Abstract
BackgroundThe use of molecular techniques has put in the spotlight the existence of a large mass of malaria sub-microscopic infections among apparently healthy populations. These sub-microscopic infections are considered an important pool for maintained malaria transmission.MethodsIn order to assess the appearance of Plasmodium vivax gametocytes in circulation, gametocyte density and the parasite infectivity to Anopheles mosquitoes, a study was designed to compare three groups of volunteers either experimentally infected with P. vivax sporozoites (early infections; n = 16) or naturally infected patients (acute malaria, n = 16 and asymptomatic, n = 14). In order to determine gametocyte stage, a quantitative reverse transcriptase PCR (RT-qPCR) assay targeting two sexual stage-specific molecular markers was used. Parasite infectivity was assessed by membrane feeding assays (MFA).ResultsIn early infections P. vivax gametocytes could be detected starting at day 7 without giving rise to infected mosquitoes during 13 days of follow-up. Asymptomatic carriers, with presumably long-lasting infections, presented the highest proportion of mature gametocytes and were as infective as acute patients.ConclusionsThis study shows the potential role of P. vivax asymptomatic carriers in malaria transmission should be considered when new policies are envisioned to redirect malaria control strategies towards targeting asymptomatic infections as a tool for malaria elimination.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-016-1104-1) contains supplementary material, which is available to authorized users.
Highlights
The use of molecular techniques has put in the spotlight the existence of a large mass of malaria submicroscopic infections among apparently healthy populations
While P. falciparum is known to differentiate into gametocytes in a relatively late phase of parasite blood development, P. vivax appears to produce mature gametocytes significantly earlier, due to the shorter developmental cycle in comparison with P. falciparum, which is believed to result in greater transmissibility [4, 5]
The current study describes the dynamics of P. vivax gametocyte production and infectivity in early, acute and asymptomatic infections
Summary
The use of molecular techniques has put in the spotlight the existence of a large mass of malaria submicroscopic infections among apparently healthy populations. These sub-microscopic infections are considered an important pool for maintained malaria transmission. Despite several features being similar among different species of malaria parasites, there are important biological differences between the two most relevant to human infections, Plasmodium falciparum and Plasmodium vivax. P. falciparum usually invades circulating erythrocytes of any age. Both species develop and multiply asexually inside erythrocytes where a small proportion of the parasite population switches from the asexually replicating to the sexual stage in a process initiated by a differentiation step [3]. While P. falciparum is known to differentiate into gametocytes in a relatively late phase of parasite blood development, P. vivax appears to produce mature gametocytes significantly earlier, due to the shorter developmental cycle in comparison with P. falciparum, which is believed to result in greater transmissibility [4, 5]
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