title: Ex vivo piperaquine resistance developed rapidly in Plasmodium falciparum isolates in northern Cambodia compared to Thailand.
abstract: BACKGROUND
  The recent dramatic decline in dihydroartemisinin-piperaquine (DHA-PPQ) efficacy in northwestern Cambodia has raised concerns about the rapid spread of piperaquine resistance just as DHA-PPQ is being introduced as first-line therapy in neighbouring countries.
  
  
  METHODS
  Ex vivo parasite susceptibilities were tracked to determine the rate of progression of DHA, PPQ and mefloquine (MQ) resistance from sentinel sites on the Thai-Cambodian and Thai-Myanmar borders from 2010 to 2015. Immediate ex vivo (IEV) histidine-rich protein 2 (HRP-2) assays were used on fresh patient Plasmodium falciparum isolates to determine drug susceptibility profiles.
  
  
  RESULTS
  IEV HRP-2 assays detected the precipitous emergence of PPQ resistance in Cambodia beginning in 2013 when 40 % of isolates had an IC90greater than the upper limit of prior years, and this rate doubled to 80 % by 2015. In contrast, Thai-Myanmar isolates from 2013 to 14 remained PPQ-sensitive, while northeastern Thai isolates appeared to have an intermediate resistance profile. The opposite trend was observed for MQ where Cambodian isolates appeared to have a modest increase in overall sensitivity during the same period, with IC50declining to median levels comparable to those found in Thailand. A significant association between increased PPQ IC50and IC90among Cambodian isolates with DHA-PPQ treatment failure was observed. Nearly all Cambodian and Thai isolates were deemed artemisinin resistant with a >1 % survival rate for DHA in the ring-stage assay (RSA), though there was no correlation among isolates to indicate cross-resistance between PPQ and artemisinins.
  
  
  CONCLUSIONS
  Clinical DHA-PPQ failures appear to be associated with declines in the long-acting partner drug PPQ, though sensitivity appears to remain largely intact for now in western Thailand. Rapid progression of PPQ resistance associated with DHA-PPQ treatment failures in northern Cambodia limits drugs of choice in this region, and urgently requires alternative therapy. The temporary re-introduction of artesunate AS-MQ is the current response to PPQ resistance in this area, due to inverse MQ and PPQ resistance patterns. This will require careful monitoring for re-emergence of MQ resistance, and possible simultaneous resistance to all three drugs (AS, MQ and PPQ).
authors: US Army Medical Component-Armed Forces Research Institute of Medical Sciences (USAMC-AFRIMS), Bangkok, Thailand.|Department of Parasitology and Entomology, Faculty of Public Health, Mahidol University, Bangkok, Thailand.
authors: Suwanna
authors: S
authors: Chaorattanakawee
authors: US Army Medical Component-Armed Forces Research Institute of Medical Sciences (USAMC-AFRIMS), Bangkok, Thailand. Chanthapl.ca@afrims.org.|USAMC-AFRIMS, Phnom Penh, Cambodia. Chanthapl.ca@afrims.org.
authors: Chanthap
authors: C
authors: Lon
authors: US Army Medical Component-Armed Forces Research Institute of Medical Sciences (USAMC-AFRIMS), Bangkok, Thailand.
authors: Krisada
authors: K
authors: Jongsakul
authors: Royal Thai Army, Bangkok, Thailand.
authors: Jariyanart
authors: J
authors: Gawee
authors: Royal Cambodian Armed Forces, Phnom Penh, Cambodia.
authors: Somethy
authors: S
authors: Sok
authors: US Army Medical Component-Armed Forces Research Institute of Medical Sciences (USAMC-AFRIMS), Bangkok, Thailand.
authors: Siratchana
authors: S
authors: Sundrakes
authors: National Center for Parasitology, Entomology and Malaria Control, Phnom Penh, Cambodia.
authors: Nareth
authors: N
authors: Kong
authors: US Army Medical Component-Armed Forces Research Institute of Medical Sciences (USAMC-AFRIMS), Bangkok, Thailand.
authors: Chatchadaporn
authors: C
authors: Thamnurak
authors: USAMC-AFRIMS, Phnom Penh, Cambodia.
authors: Soklyda
authors: S
authors: Chann
authors: US Army Medical Component-Armed Forces Research Institute of Medical Sciences (USAMC-AFRIMS), Bangkok, Thailand.
authors: Sorayut
authors: S
authors: Chattrakarn
authors: US Army Medical Component-Armed Forces Research Institute of Medical Sciences (USAMC-AFRIMS), Bangkok, Thailand.
authors: Chantida
authors: C
authors: Praditpol
authors: US Army Medical Component-Armed Forces Research Institute of Medical Sciences (USAMC-AFRIMS), Bangkok, Thailand.
authors: Nillawan
authors: N
authors: Buathong
authors: US Army Medical Component-Armed Forces Research Institute of Medical Sciences (USAMC-AFRIMS), Bangkok, Thailand.
authors: Nichapat
authors: N
authors: Uthaimongkol
authors: US Army Medical Component-Armed Forces Research Institute of Medical Sciences (USAMC-AFRIMS), Bangkok, Thailand.
authors: Philip
authors: P
authors: Smith
authors: Royal Thai Army, Bangkok, Thailand.
authors: Narongrid
authors: N
authors: Sirisopana
authors: National Center for Parasitology, Entomology and Malaria Control, Phnom Penh, Cambodia.
authors: Rekol
authors: R
authors: Huy
authors: Royal Cambodian Armed Forces, Phnom Penh, Cambodia.
authors: Satharath
authors: S
authors: Prom
authors: US Army Medical Component-Armed Forces Research Institute of Medical Sciences (USAMC-AFRIMS), Bangkok, Thailand.
authors: Mark M
authors: MM
authors: Fukuda
authors: US Army Medical Component-Armed Forces Research Institute of Medical Sciences (USAMC-AFRIMS), Bangkok, Thailand.
authors: Delia
authors: D
authors: Bethell
authors: US Army Medical Component-Armed Forces Research Institute of Medical Sciences (USAMC-AFRIMS), Bangkok, Thailand.
authors: Douglas S
authors: DS
authors: Walsh
authors: US Army Medical Component-Armed Forces Research Institute of Medical Sciences (USAMC-AFRIMS), Bangkok, Thailand.|Department of Pathology and Area Laboratory Services, Microbiology Section, Brooke Army Medical Center, San Antonio, TX, USA.
authors: Charlotte
authors: C
authors: Lanteri
authors: US Army Medical Component-Armed Forces Research Institute of Medical Sciences (USAMC-AFRIMS), Bangkok, Thailand.
authors: David
authors: D
authors: Saunders
mesh_terms: D000953:Antigens, Protozoan / Q000032:analysis; D000962:Antimalarials / Q000494:pharmacology*; D037621:Artemisinins / Q000494:pharmacology; D002160:Cambodia; D004351:Drug Resistance; D006801:Humans; D020128:Inhibitory Concentration 50; D015767:Mefloquine / Q000494:pharmacology; D021261:Parasitic Sensitivity Tests; D010963:Plasmodium falciparum / Q000187:drug effects* / Q000302:isolation & purification; D015800:Protozoan Proteins / Q000032:analysis; D011804:Quinolines / Q000494:pharmacology*; D013785:Thailand; D010879:Piperazines
chemical_list: D000953:Antigens, Protozoan; D000962:Antimalarials; D037621:Artemisinins; D015767:Mefloquine; D015800:Protozoan Proteins; D011804:Quinolines; C514457:HRP-2 antigen, Plasmodium falciparum; C039060:artenimol; C034759:piperaquine; D010879:Piperazines
keywords: Cambodia; Drug resistance; Malaria; Mefloquine; Piperaquine; Thailand