Microscopic Plasmodium falciparum Gametocytemia and Infectivity to Mosquitoes in Cambodia

Abstract

Although gametocytes are essential for malaria transmission, in Africa many falciparum-infected persons without smear-detectable gametocytes still infect mosquitoes. To see whether the same is true in Southeast Asia, we determined the infectiousness of 119 falciparum-infected Cambodian adults to Anopheles dirus mosquitoes by membrane feeding. Just 5.9% of subjects infected mosquitoes. The 8.4% of patients with smear-detectable gametocytes were >20 times more likely to infect mosquitoes than those without and were the source of 96% of all mosquito infections. In low-transmission settings, targeting transmission-blocking interventions to those with microscopic gametocytemia may have an outsized effect on malaria control and elimination.

Keywords: Anopheles dirus; Plasmodium falciparum; gametocyte; infectious reservoir; malaria transmission; membrane feeding; submicroscopic.

Figure 1.

Relationship of smear-detectable gametocytemia to prevalence of mosquito infection. Because of the logarithmic scale, only patients with smear-detectable gametocytes are depicted. Circles represent patients with Plasmodium falciparum monoinfection; squares, those with mixed P. falciparum/P. vivax infection. For patients with mixed infection, the percentage of infected mosquitoes was calculated as the proportion of 30 mosquitoes with positive falciparum-specific quantitative polymerase chain reaction results at day 9 after feeding.