Department of Molecular Tropical Medicine and Genetics, Faculty of Tropical Medicine, Mahidol University, Bangkok, 10400, Thailand.
Mahidol Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.
Malar J. 2018 Jul 16;17(1):269. doi: 10.1186/s12936-018-2413-3.
Plasmodium malariae is characterized by its long asymptomatic persistence in the human host. The epidemiology of P. malariae is incompletely understood and is hampered by the limited knowledge of genetic polymorphisms. Previous reports from Africa have shown heterogeneity within the P. malariae circumsporozoite protein (pmcsp) gene. However, comparative studies from Asian countries are lacking. Here, the genetic polymorphisms in pmcsp of Asian isolates have been characterized.
Blood samples from 89 symptomatic P. malariae-infected patients were collected, from Thailand (n = 43), Myanmar (n = 40), Lao PDR (n = 5), and Bangladesh (n = 1). pmcsp was amplified using semi-nested PCR before sequencing. The resulting 89 pmcsp sequences were analysed together with 58 previously published pmcsp sequences representing African countries using BioEdit, MEGA6, and DnaSP.
Polymorphisms identified in pmcsp were grouped into 3 populations: Thailand, Myanmar, and Kenya. The nucleotide diversity and the ratio of nonsynonymous to synonymous substitutions (dN/dS) in Thailand and Myanmar were higher compared with that in Kenya. Phylogenetic analysis showed clustering of pmcsp sequences according to the origin of isolates (Asia vs. Africa). High genetic differentiation (Fst = 0.404) was observed between P. malariae isolates from Asian and African countries. Sequence analysis of pmcsp showed the presence of tetrapeptide repeat units of NAAG, NDAG, and NAPG in the central repeat region of the gene. Plasmodium malariae isolates from Asian countries carried fewer copies of NAAG compared with that from African countries. The NAPG repeat was only observed in Asian isolates. Additional analysis of 2 T-cell epitopes, Th2R and Th3R, showed limited heterogeneity in P. malariae populations.
This study provides valuable information on the genetic polymorphisms in pmcsp isolates from Asia and advances our understanding of P. malariae population in Asia and Africa. Polymorphisms in the central repeat region of pmcsp showed association with the geographical origin of P. malariae isolates and can be potentially used as a marker for genetic epidemiology of P. malariae population.
疟原虫恶性疟原虫的特点是在人体宿主中无症状持续存在时间长。疟原虫恶性疟原虫的流行病学尚未完全了解，这是由于对遗传多态性的了解有限。来自非洲的先前报告显示，疟原虫恶性疟原虫环子孢子蛋白（pmcsp）基因内存在异质性。然而，来自亚洲国家的比较研究则缺乏。在此，对亚洲分离株中 pmcsp 的遗传多态性进行了特征描述。
采集来自泰国（n=43）、缅甸（n=40）、老挝人民民主共和国（n=5）和孟加拉国（n=1）的 89 例有症状的疟原虫恶性疟原虫感染患者的血液样本。使用半巢式 PCR 扩增 pmcsp 后进行测序。将 89 个 pmcsp 序列与代表非洲国家的 58 个先前发表的 pmcsp 序列一起使用 BioEdit、MEGA6 和 DnaSP 进行分析。
在 pmcsp 中鉴定出的多态性分为 3 个群体：泰国、缅甸和肯尼亚。与肯尼亚相比，泰国和缅甸的核苷酸多样性和非同义与同义替换比（dN/dS）更高。系统发育分析显示，根据分离株的起源（亚洲与非洲）对 pmcsp 序列进行聚类。亚洲和非洲国家的疟原虫恶性疟原虫分离株之间观察到高遗传分化（Fst=0.404）。序列分析显示，在基因的中央重复区存在 NAAG、NDAG 和 NAPG 四肽重复单元。与非洲国家相比，亚洲国家的疟原虫恶性疟原虫分离株携带的 NAAG 拷贝数较少。仅在亚洲分离株中观察到 NAPG 重复。对 2 个 T 细胞表位 Th2R 和 Th3R 的进一步分析表明，疟原虫恶性疟原虫群体的异质性有限。
本研究提供了有关亚洲 pmcsp 分离株遗传多态性的有价值信息，并增进了我们对亚洲和非洲疟原虫恶性疟原虫种群的了解。pmcsp 中央重复区的多态性与疟原虫恶性疟原虫分离株的地理起源有关，可作为疟原虫恶性疟原虫种群遗传流行病学的潜在标志物。
