Department of Biology, Faculty of Science and Technology, University of Nairobi, Nairobi, Kenya.
Sub-Saharan Africa International Centre for Excellence in Malaria Research, Homa Bay, Kenya.
PLoS One. 2022 Apr 7;17(4):e0266394. doi: 10.1371/journal.pone.0266394. eCollection 2022.
Leading transmission-blocking vaccine candidates such as Plasmodium falciparum surface protein 25 (Pfs25 gene) may undergo antigenic alterations which may render them ineffective or allele-specific. This study examines the level of genetic diversity, signature of selection and drivers of Pfs25 polymorphisms of parasites population in regions of western Kenya with varying malaria transmission intensities.
Dry blood spots (DBS) were collected in 2018 and 2019 from febrile outpatients with malaria at health facilities in malaria-endemic areas of Homa Bay, Kisumu (Chulaimbo) and the epidemic-prone highland area of Kisii. Parasites DNA were extracted from DBS using Chelex method. Species identification was performed using real-time PCR. The 460 base pairs (domains 1-4) of the Pfs25 were amplified and sequenced for a total of 180 P. falciparum-infected blood samples.
Nine of ten polymorphic sites were identified for the first time. Overall, Pfs25 exhibited low nucleotide diversity (0.04×10-2) and low mutation frequencies (1.3% to 7.7%). Chulaimbo had the highest frequency (15.4%) of mutated sites followed by Kisii (6.7%) and Homa Bay (5.1%). Neutrality tests of Pfs25 variations showed significant negative values of Tajima's D (-2.15, p<0.01) and Fu's F (-10.91, p<0.001) statistics tests. Three loci pairs (123, 372), (364, 428) and (390, 394) were detected to be under linkage disequilibrium and none had history of recombination. These results suggested that purifying selection and inbreeding might be the drivers of the observed variation in Pfs25.
Given the low level of nucleotide diversity, it is unlikely that a Pfs25 antigen-based vaccine would be affected by antigenic variations. However, continued monitoring of Pfs25 immunogenic domain 3 for possible variants that might impact vaccine antibody binding is warranted.
领先的阻断传播疫苗候选物，如恶性疟原虫表面蛋白 25（PfS25 基因），可能会发生抗原改变，从而使它们无效或具有等位基因特异性。本研究检查了肯尼亚西部疟疾传播强度不同地区寄生虫群体中 PfS25 多态性的遗传多样性水平、选择特征和驱动因素。
2018 年和 2019 年，从霍马湾、基苏木（楚拉伊博姆）和基西高发地区的疟疾流行地区的卫生设施中采集发热门诊的干血斑（DBS）。使用 Chelex 法从 DBS 中提取寄生虫 DNA。使用实时 PCR 进行物种鉴定。对 180 份感染恶性疟原虫的血样进行 PfS25 的 460 个碱基对（结构域 1-4）扩增和测序。
首次发现了十个多态性位点中的九个。总的来说，PfS25 表现出低核苷酸多样性（0.04×10-2）和低突变频率（1.3%至 7.7%）。楚拉伊博姆的突变位点频率最高（15.4%），其次是基西（6.7%）和霍马湾（5.1%）。PfS25 变异的中性检验显示 Tajima 的 D （-2.15，p<0.01）和 Fu 的 F （-10.91，p<0.001）统计检验的显著负值。检测到三个基因座对（123、372）、（364、428）和（390、394）处于连锁不平衡状态，且均无重组史。这些结果表明，纯化选择和近亲繁殖可能是 PfS25 观察到的变异的驱动因素。
鉴于核苷酸多样性水平较低，基于 PfS25 抗原的疫苗不太可能受到抗原变异的影响。然而，需要继续监测 PfS25 免疫原性结构域 3 中可能影响疫苗抗体结合的可能变体。
