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Background   Plasmodium vivax  is the most widespread human malaria parasite outside Africa and is the predominant parasite in the Americas. Increasing reports of  P. vivax  disease severity, together with the emergence of drug-resistant strains, underscore the urgency of the development of vaccines against  P. vivax . Polymorphisms on DBP-II-gene could act as an immune evasion mechanism and, consequently, limited the vaccine efficacy. This study aimed to investigate the  pvdbp -II genetic diversity in two Brazilian regions with different epidemiological patterns: the unstable transmission area in the Atlantic Forest (AF) of Rio de Janeiro and; the fixed malaria-endemic area in Brazilian Amazon (BA).    Methods  216 Brazilian  P. vivax  infected blood samples, diagnosed by microscopic examination and PCR, were investigated. The region flanking  pvdbp -II was amplified by PCR and sequenced. Genetic polymorphisms of  pvdbp -II were estimated based on the number of segregating sites and nucleotide and haplotype diversities; the degree of differentiation between-regions was evaluated applying Wright’s statistics. Natural selection was calculated using the rate of nonsynonymous per synonymous substitutions with the Z-test, and the evolutionary distance was estimated based on the reconstructed tree.    Results  79 samples from AF and 137 from BA were successfully sequenced. The analyses showed 28 polymorphic sites distributed in 21 codons, with only 5% of the samples Salvador 1 type. The highest rates of polymorphic sites were found in B- and T cell epitopes. Unexpectedly, the nucleotide diversity in  pvdbp -II was higher in AF (0.01) than in BA (0.008). Among the 28 SNPs detected, 18 are shared between  P. vivax  isolates from AF and BA regions, but 8 SNPs were exclusively detected in AF—I322 S , K371 N , E385 Q , E385 T , K386 T , K411 N , I419 L  and I419 R —and 2 (N375 D  and I419 M ) arose exclusively in BA. These findings could suggest the potential of these geographical clusters as population-specific-signatures that may be useful to track the origin of infections. The sample size should be increased in order to confirm this possibility.    Conclusions  The results highlight that the  pvdbp - II  polymorphisms are positively selected by host’s immune pressure. The characterization of  pvdbp -II polymorphisms might be useful for designing effective DBP-II-based vaccines.

Extensive genetic diversity of Plasmodium vivax dbp-II in Rio de Janeiro Atlantic Forest and Brazilian Amazon Basin: evidence of positive selection