Genetic diversity of Plasmodium Falciparum infections at varying altitudes in South-Western Uganda

Abstract

Plasmodium falciparum is a highly polymorphic parasite. This sometimes results in a high genetic diversity in the population and high complexity of infections among individuals. Although some studies indicate a relationship between genetic diversity and transmission, there is not much information about the relationship between diversity and complexity infections at varying altitudes; a surrogate for transmission intensity.

A retrospective cross-sectional study was done in two districts, Kabale (1700-2200m) and Rukungiri (1400-1600m), in South-western Uganda in 2007 from 10 villages at different altitudes to establish the relationship between diversity and complexity of infections at varying altitudes. A total of 1075 blood samples from members of the selected households were analysed by Paracheck-Pf and PCR. The diversity of Plasmodium falciparum circulating alleles was examined on the basis of the gene encoding merozoite surface protein 2 (msp2) using primers specific for the two allelic families, FC27 and 3D7.

The overall prevalence of Plasmodium falciparum infections by PCR was 8.5% and 18.5% by Paracheck-pf. Examining the districts; in Rukungiri the prevalence was 13.3% by PCR and 29.9% by Paracheck-pf whereas in Kabale the prevalence was 0.7% by PCR and 0.5% by Paracheck-Pf. To assess the variability of circulating alleles, DNA fragments were grouped into classes of 40 base pairs. A total of 14 classes representing parasite populations were identified; 8 classes (60%) for 3D7 and 6 classes (40%) for FC27 family. Infections involving more than one allele in an individual accounted for 30%. The maximum number of alleles in an individual was 4 and the mean complexity of infections was 1.35 ± 0.60. The mean number of alleles (COI) at the different altitudes were compared, and a regression analysis revealed no significant association between the two p = 0.931).

This study established the prevalence of Plasmodium falciparum infections in Kabale (<1%) and Rukungiri (~9%) and also demonstrated that no relationship exists between geneticdiversity and complexity of Plasmodium falciparum with increasing altitude. However, more studies are required in areas of higher malaria endemicities and a wider range of altitudes to evaluate this relationship further.