Heat-resistant infectivity of herpes simplex virus revealed by viral transfection

Following apparently effective inactivation of herpes simplex virus types 1 and 2 at 56 or 70 degrees, significant infectivity was found upon viral transfection using the calcium-dimethylsulfoxide technique. Infectivity was quantitated in RSB-1 (rabbit skin fibroblast) and BHK-21 cells, and dose-response curves were found to depend on both the cell system and side effects of heat. Titers were dependent upon thermal treatment, as well as initial infectivity and cell origin of virus, and showed no or only moderate decrease after 6-hour exposures. There was no liberation of DNA or DNA-protein complexes, since infectivity was DNase- and trypsin-DNase-resistant. Upon purification, activity was found associated with particles that had retained their gross physical integrity. Obviously, protein(s) involved in initiation of infection was primarily altered. Heated virus was also insensitive to antiserum, which prevented replication of unheated, transfected virus.