Construction of Vero cell-adapted rabies vaccine strain by five amino acid substitutions in HEP-Flury strain.

Rabies virus (RABV) causes fatal neurological disease. Pre-exposure prophylaxis (PrEP) and post-exposure prophylaxis (PEP) using inactivated-virus vaccines are the most effective measures to prevent rabies. In Japan, HEP-Flury, the viral strain, used as a human rabies vaccine, has historically been propagated in primary fibroblast cells derived from chicken embryos. In the present study, to reduce the cost and labor of vaccine production, we sought to adapt the original HEP-Flury (HEP) to Vero cells. HEP was repeatedly passaged in Vero cells to generate ten- (HEP-10V) and thirty-passaged (HEP-30V) strains. Both HEP-10V and HEP-30V grew significantly better than HEP in Vero cells, with virulence and antigenicity similar to HEP. Comparison of the complete genomes with HEP revealed three non-synonymous mutations in HEP-10V and four additional non-synonymous mutations in HEP-30V. Comparison among 18 recombinant HEP strains constructed by reverse genetics and vesicular stomatitis viruses pseudotyped with RABV glycoproteins indicated that the substitution P(L115H) in the phosphoprotein and G(S15R) in the glycoprotein improved viral propagation in HEP-10V, while in HEP-30V, G(V164E), G(L183P), and G(A286V) in the glycoprotein enhanced entry into Vero cells. The obtained recombinant RABV strain, rHEP-PG4 strain, with these five substitutions, is a strong candidate for production of human rabies vaccine.

Single Amino Acid Substitution in the Matrix Protein of Rabies Virus Is Associated with Neurovirulence in Mice.

Rabies is a fatal encephalitic infectious disease caused by the rabies virus (RABV). RABV is highly neurotropic and replicates in neuronal cell lines in vitro. The RABV fixed strain, HEP-Flury, was produced via passaging in primary chicken embryonic fibroblast cells. HEP-Flury showed rapid adaptation when propagated in mouse neuroblastoma (MNA) cells. In this study, we compared the growth of our previously constructed recombinant HEP (rHEP) strain-based on the sequence of the HEP (HEP-Flury) strain-with that of the original HEP strain. The original HEP strain exhibited higher titer than rHEP and a single substitution at position 80 in the matrix (M) protein M(D80N) after incubation in MNA cells, which was absent in rHEP. In vivo, intracerebral inoculation of the rHEP-M(D80N) strain with this substitution resulted in enhanced viral growth in the mouse brain and a significant loss of body weight in the adult mice. The number of viral antigen-positive cells in the brains of adult mice inoculated with the rHEP-M(D80N) strain was significantly higher than that with the rHEP strain at 5 days post-inoculation. Our findings demonstrate that a single amino acid substitution in the M protein M(D80N) is associated with neurovirulence in mice owing to adaptation to mouse neuronal cells.

Cross-Neutralization Activities of Antibodies against 18 Lyssavirus Glycoproteins.

Some lyssaviruses, including the rabies virus (RABV), cause lethal neurological symptoms in humans. However, the efficacy of commercial vaccines has only been evaluated against RABV. To assess cross-reactivity among lyssaviruses, including RABV, sera from rabbits inoculated with human and animal RABV vaccines and polyclonal antibodies from rabbits immunized with expression plasmids of the glycoproteins of all 18 lyssaviruses were prepared, and cross-reactivity was evaluated via virus-neutralization tests using Duvenhage lyssavirus (DUVV), European bat lyssavirus-1 (EBLV-1), Mokola lyssavirus (MOKV), Lagos bat lyssavirus (LBV), and RABV. The sera from rabbits inoculated with RABV vaccines showed cross-reactivity with EBLV-1 and DUVV, both belonging to phylogroup I. However, reactivity with MOKV and LBV in phylogroup II was notably limited or below the detection level. Next, we compared the cross-reactivity of the polyclonal antibodies against all lyssavirus glycoproteins. Polyclonal antibodies had high virus-neutralization titers against the same phylogroup but not different phylogroups. Our findings indicate that a new vaccine should be developed for pre- and post-exposure prophylaxis against lyssaviral infections.

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.

Detection of feline morbillivirus in cats with symptoms of acute febrile infection.

Feline morbillivirus (FeMV) was identified for the first time in cats in 2012 in Hong Kong. Although its association with chronic kidney disease in cats has attracted the attention of researchers, its clinical significance as an acute infection has not been reported. Previously, we reported FeMV detection using next-generation sequence-based comprehensive genomic analysis of plasma samples from cats with suspected acute febrile infections. Here, we conducted an epidemiological survey to detect FeMV by quantitative reverse transcription polymerase chain reaction (qRT-PCR) using blood samples from cats in Japan. FeMV was detected in 32/102 blood samples (31.4%) from cats with suspected acute viral infections. Most of the FeMV-positive cats had clinical findings consistent with acute viral infections, including fever, leukopenia, thrombocytopenia and jaundice. No FeMV was detected in healthy cats or clinically ill cats that visited veterinary hospitals. Phylogenetic analysis classified FeMV L genes into various FeMV subtypes. We also necropsied a FeMV-positive cat that died of a suspected acute infection. On necropsy, FeMV was detected in systemic organs, including the kidneys, lymph nodes and spleen by qRT-PCR and immunohistochemical staining. These results suggest that FeMV infections may cause acute symptomatic febrile infections in cats. A limitation of this study was that the involvement of other pathogens that cause febrile illnesses could not be ruled out and this prevented a definitive conclusion that FeMV causes febrile disease in infected cats. Further studies that include experimental infections are warranted to determine the pathogenicity of FeMV in cats.

Establishment of serological neutralizing tests using pseudotyped viruses for comprehensive detection of antibodies against all 18 lyssaviruses.

Rabies is a fatal zoonotic, neurological disease caused by rabies lyssavirus (RABV) and other lyssaviruses. In this study, we established novel serological neutralizing tests (NT) based on vesicular stomatitis virus pseudotypes possessing all 18 known lyssavirus glycoproteins. Applying this system to comparative NT against rabbit sera immunized with current RABV vaccines, we showed that the current RABV vaccines fail to elicit sufficient neutralizing antibodies against lyssaviruses other than to those in phylogroup I. Furthermore, comparative NT against rabbit antisera for 18 lyssavirus glycoproteins showed glycoproteins of some lyssaviruses elicited neutralizing antibodies against a broad range of lyssaviruses. This novel testing system will be useful to comprehensively detect antibodies against lyssaviruses and evaluate their cross-reactivities for developing a future broad-protective 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.

Simple and rapid detection of severe fever with thrombocytopenia syndrome virus in cats by reverse transcription-loop-mediated isothermal amplification (RT-LAMP) assay using a dried reagent.

Severe fever with thrombocytopenia syndrome virus (SFTSV) causes lethal hemorrhagic diseases in human, cats, and dogs. Several human cases involving direct transmission of SFTSV from diseased animals have been reported. Therefore, rapid diagnosis in veterinary clinics is important for preventing animal-to-human transmission. Previously, we developed a simplified reverse transcription-loop-mediated isothermal amplification (RT-LAMP) assay for human that does not require RNA extraction for detecting the SFTSV genome. In this study, we improved the simplified RT-LAMP assay for cats by introducing a dried reaction reagent and investigated the applicability of this method for diagnosing SFTS in cats. SFTSV RNA was detected in 11 of 12 cats naturally infected with SFTSV by RT-LAMP assay using both liquid and dried reagents. The RT-LAMP assay using liquid and dried reagents was also applicable to the detection of SFTSV genes 3-4 days after challenge in cats experimentally infected with SFTSV. The minimum copy number of SFTSV genes for 100% detection using the RT-LAMP assay with liquid and dried reagents was 4.3 × 104 and 9.6 × 104 copies/mL, respectively. Although the RT-LAMP assay using the dried reagent was less sensitive than that using the liquid reagent, it was sufficiently sensitive to detect SFTSV genes in cats with acute-phase SFTS. As the simplified RT-LAMP assay using a dried reagent enables detection of SFTSV genes more readily than the assay using a liquid reagent, it is applicable for use in veterinary clinics.

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.

Increased Risk of Infection with Severe Fever with Thrombocytopenia Virus among Animal Populations on Tsushima Island, Japan, Including an Endangered Species, Tsushima Leopard Cats.

To investigate the seroprevalence of severe fever with thrombocytopenia syndrome (SFTS) among wild and companion animals on Tsushima Island, Japan, SFTS virus (SFTSV)-specific ELISA and virus-neutralizing tests were conducted on 50 wild boars, 71 Sika deer, 84 dogs, 323 domestic cats, and 6 Tsushima leopard cats. In total, 1 wild boar (1.8%), 2 dogs (2.4%), 7 domestic cats (2.2%), and 1 Tsushima leopard cat (16.7%) were positive for anti-SFTSV antibodies. Among the 11 positive animals, 10 were collected after 2019, and all were found on the southern part of the island. SFTSV, thus far, seems to be circulating within a limited area of Tsushima Island. To protect humans and animals, including endangered Tsushima leopard cats, from SFTSV infection, countermeasures are needed to prevent the spread of SFTSV on Tsushima Island.

Lethal Disease in Dogs Naturally Infected with Severe Fever with Thrombocytopenia Syndrome Virus.

Severe fever with the thrombocytopenia syndrome virus (SFTSV) causes fatal disease in humans, cats, and cheetahs. In this study, the information on seven dogs with SFTS was summarized. All dogs showed anorexia, high fever, leukopenia, and thrombocytopenia, two dogs showed vomiting and loose stool, and five dogs had tick parasites. All dogs also had a history of outdoor activity. The SFTSV gene was detected in all dogs. Remarkably, three dogs (43%) died. SFTSV was isolated from six dogs and the complete genomes were determined. A significant increase in anti-SFTSV-IgG antibodies was observed in two dogs after recovery, and anti-SFTSV-IgM antibodies were detected in four dogs in the acute phase. Using an ELISA cut-off value of 0.410 to discriminate between SFTSV-negative and positive dogs, the detection of anti-SFTSV-IgM antibodies was useful for the diagnosis of dogs with acute-phase SFTS. Four out of the ninety-eight SFTSV-negative dogs possessed high anti-SFTSV IgG antibody titers, indicating that some dogs can recover from SFTSV infection. In conclusion, SFTSV is lethal in some dogs, but many dogs recover from SFTSV infection.

Different Sensitivity of Japanese Native-Bred Chickens to H5 Subtypes of Highly Pathogenic Avian Influenza Viruses.

The aim of this study was to investigate the sensitivity of three breeds of Japanese native chickens, commercial broilers, and specific-pathogen-free (SPF) white leghorns to three strains of the H5 subtype of highly pathogenic avian influenza viruses (HPAIVs). Chickens were experimentally inoculated with doses of 102, 104, and 106 50% egg infective dose of A/mandarin duck/Miyazaki/22M-765/2011 (duck-11), A/chicken/Miyazaki/7/2014 (chicken-14), and A/chicken/Kumamoto/1-2C/2016 (chicken-16). The 50% chicken lethal dose of each virus, mean death time, and viral shedding patterns were compared. The Japanese native chickens showed varied susceptibility to the three H5 HPAIV isolates. Although two of the breeds showed some degree of resistance to duck-11 and chicken-14, all three were more sensitive to chicken-16 than commercial broiler chickens. We have shown that Japanese native chickens do not necessarily have resistance to HPAIV and that the pathogenic characteristics of HPAIVs are quite different between native and commercial chickens.

Nota de investigación­Diferente sensibilidad de pollos nativos de Japón a subtipos del virus de influenza aviar H5 altamente patógenos. El objetivo de este estudio fue investigar la sensibilidad de tres razas de pollos nativos de Japón, de pollos de engorde comerciales y de aves Leghorn blancas libres de patógenos específicos (SPF) a tres cepas altamente patógenas del virus de influenza aviar (HPAIV) del subtipo H5. Los pollos se inocularon experimentalmente con dosis de 102, 104 y 106 dosis infecciosas para embrión de pollo 50% del virus A/pato mandarín/Miyazaki/22M-765/2011 (pato-11), del virus A/pollo/Miyazaki/7/2014 (pollo-14) y A/ pollo/Kumamoto/1-2C-2016 (pollo-16). Se comparó la dosis letal de pollo 50% de cada virus, el tiempo medio de muerte y los patrones de diseminación viral. Los pollos nativos japoneses mostraron una susceptibilidad variada a los tres aislados del virus de influenza aviar altamente patógeno H5. Aunque dos de las razas mostraron cierto grado de resistencia al virus de pato-11 y al pollo-14, las tres eran más sensibles al virus del pollo-16 que los pollos de engorde comerciales. Se demostró que los pollos nativos japoneses no necesariamente tienen resistencia al virus de influenza aviar altamente patógeno y que las características patógenas de los virus de influenza aviar altamente patógenos son bastante diferentes entre pollos nativos y comerciales.

Seroprevalence of severe fever with thrombocytopenia syndrome virus in animals in Kagoshima Prefecture, Japan, and development of Gaussia luciferase immunoprecipitation system to detect specific IgG antibodies.

We conducted a seroprevalence investigation of the healthy population of animals in Kagoshima Prefecture, an area in which severe fever with thrombocytopenia syndrome (SFTS) is endemic. Of 104 domestic cat and 114 dog samples, 2 (1.9%) and 11 (9.6%) were positive for anti-SFTS virus (SFTSV) IgG by indirect ELISA, respectively. Viral RNA was detected in one dog (0.9%) by RT-PCR. Of the 102 wild boar (Sus scrofa) and 107 deer (Cervus nippon) samples tested, 55 (53.9%) and 37 (34.7%) were positive for anti-SFTSV IgG, respectively. Only one wild boar (1.0%) was positive for viral RNA. Although symptomatic SFTSV infections in domestic cats have increased in this area, the seroprevalence of the healthy population of domestic cats tends to be lower than those of other animals. We developed a Gaussia luciferase immunoprecipitation system (GLIPS) using mammalian cells expressing a recombinant SFTSV nucleoprotein (SFTSV-rNP) for the detection of SFTSV-specific antibodies in samples from various animal species. The sensitivity of the assay was highly consistent with that of indirect ELISA, indicating that it could serve as a useful tool for a large-scale surveillance of SFTSV across multiple species of animals.

Non-primate hepacivirus transmission and prevalence: Novel findings of virus circulation in horses and dogs in Morocco.

Non-primate hepacivirus (NPHV) is a homolog of hepatitis C virus and has been isolated from dogs and horses. Data on NPHV prevalence and distribution are not complete, and there is a particular lack of reports from the African continent. The present study represents the first investigation of NPHV prevalence in horses and dogs in North Africa. Blood was collected from 172 horses and 36 dogs at different locations in Morocco, and screened for NPHV RNA using nested PCR targeting 5'UTR and NS3 regions and analyzed for anti-NPHV NS3 antibody using a Gaussia luciferase immunoprecipitation system-to determine seroprevalence. Eight sequences of the NS3 region isolated from positive serum samples were targeted for phylogenetic analysis. Horses and dogs showed respective NPHV RNA positivity rates of 10.5% and 5.5%, and seroprevalences of 65.7% and 8.33%. Juvenile horses appeared more susceptible to infection, with a 23.5% NHPV RNA positivity rate. Seropositivity was more extensive in mares than stallions (77.14% vs. 46.27%, p < 0.0001). Phylogenetically, that NPHV NS3 genes isolated from horses and dog are clustered together. The NPHV strains we detected showed no correlation with geographic location within Morocco. In conclusion, Moroccan horses showed much evidence of previous and/or current NPHV infection, with young age and female sex as noted potential risk factors. Interestingly, NPHV is circulating in dogs as well as horses, suggesting that it has crossed species barriers and that horses and dogs are potential vectors by which an ancestor to hepatitis C virus was transmitted into human populations.

Detection and molecular characterization of Babesia sp. in wild boar (Sus scrofa) from western Japan.

Wild animals often act as reservoirs of tick-borne Babesia and Theileria spp., which cause piroplasmosis. Therefore, epidemiological investigations about the distribution of these parasites in wild animals are important for evaluating the transmission risk to humans and livestock. In this study, we surveyed Babesia and Theileria spp. infecting wild boar (Sus scrofa) in Kagoshima and Yamaguchi prefectures and Tsushima island, which are all in western Japan, and performed molecular genetic analyses on the samples. DNA was extracted from either blood or liver samples of wild boar captured in Kagoshima prefecture in 2015, 2016, and 2018 and from blood samples from wild boar captured in Yamaguchi prefecture in 2013-2015 and Tsushima island in 2018. PCR screening for the partial 18S ribosomal RNA gene (18S rRNA) of both Babesia and Theileria spp. in wild boar revealed that 63.9 % (140 of 219 samples) were positive. Sequencing of all positive samples revealed that they were all the same Babesia species. Subsequent phylogenetic analyses showed that the parasite is closely related to Babesia sp. previously detected in the hard tick, Amblyomma testudinarium in Kagoshima, and further analyses suggested that this species is genetically related to Babesia gibsoni. On the other hand, no Theileria were detected in any of the samples. In summary, we observed a high prevalence of B. gibsoni-like Babesia sp. in wild boar in western regions of Japan. The host range, distribution, pathogenicity, and life cycle of this protozoan should be further evaluated.

Metagenomic identification, sequencing, and genome analysis of porcine hepe-astroviruses (bastroviruses) in porcine feces in Japan.

Recently, hepe-astrovirus-like RNA viruses named bastroviruses (BastVs), have been found in human, pig, bat, and rat fecal samples. In this study, we determined nearly complete genome sequences of four BastVs in the feces of healthy pigs. Genetic characterization revealed that these porcine BastVs (PBastVs) and BastVs from other animals including humans, had the same genome organization, that is, they contained three predicted conserved domains of viral methyltransferase, RNA helicase, and RdRp in the nonstructural ORF1 and the astrovirus capsid domain in the structural ORF2. Phylogenetic analyses using RNA-dependent RNA polymerase and the capsid region revealed that PBastVs branched with bat and rat BastVs; however, the groups formed by each host were distantly related to human BastVs. Pairwise amino acid sequence comparison demonstrated that PBastVs shared 95.2-98.6% and 76.1-95.5% sequence identity among each other in the ORF1 and ORF2 regions, respectively; the sequence identities between PBastVs and BastVs from other animals were 21.4-42.5% and 9.1-20.6% in the ORF1 and ORF2 regions, respectively. This suggested that BastVs were derived from a common ancestor but evolved independently in each host population during a prolonged period. Putative recombination events were identified in the PBastV genome, suggesting that PBastVs gain sequence diversity and flexibility through recombination events. In an analysis of previously obtained metagenomic data, PBastV sequence reads were detected in 7.3% (23/315) of fecal samples from pigs indicating that PBastVs are distributed among pig populations in Japan.

Detection of severe fever with thrombocytopenia syndrome virus and other viruses in cats via unbiased next-generation sequencing.

We used unbiased next-generation sequencing (NGS) to detect unknown viruses in cats. Serum or plasma samples were obtained from clinically ill cats with suspected acute viral infections. Nucleic acid was extracted from serum or plasma samples to construct a complementary DNA library for NGS. Comprehensive nucleotide sequencing analyses enabled detection of the genomes of various viruses, including the severe fever with thrombocytopenia syndrome virus, feline immunodeficiency virus, feline morbillivirus, parvovirus, and Torque teno felis virus. Our findings indicate that comprehensive nucleotide analyses of serum or plasma samples can be used to detect infections with unknown viruses in cats.

Molecular detection of tick-borne protozoan parasites in sika deer (Cervus nippon) from western regions of Japan.

The sika deer (Cervus nippon) is one of the most common species of wildlife in Japan. This study aimed to reveal the prevalence of tick-borne protozoan parasites in wild sika deer living in western Japan. We used nested polymerase chain reaction (PCR) to detect the 18S rRNA gene of tick-borne apicomplexan parasites (Babesia, Theileria, and Hepatozoon spp.) from 276 blood and liver samples from sika deer captured in the Yamaguchi, Oita, Kagoshima, Okayama, Ehime, Kochi, and Tokushima Prefectures. In total, 259 samples (259/276; 93.8%) tested positive in the nested PCR screening. Gene sequencing revealed that 99.6% (258/259) of positive samples contained Theileria sp. (sika 1), while Theileria sp. (sika 2), another Theileria species, was detected in only 3 samples. We also found that one sample from a sika deer captured in Kagoshima contained the gene of an unidentified Babesia sp. related to Babesia sp. Kh-Hj42, which was previously collected from tick in western Siberia. In conclusion, we found a high prevalence of piroplasms in sika deer from western Japan, and DNA analysis revealed that Theileria sp. (sika 1) had the highest infection rate.

Molecular detection of canine respiratory pathogens between 2017 and 2018 in Japan.

A molecular survey was conducted to understand recent distribution of pathogens associated with canine infectious respiratory disease (CIRD) in Japan. Nasal and/or pharyngeal swabs were collected from asymptomatic dogs and those with CIRD, living in private house or in kennels. PCR-based examination was conducted for detecting nine pathogens. Among private household dogs, 50.8% with CIRD, 11.1% with respiratory disease other than CIRD, and 4.3% asymptomatic were positive for more than one pathogen, whereas in kennel-housed dogs, 42.9% with CIRD and 27.3% asymptomatic were positive. Bordetella bronchiseptica was most frequently detected, followed by canine herpesvirus 1, canine parainfluenza virus, canine pneumovirus, Mycoplasma cynos, and canine adenovirus type 2. In kennel environment, asymptomatic dogs might act as reservoirs carrying the respiratory pathogens.

Serological survey of influenza A virus infection in Japanese wild boars (Sus scrofa leucomystax).

We conducted a serological survey to detect antibodies against influenza A virus (IAV) in Japanese wild boars in Kagoshima prefecture, Japan, between 2014 and 2017. Seroprevalence against a pandemic-like swine H1N1 (H1N1pdm) virus was identified in 27.1% of specimens, and 1.7% were positive for both swine H1N2 and H3N2 viruses, indicating that wild boars could play an important role in the dynamics of H1N1pdm viral dispersion in the wild. The high frequency of positive results for sera against the H1N1pdm virus suggests that cross-species IAV transmission between wild boars, livestock, and humans is a threat to veterinary and public health.