Malaria causes more than 500 million clinical cases and is responsible for about one million deaths annually, mostly among African infants and young children. Uganda bears a particularly large burden, having among the highest rates of transmission worldwide. Within Uganda, there is significant heterogeneity of malaria transmission. In the most recent malaria indicator survey, from 2009, parasite prevalence among children under five years of age ranged from <5% in urban centres to >60% in rural settings.
As utilization of malaria control interventions, including long-lasting insecticide treated bed nets (LLINs), indoor residual spraying of insecticides, and prompt treatment with artemisinin-based combination therapy (ACT) has increased, many reports have shown a substantial drop in malaria transmission, malaria-associated hospitalizations, and malaria-associated deaths.
Studies have consistently revealed that, in endemic populations, the incidence and severity of malaria decreases considerably after the first years of life, with a corresponding rise in the prevalence of asymptomatic carriage of parasites. Although widespread use of LLINs and ACT have been associated with declines in the incidence of malaria in many regions, there have been concerns over how decreasing exposure to malaria parasites may alter the natural history of disease, and possibly delay the acquisition of anti-malarial immunity. To better understand the impact of LLINs and ACT on the natural history of malaria in a high endemicity setting, the incidence of malaria and prevalence of asymptomatic parasitaemia were evaluated in a cohort of children living in Tororo, Uganda.