Differentiation of strains of the swine fever virus depending on their temperature resistance at 56 degrees C and on the size of fluorescent plaques

: In vitro and in vivo experiments were carried out to differentiate the virulent swine fever virus strain Vratsa and the vaccinal strains K and VP with regard to their resistance at 56 degrees C and to the size of the fluorescent plaques. The results obtained were comparable. The virulent strain was found to retain its viability at temperature of 56 degrees C for 30 min. The heated virus formed large, strongly fluorescent plaques in the infected cell cultures of pig kidney. The fluorescent cells were enlarged, and their cytoplasm was granular. The treated virus retained its pathogenic properties. Pigs inoculated with the inactivated Vratsa strain contracted the disease and died. Prior to heating the vaccinal strains formed small fluorescent plaques in cell cultures. The fluorescent cells had normal size and homogenic structure. Following heating at 56 degrees C for 15 min the vaccinal viruses retained partially their viability. Thus inactivated the viruses formed a limited number of fluorescent plaques of low intensity.