THE OPTIMAL PRODUCTION OF GAMETOCYTES BY PLASMODIUM-FALCIPARUM

We use a simple model of the blood-stage infection dynamics of the mal aria parasite Plasmodium falciparum to consider the adaptive significa nce of different rates of conversion from its pathogenic, asexual stag es to its transmissible, sexual forms. We find that the rates that max imize transmissivity in single-strain infections are generally greater than the highest rates reported for in vitro cultures and are several times those for which the behavior of the model is consistent with cl inical profiles of infection dynamics. When two strains that share a c ommon immune agent coinfect a host through simultaneous inoculation or sequential superinfection, however, a strain with a lower, clinically -consistent value of the conversion rate inhibits the transmissivity o f one with the higher value optimal for single-strain infection. Hence we suggest that ''apparent'' competition by way of a common immune re sponse might be responsible for selection of the former. (C) 1998 Acad emic Press.