Laboratório de Pesquisas em Malária, Instituto Oswaldo Cruz, Fundação Oswaldo Cruz (Fiocruz), Avenida Brasil 4365, Manguinhos, Rio de Janeiro, Brazil.
Centro de Pesquisa, Diagnóstico e Treinamento em Malária Reference Laboratory for Malaria in the Extra-Amazonian Region for the Brazilian Ministry of Health, SVS & Fiocruz, Rio de Janeiro, Brazil.
Malar J. 2020 Feb 19;19(1):81. doi: 10.1186/s12936-020-03159-y.
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).
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.
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.
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.
间日疟原虫是非洲以外最广泛的人类疟原虫寄生虫，也是美洲主要的寄生虫。越来越多的间日疟原虫疾病严重程度的报告，加上耐药株的出现，突显了开发针对间日疟原虫的疫苗的紧迫性。DBP-II 基因上的多态性可能作为一种免疫逃避机制，因此限制了疫苗的功效。本研究旨在调查两个具有不同流行病学模式的巴西地区的 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。
对 216 例经显微镜检查和 PCR 诊断的巴西感染间日疟原虫的血液样本进行调查。通过 PCR 扩增并测序 pvdbp-II 侧翼区。根据分离位点数量和核苷酸及单倍型多样性估计 pvdbp-II 的遗传多态性；应用 Wright 统计数据评估区域间的分化程度。通过 Z 检验计算非同义与同义替代率来计算自然选择，并根据重建树估计进化距离。
成功测序了来自 AF 的 79 个样本和来自 BA 的 137 个样本。分析表明，21 个密码子中有 28 个多态性位点，只有 5%的样本为 Salvador1 型。B 细胞和 T 细胞表位中的多态性位点比例最高。出乎意料的是，pvdbp-II 中的核苷酸多样性在 AF（0.01）高于 BA（0.008）。在检测到的 28 个 SNP 中，18 个 SNP 在来自 AF 和 BA 地区的间日疟原虫分离株中共享，但 8 个 SNP 仅在 AF-I322S、K371N、E385Q、E385T、K386T、K411N、I419L 和 I419R 中检测到，2 个（N375D 和 I419M）仅在 BA 中出现。这些发现可能表明这些地理聚类作为种群特异性特征的潜力，这可能有助于追踪感染的来源。为了证实这一可能性，应该增加样本量。
结果表明，pvdbp-II 多态性受到宿主免疫压力的正向选择。pvdbp-II 多态性的特征分析可能有助于设计有效的基于 DBP-II 的疫苗。
