Plasmodium falciparum population genetics in northern Ghana

Thesis

The main thrust of this thesis was to characterize P.falciparum genetic diversity in northern Ghana. To do this, I used simple techniques to purify P. falciparum DNA from clinical samples across a rural setting for whole-genome sequencing. The goal was to provide a framework for exploring host-parasite genetic interactions. Utilizing Illumina deep sequencing data for 277 isolates I analyzed P. falciparum genetic diversity and described within-host diversity across this area.

I observed random mating (ie no population structure) in the local parasite population, and a high genetic diversity indicative of high out-crossing. Moreover, when I aggregated my data with similar published data from Burkina Faso and Mali (sites ≈500km apart), no population structure was evident. In contrast, sites sampled in Cambodia and Thailand (≈ 800km apart) were found to have greater population structure and high potential for inbreeding. This may be driven by differences in transmission intensity between the sites sampled in West Africa and southeast Asia.

To demonstrate the utility of deep sequencing data, I focused on the genomic regions of pfdhfr, pfdhps and pfcrt, known to be under antimalarial drug selection. I surveyed the full diversity of point mutations already characterized in these genes and discovered previously unknown variants. However, in order to provide a means to follow up on new variants or interesting candidate regions in large clinical samples with limited parasite DNA, I assessed the Sequenom iPLEX platform for high-throughput genotyping of P. falciparum polymorphisms. This necessitated developing a method appropriate for assigning genotypes in haploid genome mixtures common in natural infections. Finally, I used this method to type host and parasite markers in a case-control sample set from this region for exploring host-parasite genetic interactions. I found that children who have the sickle-cell trait and carry parasites that have pfdhfr resistant alleles lose their protection against severe malaria as compared to children who have normal haemoglobin and are infected with parasites with these resistant alleles.

Authors: Amenga-Etego, NKL

• Publication date: 2012
• DOI: 10.5287/ora-z5gyovnnn
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: malaria; genetic; Population; diversity
• Subjects: Genomic; epidemiology