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

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

A highly attenuated vaccinia virus strain LC16m8-based vaccine for severe fever with thrombocytopenia syndrome.

Severe fever with thrombocytopenia syndrome (SFTS) caused by a species Dabie bandavirus (formerly SFTS virus [SFTSV]) is an emerging hemorrhagic infectious disease with a high case-fatality rate. One of the best strategies for preventing SFTS is to develop a vaccine, which is expected to induce both humoral and cellular immunity. We applied a highly attenuated but still immunogenic vaccinia virus strain LC16m8 (m8) as a recombinant vaccine for SFTS. Recombinant m8s expressing SFTSV nucleoprotein (m8-N), envelope glycoprotein precursor (m8-GPC), and both N and GPC (m8-N+GPC) in the infected cells were generated. Both m8-GPC- and m8-N+GPC-infected cells were confirmed to produce SFTSV-like-particles (VLP) in vitro, and the N was incorporated in the VLP produced by the infection of cells with m8-N+GPC. Specific antibodies to SFTSV were induced in mice inoculated with each of the recombinant m8s, and the mice were fully protected from lethal challenge with SFTSV at both 103 TCID50 and 105 TCID50. In mice that had been immunized with vaccinia virus strain Lister in advance of m8-based SFTSV vaccine inoculation, protective immunity against the SFTSV challenge was also conferred. The pathological analysis revealed that mice immunized with m8-GPC or m8-N+GPC did not show any histopathological changes without any viral antigen-positive cells, whereas the control mice showed focal necrosis with inflammatory infiltration with SFTSV antigen-positive cells in tissues after SFTSV challenge. The passive serum transfer experiments revealed that sera collected from mice inoculated with m8-GPC or m8-N+GPC but not with m8-N conferred protective immunity against lethal SFTSV challenge in naïve mice. On the other hand, the depletion of CD8-positive cells in vivo did not abrogate the protective immunity conferred by m8-based SFTSV vaccines. Based on these results, the recombinant m8-GPC and m8-N+GPC were considered promising vaccine candidates for SFTS.

Capnocytophaga catalasegens sp. nov., isolated from feline oral cavities.

Three bacterial strains, KC07075, KC07079 and KC07084T, were isolated from the oral cavity of cats in 2007 in Japan. These strains were Gram-negative rods, exhibited gliding motility, grew in air with 5 % CO2, and showed oxidase activity, but not catalase activity. The 16S rRNA gene sequences of the three strains were 100 % identical. The 16S rRNA gene sequence of strain KC07084T showed 92.1 and 91.9% identity to the type strains of Capnocytophaga canis and Capnocytophaga felis, respectively, and showed 89.3-91.6% identity to other Capnocytophaga species. The major cellular fatty acids of strain KC07084T were iso-C15 : 0 (58.4 %) and summed feature 11 (13.1 %). The G+C content of DNA from strain KC07084T was 33.7 mol%, and the genome size was 2.92 Mbp. Strains KC07075, KC07079 and KC07084T showed digital DNA-DNA hybridization values (dDDH) values of 99.9 % and average nucleotide identity (ANI) values of 99.98 % with each other, strain KC07084T had dDDH values of 18.7-28.2 % and ANI values of 67.12-72.30 % to the type strains of other Capnocytophaga species. All known species of the genus Capnocytophaga inhabiting the oral cavity of dogs and cats have catalase activity, but the three strains, including type strain KC07084T, lacked catalase activity. These results of the phylogenetic analysis of the 16S rRNA gene sequence, biochemical characteristics, and dDDH and ANI values suggest that strain KC07084T represents a novel species. We propose the name Capnocytophaga catalasegens sp. nov., with KC07084T as the type strain (=JCM 32682T=DSM 107252T).

Guest edited collection serological study of SARS-CoV-2 antibodies in japanese cats using protein-A/G-based ELISA.

BACKGROUND: Little is known about the epidemic status of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in cats in Japan due to insufficiently reliable seroepidemiological analysis methods that are easy to use in cats. RESULTS: We developed a protein-A/G-based enzyme-linked immunosorbent assay (ELISA) to detect antibodies against SARS-CoV-2 in cats. The assay was standardized using positive rabbit antibodies against SARS-CoV-2. The ELISA results were consistent with those of a conventional anti-feline-immunoglobulin-G (IgG)-based ELISA. To test the protein-A/G-based ELISA, we collected blood samples from 1,969 cats that had been taken to veterinary clinics in Japan from June to July 2020 and determined the presence of anti-SARS-CoV-2 antibodies. Nine cats were found to have SARS-CoV-2 S1-specific IgG, of which 4 had recombinant receptor-binding domain-specific IgG. Of those 9 samples, one showed neutralizing activity. Based on these findings, we estimated that the prevalence of SARS-CoV-2 neutralizing antibodies in cats in Japan was 0.05% (1/1,969 samples). This prevalence was consistent with the prevalence of neutralizing antibodies against SARS-CoV-2 in humans in Japan according to research conducted at that time. CONCLUSIONS: Protein-A/G-based ELISA has the potential to be a standardized method for measuring anti-SARS-CoV-2 antibodies in cats. The infection status of SARS-CoV-2 in cats in Japan might be linked to that in humans.

Serological methods for detection of infection with shrew-borne hantaviruses: Thottapalayam, Seewis, Altai, and Asama viruses.

The infectivity of shrew-borne hantaviruses to humans is still unclear because of the lack of a serodiagnosis method for these viruses. In this study, we prepared recombinant nucleocapsid (rN) proteins of Seewis orthohantavirus, Altai orthohantavirus (ALTV), Thottapalayam thottimvirus (TPMV), and Asama orthohantavirus. Using monospecific rabbit sera, no antigenic cross-reactivity was observed. In a serosurvey of 104 samples from renal patients and 271 samples from heathy controls from Sri Lanka, one patient serum and two healthy control sera reacted with rN proteins of ALTV and TPMV, respectively. The novel assays should be applied to investigate potential infectivity of shrew-borne hantaviruses to humans.

Prevalence of Antibodies to Crimean-Congo Hemorrhagic Fever Virus in Ruminants, Nigeria, 2015.

Crimean-Congo hemorrhagic fever virus (CCHFV) is a highly transmissible human pathogen. Infection is often misdiagnosed, in part because of poor availability of data in disease-endemic areas. We sampled 150 apparently healthy ruminants throughout Nigeria for virus seropositivity and detected virus-specific IgG in cattle (24%) and goats (2%), highlighting the need for further investigations.

Severe Fever with Thrombocytopenia Syndrome, Japan, 2013-2017.

We conducted an epidemiologic study of severe fever with thrombocytopenia syndrome (SFTS) in Japan during 2013-2017. Of 303 cases reported during that period, 133 (44%) were included in this study. The median time between onset of illness and diagnosis of SFTS shortened, from 11.5 to 3.0 days, but the case-fatality rate remained high, at 27%. In 64 patients (48%), a close contact with companion animals was reported within 2 weeks of disease onset. Of these 64 patients, 40 were surveyed further, and we confirmed that 3 had direct contact with body fluids of ill companion animals; 2 had direct contact with the saliva of an ill feral cat or pet dog. These patients reported no history of tick bite, suggesting that ill companion animals might be a source of SFTS virus transmission. Direct contact with the body fluids of ill companion animals should be avoided.

Establishment of a Virulent Full-Length cDNA Clone for Type I Feline Coronavirus Strain C3663.

Feline infectious peritonitis (FIP) is one of the most important infectious diseases in cats and is caused by feline coronavirus (FCoV). Tissue culture-adapted type I FCoV shows reduced FIP induction in experimental infections, which complicates the understanding of FIP pathogenesis caused by type I FCoV. We previously found that the type I FCoV strain C3663 efficiently induces FIP in specific-pathogen-free cats through the naturally infectious route. In this study, we employed a bacterial artificial chromosome-based reverse genetics system to gain more insights into FIP caused by the C3633 strain. We successfully generated recombinant virus (rC3663) from Fcwf-4 cells transfected with infectious cDNA that showed growth kinetics similar to those shown by the parental virus. Next, we constructed a reporter C3663 virus carrying the nanoluciferase (Nluc) gene to measure viral replication with high sensitivity. The inhibitory effects of different compounds against rC3663-Nluc could be measured within 24 h postinfection. Furthermore, we found that A72 cells derived from canine fibroblasts permitted FCoV replication without apparent cytopathic effects. Thus, our reporter virus is useful for uncovering the infectivity of type I FCoV in different cell lines, including canine-derived cells. Surprisingly, we uncovered aberrant viral RNA transcription of rC3663 in A72 cells. Overall, we succeeded in obtaining infectious cDNA clones derived from type I FCoV that retained its virulence. Our recombinant FCoVs are powerful tools for increasing our understanding of the viral life cycle and pathogenesis of FIP-inducing type I FCoV.IMPORTANCE Feline coronavirus (FCoV) is one of the most significant coronaviruses, because this virus induces feline infectious peritonitis (FIP), which is a lethal disease in cats. Tissue culture-adapted type I FCoV often loses pathogenicity, which complicates research on type I FCoV-induced feline infectious peritonitis (FIP). Since we previously found that type I FCoV strain C3663 efficiently induces FIP in specific-pathogen-free cats, we established a reverse genetics system for the C3663 strain to obtain recombinant viruses in the present study. By using a reporter C3663 virus, we were able to examine the inhibitory effect of 68 compounds on C3663 replication in Fcwf-4 cells and infectivity in a canine-derived cell line. Interestingly, one canine cell line, A72, permitted FCoV replication but with low efficiency and aberrant viral gene expression.

Effective inactivation of Nipah virus in serum samples for safe processing in low-containment laboratories.

BACKGROUND: Nipah virus (NiV) is an emerging zoonotic paramyxovirus that causes severe encephalitis and respiratory disease with a high mortality rate in humans. During large outbreaks of the viral disease, serological testing of serum samples could be a useful diagnostic tool, which could provide information on not only the diagnosis of NiV disease but also the history of an individual with previous exposure to the virus, thereby supporting disease control. Therefore, an efficient method for the inactivation of NiV in serum samples is required for serological diagnosis. METHODS: We determined the optimal conditions for the inactivation of NiV infectivity in human serum using heating and UV treatment. The inactivation method comprised UV irradiation with a cover of aluminum foil for 30 min and heating at 56 °C for 30 min. RESULTS: With an optimized protocol for virus inactivation, NiV infectivity in serum samples (containing 6.0 × 105 TCID50) was completely inactivated. CONCLUSIONS: We developed a recommended protocol for the effective inactivation of NiV. This protocol would enable a regional or local laboratory to safely transport or process samples, including NiV, for serological testing in its biosafety level-2 facility.

Capnocytophaga felis sp. nov. isolated from the feline oral cavity.

Four strains, KC07070T, KC07105, 11 025B-8C and 11 026B-8-C, were isolated from the oral cavity of cats in 2007 or 2011 in Japan. These strains were Gram-stain-negative rods, exhibited gliding motility, grew in air with 5 % CO2 and showed catalase and oxidase activity. The sequences of 16S rRNA genes of the four strains were 100 % identical. Additionally, the sequences of 16S rRNA genes of KC07070T had identity to those of the type strains of Capnocytophaga canimorsus (97.7 %), Capnocytophaga cynodegmi (97.8 %) and Capnocytophaga canis (97.4 %) and 91.2-93.8% identity to those of other species of the genus Capnocytophaga. The major cellular fatty acids of KC07070T were iso-C15 : 0 (56.2 %) and summed feature 11 (14.9 %). The G+C content of the DNA from KC07070T was 35.6 mol%, and the genome size was 2.88 Mbp. KC07070T had digital DNA-DNA hybridization (dDDH) values of 26.2-27.6% and average nucleotide identity (ANI) values of 75.4-83.3 % to the type strains of the closest relatives, C. canimorsus, C. cynodegmi and C. canis. These results of phylogenetic analysis of 16S rRNA gene sequence, cellular fatty acids compositions and dDDH and ANI values indicate that strain KC07070T represents a novel species, for which we propose the name Capnocytophaga felis sp. nov., with type strain KC07070T (=JCM 32681T=DSM 107251T).

Increased proportion of apoptotic cells in cat kidney tissues infected with feline morbillivirus.

In order to study potential pathogenic mechanisms of feline morbillivirus (FeMV) in infected kidney cells, we performed a terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and an immunofluorescence assay (IFA) with an anti-FeMV P protein antibody on a total of 38 cat kidney tissues, 12 of which were positive for FeMV. Among these samples, we detected significantly larger numbers of apoptotic cells in FeMV-positive tissues than in FeMV-negative tissues, and in these tissues, a substantial percentage of TUNEL-positive (TUNEL+) cells contained the FeMV P protein (mean, 37.4; range, 17.4-82.9), suggesting that induction of apoptosis may be an important mechanism for pathological changes associated with FeMV infection in cat kidney tissues.

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

BACKGROUND: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease that commonly has a lethal course caused by the tick-borne Huaiyangshan banyang virus [former SFTS virus (SFTSV)]. The viral load in various body fluids in SFTS patients and the best infection control measure for SFTS patients have not been fully established. CASE PRESENTATION: A 79-year-old man was bitten by a tick while working in the bamboo grove in Nagasaki Prefecture in the southwest part of Japan. Due to the occurrence of impaired consciousness, he was referred to Nagasaki University Hospital for treatment. The serum sample tested positive for SFTSV-RNA in the genome amplification assay, and he was diagnosed with SFTS. Furthermore, SFTSV-RNA was detected from the tick that had bitten the patient. He was treated with multimodal therapy, including platelet transfusion, antimicrobials, antifungals, steroids, and continuous hemodiafiltration. His respiration was assisted with mechanical ventilation. On day 5, taking the day on which he was hospitalized as day 0, serum SFTSV-RNA levels reached a peak and then decreased. However, the cerebrospinal fluid collected on day 13 was positive for SFTSV-RNA. In addition, although serum SFTSV-RNA levels decreased below the detectable level on day 16, he was diagnosed with pneumonia with computed tomography. SFTSV-RNA was detected in the bronchoalveolar lavage fluid on day 21. By day 31, he recovered consciousness completely. The pneumonia improved by day 51, but SFTSV-RNA in the sputum remained positive for approximately 4 months after disease onset. Strict countermeasures against droplet/contact infection were continuously conducted. CONCLUSIONS: Even when SFTSV genome levels become undetectable in the serum of SFTS patients in the convalescent phase, the virus genome remains in body fluids and tissues. It may be possible that body fluids such as respiratory excretions become a source of infection to others; thus, careful infection control management is needed.

Whole-genome sequence-based comparison and profiling of virulence-associated genes of Bacillus cereus group isolates from diverse sources in Japan.

BACKGROUND: The complete genome sequences of 44 Bacillus cereus group isolates collected from diverse sources in Japan were analyzed to determine their genetic backgrounds and diversity levels in Japan. Multilocus sequence typing (MLST) and core-genome single-nucleotide polymorphism (SNP) typing data from whole-genome sequences were analyzed to determine genetic diversity levels. Virulence-associated gene profiles were also used to evaluate the genetic backgrounds and relationships among the isolates. RESULTS: The 44 B. cereus group isolates, including soil- and animal-derived isolates and isolates recovered from hospitalized patients and food poisoning cases, were genotyped by MLST and core-genome SNP typing. Genetic variation among the isolates was identified by the MLST and core-genome SNP phylogeny comparison against reference strains from countries outside of Japan. Exploratory principal component analysis and nonmetric multidimensional scaling (NMDS) analyses were used to assess the genetic similarities among the isolates using gene presence and absence information and isolate origins as the metadata. A significant correlation was seen between the principal components and the presence of genes encoding hemolysin BL and emetic genetic determinants in B. cereus, and the capsule proteins in B. anthracis. NMDS showed that the cluster of soil isolates overlapped with the cluster comprising animal-derived and clinical isolates. CONCLUSIONS: Molecular and epidemiological analyses of B. cereus group isolates in Japan suggest that the soil- and animal-derived bacteria from our study are not a significant risk to human health. However, because several of the clinical isolates share close genetic relationships with the environmental isolates, both molecular and epidemiological surveillance studies could be used effectively to estimate virulence in these important pathogens.

Rabies post-exposure prophylactic vaccination for returning travelers to Japan.

BACKGROUND: Rabies post-exposure prophylaxis (PEP) in Japan is administered using 6 subcutaneous doses (on days 0, 3, 7, 14, 30, and 90), which is not in line with international recommendations of 4 or 5 intramuscular doses. For reducing dose frequency, we evaluate the immunogenicity of PEP with a regimen of 6 subcutaneous doses. METHOD: This prospective single-center cross-sectional study was performed between September 2013 and December 2014. We included patients underwent rabies PEP by purified chick embryo-cultured rabies vaccine Kaketsuken (PCEC-K) at our clinic, and excluded patients with a history of pre-exposure prophylaxis or PEP using rabies immunoglobulin. The rabies virus-neutralizing antibody tests were performed at the first visit to our office (doses 1-4) and at the fifth and sixth doses. RESULTS: Data were available for 43 of 59 enrolled patients. Thirty-two patients did not start PEP within 48 h after exposure to animals. The seroprotection rates (≥0.5 IU/mL) were 90.7% and 75.7%, at days 30 and 90, respectively. Despite receiving a fifth dose, 85.3% of the patients exhibited decreasing antibody titers during days 30-90 (p < 0.001). CONCLUSIONS: The seroprotection rates of PCEC-K induced subcutaneously were insufficient to prevent rabies at day 30 and 90.

Fatal Tickborne Phlebovirus Infection in Captive Cheetahs, Japan.

Two captive cheetahs from a zoo in Japan died of a severe fever with thrombocytopenia syndrome-like illness. Severe fever with thrombocytopenia syndrome virus, an endemic tickborne phlebovirus, was detected systemically with secretion of infectious viruses into the saliva. These cases highlight the risk for exposure of captive animals to endemic arthropodborne pathogens.

The Babesia divergens Asia Lineage Is Maintained through Enzootic Cycles between Ixodes persulcatus and Sika Deer in Hokkaido, Japan.

Parasites of the Babesiadivergens Asia lineage, which are closely related to B. divergens in Europe and Babesia sp. strain MO1 in the United States, were recently reported in sika deer (Cervus nippon) in eastern Japan. To identify the tick vector(s) for this parasite, we conducted a field survey in Hokkaido, Japan, where the infection rate in sika deer is the highest in the country. A specific PCR system which detects and discriminates between lineages within B. divergens and between those lineages and Babesia venatorum showed that Ixodes persulcatus (11/822), but not sympatric Ixodes ovatus (0/595) or Haemaphysalis sp. (0/163) ticks, carried B. divergens Asia lineage. Genomic DNA was archived from salivary glands of partially engorged I. persulcatus females and three isolates of B. divergens Asia lineage were newly described. The 18S rRNA gene sequence of the isolates formed the Asia lineage cluster with those previously described in sika deer isolates. One salivary gland also contained parasites of Babesia microti U.S. lineage, which were subsequently isolated in a hamster in vivoB. venatorum (strain Etb5) was also detected in one I. persulcatus tick. The 18S rRNA sequence of Etb5 was 99.7% identical to that of B. venatorum (AY046575) and was phylogenetically positioned in a taxon composed of B. venatorum isolates from Europe, China, and Russia. The geographical distribution of I. persulcatus is consistent with that of B. divergens in sika deer in Japan. These results suggest that I. persulcatus is a principal vector for B. divergens in Japan and Eurasia, where I. persulcatus is predominantly distributed.IMPORTANCE The Babesiadivergens Asia lineage of parasites closely related to B. divergens in Europe and Babesia sp. MO1 in the United States was recently reported in Cervus nippon in eastern Japan. In this study, specific PCR for the Asia lineage identified 11 positives in 822 host-seeking Ixodes persulcatus ticks, a principal vector for many tick-borne disease agents. Gene sequences of three isolates obtained from DNA in salivary glands of female ticks were identical to each other and to those in C. nippon We also demonstrate the coinfection of B. divergens Asia lineage with Babesia microti U.S. lineage in a tick salivary gland and, furthermore, isolated the latter in a hamster. These results suggest that I. persulcatus is the principal vector for B. divergens as well as for B. microti, and both parasites may be occasionally cotransmitted by I. persulcatus This report will be important for public health, since infection may occur through transfusion.

Characterization of three strains of Capnocytophaga canis isolated from patients with sepsis.

Capnocytophaga canimorsus and Capnocytophaga cynodegmi, both commensal bacteria in the oral cavities of dogs and cats, are zoonotic pathogens. In particular, C. canimorsus causes sepsis and fatal septic shock. Recently, a novel Capnocytophaga species, C. canis, was isolated from the oral cavities of healthy dogs. It is reportedly oxidase-negative and therefore considered avirulent in humans. In the present study, three strains of C. canis were isolated from Japanese patients with sepsis. All three strains, HP20001, HP33001 and HP40001, were oxidase-positive. Nucleotide sequence identities of the 16S rRNA gene of the three strains to the C. canimorsus type strain ATCC35979, C. cynodegmi type strain ATCC49044 and C. canis type strain LMG29146 were 96.9-97.0%, 96.9-97.0% and 99.7-99.8%, respectively. Multi-locus sequence analysis based on seven house-keeping genes, dnaJ, fumC, glyA, gyrB, murG, trpB and tuf, revealed that the oxidase-positive C. canis strains isolated in Japan and oxidase-negative strains of C. canis from canine oral cavities in Switzerland were clustered in different genetic subgroups. These results indicate that the virulence of C. canis strains in humans is associated with oxidase activity.

Evaluation of Francisella tularensis ΔpdpC as a candidate live attenuated vaccine against respiratory challenge by a virulent SCHU P9 strain of Francisella tularensis in a C57BL/6J mouse model.

Francisella tularensis, which causes tularemia, is an intracellular gram-negative bacterium. F. tularensis has received significant attention in recent decades because of its history as a biological weapon. Thus, development of novel vaccines against tularemia has been an important goal. The attenuated F. tularensis strain ΔpdpC, in which the pathogenicity determinant protein C gene (pdpC) has been disrupted by TargeTron mutagenesis, was investigated as a potential vaccine candidate for tularemia in the present study. C57BL/6J mice immunized s.c. with 1 × 106 CFUs of ΔpdpC were challenged intranasally with 100× the median lethal dose (LD50 ) of a virulent SCHU P9 strain 21 days post immunization. Protection against this challenge was achieved in 38% of immunized C57BL/6J mice administered 100 LD50 of this strain. Conversely, all unimmunized mice succumbed to death 6 days post challenge. Survival rates were significantly higher in vaccinated than in unimmunized mice. In addition, ΔpdpC was passaged serially in mice to confirm its stable attenuation. Low bacterial loads persisted in mouse spleens during the first to tenth passages. No statistically significant changes in the number of CFUs were observed during in vivo passage of ΔpdpC. The inserted intron sequences for disrupting pdpC were completely maintained even after the tenth passage in mice. Considering the stable attenuation and intron sequences, it is suggested that ΔpdpC is a promising tularemia vaccine candidate.

Seroprevalence of severe fever with thrombocytopenia syndrome (SFTS) virus antibodies in humans and animals in Ehime prefecture, Japan, an endemic region of SFTS.

Severe fever with thrombocytopenia syndrome (SFTS) was first identified as an emerging tick-borne infectious disease caused by the SFTS virus (SFTSV) in China and has also been found to be endemic to Japan and South Korea, indicating that SFTS is of great concern in East Asia. The aim of the present study was to determine the seroprevalence of SFTSV antibodies in humans and animals in SFTS-endemic regions of Japan. One of 694 (0.14%) healthy persons over 50 years of age and 20 of 107 (18.7%) wild and domestic animals in Ehime prefecture of western Japan were determined to be seropositive for SFTSV antibodies by virus neutralization test and ELISA, respectively. The seropositive person, a healthy 74-year-old woman, was a resident of the southwest part of Ehime prefecture engaged in citriculture and field work. This woman's sample exhibited neutralizing activity against SFTSV although she had neither a clear experience with tick bites nor SFTS-like clinical illness. These findings indicate that most people living in the endemic regions are not infected with SFTSV and suggest that most of the SFTS patients reported so far do not reflect the tip of an iceberg of people infected with SFTSV, but at the same time, that SFTSV infection does not always induce severe SFTS-associated symptoms. These findings also suggested that SFTSV has been maintained in nature within animal species and ticks.

Characterization of Glycoprotein-Mediated Entry of Severe Fever with Thrombocytopenia Syndrome Virus.

UNLABELLED: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging hemorrhagic fever with a high case fatality rate caused by SFTS virus (SFTSV). Effective vaccines and specific therapies for SFTS are urgently sought, and investigation into virus-host cell interactions is expected to contribute to the development of antiviral strategies. In this study, we have developed a pseudotype vesicular stomatitis virus (VSV) bearing the unmodified Gn/Gc glycoproteins (GPs) of SFTSV (SFTSVpv). We have analyzed the host cell entry of this pseudotype virus and native SFTSV. Both SFTSVpv and SFTSV exhibited high infectivity in various mammalian cell lines. The use of lysosomotropic agents indicated that virus entry occurred via pH-dependent endocytosis. SFTSVpv and SFTSV infectivity was neutralized by serial dilutions of convalescent-phase patient sera. Entry of SFTSVpv and growth of SFTSV were increased in Raji cells expressing not only the C-type lectin dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN) but also DC-SIGN-related (DC-SIGNR) and liver and lymph node sinusoidal endothelial cell C-type lectin (LSECtin). 25-Hydroxycholesterol (25HC), a soluble oxysterol metabolite, inhibited the cell entry of SFTSVpv and the membrane fusion of SFTSV. These results indicate that pH-dependent endocytosis of SFTSVpv and SFTSV is enhanced by attachment to certain C-type lectins. SFTSVpv is an appropriate model for the investigation of SFTSV-GP-mediated cell entry and virus neutralization at lower biosafety levels. Furthermore, 25HC may represent a potential antiviral agent against SFTS. IMPORTANCE: SFTSV is a recently discovered bunyavirus associated with SFTS, a viral hemorrhagic fever with a high case fatality rate endemic to China, South Korea, and Japan. Because little is known about the characteristics of the envelope protein and entry mechanisms of SFTSV, further studies will be required for the development of a vaccine or effective therapies. In this study, we investigated the mechanism of SFTSV cell entry using SFTSVpv and the native virus. SFTSV can grow in nonsusceptible cell lines in the presence of certain C-type lectins. Moreover, 25HC, an oxysterol metabolite, may represent a potential therapeutic inhibitor of SFTSV infection.