Aklilu Lemma Institute of Pathobiology, Addis Ababa University, Addis Ababa, Ethiopia.
Malar J. 2013 Oct 3;12:352. doi: 10.1186/1475-2875-12-352.
Prompt and effective malaria diagnosis not only alleviates individual suffering, but also decreases malaria transmission at the community level. The commonly used diagnostic methods, microscopy and rapid diagnostic tests, are usually insensitive at very low-density parasitaemia. Molecular techniques, on the other hand, allow the detection of low-level, sub-microscopic parasitaemia. This study aimed to explore the presence of sub-microscopic Plasmodium falciparum infections using polymerase chain reaction (PCR). The PCR-based parasite prevalence was compared against microscopy and rapid diagnostic test (RDT).
This study used 1,453 blood samples collected from clinical patients and sub-clinical subjects to determine the prevalence of sub-microscopic P. falciparum carriages. Subsets of RDT and microscopy negative blood samples were tested by PCR while all RDT and microscopically confirmed P. falciparum-infected samples were subjected to PCR. Finger-prick blood samples spotted on filter paper were used for parasite genomic DNA extraction.
The prevalence of sub-microscopic P. falciparum carriage was 19.2% (77/400) (95% CI = 15. 4-23.1). Microscopy-based prevalence of P. falciparum infection was 3.7% (54/1,453) while the prevalence was 6.9% (100/1,453) using RDT alone. Using microscopy and PCR, the estimated parasite prevalence was 20.6% if PCR were performed in 1,453 blood samples. The prevalence was estimated to be 22.7% if RDT and PCR were used. Of 54 microscopically confirmed P. falciparum-infected subjects, PCR detected 90.7% (49/54). Out of 100 RDT-confirmed P. falciparum infections; PCR detected 80.0% (80/100). The sensitivity of PCR relative to microscopy and RDT was, therefore, 90.7% and 80%, respectively. The sensitivity of microscopy and RDT relative to PCR was 16.5 (49/299) and 24.2% (80/330), respectively. The overall PCR-based prevalence of P. falciparum infection was 5.6- and 3.3 fold higher than that determined by microscopy and RDT, respectively. None of the sub-microscopic subjects had severe anaemia, though 29.4% had mild anaemia (10-11.9 g/dl).
Asymptomatic, low-density malaria infection was common in the study area and PCR may be a better tool for measuring Plasmodium prevalence than microscopy and RDT. The inadequate sensitivity of the diagnostic methods to detect substantial number of sub-microscopic parasitaemia would undoubtedly affect malaria control efforts, making reduction of transmission more difficult. RDT and microscopy-based prevalence studies and subsequent reports of reduction in malaria incidence underestimate the true pictures of P. falciparum infections in the community. PCR, on the other hand, seems to have reasonable sensitivity to detect a higher number of infected subjects with low and sub-microscopic parasite densities than RDTs or microscopy.
快速而有效的疟疾诊断不仅可以减轻个体的痛苦，还可以降低社区层面的疟疾传播。常用的诊断方法，如显微镜检查和快速诊断检测，通常对极低密度的疟原虫血症不敏感。另一方面，分子技术可以检测到低水平的亚微观疟原虫血症。本研究旨在探讨聚合酶链反应（PCR）检测恶性疟原虫亚微观感染的情况。将基于 PCR 的寄生虫流行率与显微镜检查和快速诊断检测（RDT）进行比较。
本研究使用了 1453 份来自临床患者和亚临床患者的血液样本，以确定恶性疟原虫亚微观携带的流行率。对 RDT 和显微镜检查阴性的血液样本进行子集 PCR 检测，而所有 RDT 和显微镜确认的恶性疟原虫感染样本均进行 PCR 检测。用指尖采血样在滤纸上斑点，提取寄生虫基因组 DNA。
恶性疟原虫亚微观携带率为 19.2%（77/400）（95%CI=15.4-23.1）。显微镜检查恶性疟原虫感染的流行率为 3.7%（54/1453），而单独使用 RDT 的流行率为 6.9%（100/1453）。如果对 1453 份血液样本进行 PCR 检测，使用显微镜和 PCR 估计的寄生虫流行率为 20.6%。如果使用 RDT 和 PCR，则估计流行率为 22.7%。在 54 例经显微镜证实的恶性疟原虫感染患者中，PCR 检测出 90.7%（49/54）。在 100 例 RDT 确诊的恶性疟原虫感染中；PCR 检测出 80.0%（80/100）。因此，PCR 相对于显微镜和 RDT 的灵敏度分别为 90.7%和 80.0%。显微镜和 RDT 相对于 PCR 的灵敏度分别为 16.5%（49/299）和 24.2%（80/330）。基于 PCR 的恶性疟原虫感染总体流行率分别高于显微镜和 RDT 检测的流行率的 5.6 倍和 3.3 倍。虽然 29.4%的人有轻度贫血（10-11.9 g/dl），但没有亚微观患者出现严重贫血。
在研究区域，无症状、低密度的疟疾感染很常见，PCR 可能是一种比显微镜检查和 RDT 更好的测量疟原虫流行率的工具。诊断方法检测大量亚微观寄生虫血症的敏感性不足，无疑会影响疟疾控制工作，使传播减少更加困难。基于 RDT 和显微镜的流行率研究以及随后报告的疟疾发病率降低，低估了社区中恶性疟原虫感染的真实情况。另一方面，PCR 似乎具有合理的灵敏度，可以检测到比 RDT 或显微镜更高数量的低水平和亚微观寄生虫密度感染的患者。
