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BACKGROUND Malaria remains common among native Amazonians, challenging Brazil′s elimination efforts. OBJECTIVES We examined the epidemiology of malaria in riverine populations of the country′s main hotspot - the upper Juruá Valley in Acre state, close to the Brazil-Peru border, where Plasmodium vivax accounts for > 80% of cases. METHODS Participants (n = 262) from 10 villages along the Azul River were screened for malaria parasites by microscopy and genus-specific, cytochrome b (cytb) gene-based polymerase chain reaction. Positive samples were further tested with quantitative TaqMan assays targeting P. vivax- and P. falciparum-specific cytb domains. We used multiple logistic regression analysis to identify independent correlates of P. vivax infection. FINDINGS Microscopy detected only one P. vivax and two P. falciparum infections. TaqMan assays detected 33 P. vivax infections (prevalence, 11.1%), 78.1% of which asymptomatic, with a median parasitaemia of 34/mL. Increasing age, male sex and use of insecticide-treated bed nets were significant predictors of elevated P. vivax malaria risk. Children and adults were similarly likely to remain asymptomatic once infected. MAIN CONCLUSIONS Our findings are at odds with the hypothesis of age-related clinical immunity in native Amazonians. The low virulence of local parasites is suggested as an alternative explanation for subclinical infections in isolated populations.
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Introduction: Iñapari is a town located in Peru, on the border of Brazil, between the Amazonian states of Acre and Amazonas. The local Peruvian children under five years of age present moderate anemia while the percentage of chronic child malnutrition is a major public health problem in the country as a whole. Goals: The purpose of this study was to identify the prevalence of major childhood morbidities caused by anemia, malnutrition, intestinal parasites, toxocariasis, and hepatitis A, and identify connections with the socioeconomic and environmental conditions found in Iñapari. Methods: Interviews with questionnaires; anthropometric measurements, collection of feces and venous blood samples. Results: A 20% prevalence of anemia and 8.5% prevalence of chronic malnutrition (height for age deficiency) was found. A pathogenic intestinal parasite was noted in 24.5% of the samples, where Giardia intestinalis (14.7%) was the most frequent. The seroprevalence of toxocariasis was 33.8% and hepatitis A was 21.2%. Conclusion: There is a connection between the results found and the poor living and sanitary conditions of the population. The low income noted is also linked to the malnutrition and anemia detected