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 one year with monthly sampling. Malaria was diagnosed by microscopy and molecular methods. Transmission potential in gametocytemic participants were 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 was collected from 3,792 participant visits, with 903 linked with feeding assays. Univariate analysis revealed that 6-11-year old age-group were at higher risk of harboring asexual and sexual infections than the less than 6-year-old (Odds Ratio [OR] 1.68, p < 0.001 and OR 1.81, p < 0.001), respectively. Participants with submicroscopic parasitemia were at a lower risk of gametocytemia compared to microscopic (OR 0.04, p < 0.001), but they transmitted at a significantly higher rate (OR 2.00, p = 0.002). A large proportion of the study population was continuously infected (despite treatment) with asexual (71.7%, 291/406) or sexual (37.4%, 152/406) parasites. 89.4% (365/408) of feeding assays conducted in individuals who failed treatment the previous month resulted in transmissions.
CONCLUSION
Individuals with asymptomatic infection sustain the transmission cycle, with the 6-11-year old 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.