Use of malaria rapid diagnostic test to identify Plasmodium knowlesi infection

Abstract

Reports of human infection with Plasmodium knowlesi, a monkey malaria, suggest that it and other nonhuman malaria species may be an emerging health problem. We report the use of a rapid test to supplement microscopic analysis in distinguishing the 5 malaria species that infect humans.

Figure 1

Binding specificity of different anti–Plasmodium lactate dehydrogenase (pLDH) antibodies. A) Shown are the reactivities of the indicated monoclonal antibodies (MAbs) to the LDH from 7 Plasmodium spp. Reactivity was determined by using an immunocapture assay as previously described (9). B) Example of an immunodipstick assay that detects P. knowlesi. An immunochromatographic strip assay containing the indicated antibodies was allowed to wick lysed blood infected with P. vivax, P. falciparum, P. knowlesi, P. ovale, or P. malariae. Blood was wicked in the presence of colloidal gold conjugated to antibody 6C9, which binds all pLDH isoforms. P. vivax LDH is immobilized only by 11D9 and 13H11, and P. falciparum LDH was only immobilized by 17E4. P. knowlesi LDH was immobilized by 11D9 and 13H11 antibodies and also by 17E4. C) An immunochromatographic strip assay containing the indicated antibodies was allowed to wick lysed blood infected with P. vivax, P. cynomolgi, P. inui, and P. knowlesi. Blood was wicked in the presence of colloidal gold conjugated to antibody 6C9, which binds all pLDH isoforms. Both P. cynomolgi and P. inui show the same epitope profile as P. vivax.

Figure 2

Modeling of the analysis of Plasmodium knowlesi lactate dehydrogenase (LDH). A) Sequence of LDH from P. knowlesi deduced from genomic DNA fragments sequenced by the Sanger malaria genome project (www.sanger.ac.uk/Projects/P_knowlesi). LDH isoforms from P. vivax, P. malariae, P. ovale, P. berghei, P. yoelli, and P. falciparum were compared with that of P. knowlesi. Residues unique to P. knowlesi and P. vivax are shown in blue; residues unique to P. knowlesi and P. falciparum are shown in red. B) Model of P. knowlesi LDH and specific epitopes. A model for P. knowlesi LDH was calculated by using WURST protein threading server (www.zbh.uni-hamburg.de/wurst/index.php) and the P. falciparum and P. vivax crystal structures (PDB: 2A94 and 3 2AA3). Shown is the monomer, as well as the assembled tetramer, aligned to the backbone of the P. vivax tetramer using pymol. The nicotinamide adenine dinucleotide cofactor analog 3-acetyl pyridine adenine dinucleotide is shown in black. Residues important for substrate binding and catalysis are shown in yellow. P. knowlesi residues shared only with P. vivax are shown in blue and indicate where the 11D9/13H11 epitopes could be. P. knowlesi residues shared only with P. falciparum are shown in red and indicate a critical determinant of the 17E4/7G9 epitopes.