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

Background: Plasmodium vivax and Plamodium falciparum are co-endemic in much of the Brazilian Amazon, with P. vivax comprising greater than 80% of clinical cases, especially in low transmission settings. The molecular force of blood-stage infection of P. vivax (molFOB) can provide a detailed picture of P. vivax transmission in low transmission settings and help improve malaria measures control and elimination efforts. Methodology: Monthly samples were collected in a cohort of 1,274 individuals of all ages between April 2013 and March 2014 in three peri-urban communities in the Brazilian Amazon. Regression analyses were used to test how factors including age and community were associated with P. vivax molFOB, parasite positivity and clinical episodes. Principal Findings: Respectively, 77.8% and 97.2% of the population remained free of P. vivax and P. falciparum infection. Expected heterozygosity for P. vivax was 0.69 for MSP1_F3 and 0.86 for MS2. Multiplicity of infection in P. vivax was close to the value of 1 as determined with both markers (1.06 for MSP1_F3 and 1.04 for MS2). Season was associated with P. vivax positivity [adjusted hazard ration (aHR) 2.6 (1.9-5.7)] and clinical disease [aHR 10.6 (2.4-47.2)]. P. falciparum infection was associated with previous malarial episodes [HR 9.7 (4.5-20.9)]. Subjects who reported bednet possession [incidence rate ratio (IRR) 1.6 (1.2-2.2)] or previous malaria episodes [IRR 3.0 (2.0-4.5)] were found to have significantly higher P. vivax molFOB.Conclusions: Overall, P. vivax infection prevailed in the area and infections were mostly observed as monoclonal. High proportions of symptomatic and submicroscopic infections were found. Previous malaria episodes were associated with significantly higher P. vivax molFOB, likely indicating that effective radical cure is an important strategy to be addressed in these endemic communities.