Effect of the estrous cycle on susceptibility of female mice to intravaginal inoculation of herpes simplex virus type 2 (HSV-2).

In order to explore the effect of sexual maturity on the susceptibility of mice to genital herpesvirus infections, mice were separated into the four stages of the estrous cycle and inoculated intravaginally with varying doses of HSV-2, strain 186. Deaths were observed as indicators of susceptibility and were recorded as follows: proestrous, 33%; estrous, 16%; metestrous, 9% and diestrous, 75%. To determine the course of infection in animals inoculated at different stages of estrous, cotton swabs were used to collect vaginal specimens at various times post-virus inoculation for virus titration. All mice inoculated during diestrous were positive for virus as early as 6 hours post-virus inoculation and had titers that increased over a 3 day period. Mice inoculated in other stages of estrus were positive only briefly (at 6 h) or had no detectable virus. In order to verify the susceptibility associated with diestrous, mice were ovariectomized to produce a continuous diestrous (pseudodiestrous) and when inoculated greater than or equal to 66.7% died. In contrast, none of the mice which had been ovariectomized and treated with estrogen to simulate the estrus stage died. We postulate that in stages other than diestrous virus may adsorb to epithelial cells in the lumen of the vagina and/or be expelled from the body by nonspecific resistance functions, thus reducing the likelihood of vaginal infection.