RESEARCH ARTICLE Risk Factors for Plasmodium falciparum Gametocyte Positivity in a Longitudinal Cohort

Malaria transmission intensity is highly heterogeneous even at a very small scale. Imple-menting targeted intervention in malaria transmission hotspots offers the potential to reduce the burden of disease both locally and in adjacent areas. Transmission of malaria parasites from man to mosquito requires the production of gametocyte stage parasites. Cluster analy-sis of a 19-year long cohort study for gametocyte carriage revealed spatially defined game-tocyte hotspots that occurred during the time when chloroquine was the drug used for clinical case treatment. In addition to known risk factors for gametocyte carriage, notably young age (<15 years old) and associated with a clinical episode, blood groups B and O in-creased risk compared to groups A and AB. A hotspot of clinical P. falciparum clinical epi-sodes that overlapped the gametocyte hotspots was also identified. Gametocyte positivity was found to be increased in individuals who had been treated with chloroquine, as op-posed to other drug treatment regimens, for a clinical P. falciparum episode up to 30 days previously. It seems likely the hotspots were generated by a vicious circle of ineffective treatment of clinical cases and concomitant gametocyte production in a sub-population characterized by an increased prevalence of all the identified risk factors. While rapid ac-cess to treatment with an effective anti-malarial can reduce the duration of gametocyte car-riage and onward parasite transmission, localised hotspots represent a challenge to malaria control and eventual eradication