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.
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.
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.
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