Heat-selected mutants of pigeon pox virus.

Two mutants of pigeon pox virus were derived from virus isolated from naturally infected pigeons. One (S 39) was obtained by cultivation of the original virus in chick embryo chorioallantoic membranes at 39 degrees C, and the second (S m) by heating the original virus at 56 degrees C for 30 min. The mutants were less pathogenic to pigeons than the original virus. The original virus and the mutant S 39, but not the mutant S m produced plaques in primary chick embryo cell cultures. Pigeons inoculated with the mutants were resistant to challenge with the field virus.