Model of a two serotype gonorrhea transmission system with dynamic host immune response.

Abstract

Many seroprevalence studies have reported that antigenically distinct serotypes of <italic>Neisseria gonorrhoea</italic> are not distributed randomly within host populations. This dissertation used a simple model of a gonorrhea transmission system to examine the possible effect of a serotype specific protective host immune response on serotype prevalence. The model included two serotypes of gonorrhea with defined antigenic cross-reactivity and hosts with dynamic immune responses that included antigen specificity, secondary immune response and waning protection with increasing time since infection. The model was implemented as a discrete event simulation with a closed host population of 500 male and 500 female humans. The first experiment compared steady-state prevalence in a one serotype gonorrhea transmission system under two assumptions of sex-act scheduling. There was a small but statistically significant decrease in prevalence when the within-partnership sex-act rate was adjusted downward as number of concurrent partners increased compared to the alternative model in which all partnerships had the same within-partnership sex-act rate regardless of concurrency. In the second experiment, two serotypes of gonorrhea with defined cross-reactivities were released into the host population. Both serotypes generally became endemic except when cross-reactivity against the antigenically less fit serotype was very high. The third experiment extended the second experiment by releasing a second serotype into the population after the first serotype had become endemic. If the second serotype was less antigenically fit, it tended to not become endemic; if it was more antigenically fit, it tended to become the dominant serotype and the first serotype remained endemic. The results suggest that antigenic cross-reactivity could affect the distribution of serotypes in a host population and that the dominant serotypes reported in seroepidemiology studies may be antigenically distinct.