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Browsing School of Biological Sciences by Subject "antimalarial drug resistance"

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    Tolerance Of Plasmodium Falciparum To Artemetherlumefantrine In The Gambia
    (University Of Ghana, 2020-12) Mbye, H.
    Antimalarial drug resistance contributes significantly to obstacles in reducing the global burden of malaria especially in sub-Saharan Africa (sSA) where the disease is most prevalent. Resistance to artemisinin-based combination therapies (ACTs), the only recommended frontline drugs for the treatment of uncomplicated malaria is now widespread in South East Asia (SEA). However, ACTs remain efficacious in sSA though in vivo delayed parasite clearance and in vitro reduced susceptibility to both components of the drug has been reported. Resistance to ACTs is therefore anticipated especially with its sustained use in endemic regions and the recent report of the emergence of de novo Pfk13 mutation that is now spreading in Rwanda. In The Gambia where artemether-lumefantrine (AL) is the first-line drug used for over 10 years, a steady increase in parasite tolerance to lumefantrine (LUM) was observed over a period of 4 years which strongly correlated with reported directional selection on a cysteine desulfarase gene (Pfnfs1). These findings are concerning and require continuous drug surveillance to track spontaneous development of AL resistant parasites and determine pathways to resistance development. This study therefore sought to investigate the prevalence and mechanisms of parasite tolerance to AL in The Gambia. A novel ex vivo drug susceptibility assay suitable to simultaneously assess parasite responses to both drugs used in AL was developed and used to assess drug susceptibility profiles of circulating parasites in western Gambia. This assay was then used to confirm identified potent compounds from the Medicines for Malaria Venture pathogen box effective against the erythrocytic stages of the parasite for future development into new antimalarial drugs. The prevalence of known drug resistance markers was assessed and novel markers that could be associated with drug resistance identified using both regression analysis and GWAS approach. Finally, CRISPR-Cas9 genome editing was used to functionally validate Pfnfs1 for its involvement in LUM tolerance using gene editing approaches. Antimalarial drug resistance contributes significantly to obstacles in reducing the global burden of malaria especially in sub-Saharan Africa (sSA) where the disease is most prevalent. Resistance to artemisinin-based combination therapies (ACTs), the only recommended frontline drugs for the treatment of uncomplicated malaria is now widespread in South East Asia (SEA). However, ACTs remain efficacious in sSA though in vivo delayed parasite clearance and in vitro reduced susceptibility to both components of the drug has been reported. Resistance to ACTs is therefore anticipated especially with its sustained use in endemic regions and the recent report of the emergence of de novo Pfk13 mutation that is now spreading in Rwanda. In The Gambia where artemether-lumefantrine (AL) is the first-line drug used for over 10 years, a steady increase in parasite tolerance to lumefantrine (LUM) was observed over a period of 4 years which strongly correlated with reported directional selection on a cysteine desulfarase gene (Pfnfs1). These findings are concerning and require continuous drug surveillance to track spontaneous development of AL resistant parasites and determine pathways to resistance development. This study therefore sought to investigate the prevalence and mechanisms of parasite tolerance to AL in The Gambia. A novel ex vivo drug susceptibility assay suitable to simultaneously assess parasite responses to both drugs used in AL was developed and used to assess drug susceptibility profiles of circulating parasites in western Gambia. This assay was then used to confirm identified potent compounds from the Medicines for Malaria Venture pathogen box effective against the erythrocytic stages of the parasite for future development into new antimalarial drugs. The prevalence of known drug resistance markers was assessed and novel markers that could be associated with drug resistance identified using both regression analysis and GWAS approach. Finally, CRISPR-Cas9 genome editing was used to functionally validate Pfnfs1 for its involvement in LUM tolerance using gene editing approaches. Keywords: Malaria, antimalarial drug resistance, ex vivo drug assays, high throughput screening genotyping, functional analysis, association studies