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 10400, Thailand; Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, UK.
Acta Trop. 2024 Jun;254:107187. doi: 10.1016/j.actatropica.2024.107187. Epub 2024 Mar 21.
Over the past year, P. falciparum infections have declined in Thailand, yet nonhuman primate malaria infections have correspondingly increased, including Plasmodium knowlesi and P. cynomolgi. Nevertheless, little is known about simian malaria in its natural macaque hosts, Macaca mulatta and Macaca fascicularis. This study aims to address several research questions, including the prevalence and distribution of simian malaria in these two Thai wild macaque species, variations in infection between different macaque species and between M. fascicularis subspecies, and the genetic composition of these pathogens. Blood samples were collected from 82 M. mulatta and 690 M. fascicularis across 15 locations in Thailand, as well as two locations in Vietnam and Myanmar. We employed quantitative real-time PCR targeting the Plasmodium genus-specific 18S ribosomal RNA (rRNA) gene to detect malaria infection, with a limit of detection set at 1,215.98 parasites per mL. We genotyped eight microsatellite markers, and the P. cynomolgi dihydrofolate reductase gene (DHFR) was sequenced (N = 29). In total, 100 of 772 samples (13 %) tested positive for malaria, including 45 (13 %) for P. cynomolgi, 37 (13 %) for P. inui, 16 (5 %) for P. coatneyi, and 2 (0.25 %) for Hepatocystis sp. in Saraburi, central and Ranong, southern Thailand. Notably, simian malaria infection was observed exclusively in M. fascicularis and not in M. mulatta (P = 0.0002). Particularly, P. cynomolgi was detected in 21.7 % (45/207) of M. f. fascicularis living in Wat Tham Phrapothisat, Saraburi Province. The infection with simian malaria was statistically different between M. fascicularis and M. mulatta (P = 0.0002) but not within M. fascicularis subspecies (P = 0.78). A haplotype network analysis revealed that P. cynomolgi shares a lineage with reference strains obtained from macaques. No mutation in the predicted binding pocket of PcyDHFR to pyrimethamine was observed. This study reveals a significant prevalence of simian malaria infection in M. fascicularis. The clonal genotypes of P. cynomolgi suggest in-reservoir breeding. These findings raise concerns about the potential spread of nonhuman primate malaria to humans and underscore the need for preventive measures.
过去一年，泰国的恶性疟原虫感染有所下降，但灵长类动物疟疾感染相应增加，包括疟原虫 knowlesi 和疟原虫 cynomolgi。然而，人们对猕猴和食蟹猕猴这两种泰国野生猕猴宿主中的猿猴疟疾知之甚少。本研究旨在解决几个研究问题，包括这两种泰国野生猕猴物种中猿猴疟疾的流行率和分布情况、不同猕猴物种之间以及食蟹猕猴亚种之间的感染差异，以及这些病原体的遗传组成。从泰国 15 个地点以及越南和缅甸的两个地点采集了 82 只猕猴和 690 只食蟹猕猴的血液样本。我们采用针对疟原虫属特异性 18S 核糖体 RNA（rRNA）基因的定量实时 PCR 来检测疟疾感染，检测限设定为每毫升 1,215.98 个寄生虫。我们对 8 个微卫星标记进行了基因分型，并对 29 个疟原虫 cynomolgi 二氢叶酸还原酶基因（DHFR）进行了测序。总共，772 个样本中有 100 个（13%）检测出疟疾阳性，其中 45 个（13%）为疟原虫 cynomolgi，37 个（13%）为疟原虫 inui，16 个（5%）为疟原虫 coatneyi，2 个（0.25%）为泰国萨拉布里省 Wat Tham Phrapothisat 中发现的肝胞球虫。值得注意的是，猿猴疟疾感染仅在食蟹猕猴中观察到，而在猕猴中未观察到（P = 0.0002）。特别是，在萨拉布里省 Wat Tham Phrapothisat 生活的 207 只食蟹猕猴中，有 21.7%（45 只）检测到疟原虫 cynomolgi。猿猴疟疾感染在食蟹猕猴和猕猴之间存在统计学差异（P = 0.0002），但在食蟹猕猴亚种内不存在差异（P = 0.78）。单倍型网络分析表明，疟原虫 cynomolgi 与从猕猴中获得的参考株共享一个谱系。没有观察到 PcyDHFR 对乙胺嘧啶的预测结合口袋中的突变。本研究表明，食蟹猕猴中存在显著的猿猴疟疾感染流行率。疟原虫 cynomolgi 的无性系基因型表明在水库中繁殖。这些发现引起了人们对非人类灵长类动物疟疾向人类传播的潜在担忧，并强调了采取预防措施的必要性。
