In South-East Asia, >70% of asymptomatic malaria infections are undetectable by current diagnostic tests, except for ultrasensitive PCR (uPCR). Multiplex enzyme-linked immunosorbent assay (mELISA) detection of parasite antigens could represent a simpler survey tool requiring lower sample volumes. We compared the performance of mELISA with uPCR for the detection of asymptomatic Plasmodium infection.
Venous blood was collected in EDTA tubes from asymptomatic adults in villages of Eastern Myanmar. The uPCR was performed on DNA extracts from 500 µl of pack red blood cells. The mELISA targeting Plasmodium falciparum HRP2 (pfHRP2), Plasmodium spp. LDH (pLDH) and Plasmodium vivax LDH (pvLDH) was performed on 25 μl of whole blood.
Of 1612 samples, 520 Plasmodium infections were identified by uPCR, including 191 P. falciparum positive infections.
Compared to uPCR, the sensitivity and specificity of mELISA were: for P. falciparum, 80.6% (95%CI=74.3-86.0) and 96.6% (95%CI=95.5-97.4); respectively for P. vivax, 87.1% (95%CI=82.7-90.8) and 92.9% (95%CI=91.4-94.2).
mELISA identified correctly 88% (132/150) samples positive for P. falciparum by uPCR with >100 parasites/mL, but only 54% (22/41) samples with <100 parasites/mL. Yet 55% (27/49) samples mELISA positive/uPCR negative for P. falciparum had evidence of Plasmodium DNA. Likewise uPCR identified 84% (125/148) samples positive for P. falciparum by mELISA with pfHRP2>10pg/mL, but only 55% (29/55) samples with pfHRP2<10 pg/mL, and 57% (21/37) of uPCR positive, mELISA negative samples for P. falciparum presented evidence of Plasmodium antigens.
Across 39 villages, the correlation coefficient between P. falciparum, P. vivax, and all Plasmodium prevalence measured by mELISA and by uPCR was high, respectively 0.96, 0.93 and 0.97.
The sensitivity and specificity of the mELISA compared to uPCR were around 80% and 95% respectively. Below 100 parasites/mL or pfHRP2 concentration 10 picograms/mL, the discordances between the two methods increased. At village-level, uPCR prevalence could be reliably estimated by mELISA.