Evolutionary ecology of human papillomavirus: trade-offs, coexistence, and origins of high-risk and low-risk types.

BACKGROUND We address the ecological and evolutionary dynamics of human papillomavirus (HPV) that lead to the dichotomy between high-risk (HR) and low-risk (LR) types. We hypothesize that HPV faces an evolutionary tradeoff between persistence and per-contact transmission probability. High virion production enhances transmissibility but also provokes an immune response leading to clearance and limited persistence. Alternatively, low virion production increases persistence at the cost of diminished transmission probability per sexual contact. We propose that LR HPV types use the former strategy and that HR types use the latter. Sexual behaviors in a host population determine the success of each strategy. METHODS We develop an evolutionary model of HPV epidemiology, which includes host sexual behavior, and we find evolutionarily stable strategies of HPV. RESULTS A slow turnover of sexual partners favors HR HPV, whereas high frequency of partner turnover selects for LR. When both sexual behaviors exist as subcultures in a population, disruptive selection can result in the coevolution and ecological coexistence of both HR and LR HPV types. CONCLUSIONS Our results indicate that the elimination of HR HPV through vaccines may alter the evolutionary trajectory of the remaining types and promote evolution of new HR HPV types.