Molecular Biology of Malaria and Opportunistic Parasites Research Unit, Department of Parasitology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand.
Malar J. 2010 Mar 9;9:72. doi: 10.1186/1475-2875-9-72.
Definite diagnosis of malaria relies on microscopy detection of blood stages of parasites in peripheral blood and requires blood sample collection. The nested PCR method has shown to be more sensitive and superior to microscopy in detecting co-infections of Plasmodium species in circulation while Plasmodium falciparum DNA can be identified in urine and saliva specimens of patients, albeit at a lower sensitivity.
Matched blood, saliva and urine samples were collected from 100 microscopy-positive and 20 microscopy-negative febrile patients who attended a malaria clinic in Tak Province, northwestern Thailand for nested PCR analysis targeting the small subunit ribosomal RNA gene of human malaria. Both P. falciparum and Plasmodium vivax have been known to circulate at a comparable rate in the study area.
Comparing with microscopy results, nested PCR of saliva samples had a sensitivity of 74.1% for P. falciparum detection and 84% for P. vivax detection while 44.4% and 34.0% of the corresponding values were observed for urine samples. Both nested PCR results of saliva and urine samples had a specificity of 100% for identification of P. falciparum and P. vivax when compared with nested PCR results from blood. Co-infections of both species were found in four, 26 and 8 patients by microscopy and nested PCR of blood and saliva samples, respectively. Although the positive rates of nested PCR of saliva samples for P. falciparum increased with parasite density, no tendency occurred in results from nested PCR of saliva samples for P. vivax as well as those of urine samples.
Saliva and urine samples could be alternative noninvasive sources of DNA for molecular detection of both P. falciparum and P. vivax. Further improvement of the detection method will offer an opportunity to use these samples for diagnosis of malaria.
疟疾的明确诊断依赖于外周血中寄生虫血期的显微镜检测，需要采集血样。巢式 PCR 方法已被证明比显微镜更敏感，更能检测循环中疟原虫种的合并感染，而疟原虫 falciparum DNA 可在患者的尿液和唾液标本中检测到，尽管敏感性较低。
从 100 例显微镜阳性和 20 例显微镜阴性发热患者中采集匹配的血液、唾液和尿液样本，这些患者在泰国西北部 Tak 省的疟疾诊所就诊，进行针对人疟疾小亚基核糖体 RNA 基因的巢式 PCR 分析。已知在研究区域中，恶性疟原虫和间日疟原虫的流行率相当。
与显微镜结果相比，唾液样本的巢式 PCR 对恶性疟原虫的检测灵敏度为 74.1%，对间日疟原虫的检测灵敏度为 84%，而尿液样本的相应值分别为 44.4%和 34.0%。与血液样本的巢式 PCR 结果相比，唾液和尿液样本的巢式 PCR 结果对恶性疟原虫和间日疟原虫的鉴定均具有 100%的特异性。通过显微镜和血液及唾液样本的巢式 PCR 分别在 4 例、26 例和 8 例患者中发现了两种虫种的合并感染。尽管唾液样本中恶性疟原虫巢式 PCR 的阳性率随寄生虫密度的增加而增加，但唾液样本中间日疟原虫巢式 PCR 以及尿液样本的结果均无此趋势。
唾液和尿液样本可能是用于分子检测恶性疟原虫和间日疟原虫的非侵入性替代 DNA 来源。该检测方法的进一步改进将为使用这些样本诊断疟疾提供机会。
