The role of submicroscopic parasitemia in malaria transmission: what is the evidence?

Achieving malaria elimination requires targeting the human reservoir of infection, including those with asymptomatic infection. Smear-positive asymptomatic infections detectable by microscopy are an important reservoir because they often persist for months and harbor gametocytes, the parasite stage infectious to mosquitoes. However, many asymptomatic infections are submicroscopic and can only be detected by molecular methods. Although there is some evidence that individuals with submicroscopic malaria can infect mosquitoes, transmission is much less likely to occur at submicroscopic gametocyte levels. As malaria elimination programs pursue mass screening and treatment of asymptomatic individuals, further research should strive to define the degree to which submicroscopic malaria contributes to the infectious reservoir and, in turn, what diagnostic detection threshold is needed to effectively interrupt transmission.