# Diagnostic challenges of histidine-rich protein 2-based rapid diagnostic tests due to pfhrp2 and pfhrp3 gene deletions in asymptomatic malaria in Tanzania

## TL;DR

This study in Tanzania shows that HRP2-based malaria tests are mostly effective for asymptomatic cases, but gene deletions in some parasites can cause false negatives, highlighting the need for ongoing monitoring.

## Contribution

The study evaluates the impact of pfhrp2/3 gene deletions on HRP2-based RDT performance in asymptomatic malaria in Tanzania.

## Key findings

- HRP2-based RDTs detected 77.6% of qPCR-positive cases, with higher sensitivity than light microscopy.
- Gene deletions were found in 11.8% of samples, with higher prevalence in high-transmission areas.
- RDTs showed substantial agreement with qPCR, but dual-deletion isolates were all RDT-negative.

## Abstract

Histidine-rich protein 2 (HRP2)-based rapid diagnostic tests (RDTs) are critical for malaria diagnosis in Africa, particularly in resource-limited settings. However, the spread of Plasmodium falciparum parasites with pfhrp2 and pfhrp3 gene deletions challenges their effectiveness, raising concerns in affected areas. Therefore, this study aimed to assess the prevalence of pfhrp2 and pfhrp3 gene deletions and evaluate the diagnostic performance of HRP2-based RDTs in detecting asymptomatic malaria infections in Tanzania.

This cross-sectional community survey study aimed to determine the prevalence of pfhrp2/3 gene deletions from asymptomatic malaria population in Tanzania. Moreover, the study intended to assess the performance of HRP2-based RDT and light microscopy (LM) in detecting asymptomatic malaria infections. The survey was conducted from December 2022 to July 2023 in twelve villages (8 villages from high malaria transmission areas and 4 in low endemicity). Diagnosis was done by RDT, LM and quantitative polymerase chain reaction (qPCR). A multiplex qPCR was employed on P. falciparum mono-infection isolates to assess the prevalence of pfhrp2/3 gene deletions. Unpaired t-tests and one-way ANOVA were performed to evaluate associations between log10-transformed parasitaemia levels and gene deletion profiles.

Among 3489 participants, RDT detected 710 (77.6%) of 915 qPCR-positive cases, compared to 492 (53.8%) by LM. Compared with qPCR, RDT produced 143 (5.6%) false positives and 205 (22.4%) false negatives, whereas LM had 60 (2.3%) false positives and 423 (46.2%) false negatives. Overall accuracy was similar for RDT (90.0%) and LM (86.2%), with higher sensitivity for RDT. Agreement with qPCR in asymptomatic cases was substantial for RDT (κ = 0.736), whereas it was moderate for LM (κ = 0.590). Multiplex qPCR revealed pfhrp2 or pfhrp3 deletions in 93 (11.8%) of 787 samples, including 19 (2.4%) dual-deletion isolates, all of which were RDT negative. Deletions were more frequent in high-transmission villages (76 cases, 9.7%) than in low-transmission villages (17 cases, 2.2%).

The findings support the continued effectiveness of HRP2-based RDTs in detecting asymptomatic P. falciparum infections in Tanzania, despite the presence of some pfhrp2/3 gene deletions. However, the potential increase in deletion prevalence and the limitations of cross-sectional data highlight the need for ongoing molecular surveillance. Collectively, these findings provide a critical foundation for sustained surveillance and for clarifying the epidemiological significance of asymptomatic malaria in Tanzania.

The online version contains supplementary material available at 10.1186/s40249-025-01397-3.