Evaluation of the sensitivity of a pLDH-based and an aldolase-based rapid diagnostic test for diagnosis of uncomplicated and severe malaria caused by PCR-confirmed Plasmodium knowlesi, Plasmodium falciparum, and Plasmodium vivax

Abstract

Plasmodium knowlesi can cause severe and fatal human malaria in Southeast Asia. Rapid diagnosis of all Plasmodium species is essential for initiation of effective treatment. Rapid diagnostic tests (RDTs) are sensitive for detection of uncomplicated and severe falciparum malaria but have not been systematically evaluated in knowlesi malaria. At a tertiary referral hospital in Sabah, Malaysia, we prospectively evaluated the sensitivity of two combination RDTs for the diagnosis of uncomplicated and severe malaria from all three potentially fatal Plasmodium species, using a pan-Plasmodium lactate dehydrogenase (pLDH)-P. falciparum histidine-rich protein 2 (PfHRP2) RDT (First Response) and a pan-Plasmodium aldolase-PfHRP2 RDT (ParaHIT). Among 293 hospitalized adults with PCR-confirmed Plasmodium monoinfection, the sensitivity of the pLDH component of the pLDH-PfHRP2 RDT was 74% (95/129; 95% confidence interval [CI], 65 to 80%), 91% (110/121; 95% CI, 84 to 95%), and 95% (41/43; 95% CI, 85 to 99%) for PCR-confirmed P. knowlesi, P. falciparum, and P. vivax infections, respectively, and 88% (30/34; 95% CI, 73 to 95%), 90% (38/42; 95% CI, 78 to 96%), and 100% (12/12; 95% CI, 76 to 100%) among patients tested before antimalarial treatment was begun. Sensitivity in severe malaria was 95% (36/38; 95% CI, 83 to 99), 100% (13/13; 95% CI, 77 to 100), and 100% (7/7; 95% CI, 65 to 100%), respectively. The aldolase component of the aldolase-PfHRP2 RDT performed poorly in all Plasmodium species. The pLDH-based RDT was highly sensitive for the diagnosis of severe malaria from all species; however, neither the pLDH- nor aldolase-based RDT demonstrated sufficiently high overall sensitivity for P. knowlesi. More sensitive RDTs are needed in regions of P. knowlesi endemicity.

Fig 1

Parasite count by pLDH-band intensity for all samples. Horizontal lines indicate medians; boxes indicate interquartile ranges; vertical lines indicate ranges. Among patients with P. knowlesi infection, the pLDH band was negative in 34 (26%), 1+ in 34 (26%), 2+ in 17 (13%), 3+ in 17 (13%), 4+ in 24 (18%), and recorded only as positive in 3 (2%). Among patients with P. falciparum infection, the pLDH band was negative in 11 (9%), 1+ in 35 (29%), 2+ in 17 (14%), 3+ in 24 (20%), 4+ in 30 (25%), and recorded as positive in 4 (3%). Among patients with P. vivax infection, the pLDH band was negative in 2 (5%), 1+ in 4 (9%), 2+ in 5 (12%), 3+ in 7 (16%), 4+ in 20 (47%), and recorded as positive in 5 (12%).

Fig 2

Sensitivity of the pLDH-component of the First Response RDT by parasite count. Wide horizontal bars indicate sensitivity. Vertical lines represent 95% confidence intervals. Among patients with P. knowlesi infection, 18 (14%) had <10³ parasites/μl, 52 (40%) had 10³ to <10⁴ parasites/μl, 41 (32%) had 10⁴ to <10⁵ parasites/μl, and 18 (14%) had >10⁵ parasites/μl. Among patients with P. falciparum infection, 10 (8%) had <10³ parasites/μl, 42 (35%) had 10³ to <10⁴ parasites/μl, 60 (50%) had 10⁴ to <10⁵ parasites/μl, and 9 (7%) had >10⁵ parasites/μl. Among patients with P. vivax infection, 8 (19%) had <10³ parasites/μl, 21 (49%) had 10³ to <10⁴ parasites/μl, and 14 (33%) had 10⁴ to <10⁵ parasites/μl.