Abstract
In the Amazon basin, indigenous forest-dwelling communities typically suffer from a high burden of infectious diseases, including malaria. Difficulties in accessing these isolated ethnic groups, such as the semi-nomadic Yanomami, make official malaria data largely underestimated. In the current study, we longitudinally surveyed microscopic and submicroscopic malaria infection in four Yanomami villages of the Marari community in the northern-most region of the Brazilian Amazon. Malaria parasite species-specific PCR-based detection of ribosomal and non-ribosomal targets showed that approximately 75% to 80% of all malaria infections were submicroscopic, with the ratio of submicroscopic to microscopic infection remaining stable over the 4-month follow-up period. Although the prevalence of malaria infection fluctuated over time, microscopically-detectable parasitemia was only found in children and adolescents, presumably reflecting their higher susceptibility to malaria infection. As well as temporal variation, the prevalence of malaria infection differed significantly between villages (from 1% to 19%), demonstrating a marked heterogeneity at micro-scales. Over the study period, Plasmodium vivax was the most commonly detected malaria parasite species, followed by P. malariae, and much less frequently P. falciparum. Consecutive blood samples from 859 out of the 981 studied Yanomami showed that malaria parasites were detected in only 8% of the previously malaria-positive individuals, with most of them young children (median age 3 yrs). Overall, our results show that molecular tools are more sensitive for the identification of malaria infection among the Yanomami, which is characterized by heterogeneous transmission, a predominance of low-density infections, circulation of multiple malaria parasite species, and a higher susceptibility in young children. Our findings are important for the design and implementation of the new strategic interventions that will be required for the elimination of malaria from isolated indigenous populations in Latin America.
Highlights
We prospectively evaluated the prevalence of malaria infection in four Yanomami villages of the Marari community in the northern-most region of the Brazilian Amazon, close to the border with Venezuela
Malaria is known to cause a significant burden of disease for many populations of indigenous people in Latin America, inequitable access to healthcare leads to sparse and fragmented data on malaria prevalence [7], which are likely to be underestimates due to the use of conventional diagnosis by light microscopy
Using distinct multi-copy PCR-based protocols–ribosomal and more sensitive non-ribosomal targets [21]–it was possible to demonstrate that in this group of semi-isolated people approximately 75% to 80% of all malaria infections were submicroscopic, with the ratio of submicroscopic to microscopic infections remaining stable overtime. These results are important for disease control in the Brazilian Amazon region as individuals with submicroscopic malaria infection are likely to be asymptomatic and, remain an untreated and potentially infectious reservoir [24]
Summary
In the Americas, of the 17 malaria endemic countries, 11 are on target to achieve a 40% reduction in case incidence by 2020, while the remaining six are on target for a 20–40% reduction [1]. Malaria control in the Amazon region is difficult due to its low population density and scarcity of reliable transport routes, which make it challenging to deliver and sustain preventive healthcare measures [4] In this context, local control measures need to characterize areas and populations according to their levels of disease transmission, while considering socio-economic, political and environmental factors. According to the Brazilian Surveillance Secretary of the Ministry of Health (SVS/MS), while malaria increased by 3% among some vulnerable populations living in the Brazilian Amazon, such as gold-miners, in indigenous areas the number of cases increased about 30% over the same period of time (2017–2018) [6] In this region, indigenous communities, including the traditionally seminomadic and widely dispersed Yanomami ethnic group, suffer from a high burden of infectious diseases [7]. Due to the impact of the current political instability in Venezuela and its associated healthcare crisis, the Yanomami people–who have great vulnerability to malaria, measles, malnutrition and mercury pollution in rivers–are currently confronted with environmental destruction of their homeland and potential ethnocide [9]
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