Higher multiplication rates of Plasmodium falciparum in isolates from hospital cases compared with community infections

BackgroundParasite multiplication rates vary among Plasmodium falciparum isolates from patients with malaria, suggesting differences in virulence potential, although direct comparisons between hospital-based clinical cases and community infections are needed. MethodsCryopreserved blood samples from malaria cases presenting to a district hospital in The Gambia and infections detected in local communities were introduced to continuous culture under the same conditions. Thirty-four isolates (23 hospital-based and 11 community-based) were successfully established and then tested under exponential growth conditions over six days to derive estimated P. falciparum multiplication rates per cycle based on a 48-hour typical cycle length. ResultsA range of parasite multiplication rates in culture was seen across isolates, from 1.5-fold to 5.0-fold per cycle. Multiplication rates were significantly higher in the hospital-based isolates than the community-based isolates. There was a significantly positive correlation between parasitaemia in peripheral blood and multiplication rates in culture. There was no significant difference in multiplication rates between isolates with single or multiple parasite genotypes. ConclusionsThese findings are consistent with a hypothesis that intrinsic natural variation in parasite multiplication rate may affect levels of parasitaemia achieved during infection, and that this affects likelihood of hospital presentation. Results do not support a hypothesis that parasites modify their multiplication rates in response to competing parasites with different genotypes. SummaryRelevant to understanding parasite virulence, this study finds higher Plasmodium falciparum multiplication rates in cultured isolates from malaria cases presenting to hospital than in isolates from local community infections, and positive correlation with parasitaemia in peripheral blood of individuals.