Association Between Age and Plasmodium falciparum Infection Dynamics

Abstract

Few data exist on the incidence or duration of natural Plasmodium falciparum infections in high transmission settings. School-aged children (SAC) carry a disproportionate burden of infections, suggesting either increased incidence or duration. We estimated the incidence and duration of unique infections by age groups. The Mfera Cohort Study (2012–2017) had two years of follow-up with 120 participants tested monthly and during sick visits. Blood samples were collected to detect P. falciparum by microscopy and polymerase chain reaction. Positive samples underwent genotyping. Simulation was used to account for high non-detection of infection among low parasitemia infections, which increase in frequency with age. Adults had significantly fewer unique infections per person per year (median, 2.5) compared to SAC and under-five children (6.3 and 6.6, respectively). Over half of all genotypes were persistent. Infections lasted significantly longer in adults (median, 180 days) and SAC (median, 163 days) compared to under-five children (median, 97 days), after accounting for age-dependent, non-detection of infection. SAC acquired new infections at the same rate as under-five children, but maintained these infections for longer periods of time, similar to adults. This study provides new insights into P. falciparum infection dynamics that should be considered when designing malaria control strategies.