Determinants and consequences of asymptomatic carriage of malaria parasites: population-based survey in rural Brazilian Amazonia

Abstract

Despite five decades of intensive control efforts, malaria remains a major public health concern in Brazil. The most recent incidence data available are for 2007, when 458,041 slide-confirmed malaria cases were reported countrywide, 99.9% of which acquired in the Amazon Basin. The increasing interest on malaria epidemiology in Brazil originates mainly from the high morbidity observed in exposed populations, but subclinical malaria infections are also a major target of research. Here we focus on the epidemiology of asymptomatic malarial infections in an agricultural settlement. We aim to: (a) estimate the prevalence of asymptomatic malaria parasite carriage and characterize risk factors for clinical disease among parasite carriers; (b) estimate the prevalence and risk factors for gametocyte carriage in symptomatic and asymptomatic infections; (c) estimate the risk of subsequent clinical malaria among asymptomatic parasite carriers and non-infected subjects; (d) determine whether subsequent clinical malaria episodes diagnosed during the follow-up of asymptomatic parasite carriers are asociated with persistent parasite lineages or with infections with unrelated parasites; (e) compare levels of genetic diversity in parasites recovered from symptomatic and asymptomatic infections.