Declining Efficacy of Artemisinin Combination Therapy Against P. Falciparum Malaria on the Thai-Myanmar Border (2003-2013): The Role of Parasite Genetic Factors

Abstract

Background: Deployment of mefloquine-artesunate (MAS3) on the Thailand-Myanmar border has led to a sustained reduction in falciparum malaria, although antimalarial efficacy has declined substantially in recent years. The role of Plasmodium falciparum K13 mutations (a marker of artemisinin resistance) in reducing treatment efficacy remains controversial.

Methods: Between 2003 and 2013, we studied the efficacy of MAS3 in 1005 patients with uncomplicated P. falciparum malaria in relation to molecular markers of resistance.

Results: Polymerase chain reaction (PCR)-adjusted cure rates declined from 100% in 2003 to 81.1% in 2013 as the proportions of isolates with multiple Pfmdr1 copies doubled from 32.4% to 64.7% and those with K13 mutations increased from 6.7% to 83.4%. K13 mutations conferring moderate artemisinin resistance (notably E252Q) predominated initially but were later overtaken by propeller mutations associated with slower parasite clearance (notably C580Y). Those infected with both multiple Pfmdr1 copy number and a K13 propeller mutation were 14 times more likely to fail treatment. The PCR-adjusted cure rate was 57.8% (95% confidence interval [CI], 45.4, 68.3) compared with 97.8% (95% CI, 93.3, 99.3) in patients with K13 wild type and Pfmdr1 single copy. K13 propeller mutation alone was a strong risk factor for recrudescence (P = .009). The combined population attributable fraction of recrudescence associated with K13 mutation and Pfmdr1 amplification was 82%.

Conclusions: The increasing prevalence of K13 mutations was the decisive factor for the recent and rapid decline in efficacy of artemisinin-based combination (MAS3) on the Thailand-Myanmar border.

Keywords: K13 mutation; Pfmdr1; Plasmodium falciparum malaria; artemisinin resistance; mefloquine–artesunate.

Figure 1.

Patient flow diagram after 3-day treatment with mefloquine plus artesunate.

Figure 2.

A, Primary amino acid positions and frequencies of K13 mutations. (B) Annual proportions of K13 propeller mutations (summed) and 4 individual genotypes (for which n > 25).

Figure 3.

Annual proportions of day 42 polymerase chain reaction (PCR)–adjusted cure rates, summed K13 mutations, and amplified Pfmdr1. Abbreviations: ACT, artemisinin-based combination treatment; SNP, single-nucleotide polymorphism; WHO, World Health Organization.

Figure 4.

Kaplan–Meier curves showing cumulative proportions of patients free from recrudescence stratified by presence of Pfmdr1 copy number and K13 genotype. The numbers in parentheses are the recrudescences during the indicated time. K13 Prop refers to samples with mutation in the K13 propeller.