Abstract
BackgroundReported malaria cases in the Americas had been reduced to about one-half million by 2012. To advance towards elimination of this disease, it is necessary to gain insights into how the malaria parasite is evolving, including the emergence, spread and persistence of new haplotypes in affected regions. In here, the genetic diversity of the three major P. vivax merozoite genes was analyzed.MethodsFrom P. vivax-infected blood samples obtained in southern Mexico (SMX) during 2006–2007, nucleotide sequences were achieved for: the 42 kDa carboxyl fragment of the merozoite surface protein-1 (msp142), domains I-II of the apical membrane antigen-1 (ama1I-II), and domain II of the Duffy binding protein (dbpII). Gene polymorphism was examined and haplotype networks were developed to depict parasite relationships in SMX. Then genetic diversity, recombination and natural selection were analyzed and the degree of differentiation was determined as FST values.ResultsThe diversity of P. vivax merozoite genes in SMX was less than that of parasites from other geographic origins, with dbpII < ama1I-II < msp142. Ama1I-II and msp142 exposed the more numerous haplotypes exclusive to SMX. While, all dbpII haplotypes from SMX were separated from one to three mutational steps, the networks of ama1I-II and msp142 were more complex; loops and numerous mutational steps were evidenced, likely due to recombination. Sings of local diversification were more evident for msp142. Sixteen combined haplotypes were determined; one of these haplotypes not detected in 2006 was highly frequent in 2007. The Rm value was higher for msp142than for ama1I-II, being insignificant for dbpII. The dN-dS value was highly significant for ama1I-II and lesser so for dbpII. The FST values were higher for dbpII than msp142, and very low for ama1I-II.ConclusionsIn SMX, P. vivax ama1I-II, dbpII and msp142 demonstrated limited diversity, and exhibited a differentiated parasite population. The results suggest that differential intensities of selective forces are operating on these gene fragments, and probably related to their timing, length of exposure and function during reticulocyte adhesion and invasion. Therefore, these finding are essential for mono and multivalent vaccine development and for epidemiological surveillance.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-015-1266-7) contains supplementary material, which is available to authorized users.
Highlights
Reported malaria cases in the Americas had been reduced to about one-half million by 2012
Haplotype relationships for different merozoite genes and the haplotype configuration for P. vivax isolates in southern Mexico (SMX) Each gene fragment produced a haplotype network with a different pattern (Fig. 2). 1) The SMX dbpII network was the simplest; the haplotypes were separated by one to three mutational steps
In SMX, the results suggest a moderate recombination rate for msp142in the P. vivax sample
Summary
Reported malaria cases in the Americas had been reduced to about one-half million by 2012. In the Americas, the number of malaria cases gradually declined from 2000 to 2012 due to the improvement and intensification of control measures. Around the world there are countries that have advanced to the pre-elimination phase, while others have reported little decline or even an increase in the number of malaria cases [5, 6]. To contribute to better control efforts and accelerate malaria elimination, more knowledge is needed about the parasites circulating in each region. In this sense, analysis of the evolutionary forces that shape malaria antigen diversity can be useful for monitoring and designing vaccines, describing transmission dynamics, and conducting epidemiological surveillance
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