The online version of this article (doi:10.1186/s12936-017-1768-1) contains supplementary material, which is available to authorized users.
Rapid diagnostic tests (RDTs) for histidine rich protein 2 (HRP2) are often used to determine whether persons with fever should be treated with anti-malarials. However, Plasmodium falciparum parasites with a deletion of the hrp2 gene yield false-negative RDTs and there are concerns the sensitivity of HRP2-based RDTs may fall when the intensity of transmission decreases.
This observational study enrolled 9226 patients at three health centres in Rwanda from April 2014 to April 2015. It then compared the sensitivity of RDTs based on HRP2 and the Plasmodium lactate dehydrogenase (pLDH) to microscopy (thick smears) for the diagnosis of malaria. PCR was used to determine whether deletions of the histidine-rich central repeat region of the hrp2 gene (exon 2) were associated with false-negative HRP2-based RDTs.
In comparison to microscopy, the sensitivity and specificity of HRP2- and pLDH-based RDTs were 89.5 and 86.2% and 80.2 and 94.3%, respectively. When the results for both RDTs were combined, sensitivity rose to 91.8% and specificity was 85.7%. Additionally, when smear positivity fell from 46 to 3%, the sensitivity of the HRP2-based RDT fell from 88 to 67%. Of 370 samples with false-negative HRP2 RDT results for which PCR was performed, 140 (38%) were identified as P. falciparum by PCR. Of the isolates identified as P. falciparum by PCR, 32 (23%) were negative for the hrp2 gene based on PCR. Of the 32 P. falciparum isolates negative for hrp2 by PCR, 17 (53%) were positive based on the pLDH RDT.
This prospective study of RDT performance coincided with a decline in the intensity of malaria transmission in Kibirizi (fall in slide positivity from 46 to 3%). This decline was associated with a decrease in HRP2 RDT sensitivity (from 88 to 67%). While P. falciparum isolates without the hrp2 gene were an important cause of false-negative HRP2-based RDTs, most were identified by the pLDH-based RDT. Although WHO does not recommend the use of combined HRP2/pLDH testing in sub-Saharan Africa, these results suggest that combination HRP2/pLDH-based RDTs could reduce the impact of false-negative HRP2-based RDTs for detection of symptomatic P. falciparum malaria.
Additional file 1. Primer sequences used to amplify hrp2 and P. falciparum, P. vivax, P. malariae and P. ovale 18S rRNA, expected product sizes and PCR conditions.
Additional file 2. PCR products visualized on an agarose gel. DNA is from two thick-smear positive subjects with negative HRP2-based RDTs. Lane 1: 100 bp marker. Lane 2: PCR targeting hrp2 with DNA from subject #1 (shows amplicon of expected size of ~900 bp). Lanes 3–5: PCR with DNA from subject #2. Lane 3 shows the absence of hrp2 amplicons. Lane 4 shows results of multiplex PCR for 18S rRNA with an amplicon of 276 bp (expected size for P. falciparum). Lane 5 shows results of nested PCR with species-specific primers for P. falciparum 18S rRNA with an amplicon of the expected size of 205 bp.
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- False-negative malaria rapid diagnostic tests in Rwanda: impact of Plasmodium falciparum isolates lacking hrp2 and declining malaria transmission
Christina T. Kozycki
Emil I. Mwikarago
Jean Pierre Musabyimana
Jean Pierre Habimana
Donald J. Krogstad
- BioMed Central
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