Behavior of intertypic recombinants between virulent and attenuated aphthovirus strains in tissue culture and cattle

Two aphthovirus intertypic recombinants between the virulent strain A Venceslau and guanidine-resistant attenuated mutants of either strain C3 Resende or O1 Campos were obtained in an attempt to establish the region(s) of the viral genome responsible for attenuation in cattle. Recombinants that inherited the 3' half of the genome from either attenuated parent and the 5' half from the virulent strain were selected and analyzed with respect to their ability to grow in cells of bovine origin and for their virulence in cattle. The results obtained support our previous conclusion, derived from studies with homotypic recombinants between attenuated aphthovirus type O1 and its original virulent strain, that the host range restriction phenotype for fetal bovine kidney cells of the attenuated strain is inherited from the 3' half of the genome. For the intertypic recombinants, however, this restriction is enhanced, presumably by the presence of a heterologous 5' half of the genomic region. In addition, we demonstrate that the results in vitro correlate with those of virulence tests in cattle.