A Mathematical Model for the Spread of a Recurrent Disease: Genital Herpes

Abstract

Background and Rationale: Up to 20% of the population of western countries are infected with herpes simplex virus type 2 (HSV-2). In a wide percentage (20%-80%) of seropositive individuals, this infection causes genital herpes (GH), a disease that is both painful and socially distressing. Objectives: To study the factors linked with the overall prevalence of GH. To determine the potential impact of treatment. Methods: Mathematical model. Three main compartments were specified: susceptibles (S), symptomatic infected (I), and asymptomatic infected (A). Viral shedding from I and A individuals assured transmission to susceptibles at different rates. Symptomatic individuals might be cured and become asymptomatic. Antiviral treatment reduced the rate of transmission in symptomatic individuals. Results: The prevalence of GH is less than HSV-2 seroprevalence. If the symptomatic disease lasted on average for 20% of the sexual life, only one sixth of seropositive individuals would report GH. In certain situations, episode-based antiviral treatment was sufficient to eradicate the disease. However, if transmission was assured mainly by asymptomatic transmission, the impact of treatment on the spread of the disease would be negligible. In a sensitivity analysis, the effective reproductive ratio showed a dependence, in order of importance, on the percentage of effective contacts, the duration of sexual activity, the relative infectivity, the duration of the symptomatic disease, and the size of the population. Conclusions: This model confirms the importance of asymptomatic viral excretion in the spread of GH. Wider use of antiviral treatment targeted at symptomatic individuals is unlikely to eradicate the disease.