Artemisinin resistance has been reported in patients with uncomplicated malaria. Polymorphisms at the propeller domain of the Kelch 13 (K13) protein encoded by the Plasmodiumfalciparumk13 (pfk13) gene are associated with delayed parasite clearance after artemisinin combination therapy (ACT). We have previously described a cohort of patients with severe malaria who had a slow parasite and fever clearance despite adequate artesunate levels. These archived blood samples were sequenced to determine if they had the above mutations.
Blood samples were collected from patients >18 years, with P.falciparum or mixed (P.falciparum and P.vivax) malaria on ACT every 12 hours to document clearance of parasites. The parasite clearance half-life was calculated with use of the Worldwide Antimalarial Resistance Network (WWARN) online parasite clearance estimator (PCE). Longitudinally archived DNA samples obtained pre-treatment (day 0) were genotyped to study the pfk13 propeller domain, amplifying about 800 bp sequences, using the strain PF3D7_1343700 as the reference genome.
A total of 54 patients with malaria were included and of these 74% were hospitalised with severe malaria. The mean age in the cohort was 37.59 + 14.14 (17-75) years. The median parasite clearance time was estimated to be 36 hours (95%CI: 27.08 – 44.91) and the median fever clearance time was estimated to be 24 hours (95% CI: 18.69 – 29.30). The median parasite clearance slope half - life was estimated at 6.44 hours (IQR; 4.79 to 10.24), thus fulfilling the definition of partial artemisinin resistance. Artesunate pharmacokinetic variables assessed in 17 patients were found to be similar in the groups with rapid (<2 days) and slow clearance (>2 days) of parasites. No known mutations associated with artemisinin resistance in Southeast Asia were observed in our study participants despite delayed parasite and fever clearance.
Slow parasite clearance is common with a high parasite burden and hence standardization of artemisinin resistance definitions is required. Lack of known mutations with slow parasite clearance in areas of high endemicity like India, should prompt sequencing of whole parasite genome to identify novel mutations.
B. Mathew, None
P. Rupali, None