Abstract
BackgroundPlasmodium vivax is the second most prevalent malaria parasite affecting more than 75 million people each year, mostly in South America and Asia. In addition to major morbidity this parasite is associated with relapses and a reduction in birthweight. The emergence and spread of drug resistance in Plasmodium falciparum is a major factor in the resurgence of this parasite. P. vivax resistance to drugs has more recently emerged and monitoring the situation would be helped, as for P. falciparum, by molecular methods that can be used to characterize parasites in field studies and drug efficacy trials.MethodsPractical PCR genotyping protocols based on polymorphic loci present in two P. vivax genetic markers, Pvcs and Pvmsp1, were developed. The methodology was evaluated using 100 P. vivax isolates collected in Thailand.Results and DiscussionAnalysis revealed that P. vivax populations in Thailand are highly diverse genetically, with mixed genotype infections found in 26 % of the samples (average multiplicity of infection = 1.29). A large number of distinguishable alleles were found for the two markers, 23 for Pvcs and 36 for Pvmsp1. These were generally randomly distributed amongst the isolates. A total of 68 distinct genotypes could be enumerated in the 74 isolates with a multiplicity of infection of 1.ConclusionThese results indicate that the genotyping protocols presented can be useful in the assessment of in vivo drug efficacy clinical trials conducted in endemic areas and for epidemiological studies of P. vivax infections.
Highlights
Plasmodium vivax is the second most prevalent malaria parasite affecting more than 75 million people each year, mostly in South America and Asia
Most of the populations at risk in these countries reside in hypoendemic and mesoendemic areas, where half of the recorded infections are due to P. vivax, suggesting that the global burden of vivax malaria morbidity must be close to that of falciparum malaria
The specificity of all the primer pairs was confirmed since amplification products were only observed when P. vivax DNA was included in the reaction, but not when genomic DNA from P. falciparum, Plasmodium malariae, Plasmodium ovale or humans were used as a template
Summary
Plasmodium vivax is the second most prevalent malaria parasite affecting more than 75 million people each year, mostly in South America and Asia. The emergence and global spread of P. falciparum parasites resistant to chloroquine and pyrimethamine – sulfadoxine has led to an increase in morbidity and mortality [4], forcing many countries to abandon these relatively cheap drugs. In vivo drug efficacy studies conducted in endemic areas are to some extent compromised by their inability to distinguish true recrudescences, i.e. treatment failures, from re-infections which become clinically or parasitologically manifest during the follow-up period, i.e. treatment successes. This has been largely overcome for P. falciparum by the application of genotyping based on well characterized polymorphic regions within the gene encoding msp, msp and glurp [16]
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