Piperaquine-resistant P. falciparum strains lessen response to artemisinin
Emergent piperaquine-resistant strains of Plasmodium falciparum have reduced patient response to artemisinin producing nationwide treatment failure rates of more than 20 percent, a new study from Vietnam has shown.
The study included 489 uncomplicated P. falciparum malaria patients recruited from three provinces in southern Vietnam: Binh Phuoc, Ninh Thuan and Gia Lai. Of the patients, 95 percent (n=471) were febrile upon admission.
The highest treatment failure rates were reported in the Binh Phuoc province, with a failure rate of 0 percent in 2012 and 2013, 7 percent in 2014, and 26 percent in 2015. The increasing trend reached statistical significance (p<0.001).
In contrast, data from Ninh Thuan province showed only two failures of late treatment, while no treatment failures were reported for the Gia Lai province.
In Binh Phuoc province, median parasite clearance time increased from 63 hours in 2012 to 78 hours in both 2014 and 2015 (p=0.002 for trend). Similarly, median parasite clearance half-life increased significantly from 3.75 hours in 2012 to 6.60 hours in 2015 (p<0.001 for trend).
Median parasite clearance time also increased significantly in the Gia Lai province, jumping from 36 to 96 hours from 2011 to 2015 (p<0.001 for trend). Parasite clearance half-life also rose significantly from 1.97 to 6.88 hours, respectively (p<0.001 for trend).
In contrast, parasite clearance time (p=0.29) and parasite clearance half-life (p=0.29) did not show significant changes from 2013 to 2015 in Ninh Thuan province.
Additional ring stage assay of nine P. falciparum isolates collected in 2015 showed that all samples were resistant to dihydroartemisinin (DHA; survival rate >1). The median survival rate was 14.29 percent. Subsequent piperaquine survival assay also showed strong resistance to piperaquine (survival rate ≥10 percent; median survival rate 20.72 percent).