinese patients and belonged to genotype J3. These results indicated that SFTSV has already spread among animals in Thailand.

Epidemiology of Severe Fever with Thrombocytopenia Syndrome in Dogs and Cats in Taiwan.

Severe Fever with Thrombocytopenia Syndrome (SFTS), caused by the SFTS Virus (SFTSV), is a global health threat. SFTSV in Taiwan has only been reported in ruminants and wild animals. Thus, we aimed to investigate the infection statuses of dogs and cats, the animals with closer human interactions. Overall, the SFTSV RNA prevalence was 23% (170/735), with dogs showing a 25.9% (111/429) prevalence and cats at 19.3% (59/306) prevalence. Noticeably, the prevalence in stray animals (39.8% 77/193) was significantly higher than in domesticated ones (17.2%, 93/542). Among the four categories analyzed, the highest SFTSV prevalence was found in the stray dogs at 53.9% (120/193), significantly higher than the 24.2% prevalence noted in stray cats. In contrast, domesticated animals exhibited similar prevalence rates, with 17.1% for dogs and 17.2% for cats. It is noteworthy that in the domesticated animal groups, a significantly elevated prevalence (45%, 9/20) was observed among cats exhibiting thrombocytopenia compared to those platelet counts in the reference range (4.8%, 1/21). The high infection rate in stray animals, especially stray dogs, indicated that exposure to various outdoor environments influences the prevalence of infections. Given the higher human interaction with dogs and cats, there is a need for proactive measures to reduce the risk associated with the infection of SFTSV in both animals and humans.

Identification of Mudanjiang Phlebovirus in the Daxing'anling Region of China.

Mudanjiang phlebovirus (MJPV) is a newly discovered phlebovirus, initially detected from Ixodes persulcatus ticks in China in 2022. In this study, by next-generation sequencing (NGS) on a wide variety of ticks and wild small animals in China, we detected MJPV from I. persulcatus and Meriones meridianus. Additionally, we conducted RT-PCR and sequencing on 1815 adult ticks and 805 wild small mammals collected from eight provinces in China between 2017 and 2021. MJPV RNA-positive results were found in 0.22% (4/1815) of tick samples, as well as in 0.12% (1/805) of rodent samples. All positive detections were obtained from Heilongjiang and Inner Mongolia. Sequencing analysis revealed nucleotide similarities ranging from 98.23% to 99.11%, as well as amino acid similarities ranging from 99.12% to100%, between the current MJPV strain and previously reported strains of MJPV. Phylogenetic tree analysis demonstrated that the previously reported MJPV strain along with our two variants clustered together with other tick-borne phenuiviruses, indicating their close relationship within this viral group. This study represents the first detection of MJPV infection in wild rodents, expanding the known host range for this virus in the endemic regions.

SFTSV Gn-Head mRNA vaccine confers efficient protection against lethal viral challenge.

Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging tick-borne virus, causing thrombocytopenia and hemorrhagic fever, with a fatality rate ranging from 12% to 30%. SFTSV possesses Gn and Gc glycoproteins, which are responsible for host cell receptor attachment and membrane fusion, respectively, to infect host cells. We have previously reported a protein subunit vaccine candidate (sGn-H-FT) of the SFTSV soluble Gn head region (sGn-H) fused with self-assembling ferritin (FT) nanoparticles, displaying strong protective immunogenicity. In this study, we present messenger RNA (mRNA) vaccine candidates encoding sGn-H or sGn-H-FT, both of which exhibit potent in vivo immunogenicity and protection capacity. Mice immunized with either sGn-H or sGn-H-FT mRNA lipid nanoparticle (LNP) vaccine produced strong total antibodies and neutralizing antibodies (NAbs) against sGn-H. Importantly, NAb titers remained high for an extended period. Finally, mice immunized with sGn-H or sGn-H-FT mRNA LNP vaccine were fully protected from a lethal dose of SFTSV challenge, showing no fatality. These findings underscore the promise of sGn-H and sGn-H-FT as vaccine antigen candidates capable of providing protective immunity against SFTSV infection.

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.