Insight into k13-propeller gene polymorphism and ex vivo DHA-response profiles from Cameroonian isolates

The spread of Plasmodium falciparum resistance to artemisinin derivatives in Southeast Asia is a major source of concern and the emergence of resistance in Africa would have dramatic consequences, by increasing malaria mortality and morbidity. It is therefore urgent to implement regular monitoring in sentinel sites in sub-Saharan Africa using robust and easy-to-implement tools. The prevalence of k13-propeller mutations and the phenotypic profiles are poorly known in sub-Saharan Africa. Here, the k13-propeller polymorphism was compared to both ex vivo susceptibility to DHA and early parasitological and clinical responses to artemisinin combination therapy (ACT).

Plasmodium falciparum isolates were collected in 2015 in Yaoundé (Cameroon) from patients treated with dihydroartemisinin-piperaquine combination. Samples were analysed for their susceptibility to artemisinin using the k13-propeller sequencing, the ex vivo ring-stage survival assay, the in vivo parasite positive rate and the clinical statute at day 2.

None of the collected isolates revealed the presence of resistance mutations in the k13-propeller sequence. The median ring-stage survival rate for all the 64 interpretable isolates after a 6-hour pulse of 700 nM dihydroartemisinin was low, 0.49% (IQR: 0-1.3). Total parasite clearance was observed for 87.5% of patients and the remaining parasitaemic isolates (12.5%) showed a high reduction of parasite load, ranging from 97.5 to 99.9%. Clinical symptoms disappeared in 92.8% of cases.

This study demonstrated the absence of k13-resistant genotypes in P. falciparum isolates from Cameroon. Only synonymous mutations were found with a low prevalence (4.3%). A good association between k13 genotypes and the ex vivo ring-stage survival assay or parasitological and clinical data was obtained. These results give a baseline for the long-term monitoring of artemisinin derivative efficacy in Africa.