Abstract
BackgroundAntigen-detecting rapid diagnostic tests (RDTs) have been recommended by the World Health Organization for use in remote areas to improve malaria case management. Lactate dehydrogenase (LDH) of Plasmodium falciparum is one of the main parasite antigens employed by various commercial RDTs. It has been hypothesized that the poor detection of LDH-based RDTs is attributed in part to the sequence diversity of the gene. To test this, the present study aimed to investigate the genetic diversity of the P. falciparum ldh gene in Thailand and to construct the map of LDH sequence diversity in P. falciparum populations worldwide.MethodsThe ldh gene was sequenced for 50 P. falciparum isolates in Thailand and compared with hundreds of sequences from P. falciparum populations worldwide. Several indices of molecular variation were calculated, including the proportion of polymorphic sites, the average nucleotide diversity index (π), and the haplotype diversity index (H). Tests of positive selection and neutrality tests were performed to determine signatures of natural selection on the gene. Mean genetic distance within and between species of Plasmodium ldh was analysed to infer evolutionary relationships.ResultsNucleotide sequences of P. falciparum ldh could be classified into 9 alleles, encoding 5 isoforms of LDH. L1a was the most common allelic type and was distributed in P. falciparum populations worldwide. Plasmodium falciparum ldh sequences were highly conserved, with haplotype and nucleotide diversity values of 0.203 and 0.0004, respectively. The extremely low genetic diversity was maintained by purifying selection, likely due to functional constraints. Phylogenetic analysis inferred the close genetic relationship of P. falciparum to malaria parasites of great apes, rather than to other human malaria parasites.ConclusionsThis study revealed the global genetic variation of the ldh gene in P. falciparum, providing knowledge for improving detection of LDH-based RDTs and supporting the candidacy of LDH as a therapeutic drug target.
Highlights
Antigen-detecting rapid diagnostic tests (RDTs) have been recommended by the World Health Organization for use in remote areas to improve malaria case management
Nucleotide sequences of the ldh gene in Thai Plasmodium falciparum isolates The ldh gene of P. falciparum was amplified from genomic DNA of 50 P. falciparum isolates and sequenced using a Sanger sequencing method as described in “Methods”
Nucleotide sequences of the ldh gene in worldwide Plasmodium falciparum isolates Having demonstrated the fixation of the ldh allele in Thai P. falciparum populations, the global diversity of the ldh gene in P. falciparum was further investigated
Summary
Antigen-detecting rapid diagnostic tests (RDTs) have been recommended by the World Health Organization for use in remote areas to improve malaria case management. Lactate dehydrogenase (LDH) of Plasmodium falciparum is one of the main parasite antigens employed by various commercial RDTs. It has been hypothesized that the poor detection of LDH-based RDTs is attributed in part to the sequence diversity of the gene. There are multiple formats of LDHbased detecting RDTs that are routinely employed for clinical malaria diagnostics This includes OptiMAL-IT (Cressier, Switzerland), which identifies and differentiates P. falciparum from non-P. falciparum species (Plasmodium vivax, Plasmodium ovale and Plasmodium malariae) on the basis of P. falciparum LDH in a patient’s whole blood [1]. The data showed that the sensitivity of the OptiMAL assay for P. falciparum was 25% with > 500 parasites/μl and 10.5% with > 100 parasites/ μl It is not clear from the studies whether the poor performance of RDTs was due to how they were engineered or whether it was due to the genetic variability of LDH itself. Whether the genetic diversity of the gene encoding LDH of P. falciparum led to the poor performance of LDH-detecting RDTs has not been evaluated
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
