Jomo Kenyatta University of Agriculture and Technology, Nairobi, Kenya.
National Institute for Medical Research, Tanga Research Centre, Tanga, Tanzania.
Malar J. 2020 Nov 4;19(1):391. doi: 10.1186/s12936-020-03459-3.
Histidine-rich protein 2 (HRP2)-based malaria rapid diagnostic tests (RDTs) are effective and widely used for the detection of wild-type Plasmodium falciparum infections. Although recent studies have reported false negative HRP2 RDT results due to pfhrp2 and pfhrp3 gene deletions in different countries, there is a paucity of data on the deletions of these genes in Tanzania.
A community-based cross-sectional survey was conducted between July and November 2017 in four regions: Geita, Kigoma, Mtwara and Ruvuma. All participants had microscopy and RDT performed in the field and provided a blood sample for laboratory multiplex antigen detection (for Plasmodium lactate dehydrogenase, aldolase, and P. falciparum HRP2). Samples showing RDT false negativity or aberrant relationship of HRP2 to pan-Plasmodium antigens were genotyped to detect the presence/absence of pfhrp2/3 genes.
Of all samples screened by the multiplex antigen assay (n = 7543), 2417 (32.0%) were positive for any Plasmodium antigens while 5126 (68.0%) were negative for all antigens. The vast majority of the antigen positive samples contained HRP2 (2411, 99.8%), but 6 (0.2%) had only pLDH and/or aldolase without HRP2. Overall, 13 samples had an atypical relationship between a pan-Plasmodium antigen and HRP2, but were positive by PCR. An additional 16 samples with negative HRP2 RDT results but P. falciparum positive by microscopy were also chosen for pfhrp2/3 genotyping. The summation of false negative RDT results and laboratory antigen results provided 35 total samples with confirmed P. falciparum DNA for pfhrp2/3 genotyping. Of the 35 samples, 4 (11.4%) failed to consistently amplify positive control genes; pfmsp1 and pfmsp2 and were excluded from the analysis. The pfhrp2 and pfhrp3 genes were successfully amplified in the remaining 31 (88.6%) samples, confirming an absence of deletions in these genes.
This study provides evidence that P. falciparum parasites in the study area have no deletions of both pfhrp2 and pfhrp3 genes. Although single gene deletions could have been missed by the multiplex antigen assay, the findings support the continued use of HRP2-based RDTs in Tanzania for routine malaria diagnosis. There is a need for the surveillance to monitor the status of pfhrp2 and/or pfhrp3 deletions in the future.
组氨酸丰富蛋白 2（HRP2）-基于疟疾快速诊断检测（RDT）是有效的，广泛用于检测野生型疟原虫感染。虽然最近的研究报告了由于 pfhrp2 和 pfhrp3 基因缺失导致的假阴性 HRP2 RDT 结果，但在坦桑尼亚，这些基因缺失的数据很少。
2017 年 7 月至 11 月在四个地区（盖塔、基戈马、姆特瓦拉和鲁伍马）进行了一项基于社区的横断面调查。所有参与者均在现场进行显微镜检查和 RDT，并提供了一份血液样本进行实验室多重抗原检测（用于检测疟原虫乳酸脱氢酶、醛缩酶和 P. falciparum HRP2）。显示 RDT 假阴性或 HRP2 与泛疟原虫抗原关系异常的样本进行基因分型，以检测 pfhrp2/3 基因的存在/缺失。
在通过多重抗原检测筛查的所有样本中（n=7543），2417 个（32.0%）样本对任何疟原虫抗原呈阳性，5126 个（68.0%）样本对所有抗原均呈阴性。绝大多数抗原阳性样本含有 HRP2（2411 个，99.8%），但有 6 个（0.2%）仅含有 pLDH 和/或 aldolase 而没有 HRP2。总体而言，有 13 个样本的泛疟原虫抗原与 HRP2 之间存在非典型关系，但 PCR 呈阳性。另外还有 16 个 HRP2 RDT 结果阴性但显微镜检查为恶性疟原虫阳性的样本也选择进行 pfhrp2/3 基因分型。阴性 HRP2 RDT 结果和实验室抗原结果的总和为 35 个确认恶性疟原虫 DNA 的样本，用于 pfhrp2/3 基因分型。在 35 个样本中，有 4 个（11.4%）未能一致扩增阳性对照基因；pfmsp1 和 pfmsp2 被排除在分析之外。在其余 31 个（88.6%）样本中成功扩增了 pfhrp2 和 pfhrp3 基因，证实这些基因不存在缺失。
本研究提供了证据表明，研究地区的恶性疟原虫寄生虫没有 pfhrp2 和 pfhrp3 基因的缺失。尽管多重抗原检测可能漏掉了单个基因缺失，但研究结果支持在坦桑尼亚继续使用基于 HRP2 的 RDT 进行常规疟疾诊断。未来需要进行监测，以监测 pfhrp2 和/或 pfhrp3 缺失的情况。
