Our long-term goal is to provide scientific evidence that can be translated into effective public health interventions for malaria control in Amazonia. We aim to determine whether asymptomatic parasite carriage is a major contributor to malaria transmission across the region by: (a) estimating the prevalence, incidence and risk factors for asymptomatic malaria parasite carriage in rural Amazonia; (b) estimating the prevalence, incidence, average duration and risk factors for gametocyte carriage; (c) comparing prospectively the risk of subsequent clinical malaria among asymptomatic parasite carriers and non-infected controls living in the same communities and determining whether these episodes are due to persistent parasite lineages or to new infections; and (d) testing whether intra-host competition of genetically distinct parasite clones contributes to increased parasite virulence, greater risk of disease, and increased gametocyte production. These aims have been achieved with population based surveys in epidemiologically diverse Amazonian settings. Field-based clinical and epidemiological analyses are complemented with measurements of immunological parameters and extensive parasite genotyping, providing a unique multidisciplinary perspective on the public health significance of asymptomatic parasite carriage in the Amazon.