Abstract
BackgroundPopulation-based studies conducted in Latin America have shown a high proportion of asymptomatic and submicroscopic malarial infections. Considering efforts aiming at regional elimination, it is important to investigate the role of this asymptomatic reservoir in malaria transmission in peri-urban areas. This study aimed to estimate the prevalence of Plasmodium spp. and gametocyte burden on symptomatic and asymptomatic infections in the Brazilian Amazon.ResultsTwo cross-sectional household surveys (CS) were conducted including all inhabitants in a peri-urban area of Manaus, western Amazonas State, Brazil. Malaria parasites were detected by light microscopy (LM) and qPCR. Sexual stages of Plasmodium spp. were detected by LM and RT-qPCR. A total of 4083 participants were enrolled during the two surveys. In CS1, the prevalence of Plasmodium vivax infections was 4.3% (86/2010) by qPCR and 1.6% (32/2010) by LM. Fifty percent (43/86) of P. vivax infected individuals (qPCR) carried P. vivax gametocytes. In CS2, 3.4% (70/2073) of participants had qPCR-detectable P. vivax infections, of which 42.9% (30/70) of infections were gametocyte positive. The P. vivax parasite density was associated with gametocyte carriage (P < 0.001). Sixty-seven percent of P. vivax infected individuals and 53.4% of P. vivax gametocyte carriers were asymptomatic.ConclusionsThis study confirms a substantial proportion of asymptomatic and submicroscopic P. vivax infections in the study area. Most asymptomatic individuals carried gametocytes and presented low asexual parasitemia. This reservoir actively contributes to malaria transmission in the Brazilian Amazon, underscoring a need to implement more efficient control and elimination strategies.
Highlights
Population-based studies conducted in Latin America have shown a high proportion of asymptomatic and submicroscopic malarial infections
Despite the relative success of control efforts, malaria transmission still occurs in the Amazon region with major outbreaks recorded in 1999 and 2005 that may have been in part due to deforestation, mining activities and new unplanned rural settlements resulting in environmental changes favouring malaria transmission [2, 5]
In order to estimate the reservoir of Plasmodium spp. infected individuals contributing to malaria transmission, we conducted two large-scale cross-sectional surveys in a peri-urban area of Manaus, located in the western part of the Amazonas State, Brazil
Summary
Population-based studies conducted in Latin America have shown a high proportion of asymptomatic and submicroscopic malarial infections. Considering efforts aiming at regional elimination, it is important to investigate the role of this asymptomatic reservoir in malaria transmission in peri-urban areas. The past two decades have witnessed impressive success in the reduction of malaria incidence in Latin America, with the number of confirmed cases decreasing by 31.0% from 2000 to 2015. Almeida et al Parasites & Vectors (2018) 11:194 predominance progressively increasing to peak at 88.4% of total malaria cases in 2015 [3]. Such an impressive reduction of cases is likely attributable to the governmental program focusing on early case detection and treatment [4]. In Brazilian Amazon, Anopheles darlingi is the main malaria vector [8, 9]
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