Center for Evolutionary Medicine and Informatics, The Biodesign Institute, Arizona State University, Tempe, AZ, USA.
Malar J. 2013 Aug 21;12:288. doi: 10.1186/1475-2875-12-288.
Plasmodium vivax is the most widespread of the human malaria parasites in terms of geography, and is thought to present unique challenges to local efforts aimed at control and elimination. Parasite molecular markers can provide much needed data on P. vivax populations, but few such markers have been critically evaluated. One marker that has seen extensive use is the gene encoding merozoite surface protein 3-alpha (MSP-3α), a blood-stage antigen known to be highly variable among P. vivax isolates. Here, a sample of complete msp-3α gene sequences is analysed in order to assess its utility as a molecular marker for epidemiologic investigations.
Amplification, cloning and sequencing of additional P. vivax isolates from different geographic locations, including a set of Venezuelan field isolates (n = 10), yielded a sample of 48 complete msp-3α coding sequences. Characterization of standard population genetic measures of diversity, phylogenetic analysis, and tests for recombination were performed. This allowed comparisons to patterns inferred from the in silico simulation of a polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) protocol used widely.
The larger sample of MSP-3α diversity revealed incongruence between the observed levels of nucleotide polymorphism, which were high in all populations, and the pattern of PCR-RFLP haplotype diversity. Indeed, PCR-RFLP haplotypes were not informative of a population's genetic diversity and identical haplotypes could be produced from analogous bands in the commonly used protocol. Evidence of frequent and variable insertion-deletion mutations and recurrent recombination between MSP-3α haplotypes complicated the inference of genetic diversity patterns and reduced the phylogenetic signal.
The genetic diversity of P. vivax msp-3α involves intragenic recombination events. Whereas the high genetic diversity of msp-3α makes it a promising marker for some epidemiological applications, the ability of msp-3α PCR-RFLP analysis to accurately track parasites is limited. Local studies of the circulating alleles are needed before implementing PCR-RFLP approaches. Furthermore, evidence from the global sample analysed here suggests such msp-3α PCR-RFLP methods are not suitable for broad geographic studies or tracking parasite populations for an extended period of time.
就地理位置而言，间日疟原虫是最广泛的人类疟原虫，被认为对旨在控制和消除疟疾的当地工作提出了独特的挑战。寄生虫分子标记可以提供对间日疟原虫种群非常需要的数据，但很少有这样的标记受到严格评估。一个被广泛使用的标记是编码裂殖子表面蛋白 3-阿尔法（MSP-3α）的基因，这是一种已知在间日疟原虫分离株中高度变异的血期抗原。在这里，分析了一组完整的 msp-3α 基因序列，以评估其作为流行病学研究分子标记的效用。
从不同地理位置扩增、克隆和测序了更多的间日疟原虫分离株，包括一组委内瑞拉现场分离株（n=10），获得了 48 个完整的 msp-3α 编码序列。进行了多样性的标准群体遗传特征描述、系统发育分析和重组测试。这允许与从广泛使用的聚合酶链反应限制性片段长度多态性（PCR-RFLP）协议的计算机模拟推断的模式进行比较。
更大的 MSP-3α 多样性样本显示出观察到的核苷酸多态性水平与 PCR-RFLP 单倍型多样性模式之间存在不一致。事实上，PCR-RFLP 单倍型与群体的遗传多样性无关，并且通常使用的协议中类似的条带可以产生相同的单倍型。MSP-3α 单倍型之间频繁和可变的插入-缺失突变和反复重组的证据使遗传多样性模式的推断复杂化，并降低了系统发育信号。
间日疟原虫 msp-3α 的遗传多样性涉及基因内重组事件。虽然 msp-3α 的高遗传多样性使其成为一些流行病学应用的有前途的标记，但 msp-3α PCR-RFLP 分析准确跟踪寄生虫的能力有限。在实施 PCR-RFLP 方法之前，需要对循环等位基因进行局部研究。此外，这里分析的全球样本中的证据表明，这种 msp-3α PCR-RFLP 方法不适合广泛的地理研究或在较长时间内跟踪寄生虫种群。
