Dynamics of Afebrile Plasmodium falciparum Infections in Mozambican Men

Abstract

Background: Afebrile Plasmodium falciparum infections usually remain undetected and untreated in the community and could potentially contribute to sustaining local malaria transmission in areas aiming for malaria elimination. Methods: Thirty-two men with afebrile P. falciparum infections detected with rapid diagnostic test (RDTs) were followed for 28 days. Kaplan-Meier estimates were computed to estimate probability of parasite positivity and of reducing parasitaemia by half of its initial level by day 28. Trends of parasite densities quantified by microscopy and qPCR were assessed using Poisson regression models, and the microscopy to qPCR positivity ratio was calculated at each time point. Three survival distributions (Gompertz, Weibull, and gamma) were used to evaluate their strength of fit to the data and to predict the median lifetime of infection. Results: The cumulative probability of parasite qPCR positivity by day 28 was 81% (95% CI 60.2-91.6). Geometric mean parasitemia at recruitment was 516.1 parasites/muL and fell to <100 parasites/muL by day 3, reaching 56.7 parasites/muL on day 28 (p-value<0.001). The ratio of P. falciparum positive samples by microscopy to qPCR decreased from 0.9 to 0.52 from recruitment to day 28. The best model fit to the data was obtained assuming a Gompertz distribution. Conclusions: Afebrile P.falciparum infections detectable by RDT in semi-immune adults fall and stabilize at low-density levels during the first four days since detection, suggesting a rapid decline of potential transmissibility in this hidden parasite reservoir.