Photosensitization of herpes simplex virus type 1 with neutral red

Commercial neutral red (NR) originally containing at least 8 components was purified by thin layer chromatography. Herpes simplex virus type 1 (HSV-1) treated in vitro with 30 microgram/ml of purified NR became sensitive to light inactivation within 2 min but rapidly lost this sensitivity upon dilution. Similarly, virus grown in the presence of NR lost its photosensitivity upon dilution of the virus stock. In both cases the kinetics of inactivation appeared to be multi-hit. Photoinactivation of intracellular virus was most effective when NR was applied between 6 and 12 h post-infection. The most efficient inactivation occurred when virus at pH 8.8 was irradiated by light at a wavelength of 470 nm.