title: Where chloroquine still works: the genetic make-up and susceptibility of Plasmodium vivax to chloroquine plus primaquine in Bhutan.
abstract: Bhutan has made substantial progress in reducing malaria incidence. The national guidelines recommend chloroquine (CQ) and primaquine (PQ) for radical cure of uncomplicated Plasmodium vivax, but the local efficacy has not been assessed. The impact of cases imported from India on the genetic make-up of the local vivax populations is currently unknown.
  
  
  
  Patients over 4 years of age with uncomplicated P. vivax mono-infection were enrolled into a clinical efficacy study and molecular survey. Study participants received a standard dose of CQ (25 mg/kg over 3 days) followed by weekly review until day 28. On day 28 a 14-day regimen of PQ (0.25 mg/kg/day) was commenced under direct observation. After day 42, patients were followed up monthly for a year. The primary and secondary endpoints were risk of treatment failure at day 28 and at 1 year. Parasite genotyping was undertaken at nine tandem repeat markers, and standard population genetic metrics were applied to examine population diversity and structure in infections thought to be acquired inside or outside of Bhutan.
  
  
  
  A total of 24 patients were enrolled in the clinical study between April 2013 and October 2015. Eight patients (33.3 %) were lost to follow-up in the first 6 months and another eight patients lost between 6 and 12 months. No (0/24) treatment failures occurred by day 28 and no (0/8) parasitaemia was detected following PQ treatment. Some 95.8 % (23/24) of patients were aparasitaemic by day 2. There were no haemolytic or serious events. Genotyping was undertaken on parasites from 12 autochthonous cases and 16 suspected imported cases. Diversity was high (H E 0.87 and 0.90) in both populations. There was no notable differentiation between the autochthonous and imported populations.
  
  
  
  CQ and PQ remains effective for radical cure of P. vivax in Bhutan. The genetic analyses indicate that imported infections are sustaining the local vivax population, with concomitant risk of introducing drug-resistant strains.
authors.affiliation: Public Health Laboratory, Department of Public Health, Ministry of Health, Thimphu, Bhutan.
authors.forename: Sonam
authors.initials: S
authors.lastname: Wangchuk
authors.affiliation: Vector Borne Disease Control Programme in Gelephu, Communicable Disease Division, Department of Public Health, Ministry of Health, Thimphu, Bhutan.
authors.forename: Tobgyel
authors.initials: T
authors.lastname: Drukpa
authors.affiliation: Sarpang District Hospital, Ministry of Health, Sarpang District, Bhutan.
authors.forename: Kinley
authors.initials: K
authors.lastname: Penjor
authors.affiliation: Gelephu Regional Referral Hospital, Ministry of Health, Gelephu, Bhutan.
authors.forename: Tashi
authors.initials: T
authors.lastname: Peldon
authors.affiliation: Yebilaptsa Hospital, Ministry of Health, Zhemgang District, Bhutan.
authors.forename: Yeshey
authors.initials: Y
authors.lastname: Dorjey
authors.affiliation: Public Health Laboratory, Department of Public Health, Ministry of Health, Thimphu, Bhutan.
authors.forename: Kunzang
authors.initials: K
authors.lastname: Dorji
authors.affiliation: Gelephu Regional Referral Hospital, Ministry of Health, Gelephu, Bhutan.
authors.forename: Vishal
authors.initials: V
authors.lastname: Chhetri
authors.affiliation: Eijkman Institute for Molecular Biology, Jl. Diponegoro 69, Jakarta Pusat, 10430, Indonesia.|The Ministry of Research and Technology (RISTEK), Jakarta, Indonesia.|Agency for Assessment and Application of Technology, Jl. MH Thamrin 8, Jakarta, 10340, Indonesia.
authors.forename: Hidayat
authors.initials: H
authors.lastname: Trimarsanto
authors.affiliation: Global and Tropical Health Division, Menzies School of Health Research and Charles Darwin University, Darwin, NT, 0810, Australia.
authors.forename: Sheren
authors.initials: S
authors.lastname: To
authors.affiliation: Global and Tropical Health Division, Menzies School of Health Research and Charles Darwin University, Darwin, NT, 0810, Australia.|Faculty of Medicine and Biomedical Sciences, School of Population Health, The University of Queensland, Brisbane, Australia.
authors.forename: Amanda
authors.initials: A
authors.lastname: Murphy
authors.affiliation: Mahidol Oxford Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.|Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine Research Building, University of Oxford Old Road Campus, Oxford, UK.
authors.forename: Lorenz
authors.initials: L
authors.lastname: von Seidlein
authors.affiliation: Global and Tropical Health Division, Menzies School of Health Research and Charles Darwin University, Darwin, NT, 0810, Australia.|Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine Research Building, University of Oxford Old Road Campus, Oxford, UK.
authors.forename: Ric N
authors.initials: RN
authors.lastname: Price
authors.affiliation: Global and Tropical Health Division, Menzies School of Health Research and Charles Darwin University, Darwin, NT, 0810, Australia. kamala.ley-thriemer@menzies.edu.au.
authors.forename: Kamala
authors.initials: K
authors.lastname: Thriemer
authors.affiliation: Global and Tropical Health Division, Menzies School of Health Research and Charles Darwin University, Darwin, NT, 0810, Australia. sarah.auburn@menzies.edu.au.
authors.forename: Sarah
authors.initials: S
authors.lastname: Auburn
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000962:Antimalarials / Q000008:administration & dosage* / Q000494:pharmacology; D001631:Bhutan; D002738:Chloroquine / Q000008:administration & dosage* / Q000494:pharmacology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D010966:Plasmodium vivax / Q000145:classification / Q000187:drug effects* / Q000235:genetics; D011319:Primaquine / Q000008:administration & dosage* / Q000494:pharmacology; D011795:Surveys and Questionnaires; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D000962:Antimalarials; D002738:Chloroquine; D011319:Primaquine
keywords: Bhutan; Chloroquine; Imported malaria; India; Malaria; Plasmodium vivax; Population genetics; Primaquine