Environmental Health Institute, National Environment Agency, Singapore.
Parasitology Department, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia.
PLoS Negl Trop Dis. 2021 Jan 25;15(1):e0009110. doi: 10.1371/journal.pntd.0009110. eCollection 2021 Jan.
Plasmodium knowlesi is a simian malaria parasite currently recognized as the fifth causative agent of human malaria. Recently, naturally acquired P. cynomolgi infection in humans was also detected in Southeast Asia. The main reservoir of both parasites is the long-tailed and pig-tailed macaques, which are indigenous in this region. Due to increased urbanization and changes in land use, there has been greater proximity and interaction between the long-tailed macaques and the general population in Singapore. As such, this study aims to determine the prevalence of simian malaria parasites in local macaques to assess the risk of zoonosis to the general human population. Screening for the presence of malaria parasites was conducted on blood samples from 660 peridomestic macaques collected between Jan 2008 and Mar 2017, and 379 wild macaques collected between Mar 2009 and Mar 2017, using a Pan-Plasmodium-genus specific PCR. Positive samples were then screened using a simian Plasmodium species-specific nested PCR assay to identify the species of parasites (P. knowlesi, P. coatneyi, P. fieldi, P. cynomolgi, and P. inui) present. All the peridomestic macaques sampled were tested negative for malaria, while 80.5% of the 379 wild macaques were infected. All five simian Plasmodium species were detected; P. cynomolgi being the most prevalent (71.5%), followed by P. knowlesi (47.5%), P. inui (42.0%), P. fieldi (32.5%), and P. coatneyi (28.5%). Co-infection with multiple species of Plasmodium parasites was also observed. The study revealed that Singapore's wild long-tailed macaques are natural hosts of the five simian malaria parasite species, while no malaria was detected in all peridomestic macaques tested. Therefore, the risk of simian malaria transmission to the general human population is concluded to be low. However, this can be better demonstrated with the incrimination of the vectors of simian malaria parasites in Singapore.
疟原虫 knowlesi 是一种灵长类疟疾寄生虫，目前被认为是人类疟疾的第五种病原体。最近，东南亚也发现了人类自然感染疟原虫 cynomolgi。这两种寄生虫的主要宿主是长尾猕猴和猪尾猕猴，它们是该地区的本地物种。由于城市化的增加和土地利用的变化，长尾猕猴与新加坡的普通人群之间的距离更近，互动更多。因此，本研究旨在确定当地猕猴中灵长类疟疾寄生虫的流行率，以评估向普通人群传播的风险。2008 年 1 月至 2017 年 3 月期间，从 660 只圈养猕猴和 2009 年 3 月至 2017 年 3 月期间从 379 只野生猕猴采集的血液样本中，使用泛疟原虫属特异性 PCR 进行疟疾寄生虫存在的筛查。对阳性样本进行灵长类疟原虫种特异性巢式 PCR 检测，以鉴定存在的寄生虫种类（疟原虫 knowlesi、疟原虫 coatneyi、疟原虫 fieldi、疟原虫 cynomolgi 和疟原虫 inui）。所有圈养猕猴的样本均检测为疟疾阴性，而 379 只野生猕猴中有 80.5%感染。共检测到五种灵长类疟原虫，其中疟原虫 cynomolgi 最为常见（71.5%），其次是疟原虫 knowlesi（47.5%）、疟原虫 inui（42.0%）、疟原虫 fieldi（32.5%）和疟原虫 coatneyi（28.5%）。还观察到多种疟原虫寄生虫的混合感染。该研究表明，新加坡的野生长尾猕猴是五种灵长类疟原虫的天然宿主，而所有检测的圈养猕猴均未发现疟疾。因此，结论是灵长类疟疾向普通人群传播的风险较低。然而，如果能够确定新加坡灵长类疟疾寄生虫的媒介，这一结论可以得到更好的证明。
