Multiplication rate variation of malaria parasites from hospital cases and community infections

The significance of multiplication rate variation in malaria parasites needs to be determined, particularly for Plasmodium falciparum, the species that causes most virulent infections. To investigate this, parasites from cases presenting to hospital in The Gambia and from local community infections were culture-established and then tested under exponential growth conditions in a standardised six-day multiplication rate assay. The multiplication rate distribution was lower than seen previously in clinical isolates from another area in West Africa where infection is more highly endemic. Multiplication rates were higher in cultured isolates derived from hospital cases (N = 23, mean = 2.9-fold per 48 h) than in those from community infections (N = 11, mean = 1.8-fold)(Mann-Whitney P < 0.001). There was a positive correlation between levels of parasitaemia in peripheral blood of sampled individuals and multiplication rates of the isolates in culture (Spearman's rho = 0.45, P = 0.017). There was no significant difference between isolates containing single parasite genotypes or multiple genotypes at the time of assay, suggesting that parasites do not modify their multiplication rates in response to the presence of different genotypes. It will be important to uncover the mechanisms of this intrinsic multiplication rate variation, and to also investigate the epidemiological distribution and potential associations with infection phenotypes in other populations.