THE DYNAMICS OF PLASMODIUM-FALCIPARUM BLOOD-STAGE INFECTION

We develop a system of ordinary differential equations to model the dy namics of the brood-stages of the malaria parasite, Plasmodium falcipa rum. Variants of the model allow the study of a set of hypotheses abou t the interaction of the parasite with the host immune system, in part icular with regard to the stimulation of the immune response and the r egulation of the rate of conversion from the pathogenic, asexual to th e transmissible, sexual blood stage. The values of several parameters of our models can be estimated from previous empirical work. Although the dynamics of the variants differ somewhat, in each variant some set of values of the three unconstrained parameters, different from one v ariant to the next, produces a range of behaviours quantitatively cons istent with those reported from clinical studies. Some parameter value s produce infections which quickly terminate, while others approach a chronic equilibrium level or produce oscillations, with repeated sever e peaks separated by periods of undetectable parasitemia. We examine t hese and several other distinctions that might be used to assess model variants and focus further empirical research. (C) 1997 Academic Pres s Limited.