Malaria Transmission Dynamics in a High-Transmission Setting of Western Kenya and the Inadequate Treatment Response to Artemether-Lumefantrine in an Asymptomatic Population

Background Assessing the infectious reservoir is critical in malaria control and elimination strategies. We conducted a longitudinal epidemiological study in a high-malaria-burden region in Kenya to characterize transmission in an asymptomatic population. Methods 488 study participants encompassing all ages in 120 households within 30 clusters were followed for 1 year with monthly sampling. Malaria was diagnosed by microscopy and molecular methods. Transmission potential in gametocytemic participants was assessed using direct skin and/or membrane mosquito feeding assays, then treated with artemether-lumefantrine. Study variables were assessed using mixed-effects generalized linear models. Results Asexual and sexual parasite data were collected from 3792 participant visits, with 903 linked with feeding assays. Univariate analysis revealed that the 6-11-year-old age group was at higher risk of harboring asexual and sexual infections than those <6 years old (odds ratio [OR] 1.68, P < .001; and OR 1.81, P < .001), respectively. Participants with submicroscopic parasitemia were at a lower risk of gametocytemia compared with microscopic parasitemia (OR 0.04, P < .001), but they transmitted at a significantly higher rate (OR 2.00, P = .002). A large proportion of the study population who were infected at least once remained infected (despite treatment) with asexual (71.7%, 291/406) or sexual (37.4%, 152/406) parasites. 88.6% (365/412) of feeding assays conducted in individuals who failed treatment the previous month resulted in transmissions. Conclusions Individuals with asymptomatic infection sustain the transmission cycle, with the 6-11-year age group serving as an important reservoir. The high rates of artemether-lumefantrine treatment failures suggest surveillance programs using molecular methods need to be expanded for accurate monitoring and evaluation of treatment outcomes. Primary school children are the most important infectious reservoir for transmission of malaria. Asymptomatic participants with submicroscopic parasitemia transmit malaria at a significantly higher rate compared with microscopic parasitemia. One-third of the study population failed treatment with artemether-lumefantrine.

Automated summary

This study investigated the transmission dynamics in an asymptomatic population in a high-malaria-burden region in Kenya and identified primary school children as the most important infectious reservoir for malaria transmission. Asymptomatic individuals with submicroscopic parasitemia transmitted malaria at a significantly higher rate compared with those with microscopic parasitemia. The high rates of treatment failures with artemether-lumefantrine suggest the need for expanded surveillance programs using molecular methods for accurate monitoring and evaluation of treatment outcomes.