High Burden of Asymptomatic Malaria Among Schoolchildren in Nigeria: Diagnosis Challenges and pfhrp2 Deletions

Background: Nigeria has a high prevalence of malaria, with asymptomatic patients being one of the possible reservoirs. In this context, accurate diagnosis is essential for malaria control. The efficacy of rapid diagnostic tests (RDTs) is being threatened by false negatives due to pfhrp2 and pfhrp3 deletions. This study aims to describe malaria in asymptomatic schoolchildren in Osun State, Southwestern Nigeria and to assess the performance of malaria diagnosis, including the characterisation of pfhrp2 and pfhrp3 deletions. Methods: A total of 350 dried blood spot (DBS) samples from schoolchildren were used for malaria diagnosis using microscopy, RDTs, and polymerase chain reaction (PCR). Sensitivity and specificity were calculated for microscopy and RDTs, using PCR as the gold standard. Pfhrp2 and pfhrp3 deletions were analysed for all P. falciparum-positive samples using multiplex qPCR. Results: The P. falciparum infection frequency among asymptomatic schoolchildren in Osun State was 89%. Considering PCR as the gold standard, microscopy presented better sensitivity at 100% (86% for RDTs), but RDTs had better specificity at 76% (60% for microscopy). The deletion frequency of the pfhrp2 gene among positive samples was 16.6%, while it was 1.3% for pfhrp3 and 0.9% for double deletion. However, considering all positive samples, only 3% of samples yielded false negatives by RDT with deletion in pfhrp2. Conclusions: P. falciparum infection has a high frequency in asymptomatic schoolchildren, being a potential hotspot for malaria. The combination of RDTs and microscopy could increase the accuracy of malaria diagnosis. Deletions in pfhrp2 and pfhrp3 are highly common in Osun State, but their impact on RDT results is still limited. More surveillance studies are recommended to assess the contribution of asymptomatic children to malaria transmission and the impact of deletions.