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Background  Malaria rapid diagnostic tests (RDTs) have greatly improved access to diagnosis in endemic countries. Most RDTs detect  Plasmodium falciparum  histidine-rich protein 2 (HRP2), but their sensitivity is seriously threatened by the emergence of  pfhrp2 -deleted parasites. RDTs detecting  P. falciparum  or pan-lactate dehydrogenase (Pf- or pan-LDH) provide alternatives. The objective of this study was to systematically assess the performance of malaria RDTs against well-characterized  pfhrp2 -deleted  P. falciparum  parasites.    Methods  Thirty-two RDTs were tested against 100 wild-type clinical isolates (200 parasites/µL), and 40 samples from 10 culture-adapted and clinical isolates of  pfhrp2 -deleted parasites. Wild-type and  pfhrp2 -deleted parasites had comparable Pf-LDH concentrations. Pf-LDH-detecting RDTs were also tested against 18 clinical isolates at higher density (2,000 parasites/µL) lacking both  pfhrp2  and  pfhrp3.Results  RDT positivity against  pfhrp2 -deleted parasites was highest (> 94%) for the two pan-LDH-only RDTs. The positivity rate for the nine Pf-LDH-detecting RDTs varied widely, with similar median positivity between double-deleted ( pfhrp2/3  negative; 63.9%) and single-deleted ( pfhrp2 -negative/ pfhrp3 -positive; 59.1%) parasites, both lower than against wild-type  P. falciparum  (93.8%). Median positivity for HRP2-detecting RDTs against 22 single-deleted parasites was 69.9 and 35.2% for HRP2-only and HRP2-combination RDTs, respectively, compared to 96.0 and 92.5% for wild-type parasites. Eight of nine Pf-LDH RDTs detected all clinical, double-deleted samples at 2,000 parasites/µL.    Conclusions  The pan-LDH-only RDTs evaluated performed well. Performance of Pf-LDH-detecting RDTs against wild-type  P. falciparum  does not necessarily predict performance against  pfhrp2 -deleted parasites. Furthermore, many, but not all HRP2-based RDTs, detect  pfhrp2 -negative/ pfhrp3 -positive samples, with implications for the HRP2-based RDT screening approach for detection and surveillance of HRP2-negative parasites.

Impact of Plasmodium falciparum gene deletions on malaria rapid diagnostic test performance