AUTHOR=Tan Angelica F. , Sakam Sitti Saimah binti , Rajahram Giri S. , William Timothy , Abd Rachman Isnadi Mohammad Faruq , Daim Sylvia , Barber Bridget E. , Kho Steven , Sutherland Colin J. , Anstey Nicholas M. , Yerlikaya Seda , van Schalkwyk Donelly A. , Grigg Matthew J. 

TITLE=Diagnostic accuracy and limit of detection of ten malaria parasite lactate dehydrogenase-based rapid tests for Plasmodium knowlesi and P. falciparum

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=12

YEAR=2022

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2022.1023219

DOI=10.3389/fcimb.2022.1023219

ISSN=2235-2988

ABSTRACT=<sec><title>Background</title><p><italic>Plasmodium knowlesi</italic> causes zoonotic malaria across Southeast Asia. First-line diagnostic microscopy cannot reliably differentiate <italic>P. knowlesi</italic> from other human malaria species. Rapid diagnostic tests (RDTs) designed for <italic>P. falciparum</italic> and <italic>P. vivax</italic> are used routinely in <italic>P. knowlesi</italic> co-endemic areas despite potential cross-reactivity for species-specific antibody targets.</p></sec><sec><title>Methods</title><p>Ten RDTs were evaluated: nine to detect clinical <italic>P. knowlesi</italic> infections from Malaysia, and nine assessing limit of detection (LoD) for <italic>P. knowlesi (PkA1-H.1)</italic> and <italic>P. falciparum</italic> (<italic>Pf3D7</italic>) cultures. Targets included <italic>Plasmodium</italic>-genus parasite lactate dehydrogenase (pan-pLDH) and <italic>P. vivax</italic> (<italic>Pv</italic>)-pLDH.</p></sec><sec><title>Results</title><p>Samples were collected prior to antimalarial treatment from 127 patients with microscopy-positive PCR-confirmed <italic>P. knowlesi</italic> mono-infections. Median parasitaemia was 788/µL (IQR 247-5,565/µL). Pan-pLDH sensitivities ranged from 50.6% (95% CI 39.6–61.5) (SD BIOLINE) to 87.0% (95% CI 75.1–94.6) (First Response<sup>®</sup> and CareStart™ PAN) compared to reference PCR. <italic>Pv</italic>-pLDH RDTs detected <italic>P. knowlesi</italic> with up to 92.0% (95% CI 84.3-96.7%) sensitivity (Biocredit™). For parasite counts ≥200/µL, pan-pLDH (Standard Q) and <italic>Pv</italic>-pLDH RDTs exceeded 95% sensitivity. Specificity of RDTs against 26 PCR-confirmed negative controls was 100%. Sensitivity of six highest performing RDTs were not significantly different when comparing samples taken before and after (median 3 hours) antimalarial treatment. Parasite ring stages were present in 30% of pre-treatment samples, with ring stage proportions (mean 1.9%) demonstrating inverse correlation with test positivity of Biocredit™ and two CareStart™ RDTs.</p><p>For cultured <italic>P. knowlesi</italic>, CareStart™ PAN demonstrated the lowest LoD at 25 parasites/µL; LoDs of other pan-pLDH ranged from 98 to &gt;2000 parasites/µL. <italic>Pv</italic>-pLDH LoD for <italic>P. knowlesi</italic> was 49 parasites/µL. No false-positive results were observed in either <italic>P. falciparum</italic>-pLDH or histidine-rich-protein-2 channels.</p></sec><sec><title>Conclusion</title><p>Selected RDTs demonstrate sufficient performance for detection of major human malaria species including <italic>P. knowlesi</italic> in co-endemic areas where microscopy is not available, particularly for higher parasite counts, although cannot reliably differentiate among <italic>non-falciparum</italic> malaria.</p></sec>