Simple Real-Time PCR and Amplicon Sequencing Method for Identification of Plasmodium Species in Human Whole Blood

Abstract

Malaria is the leading identifiable cause of fever in returning travelers. AccuratePlasmodiumspecies identification has therapy implications forP. vivaxandP. ovale, which have dormant liver stages requiring primaquine. Compared to microscopy, nucleic acid tests have improved specificity for species identification and higher sensitivity for mixed infections. Here, we describe a SYBR green-based real-time PCR assay forPlasmodiumspecies identification from whole blood, which uses a panel of reactions to detect species-specific non-18S rRNA gene targets. A pan-Plasmodium18S rRNA target is also amplified to allow species identification or confirmation by sequencing if necessary. An evaluation of assay accuracy, performed on 76 clinical samples (56 positives using thin smear microscopy as the reference method and 20 negatives), demonstrated clinical sensitivities of 95.2% forP. falciparum(20/21 positives detected) and 100% for thePlasmodiumgenus (52/52),P. vivax(20/20),P. ovale(9/9), andP. malariae(6/6). The sensitivity of theP. knowlesi-specific PCR was evaluated using spiked whole blood samples (100% [10/10 detected]). The specificities of the real-time PCR primers were 94.2% forP. vivax(49/52) and 100% forP. falciparum(51/51),P. ovale(62/62),P. malariae(69/69), andP. knowlesi(52/52). Thirty-three specimens were used to test species identification by sequencing the pan-Plasmodium18S rRNA PCR product, with correct identification in all cases. The real-time PCR assay also identified two samples with mixedP. falciparumandP. ovaleinfection, which was confirmed by sequencing. The assay described here can be integrated into a malaria testing algorithm in low-prevalence areas, allowing definitivePlasmodiumspecies identification shortly after malaria diagnosis by microscopy.