African swine fever. V. Cultivation of the virus in primary pig kidney cells.

Six strains of African swine fever (ASF) virus were propagated in culture of primary pig kidney (PK) cells. The course of virus growth was followed by means of the fluorescent antibody staining technique. All 6 strains multiplied in the cultures, and 5 of these eventually showed cytopathic effects leading to cell death. Three of the strains were tested for pathogenicity in pigs at various passage levels. Each showed evidence of modification in virulence after a relatively few passages in PK cells. In one case modified virus produced resistance to challenge with homologous virulent virus. All strains rendered the PK cultures capable of hemadsorption of pig erythrocytes.