US Army Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand.
Ministry of Public Health (MoPH), Vector Borne Disease Control Center 12.1, Yala, Thailand.
Malar J. 2022 May 6;21(1):142. doi: 10.1186/s12936-022-04167-w.
While human cases of Plasmodium knowlesi are now regularly recognized in Southeast Asia, infections with other simian malaria species, such as Plasmodium cynomolgi, are still rare. There has been a handful of clinical cases described, all from Malaysia, and retrospective studies of archived blood samples in Thailand and Cambodia have discovered the presence P. cynomolgi in isolates using polymerase chain reaction (PCR) assays.
In Thailand, an ongoing malaria surveillance study enrolled two patients from Yala Province diagnosed with Plasmodium vivax by blood smear, but who were subsequently found to be negative by PCR. Expanded PCR testing of these isolates detected mono-infection with P. cynomolgi, the first time this has been reported in Thailand. Upon re-testing of 60 isolates collected from Yala, one other case was identified, a co-infection of P. cynomolgi and P. vivax. The clinical course for all three was relatively mild, with symptoms commonly seen in malaria: fever, chills and headaches. All infections were cured with a course of chloroquine and primaquine.
In malaria-endemic areas with macaque populations, cases of simian malaria in humans are being reported at an increasing rate, although still comprise a very small percentage of total cases. Plasmodium cynomolgi and P. vivax are challenging to distinguish by blood smear; therefore, PCR can be employed when infections are suspected or as part of systematic malaria surveillance. As Thai MoPH policy schedules regular follow-up visits after each malaria infection, identifying those with P. cynomolgi will allow for monitoring of treatment efficacy, although at this time P. cynomolgi appears to have an uncomplicated clinical course and good response to commonly used anti-malarials.
虽然现在东南亚经常发现人类感染疟原虫 knowlesi 的病例，但感染其他灵长类疟原虫，如疟原虫 cynomolgi 的情况仍然很少见。虽然已经有少数临床病例报告，但均来自马来西亚，对泰国和柬埔寨存档血液样本的回顾性研究发现，使用聚合酶链反应 (PCR) 检测，这些样本中存在疟原虫 cynomolgi。
在泰国，一项正在进行的疟疾监测研究招募了两名来自也拉府的患者，他们的血液涂片诊断为间日疟原虫，但随后 PCR 检测结果为阴性。对这些分离株进行扩展 PCR 检测，发现了疟原虫 cynomolgi 的单一感染，这是在泰国首次报告。对也拉收集的 60 个分离株进行重新检测，又发现了 1 例感染，为疟原虫 cynomolgi 和间日疟原虫的混合感染。所有三种感染的临床过程都相对较轻，症状通常见于疟疾：发热、寒战和头痛。所有感染均经氯喹和伯氨喹治疗治愈。
在有猕猴种群的疟疾流行地区，人类感染灵长类疟原虫的报告率正在增加，尽管仍占总病例的很小比例。疟原虫 cynomolgi 和间日疟原虫通过血液涂片难以区分；因此，在怀疑感染时或作为系统疟疾监测的一部分，可以使用 PCR。由于泰国卫生部的政策规定每次疟疾感染后都要定期随访，因此确定是否感染疟原虫 cynomolgi 将有助于监测治疗效果，尽管目前疟原虫 cynomolgi 似乎具有简单的临床过程和对常用抗疟药物的良好反应。
