Hybrids Derived from the Viruses of Variola Major and Cowpox.

The isolation of presumptive hybrids from the viruses of variola major and cowpox has already been described (Dumbell & Bedson, 1964). We report here the detailed characterization of the 16 clones of virus obtained. As with the alastrimrabbit pox hybrids considered in the previous paper (Bedson & Dumbell, 1964), attention has been paid to the behaviour of the ceiling temperature character in recombination and to the possible relationship it and other markers might have to the virulence of these viruses. Both sets of hybrids may also be regarded as making a minor contribution to pox virus genetics, in that variola viruses have now been shown to form hybrids with other members of the variola-vaccinia group.