Swine vesicular disease viruses isolated from healthy pigs in non-epizootic period. I. Isolation and identification.

A total of 524 fecal samples were collected from healthy swine of 36 hog farms scattered all over Japan from which had been detected neutralizing antibody against swine vesicular disease (SVD) virus. A virus was isolated from 21 of them. It was neutralized by antiserum against SVD virus. Of the 21 samples, 19 were derived from six farms, in areas which remained to be free from SVD in the past years and two from a farm where SVD broke out 18 months before. The cross-neutralization test was carried out with seven strains of SVD virus isolated from healthy pigs (SVDV-H) and five strains of SVD virus isolated from diseased pigs (SVDV-D). There was, however, no significant difference in antigenicity between the two groups. Some strains of SVDV-H were antigenically close to the Faulkner strain of Coxsackie B5 virus, and others to the freshly isolated strain of this virus. Neutralizing antibody of low titer against SVD virus was detected from pigs kept in areas free from SVD. It was presumed to have been produced in these pigs involved in silent infection with this virus.