Dynamics of Resistant Plasmodium falciparum Parasites

Abstract: Persistence of drug resistant Plasmodium falciparum is a major problem to management and control malaria in endemic areas. The focus of this thesis was to study the dynamics of resistant P. falciparum parasites. The study was performed in two African countries: 1) Sudan: Asar village in eastern Sudan, here we examined the persistence of drug sensitive and resistant P. falciparum genotypes among individuals with single-clone and multiple clones infection during the dry season. We genotyped microsatellite loci in the vicinity of the dihydrofolate reductase gene (dhfr) and the dihydropteroate synthase gene (dhps). Microsatellite investigation showed that asymptomatic parasitemia persisted in some patients for several months throughout the dry season and into the next transmission season. In some samples mixed infections were detected, and we noted several cases where the microsatellite haplotype varied from month to month, suggesting turnover of different parasite populations in the blood. This demonstrates that even during asymptomatic infections there can be dynamics within the parasite population in an individual. In addition, we calculated the parasite density throughout the dry season to the next transmission season by using allele-specific quantitative PCR. Parasite density during the dry season fluctuated, but was generally lower than in the first transmission season. A significant difference (P<0.05) between dry and first transmission season was found in regard to the parasite density, whereas no significant difference was observed when dry and second transmission season were compared (P>0.05). 2) Ethiopia: West Arsi zone, one of the malaria endemic zones of the Oromia region. In the first study we determined the prevalence of asymptomatic malaria carriages from November-December 2012. According to PCR the prevalence of sub-microscopic P. falciparum carriage was 19.2%, microscopy-based prevalence was 3.7% while the prevalence was 6.9% using RDT. Based on this, PCR was considered a better tool for measuring Plasmodium prevalence than microscopy and RDT. A second study addressed the genetic diversity of chloroquine resistance (CQR) in P. falciparum by analysing four microsatellite markers in and around the pfcrt gene. Although CQ was withdrawn for more than a decade, 100% of the parasites still carried the Pfcrt K76T mutation. Only the CVIET haplotype was identified. Based on combinations of MS markers, seven different Ethiopian CQR variants (E1-E7) were identified. Both intronic and MS flanking the pfcrt gene showed low levels of diversity.