Assessing Performance of HRP2 Antigen Detection for Malaria Diagnosis in Mozambique

Abstract

Rapid diagnostic tests (RDTs) that detect the Plasmodium falciparum-specific histidine-rich protein 2 (PfHRP2) antigen are the primary methods for malaria diagnosis in Mozambique. However, these tests do not detect infections with non-falciparum malaria or Pfhrp2- and Pfhrp3-deleted P. falciparum parasites. To assess the appropriateness of conventional PfHRP2-only RDTs for malaria diagnosis in Mozambique, samples collected during a health facility survey conducted in three provinces of Mozambique were screened using antigen detection methods and further characterized by molecular techniques. Samples from 1,861 outpatients of all ages and symptoms attending 117 randomly selected public health facilities in 2018 were analyzed with an ultrasensitive bead-based immunoassay for the presence of PfHRP2, pan-Plasmodium aldolase (pAldo), and pan-Plasmodium lactate dehydrogenase (pLDH). The presence of PfHRP2 in patient blood detected using the bead-based assay was compared to the results of PfHRP2-based RDTs performed during the routine health facility consult and during the survey reexamination at the exit interview. Samples with discordant antigen profiles (negative for PfHRP2 but positive for pAldo and/or pLDH) were further characterized by photoinduced electron transfer PCR (PET-PCR). Using the bead-based laboratory assay as the gold standard, the sensitivities of the conventional RDTs administered during the routine health facility consult and the exit interview were 90% and 83%, respectively, and the specificities were 91% and 97%, respectively. Of 710 samples positive for at least one antigen, 704 (99.2%) were positive for PfHRP2. Six (0.8% of total) discordant samples lacked PfHRP2 but were positive for pAldo and/or pLDH; 3 of these (0.4% of total) were Plasmodium ovale monoinfections or coinfections where P. ovale was the dominant species. The remaining 3 discordant samples were negative by PET-PCR. The sensitivity and specificity of the conventional RDTs performed in the routine health facility consults and survey exit interviews were acceptable, and there was no evidence of Pfhrp2- and Pfhrp3-deleted parasites. Monoinfections with non-falciparum malaria species comprised <1% of the total malaria infections. Nearly all malaria antigen-positive patients had detectable PfHRP2, confirming that this antigen remains an appropriate malaria diagnostic target in the surveyed provinces.

Keywords: HRP2 deletion; Plasmodium ovale; rapid diagnostic test.