The prevalence of chloroquine resistance decreased to less than 30% since the 2002 emergence of C350R allele within the Plasmodium falciparum population in French Guiana, according to a recent study.
Previously, chloroquine was withdrawn from first-line treatment of P. falciparum in 1995. Chloroquine susceptibility was observed with the regrowth of the wild-type allele K76 of the chloroquine-resistance transporter gene (pfcrt), however, a reduction in the resistance threshold (< 100 nM) and an elevated presence of K76T indicated the marker’s predictive value had decreased.
“These findings have important implications for understanding drug resistance evolution in a low-endemicity context where drug resistance alleles can reach fixation, a scenario that will become increasingly dominant as successful control efforts progressively reduce the burden of malaria,” Stéphane Pelleau, PhD, from the parasitology laboratory at the WHO Collaborating Center for Surveillance of Anti-Malarial Drug Resistance, and colleagues wrote.
Pelleau and colleagues collected P. falciparum isolates from 1994 to 2013 in symptomatic patients from French Guiana. The researchers analyzed 1,054 isolates that were genotyped for pfcrt and found that 99% contained PfCRT/PfMDR1 haplotypes SVMNT/NFCDY (7G8-type; n = 688) and SVMNT/NFSDY (n = 108), confirming that PfCRT K76T and PfMDR1 are no longer predictive of chloroquine resistance. They observed a substantial decrease in chloroquine resistance between 1995 and 2000 (90% vs. 40%), a slight increase between 2000 and 2006 and another decrease (25%) after introducing an artemisinin-based combination therapy in 2007.
A whole-genome sequence analysis and genomewide association study on 35 isolates collected from patients infected with malaria between 2009 and 2013 revealed that C350R was the single mutation associated with chloroquine susceptibility. A 7G8 chloroquine-resistance reference strain genomically edited to incorporate PfCRT C350R demonstrated a 24-fold reduction of chloroquine resistance (P < .0001). In a parallel molecular survey of 580 isolates collected between 1997 and 2012, all 168 PfCRT C350R mutant isolates were chloroquine resistant and had significantly lower values compared with PfCRT C350 parasites (P < .0001).
“Altogether, these results provide compelling evidence that the emergence of the PfCRT C350R mutation is primarily responsible for the recent gain of [chloroquine-resistance] susceptibility in PfCRT K76T isolates from French Guiana,” Pelleau and colleagues wrote.
Further analysis showed the C350R mutation emerged in 2002 and rapidly increased from 2.7% to 58% in 2012 in the P. falciparum population.
In a separate analysis, C350R incorporated into a 7G8 clone was associated with 1.4-fold decrease in piperaquine susceptibility compared with wild-type C350 isolates (P < .001). The researchers recommended that further research observing the reversion of chloroquine resistance on a larger scale is warranted. – by Stephanie Viguers
Disclosure: The researchers report no relevant financial disclosures.