Did malaria rapid tests miss parasites with two gene deletions in Malawi?

Details

Histidine Rich Protein 2-based rapid diagnostic tests (HRP2-based RDTs) are widely used to diagnose malaria in Malawi, but parasites of the species Plasmodium falciparum lacking the pfhrp2 and pfhrp3 genes may compromise their accuracy. Such deletions had been reported in other malaria-endemic countries, but their presence and diagnostic impact in Malawi were unknown. The study aimed to determine the prevalence of these deletions in Malawi and their effect on HRP2-based RDT accuracy relative to light microscopy and qPCR.

In a cross-sectional study from December 2020 to June 2021, researchers enrolled 1,582 participants from referral hospitals in Mzuzu (1,186) and Lilongwe (396). Malaria was diagnosed using RDTs, microscopy and qPCR. Researchers analyzed 391 P. falciparum-positive samples for pfhrp2 and pfhrp3 deletions using multiplex qPCR. Sensitivity, specificity and other diagnostic accuracy measures were calculated with 95% confidence intervals. Spearman correlation was used to assess associations involving log-transformed parasitemia, unpaired t-tests to compare diagnostic methods, and Mann-Whitney tests to compare symptomatic and asymptomatic groups.

Malaria prevalence was higher in Lilongwe (45.2%) than in Mzuzu (22.9%). In Lilongwe, 94.2% of infections were asymptomatic, whereas 97.1% of cases in Mzuzu were symptomatic (P < 0.0002). RDT sensitivity was higher than microscopy sensitivity: 78.5% (95% CI: 74.6–82.1%) versus 64.8% (95% CI: 60.3–69.1%). RDT specificity was slightly lower: 93.6% (95% CI: 92.0–95.0%) versus 95.4% (95% CI: 94.0–96.6%) for microscopy.

Dual pfhrp2/3 deletions were found in 24 isolates from Lilongwe (15.0%) and 24 from Mzuzu (10.4%). All dual-deleted samples were false negative by RDT but positive by microscopy and qPCR. The authors describe this as the first report of pfhrp2/3 deletions in Malawi. They conclude that these deletions may compromise HRP2-based RDT performance and that diagnostic strategies in affected regions need reassessment.