Avaliação prospectiva de infecções maláricas em uma comunidade indígena Yanomami da Amazônia Brasileira

Abstract

A recent increase in malaria case incidence occurred in the Americas as a result of sociopolitical, ecological and economic factors, particularly, in the Brazilian- Venezuelan border. In this scenario, it seems critical to target vulnerable populations in risk areas. In Amazon region, indigenous forest-dwelling communities suffer from a high burden of infectious diseases, including malaria. In these areas, official malaria data are underestimated due to the low sensitivity of routine diagnostic methods and the difficulty of access semi-isolated groups, as is the case of Yanomami ethnic group. In the current study, we prospectively surveyed for microscopic and submicroscopic malaria infections in four Yanomami villages of the Marari community in the northern-most region of the Brazilian Amazon, close to the border with Venezuela. The studied population involved 981 individuals, with a median age of 14 years (IQR 6-33 years; range 1-79 years). The methodological approach involved three cross sectional surveys at two months intervals, which were carried out during dry season (September/November, 2014) and at the beginning of the rainy season (January, 2015). Different real-time PCR protocols -- ribosomal and non-ribossomal plasmodial targets -- were used to increase sensitivity in detection of submicroscopic and mixed malarial infection. Taken together, the results demonstrated that: (i) the frequency of malaria infection was similar between genders (male and female), probably reflecting social and cultural habits of exposed-populations; (ii) regardless the cross-sectional survey, roughly 75% to 80% of all malaria infections were submicroscopic; consequently, (iii) high densities parasite infections (microscopicallydetectable) were detected only in children and adolescents (>16 years), with adults characterized by low densities infections detected by PCR-based protocols. This profile of age-associated malaria suggests acquired immunity induced by successive malaria infections; (iv) the prevalence of malaria infection differed significantly between villages (from 1% to 19%), demonstrating a marked heterogeneity at microscales; (v) Plasmodium vivax was the most commonly detected malaria parasite species, followed by P. malariae and much less frequently P. falciparum; (vi) the circulation of “P. vivax like” malaria (P. simium) in the studied area was discarded; finally, (vii) consecutive blood samples showed that malaria infection (detection of parasite and/or DNA plasmodial) persisted only in 8% of the previously malariapositive individuals, with most of them young children (median age of 3 years). Overall, our results show that molecular tools are more sensitive for the identification of malaria infection among the Yanomami community studied, which was characterized by heterogeneous transmission, a predominance of low-density infections, circulation of multiple malaria parasite species and a higher susceptibility of young children. Our findings are important for the design and implementation of the new strategic interventions that will be required for the control and elimination of malaria in Amazon amerindians populations.