Stabilization of isometric DNA viruses against thermoinactivation by lowered ionic strength

The thermostability of isometric DNA viruses increases, if the ionic strength is diminished before heating. When unpurified virus material from cell cultures is heated under conditions (temperature, time) which lead to a reduction in infectivity by 3 to 4 log10, this loss in titer is 1 to 3 log10 less, if the ionic strength is decreased by diluting the material in dist. water (1:100) before heating. A dilution in Eagle's MEM (1:100) or a previous dialysis against water does not have the same effect. This property was found in the following members of 4 DNA virus families: adenovirus 5, herpesvirus 1, SV 40 and bovine parvovirus 1. In contrast, members of pox- (vaccinia) and picornaviruses (polio 2, coxsackie B5) were found to be less thermostable under conditions of low ionic strength. Reovirus 3 showed no difference in inactivation. The observed effect may be of practical importance for heat disinfection of viruses and for their persistence in the environment.