Risk of transmission of foot-and-mouth disease by wild animals: infection dynamics in Japanese wild boar following direct inoculation or contact exposure.

Understanding of disease dynamics and viral shedding in wild boar and of the potential for disease spreading within wild boar and domestic pig populations is critical for developing effective control and eradication measures for foot-and-mouth disease (FMD). Accordingly, we infected experimentally wild boar and domestic pigs with FMD virus (FMDV) strains O/TAI/315/2016 and A/MOG/2013, and studied their susceptibility and viral transmissibility in both populations. Similar to FMDV-infected pigs, wild boar inoculated with both viruses exhibited vesicular lesions on their feet, snout, tongue and lip, although they did not show lameness. Further, inoculated wild boar were equally capable of transmitting the virus to all of their contact animals. While all contact pigs developed vesicular lesions after contact with inoculated animals, in contrast, no wild boar when exposed to the same infected animals showed obvious clinical signs. These results will be useful for further understanding of the critical roles in occurring and sustaining an FMD outbreak, and will be useful for establishing epidemiological surveillance programs and effective countermeasures for wild boar.

Dose-dependent responses of pigs infected with foot-and-mouth disease virus O/JPN/2010 by the intranasal and intraoral routes.

Foot-and-mouth disease virus (FMDV) infection was successfully initiated in pigs by intraoral inoculation of both 10(6) and 10(3) TCID50 of FMDV O/JPN/2010 isolated from the 2010 epidemic in Japan. By intranasal inoculation, infection was established in pigs with 10(6) TCID50 of the isolate, but not with 10(3) TCID50 of the isolate. In the pigs inoculated with 10(6) TCID50 of the isolate, viruses and viral RNAs were obtained earlier from the pigs inoculated by the intraoral route than from the pigs inoculated by the intranasal route. These results support the theory that primary infection of a pig herd is more likely to occur by ingestion than by inhalation and that the oral cavity is likely to be a major entry route for FMDV in naturally exposed pigs.

Experimental infection of cattle and goats with a foot-and-mouth disease virus isolate from the 2010 epidemic in Japan.

In this study, we carried out experimental infections in cattle and goats using a foot-and-mouth disease virus (FMDV) isolate from the 2010 epidemic in Japan to analyze clinical manifestations, virus-shedding patterns and antibody responses in the animals. We found that the FMDV O/JPN/2010 isolate is virulent in cattle and goats, produces clinical signs, is spread efficiently by direct contact within the same species, and is persistently infectious in cattle. Quantitative analysis of levels of viral RNA in the tissues of cattle and goats infected with the isolate showed that the pharyngeal region is an important major target of the FMDV O/JPN/2010. Time course data of viral loads, excretion and transmission of the FMDV O/JPN/2010 in this study are key in providing quantitative data essential for epidemiological investigation and risk analysis in relation to disease controls.

Effect of doubled dose administration of foot-and-mouth disease vaccine against heterologous virus infection in cattle.

Vaccination is a feasible approach for controlling foot-and-mouth disease (FMD). In FMD-free countries, vaccines are stored as a precautionary measure to control potential outbreaks. However, the challenge lies in pre-stocking optimal vaccines against the newly emerging strains. This study examined the potency of pre-stocked vaccines administered at elevated doses during emergencies. We vaccinated the cows with either a single or double trivalent vaccine dose containing two serotype O and one serotype A strains. Subsequently, vaccinated and unvaccinated cows were exposed to virulent strains of serotype O (O/JPN/2010; topotype Southeast Asia/Mya-98 lineage) or A (A/IRN/2016; topotype ASIA/G-VII lineage), which were genetically and antigenically distinct from the vaccine strains. Following challenge infections, all cows that received a single dose vaccination exhibited vesicular lesions with excreted viruses in the oral and nasal discharges. However, a substantial reduction was observed in the total clinical scores and virus titers in the sera and nasal discharges compared to those in the unvaccinated group. Cows receiving a doubled dose vaccination were completely protected from infection with O/JPN/2010 or demonstrated a significant decrease in viral shedding and clinical scores against A/IRN/2016. To note, vesicular lesions harbor significant amounts of viruses; thus, by mitigating their formation, viral transmission can be impeded, thereby slowing viral spread in the field. Furthermore, increasing the vaccine dose induced higher neutralizing antibody titers against heterologous strains. These findings suggest an alternative strategy for the effective management of future epidemics using pre-stocked vaccines.

Near-Complete Genome Sequences of Three Foot-and-Mouth Disease Virus O/ME-SA/Ind-2001e Isolates Obtained from Cattle and Pigs in Thailand in 2016.

Here, we report near-complete genome sequences of three foot-and-mouth disease viruses isolated in 2016 from bovine and porcine epithelial tissue samples collected in Nonthaburi, Songkhla, and Ratchaburi provinces, Thailand. These viruses were classified as serotype O, topotype ME-SA, and sublineage Ind-2001e.

Southeast Asian foot-and-mouth disease viruses in Eastern Asia.

Foot-and-mouth disease (FMD) outbreaks recently affected 2 countries (Japan and South Korea) in eastern Asia that were free of FMD without vaccination. Analysis of viral protein 1 nucleotide sequences indicated that FMD serotype A and O viruses that caused these outbreaks originated in mainland Southeast Asia to which these viruses are endemic.

Administration of the antiviral agent T-1105 fully protects pigs from foot-and-mouth disease infection.

Foot-and-mouth disease (FMD) is a contagious disease affecting cloven-hoofed animals. Its transmissibility and antigenic variety make this disease difficult to control. Antiviral agents are expected to have an immediate effect that is independent of viral antigenicity; thus, they can serve as effective tools for inhibiting the spread of the causative agent, the FMD virus (FMDV), from infected animals. In this study, we investigated the antiviral activity of a pyrazinecarboxamide derivative, T-1105, against FMDV. Cytopathic effect inhibition assays revealed that T-1105 strongly inhibited the replication of 28 reference strains of all seven FMDV serotypes at non-cytotoxic concentrations. The antiviral effect of T-1105 against FMDV was also evaluated by experimental infection of domestic pigs. T-1105 was administered orally to pigs starting 1 h before or 6 h after the inoculation of a porcinophilic FMDV serotype O, topotype CATHAY. None of the pigs administered with T-1105 showed clinical signs of FMD. Moreover, no infectious FMDVs or FMDV-specific genes were detected in their sera, oral and nasal discharges, or tissues collected 48 h after virus inoculation. These findings strongly suggest that administration of T-1105 is effective in controlling the spread of FMDV in pigs.

Evolutionary Dynamics of Foot and Mouth Disease Virus Serotype A and Its Endemic Sub-Lineage A/ASIA/Iran-05/SIS-13 in Pakistan.

Foot and mouth disease (FMD) causes severe economic losses to the livestock industry of endemic countries, including Pakistan. Pakistan is part of the endemic pool 3 for foot and mouth disease viruses (FMDV), characterized by co-circulating O, A, and Asia 1 serotypes, as designated by the world reference laboratory for FMD (WRL-FMD). FMDV serotype A lineage ASIA/Iran-05 is widespread in buffalos and cattle populations and was first reported in Pakistan in 2006. This lineage has a high turnover, with as many as 10 sub-lineages reported from Pakistan over the years. In this study, we reconstructed the evolutionary, demographic, and spatial history of serotype A and one of its sub-lineages, A/ASIA/Iran-05/SIS-13, prevalent in Pakistan. We sequenced nearly complete genomes of three isolates belonging to sub-lineage A/ASIA/Iran-05/SIS-13. We estimated recombination patterns and natural selection acting on the serotype A genomes. Source and transmission routes in Pakistan were inferred, and the clustering pattern of isolates of the SIS-13 sub-lineage were mapped on a tree. We hereby report nearly complete genome sequences of isolates belonging to sub-lineage A/ASIA/Iran-05/SIS-13, along with purported recombinant genomes, and highlight that complete coding sequences can better elucidate the endemic history and evolutionary pressures acting on long-term co-circulating FMDV strains.

Characterization of the complete genomic sequence of the rinderpest virus Fusan strain cattle type, which is the most classical isolate in Asia and comparison with its lapinized strain.

In this study, we characterized the rinderpest virus (RPV) Fusan strain cattle type (B), which is the most classical isolate in Asia, by complete genomic sequence analysis and compared it with its lapinized Nakamura III (L) strain. The transversion rates of the M, F, and H genes were higher than those of other genes. In contrast, the deduced amino acid (aa) substitution rates of the P, C, and V genes were higher than those of other genes, although their transversion rates were not higher. The characteristic nucleotide (nt) or aa residues of the cattle-virulent B and Kabete 'O' strains were observed in the P/C/V, M, and L genes. According to these results, we speculate that nt/aa substitution in the P/C/V genes is one of the key determinants for the difference in the pathogenicity to cattle of the B and L strains.

Quantitative analysis of infection dynamics of foot-and-mouth disease virus strain O/CATHAY in pigs and cattle.

Foot-and-mouth disease virus (FMDV) serotype O, topotype CATHAY is a known porcinophilic virus that has caused devastating damage to the pig industry. However, the minimum infectious dose via a natural infection route in pigs, the infection dynamics in cattle, and risk of viral transmission from infected cattle to pigs have not been quantitatively analyzed. The FMDV strain O/HKN/1/2015 was serially diluted and inoculated into pigs via an intraoral route to determine the infectious dose. We found that a 104.0 tissue culture infectious dose (TCID50) of the virus was insufficient, but 105.5 TCID50 was sufficient to infect pigs via the oral route. While cows inoculated with the strain showed increased temperature in their feet, typical clinical signs including vesicular development were not observed. The cows showed short-term and low levels of viremia and virus excretion only before the detection of virus neutralizing antibodies. FMDV genes were not detected in esophageal-pharyngeal fluid from cows after 14 days post inoculation. No genetic insertions that could be associated with host adaptation were observed in viruses isolated from infected cows. These findings indicate that cows infected with FMDV of O/CATHAY have a low risk of viral transmission or persistence. Information on the dynamics of virus infection is essential for ensuring the rapid and accurate diagnosis of this disease, and its surveillance.

Horizontal transmission of foot-and-mouth disease virus O/JPN/2010 among different animal species by direct contact.

Foot-and-mouth disease (FMD) is highly contagious and easily transmitted among species of cloven-hoofed animals. To investigate the transmission of FMD virus (FMDV) among different animal species, experimental infections using the O/JPN/2010 strain were performed in cows, goats and pigs. One cow or two goats/pigs were housed with a different species of inoculated animals, and clinical observations, virus shedding and antibody responses were analysed daily. Whilst all cows and goats were infected horizontally by contact with inoculated pigs, transmission from cows to goats/pigs and from goats to cows/pigs was not observed in all in-contact animals. In particular, no pigs were infected horizontally by contact with inoculated goats. Comparison with our previous study on experimental infections among animals of the same species indicates that horizontal transmission occurred more easily between animals of the same species than between those of the different species. These findings will be useful for establishing and performing species-specific countermeasures in farms and regions where multiple species of animals coexist in potential future outbreaks.

Development and evaluation of silver amplification immunochromatography kit for foot-and-mouth disease virus antigen detection.

A silver amplification immunochromatography (SAI) kit for the detection of all seven serotypes of foot-and-mouth disease virus (FMDV)-FMDV-Ag SAI-was developed using the monoclonal antibody 1H5 recognizing the highly conserved N terminus region of VP2. The FMDV-Ag SAI can be used under conditions of high biosecurity containment as it does not require any apparatus. The FMDV-Ag SAI exhibited 10-100 times higher sensitivity against the five serotypes (O, A, Asia1, C, and SAT1) and similar sensitivity against SAT2 and SAT3, compared with the Svanodip® FMDV-Ag kit immunochromatography kit. The Svanodip kit showed inhibitory results with several saliva samples but not with the FMDV-Ag SAI kit. In a validation study using clinical samples (n = 132; vesicular epithelium = 92, vesicular lesion swabs = 20, saliva = 20) in Mongolia, the sensitivity of FMDV-Ag SAI in comparison with real-time reverse transcription-polymerase chain reaction revealed the following data: vesicular epithelium, 85.4% (76/89); vesicular lesion swab, 46.7% (7/17); and saliva, 36.8% (7/19). No cross-reactivity with the non-FMDV vesicular-forming viruses and taxonomically related viruses of the Picornaviridae family occurred. The FMDV-Ag SAI is a highly sensitive diagnostic tool that enables pen-side diagnosis without requiring the use of any equipment.

Foot-and-mouth disease virus antigen detection enzyme-linked immunosorbent assay using multiserotype-reactive monoclonal antibodies.

Monoclonal antibody (MAb)-based sandwich direct enzyme-linked immunosorbent assay (MSD-ELISA) methods that can detect foot-and-mouth disease virus (FMDV) antigens, both multiserotype (MSD-ELISA/MS) (for O, A, C, and Asia 1) and single-serotype (MSD-ELISA/SS) (for O, A, and Asia 1, specifically), were developed. MAb 1H5 was used as an antigen-trapping antibody that reacted with all seven serotypes of FMDV. The MAbs 71F2, 70C4, 16C6, and 7C2 were used as peroxidase-labeled detecting antibodies for multiple serotypes (O, A, C, and Asia 1), type O, type A, and type Asia 1, respectively, in both MSD-ELISA/MS and MSD-ELISA/SS. Our MSD-ELISAs showed high specificity. They produced a very low background of negative samples (buffer, plasma, and saliva) and were able to detect FMDV antigens from clinical samples (plasma and saliva), with results correlating with those of real-time reverse transcription-PCR. In terms of sensitivity, the MSD-ELISAs showed higher optical density values against each diluted serotype antigen than the indirect sandwich ELISA method, which is currently recommended in the manual of the World Organization for Animal Health. The sensitivity and specificity of the MSD-ELISAs seem to be sufficient for the antigenic diagnosis of FMDV.

Neutralizing monoclonal antibody sandwich liquid-phase blocking enzyme-linked immunosorbent assay for detection of Foot-and-mouth disease virus type O antibodies.

Liquid-phase blocking enzyme-linked immunosorbent assay (LPBE) using the neutralizing monoclonal antibody (mAb) sandwich method (M-LPBE) for detection of Foot-and-mouth disease virus (FMDV) type O antibodies was developed. Two neutralizing mAbs, 72C1 and 65H6, were raised against the FMDV O/JPN/2000 strain, and used as trapping and peroxidase-labeled detecting antibodies, respectively. Sera from animals experimentally infected with FMDV showed specific positive results by M-LPBE, which were correlated with the results of the virus neutralization test (VNT). When 303 negative bovine and 302 negative swine sera were tested, the specificity of M-LPBE was 100% and 99.7%, respectively. In addition, nine samples that had been collected in 2000 in Japan and regarded as evidently false positives by LPBE (supplied by the World Reference Laboratory for Foot-and-Mouth Disease) were uniformly negative by M-LPBE, just like VNT. Therefore, M-LPBE seems to have sufficient specificity for FMDV type O antibody screening and diagnosis.

Genetic Determinants of Virulence between Two Foot-and-Mouth Disease Virus Isolates Which Caused Outbreaks of Differing Severity.

Individual foot-and-mouth disease virus (FMDV) strains reveal different degrees of infectivity and pathogenicity in host animals. The differences in severity among outbreaks might be ascribable to these differences in infectivity among FMDV strains. To investigate the molecular mechanisms underlying these differences, we estimated the infectivity of O/JPN/2000 and O/JPN/2010, which caused outbreaks of markedly different scales, in cell lines, Holstein cattle, and suckling mice. Viral growth of the two strains in cells was not remarkably different; however, O/JPN/2000 showed apparently low transmissibility in cattle. Mortality rates of suckling mice inoculated intraperitoneally with a 50% tissue culture infective dose (TCID50) of 10 for O/JPN/2000 and O/JPN/2010 also differed, at 0% and 100%, respectively. To identify genes responsible for this difference in infectivity, genetic regions of the full-length cDNA of O/JPN/2010 were replaced with corresponding fragments of O/JPN/2000. A total of eight recombinant viruses were successfully recovered, and suckling mice were intraperitoneally inoculated. Strikingly, recombinants having either VP1 or 3D derived from O/JPN/2000 showed 0% mortality in suckling mice, whereas other recombinants showed 100% mortality. This finding indicates that VP1, the outermost component of the virus particle, and 3D, an RNA-dependent RNA polymerase, are individually involved in the virulence of O/JPN/2010. Three-dimensional structural analysis of VP1 confirmed that amino acid differences between the two strains were located mainly at the domain interacting with the cellular receptor. On the other hand, measurement of their mutation frequencies demonstrated that O/JPN/2000 had higher replication fidelity than O/JPN/2010.IMPORTANCE Efforts to understand the universal mechanism of foot-and-mouth disease virus (FMDV) infection may be aided by knowledge of the molecular mechanisms which underlie differences in virulence beyond multiple topotypes and serotypes of FMDV. Here, we demonstrated independent genetic determinants of two FMDV isolates which have different transmissibility in cattle, namely, VP1 and 3D protein. Findings suggested that the selectivity of VP1 for host cell receptors and replication fidelity during replication were important individual factors in the induction of differences in virulence in the host as well as in the severity of outbreaks in the field. These findings will aid the development of safe live vaccines and antivirals which obstruct viral infection in natural hosts.

Reverse transcription-PCR using a primer set targeting the 3D region detects foot-and-mouth disease virus with high sensitivity.

The potential of foot-and-mouth disease (FMD) to spread extensively means that rapid and accurate methods are needed for its diagnosis. Therefore, reverse transcription-PCR (RT-PCR) plays an important diagnostic role. Here, we designed the primer set FM8/9 to amplify 644 bases in the conserved 3D region of all seven serotypes of the FMD virus (FMDV). We compared the performance of RT-PCR assays using FM8/9 with those using the primer set 1F/R, which targets the 5'-UTR, and real-time RT-PCR (rRT-PCR) assays described in the World Organization for Animal Health manual. Detection limits of the RT-PCR assays were determined for 24 strains, representing all serotypes. The sensitivities of RT-PCR assays using FM8/9 were 100.6 - to 103.8 -fold higher than those of 1F/R assays for 21 strains. To assess the validity of the methods for analysing clinical samples, sera and saliva samples collected daily from pigs and cows infected with FMDV were analysed using the four PCR assays. FM8/9 assays detected FMDV from all infected pigs and cows for longer periods than 1F/R assays, indicating that FM8/9 assays have higher sensitivity for the clinical samples. Our results suggest that the FM8/9 RT-PCR assay is highly sensitive and is therefore suitable for the diagnosis of FMD.

Experimental infection of pigs with a classical swine fever virus isolated in Japan for the first time in 26 years.

Following an outbreak of classical swine fever (CSF) in Japan, 2018, CSFV JPN/1/2018 was isolated from an infected pig sample. In this study, we carried out a comparative experimental infection in pigs using this strain and the highly virulent ALD strain and compared outcomes, including clinical manifestation, virus shedding patterns and antibody responses. Although pigs inoculated orally or intramuscularly with JPN/1/2018 developed hyperthermia and had decreased leucocyte numbers, they survived for the whole experimental period and showed less severe clinical signs than those infected with the ALD strain. We confirmed the presence of characteristic multifocal infarction of the margin of the spleen that arises following infection with JPN/1/2018, albeit that this finding was not observed in all infected pigs. Both viruses efficiently spread to contact pigs in a similar manner, suggesting in transmissibility between the two strains. Viral RNAs were detected in all clinical samples, especially whole blood samples, before the pigs developed hyperthermia until at least approximately 2 weeks after inoculation. Our findings will be valuable for the investigations into epidemic events occurring in Japan and for establishing diagnostic strategies and control measures against CSF.

Comparison of the characters of the plaque-purified viruses from foot-and-mouth disease virus O/JPN/2000.

At least two biotypes were observed at the 2nd passage stage after the isolation of Foot-and-mouth disease Virus (FMDV) O/JPN/2000 strain. These 2 types of viruses differed from their plaque phenotypes and were distinguishable by using a monoclonal antibody (MAb) 64G8 that was made for the FMDV O/JPN/2000 strain. One of these 2 biotypes formed small plaque (SP) and with immuno staining showed a positive reaction to MAb 64G8, while the other formed clear large plaque (LP) and did not react with MAb 64G8. The amino acid sequences of the capsid coding region (VP1-VP4) of the SP virus (SPV) and the LP virus (LPV) revealed two substitutions on the 133rd amino acid in VP2, and the 56th amino acid in VP3. These amino acid changes of SPV and LPV are Asn to Asp, Arg to His, respectively. The Arg of the 56th amino acid in VP3 that have been known as critical position of cell culture adapted virus. Only LPV showed high pathogenicity in suckling mice, and its LD(50) was calculated to be about 10(2) TCID(50)/0.1 ml. These results showed that the SPV that existed at the 2nd passage stage from isolation was a low virulence virus, which may suggest why the pathogenicity of O/JPN/2000 did not show clear symptoms in infected cattle.

Differentiation of foot-and-mouth disease virus-infected pigs from vaccinated pigs using a western blotting assay based on baculovirus-expressed nonstructural proteins 2C and 3D.

Baculovirus-expressed foot-and-mouth disease virus (FMDV) nonstructural proteins 2C and 3D were used as the antigens in a western blotting assay. This assay allowed for differentiation of FMDV-infected pigs from vaccinated pigs. Serial studies were performed using sera collected from experimentally infected and vaccinated pigs. Positive reactions were found in the sera derived from the experimentally infected pigs. There was, however, no positive reaction in the vaccinated pigs. These results suggest that this western blotting assay is a useful method for differentiation of infected pigs from vaccinated pigs.

Comparative evaluation of two ELISA kits for detecting antibodies to a nonstructural protein of foot-and-mouth disease virus using serum samples collected from naturally and experimentally infected cows.

When foot-and-mouth disease (FMD) occurs and a "vaccination-to-live" policy is adopted in a country, the country must perform serological surveillance of a nonstructural protein (NSP) of FMD virus. The NCPanaftosa kit is the only kit for detecting antibodies to NSPs that is officially recognized as the reference regent by the World Organization for Animal Health; however, it is only used in South American countries. In this study, the specificity and sensitivity of the NCPanaftosa kit were compared with those of the PrioCHECK kit sold by an international company. Results in this study suggest that the PrioCHECK kit performs similarly to the NCPanaftosa kit in detecting antibodies to the NSP in the cattle population.