Malaria outbreak in Laos driven by a selective sweep for Plasmodium falciparum kelch13 R539T mutants: a genetic epidemiology analysis

Varanya Wasakul, Areeya Disratthakit, Mayfong Mayxay, Keobouphaphone Chindavongsa, Viengphone Sengsavath, Nguyen Thuy-Nhien, Richard D. Pearson, Sonexay Phalivong, Saiamphone Xayvanghang, Richard J. Maude, S. nia Gonçalves, Nicholas P. Day, Paul N. Newton, Elizabeth A. Ashley, Dominic P. Kwiatkowski, Arjen M. Dondorp, Olivo Miotto

Research output: Contribution to journalArticleAcademicpeer-review

9 Citations (Scopus)

Abstract

Background: Malaria outbreaks are important public health concerns that can cause resurgence in endemic regions approaching elimination. We investigated a Plasmodium falciparum outbreak in Attapeu Province, Laos, during the 2020–21 malaria season, using genomic epidemiology methods to elucidate parasite population dynamics and identify its causes. Methods: In this genetic analysis, 2164 P falciparum dried blood spot samples were collected from southern Laos between Jan 1, 2017, and April 1, 2021, which included 249 collected during the Attapeu outbreak between April 1, 2020, and April 1, 2021, by routine surveillance. Genetic barcodes obtained from these samples were used to investigate epidemiological changes underpinning the outbreak, estimate population diversity, and analyse population structure. Whole-genome sequencing data from additional historical samples were used to reconstruct the ancestry of outbreak strains using identity-by-descent analyses. Findings: The outbreak parasite populations were characterised by unprecedented loss of genetic diversity, primarily caused by rapid clonal expansion of a multidrug-resistant strain (LAA1) carrying the kelch13 Arg539Thr (R539T) mutation. LAA1 replaced kelch13 Cys580Tyr (C580Y) mutants resistant to dihydroartemisinin–piperaquine (KEL1/PLA1) as the dominant strain. LAA1 inherited 58·8% of its genome from a strain circulating in Cambodia in 2008. A secondary outbreak strain (LAA2) carried the kelch13 C580Y allele, and a genome that is essentially identical to a Cambodian parasite from 2009. A third, low-frequency strain (LAA7) was a recombinant of KEL1/PLA1 with a kelch13 R539T mutant. Interpretation: These results strongly suggest that the outbreak was driven by a selective sweep, possibly associated with multidrug-resistant phenotypes of the outbreak strains. Established resistant populations can circulate at low frequencies for years before suddenly overwhelming dominant strains when the conditions for selection become favourable—eg, when front-line therapies change. Genetic surveillance can support elimination by characterising key properties of outbreaks such as population diversity, drug resistance marker prevalence, and the origins of outbreak strains. Funding: Bill & Melinda Gates Foundation; The Global Fund to Fight AIDS, Tuberculosis and Malaria; Wellcome Trust. Translation: For the Lao translation of the abstract see Supplementary Materials section.
Original languageEnglish
Pages (from-to)568-577
Number of pages10
JournalThe Lancet Infectious Diseases
Volume23
Issue number5
Early online date2023
DOIs
Publication statusPublished - May 2023
Externally publishedYes

Cite this