Plasmodium vivax gametocyte infectivity in sub-microscopic infections

Background: 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. Methods: In 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). Results: In 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. Conclusions: This 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.