In vivo and in vitro studies on temperature-sensitive mutants of swine vesicular disease virus.

Two temperature-sensitive mutants of the Ukg 27/72 strain of swine vesicular disease virus were isolated in tissue culture and a third was derived following adaptation in mice. All three were found to have similar growth restrictive temperatures, but varied considerably in their virulence when administered to pigs. The route of inoculation appeared to exert a considerable influence on the apparent degree of attenuation, the antibody titre engendered and the transmission of disease to pigs held in contact with inoculated animals. One strain appeared almost totally attenuated when inoculated animals. One strain appeared almost totally attenuated when inoculated into pigs but spread to animals in contact causing severe disease. Virus re-isolated from one such animal was found to have retained its temperature sensitive phenotype, suggesting that virulence in this case was not directly related to temperature sensitivity. Pigs with high antibody titres were found to be susceptible when placed in contact with challenge animals, although the lesions which developed were mild.