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-I322S, K371N, E385Q, E385T, K386T, K411N, I419L and I419R-and 2 (N375D and I419M) 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.

中文翻译：

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里约热内卢大西洋森林和巴西亚马逊河流域间日疟原虫dbp-II的广泛遗传多样性：阳性选择的证据。

背景间日疟原虫是非洲以外最广泛的人类疟疾寄生虫，并且是美洲的主要寄生虫。关于间日疟原虫疾病严重性的报道不断增加，以及耐药菌株的出现，突显了开发针对间日疟原虫疫苗的紧迫性。DBP-II基因的多态性可以作为免疫逃逸的机制，因此限制了疫苗的功效。本研究旨在调查两个流行病学模式不同的巴西地区的pvdbp-II遗传多样性：里约热内卢大西洋森林（AF）的不稳定传播区；以及 巴西亚马逊（BA）的固定疟疾流行区。方法对216例巴西间日疟原虫感染的血液样本进行显微镜检查和PCR分析。通过PCR扩增pvdbp-II侧翼的区域并测序。pvdbp-II的遗传多态性是根据分离位点的数量以及核苷酸和单倍型多样性来估计的。使用赖特的统计数据评估区域之间的差异程度。使用Z检验，使用每个同义词替换的非同义词比率来计算自然选择，并基于重构树估计进化距离。结果成功地从AF提取了79个样品，从BA提取了137个样品。分析显示28个多态性位点分布在21个密码子中，只有5％的样品萨尔瓦多1型。在B细胞和T细胞表位中发现多态性位点的比率最高。出乎意料的是，AF（0.01）中pvdbp-II的核苷酸多样性高于BA（0.008）。在检测到的28个SNP中，AF和BA地区的间日疟原虫分离株共有18个SNP，但在AF-I322S，K371N，E385Q，E385T，K386T，K411N，I419L和I419R-和2（N375D和I419M）专用于BA。这些发现可能表明这些地理集群作为特定人群特征的潜力，可能有助于追踪感染源。为了确定这种可能性，应增加样本量。结论结果强调，pvdbp-II多态性是由宿主的免疫压力正选择的。pvdbp-II多态性的表征可能对设计有效的基于DBP-II的疫苗有用。K411N，I419L和I419R-和2（N375D和I419M）专门出现在BA中。这些发现可能表明这些地理集群作为特定人群特征的潜力，可能有助于追踪感染源。为了确定这种可能性，应增加样本量。结论结果强调，pvdbp-II多态性是由宿主的免疫压力正选择的。pvdbp-II多态性的表征可能对设计有效的基于DBP-II的疫苗有用。K411N，I419L和I419R-和2（N375D和I419M）专门出现在BA中。这些发现可能表明这些地理集群作为特定人群特征的潜力，可能有助于追踪感染源。为了确定这种可能性，应增加样本量。结论结果强调，pvdbp-II多态性是由宿主的免疫压力正选择的。pvdbp-II多态性的表征可能对设计有效的基于DBP-II的疫苗有用。结论结果强调，pvdbp-II多态性是由宿主的免疫压力正选择的。pvdbp-II多态性的表征可能对设计有效的基于DBP-II的疫苗有用。结论结果强调，pvdbp-II多态性是由宿主的免疫压力正选择的。pvdbp-II多态性的表征可能对设计有效的基于DBP-II的疫苗有用。