Genetic structure of Plasmodium falciparum populations across the Honduras-Nicaragua border

Abstract

Background: The Caribbean coast of Central America remains an area of malaria transmission caused by Plasmodium falciparum despite the fact that morbidity has been reduced in recent years. Parasite populations in that region show interesting characteristics such as chloroquine susceptibility and low mortality rates. Genetic structure and diversity of P. falciparum populations in the Honduras-Nicaragua border were analysed in this study.

Methods: Seven neutral microsatellite loci were analysed in 110 P. falciparum isolates from endemic areas of Honduras (n = 77) and Nicaragua (n = 33), mostly from the border region called the Moskitia. Several analyses concerning the genetic diversity, linkage disequilibrium, population structure, molecular variance, and haplotype clustering were conducted.

Results: There was a low level of genetic diversity in P. falciparum populations from Honduras and Nicaragua. Expected heterozigosity (H(e)) results were similarly low for both populations. A moderate differentiation was revealed by the F(ST) index between both populations, and two putative clusters were defined through a structure analysis. The main cluster grouped most of samples from Honduras and Nicaragua, while the second cluster was smaller and included all the samples from the Siuna community in Nicaragua. This result could partially explain the stronger linkage disequilibrium (LD) in the parasite population from that country. These findings are congruent with the decreasing rates of malaria endemicity in Central America.

Figure 1

Partial map of Central America showing collection sites of samples infected by Plasmodium falciparum. Municipalities have been coloured with different shades to indicate the proportion of samples collected in each location. Dot lines indicate approximate Moskitia region limits.

Figure 2

Bayesian clustering of 110 isolates assigned to K populations based on seven SSR markers. Each bar represents the proportion of each haplotype with ancestry in the defined clusters, each cluster being indicated by a different colour. OG: outgroup of reference clones parasites with an African origin.

Figure 3

Haplotype distribution by geographic region. Less common haplotypes are shaded in grey. Circle sizes indicate the number of isolates collected in those communities.

Figure 4

UPGMA dendrogram showing the relationships between Plasmodium falciparum isolates and a putative population structure. Isolates are coloured according to geographic location in the dendrogram.