Effects of heat and gamma radiation on selected substrains of Newcastle disease virus

Abstract

S>Eight chicken embryo propagated laboratory strains of Newcastle disease virus, defined with respect to the thermostability of their hemagglutinating property were propagated in tissue culture monolayers to determine their cytopathogenic effect in chicken embryo fibroblasts. All strains with the exception of one produced a cytopathogenic effect evidenced by plaque formation. The strain multiplied in the system but did not form plaques. Small, medium, and large plaques were observed in the first passage for all of the substrains. The percentage of large plaques decreased with each subsequent passage of the medium and large plaque isolates. No large plaques resulted from the pas sage of small plaque isolates. After three passages through tissue culture cells, the tissue culture substrains were evaluated for the thermostability of their hemagglutinating, infective, and hemolytic properties. All of the substrains could be placed in either a heat sensitive or heat resistant group. The hemolysin, hemagglutinin, and infectivity were group. The hemolysin, hemagglutinin, and infectivity were inactivated by heat in the order named. The most heat sensitive substrain and the most sensitive of the heat resistant group was derived from the same parent population. The substrains were sub~ected to gamma radiation (Co/sup 60/) and the decrease in titersmore » of the infective property was determined. Exponential inactivation curves were similar for all substrains, indicating that the structure(s) associated with the infective property were similar in size. The fact that the infectivity of the various substrains tested was equally sensitive to gamma radiation but could be placed into two distinct groups with regard to heat sensitivity means that the component(s) of the virus which are affected by heat differ between the resistant and sensitive substrains.« less