Molecular epidemiology of resistance to antimalarial drugs in the Greater Mekong subregion: an observational study

Abstract

Summary Background The Greater Mekong subregion is a recurrent source of antimalarial drug resistance in Plasmodium falciparum malaria. This study aimed to characterise the extent and spread of resistance across this entire region between 2007 and 2018. Methods P falciparum isolates from Myanmar, Thailand, Laos, and Cambodia were obtained from clinical trials and epidemiological studies done between Jan 1, 2007, and Dec 31, 2018, and were genotyped for molecular markers ( pfkelch, pfcrt, pfplasmepsin2 , and pfmdr1 ) of antimalarial drug resistance. Genetic relatedness was assessed using microsatellite and single nucleotide polymorphism typing of flanking sequences around target genes. Findings 10 632 isolates were genotyped. A single long pfkelch Cys580Tyr haplotype (from −50 kb to +31·5 kb) conferring artemisinin resistance (PfPailin) now dominates across the eastern Greater Mekong subregion. Piperaquine resistance associated with pfplasmepsin2 gene amplification and mutations in pfcrt downstream of the Lys76Thr chloroquine resistance locus has also developed. On the Thailand–Myanmar border a different pfkelch Cys580Tyr lineage rose to high frequencies before it was eliminated. Elsewhere in Myanmar the Cys580Tyr allele remains widespread at low allele frequencies. Meanwhile a single artemisinin-resistant pfkelch Phe446Ile haplotype has spread across Myanmar. Despite intense use of dihydroartemisinin–piperaquine in Kayin state, eastern Myanmar, both in treatment and mass drug administrations, no selection of piperaquine resistance markers was observed. pfmdr1 amplification, a marker of resistance to mefloquine, remains at low prevalence across the entire region. Interpretation Artemisinin resistance in P falciparum is now prevalent across the Greater Mekong subregion. In the eastern Greater Mekong subregion a multidrug resistant P falciparum lineage (PfPailin) dominates. In Myanmar a long pfkelch Phe446Ile haplotype has spread widely but, by contrast with the eastern Greater Mekong subregion, there is no indication of artemisinin combination therapy (ACT) partner drug resistance from genotyping known markers, and no evidence of spread of ACT resistant P falciparum from the east to the west. There is still a window of opportunity to prevent global spread of ACT resistance. Funding Thailand Science Research and Innovation, Initiative 5%, Expertise France, Wellcome Trust.

Expansion of a Specific Plasmodium falciparum PfMDR1 Haplotype in Southeast Asia with Increased Substrate Transport

“…This combination was associated with a rapid decline in pfmdr1 copy number (55,56), which could have resulted from PPQmediated selection against multicopy pfmdr1 and/or selective pressure against multicopy pfmdr1 parasites that show some loss of fitness and can therefore be outcompeted by single-copy pfmdr1 parasites (2,57,58). In Cambodia, the loss of DHA-PPQ efficacy led to the resumption of artesunate-MFQ use beginning in 2011, and this combination retains good efficacy with pfmdr1 copy number generally remaining at one (59). In contrast, the MalariaGEN data illustrate pfmdr1 amplifications as a rare event in Africa.…”

P. falciparum K13 mutations present varying degrees of artemisinin resistance and reduced fitness in African parasites

“…Our spatio-temporal analysis of K13 sequence diversity in Cambodia highlights the emergence of C580Y in western Cambodia and its progressive replacement of other variants (Imwong et al ., 2020). The success of this mutation in SEA cannot be explained by resistance alone, as we previously reported that the less common R539T and I543T variants conferred greater ART resistance in vitro (Straimer et al ., 2015).…”

Choosing interventions to eliminate forest malaria: preliminary results of two operational research studies inside Cambodian forests

“…The problem of using AS-MQ is that it is the current first-line treatment in Cambodia, and use as IPTfg might accelerate development of resistance. However, data suggest resistance levels are currently low, and theoretical models have shown that chemoprophylaxis could in some circumstances reduce resistance in the population by reducing treatment of symptomatic cases [ 38 , 39 ]; this could be the case if such deployment of AS-MQ were to substantially accelerate malaria elimination in the forest. DP is another appealing option, but experienced high failure rates in 2016 and susceptibility has not yet fully returned.…”