Dynamics of multiple Plasmodium falciparum infections in infants in a highly endemic area of Tanzania.

The force of infection and recovery rate for malaria in infants in a highly endemic area of Tanzania were analysed using polymerase chain reaction-restriction fragment length polymorphism genotyping of the Plasmodium falciparum msp2 locus in 99 paired blood samples. Overall, new genotypes were acquired at a rate of 0.064 per day, and the average duration of infections was estimated to be 23 d. The highest recovery rates were in children under 4 months of age. The higher susceptibility of infants to clinical malaria in comparison with older children, in areas of very high transmission, may be largely a consequence of the short duration of infections which precludes the establishment of concomitant immunity. The high turnover of infections also implies that infection prevalence and multiplicity approach an equilibrium even in very young children, and calls into question the use of infant conversion rates as a measure of transmission intensity.