Temperature-sensitive and Other Mutants of the Essex 70 Strain of Newcastle Disease Virus as Vaccines

Publisher Website
Google Scholar
Abstract
The most reliable method of distinguishing strains of low virulence among a collection of stock strains of Newcastle disease virus (NDV) was by their failure to produce a good CPE [cytopathic effects] in monolayers of baby hamster kidney cells and of chick embryo cells. This method was of no help in identifying avirulent mutants that emerged in the Essex 70 strain of NDV following UV light, nitrous acid, hydroxylamine or N-methyl-N''-nitro-N-nitrosoguanidine (NTG) treatment. A marked reduction in the ability to kill developing chick embryos at 41.degree. C was a more reliable indicator. Several of these temperature-sensitive mutants, most of which were isolated from NTG-treated virus, were non-lethal for young chicks but they did have a depressive effect on their growth rate. The immunity produced by 3 of these mutants in chicks free of NDV antibody, but not in chicks possessing appreciable amounts of antibody, was probably even better than that produced by Hitchner B1 strain. All 3 mutants reverted to virulence during passage in chicks, although in no case were the revertants as virulent as the original Essex 70 strain. The virulent revertants obtained from 1 mutant had lost their temperature-sensitivity and proliferated in large numbers in the tissues of infected chicks. Those obtained from the other 2 had not lost, or only partly lost, their temperature-sensitivity; they were found only in low concentrations in the tissues of infected chicks, their concentrations being little different from that found in the tissues of chicks infected with the mutants from which they were derived.

This publication has 2 references indexed in Scilit: