High proportions of asymptomatic and submicroscopic Plasmodium vivax infections in a peri-urban area of low transmission in the Brazilian Amazon

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.Electronic supplementary materialThe online version of this article (10.1186/s13071-018-2787-7) contains supplementary material, which is available to authorized users.

Prevalence and Force of Plasmodium Vivax and Plasmodium Falciparum Blood Stage Infection and Associated Clinical Malaria Burden in the Brazilian Amazon

“…Recent studies in the Amazon region and other malaria endemic areas in the world have shown a high proportion of submicroscopic P. vivax infections [7,17,34]. In the present study, factors associated with P. vivax positivity were age (20-60 years), seasonality, use of mosquito nets and IRS.…”

“…This cohort study was conducted in the Brasileirinho, Ipiranga and Puraquequara communities, located in Manaus peri-urban area, between April 2013 and March 2014 ( Figure 1A). A detailed description of the study area has been presented elsewhere [17]. According to a census performed by a Fundação de Medicina Tropical Doutor Heitor Vieira Dourado (FMT-HVD) eld team, the population of the study area was estimated to be approximately 2,400 inhabitants before the start of the study, in 2012.…”

“…A second challenge is the early production of P. vivax gametocytes, along with asymptomatic cases, which enables the transmission of parasites even before the infected individual develops clinical symptoms. Thirdly, P. vivax parasite densities are generally lower than those seen in P. falciparum infections, especially in hypoendemic areas such as in Brazil, therefore requiring more sensitive diagnostic tools [17]. Research has shown that a high proportion of submicroscopic and asymptomatic P. vivax infections usually exist in such settings, and that these infections can easily be missed by routine active and passive case detection [17].…”

“…Thirdly, P. vivax parasite densities are generally lower than those seen in P. falciparum infections, especially in hypoendemic areas such as in Brazil, therefore requiring more sensitive diagnostic tools [17]. Research has shown that a high proportion of submicroscopic and asymptomatic P. vivax infections usually exist in such settings, and that these infections can easily be missed by routine active and passive case detection [17]. It has been shown that asymptomatically infected individuals are able to infect mosquitoes of the Amazon region, therefore these infections might fuel residual malaria transmission, thereby complicating malaria elimination [18][19][20][21].…”

Molecular evidence of sustained urban malaria transmission in Amazonian Brazil, 2014–2015

“…Malaria rates tend to be lower in cities and towns compared with neighbouring rural settings, due to multiple factors such as improved housing and access to healthcare and limited availability of suitable vector-breeding habitats [2]. Nevertheless, malaria cases have been increasingly reported within and near urban centres across the Amazon Basin [3][4][5][6][7] and the Pacific Coast of South America [8][9][10][11][12][13].…”