Ex vivo drug sensitivity profiles of Plasmodium falciparum field isolates from Cambodia and Thailand, 2005 to 2010, determined by a histidine-rich protein-2 assay

Stuart D Tyner ,Youry Se,Wiriya Rutvisuttinunt,Soklyda Chann,Kritsanai Yingyuen,Nillawan Buathong,Suwanna Chaorattanakawee,Sabaithip Sriwichai,Piyaporn Saingam,Siratchana Sundrakes,Darapiseth Sea,Chanthap Lon,Ans Timmermans,Wichai Satimai,Doung Socheat,Delia Bethell,Harald Noedl,Panjaporn Chaichana,David Saunders ,Kurt E Schaecher ,Mark M Fukuda ,Douglas S Walsh

doi:10.1186/1475-2875-11-198

Abstract

BackgroundIn vitro drug susceptibility assay of Plasmodium falciparum field isolates processed “immediate ex vivo” (IEV), without culture adaption, and tested using histidine-rich protein-2 (HRP-2) detection as an assay, is an expedient way to track drug resistance.MethodsFrom 2005 to 2010, a HRP-2 in vitro assay assessed 451 P. falciparum field isolates obtained from subjects with malaria in western and northern Cambodia, and eastern Thailand, processed IEV, for 50% inhibitory concentrations (IC50) against seven anti-malarial drugs, including artesunate (AS), dihydroartemisinin (DHA), and piperaquine.ResultsIn western Cambodia, from 2006 to 2010, geometric mean (GM) IC50 values for chloroquine, mefloquine, quinine, AS, DHA, and lumefantrine increased. In northern Cambodia, from 2009–2010, GM IC50 values for most drugs approximated the highest western Cambodia GM IC50 values in 2009 or 2010.ConclusionsWestern Cambodia is associated with sustained reductions in anti-malarial drug susceptibility, including the artemisinins, with possible emergence, or spread, to northern Cambodia. This potential public health crisis supports continued in vitro drug IC50 monitoring of P. falciparum isolates at key locations in the region.

Highlights

In vitro drug susceptibility assay of Plasmodium falciparum field isolates processed “immediate ex vivo” (IEV), without culture adaption, and tested using histidine-rich protein-2 (HRP-2) detection as an assay, is an expedient way to track drug resistance
HRP-2 assay, when field deployed proximal to P. falciparum collection sites, allows for “immediate ex vivo” (IEV) field isolate processing [7]
Among P. falciparum field isolates obtained in western Cambodia from 2005 to 2010, steady increases were observed for geometric mean (GM) IC50 values measured by a HRP-2 in vitro assay against a range of anti-malarial drugs, including AS and DHA

Summary

Introduction

In vitro drug susceptibility assay of Plasmodium falciparum field isolates processed “immediate ex vivo” (IEV), without culture adaption, and tested using histidine-rich protein-2 (HRP-2) detection as an assay, is an expedient way to track drug resistance. In Southeast Asia, especially along the Thailand-Cambodia border, changes in drug susceptibility often emerge first, with worldwide implications, In 2003, artesunate (AS) + mefloquine (MQ) was implemented as the first-line artemisinin-combination therapy (ACT) for falciparum malaria in Cambodia. By 2005, subjects with falciparum malaria along Thai-Cambodia border treated with oral artesunate were showing longer parasite clearance times, suggesting the emergence of reduced susceptibility to artemisinins, as well as to the partner drug [4]. The non-radioisotope histidine-rich protein-2 (HRP-2) ELISA, a relatively sensitive assay, which reliably depicts drug IC50 values for P. falciparum isolates, reduces obstacles for conducting assays in remote settings [5,6]. IEV, by avoiding cryopreservation and culture-adaptation before IC50 determination, may reduce clonal selection, better preserving parasite subpopulations with variable drug susceptibility profiles, the latter likely present in a smaller proportion than wild-type drug susceptible parasites

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Results

Conclusion