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Longitudinal in vitro surveillance of Plasmodium falciparum sensitivity to common anti-malarials in Thailand between 1994 and 2010

Daniel Parker12, Rujira Lerdprom3, Wanna Srisatjarak3, Guiyun Yan4, Jetsumon Sattabongkot5, James Wood12, Jeeraphat Sirichaisinthop3* and Liwang Cui6*

Author Affiliations

1 Department of Anthropology, The Pennsylvania State University, 409 Carpenter Building, University Park, PA, 16802, USA

2 Population Research Institute, The Pennsylvania State University, 601 Oswald Tower, University Park, PA, 16802, USA

3 Vector Borne Disease Training Center, Pra Budhabat, Saraburi, 18120, Thailand

4 Public Health, University of California, Irvine, CA, 92697, USA

5 Faculty of Tropical Medicine, Mahidol University, Bangkok, 10400, Thailand

6 Department of Entomology, The Pennsylvania State University, 501 ASI Building, University Park, PA, 16801, USA

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Malaria Journal 2012, 11:290  doi:10.1186/1475-2875-11-290

Published: 21 August 2012



Drug and multidrug-resistant Plasmodium falciparum malaria has existed in Thailand for several decades. Furthermore, Thailand serves as a sentinel for drug-resistant malaria within the Greater Mekong sub-region. However, the drug resistance situation is highly dynamic, changing quickly over time. Here parasite in vitro drug sensitivity is reported for artemisinin derivatives, mefloquine, chloroquine and quinine, across Thailand.


Blood was drawn from patients infected with P. falciparum in seven sentinel provinces along Thai international borders with Cambodia, Myanmar, Laos, and Malaysia. In vitro parasite sensitivity was tested using the World Health Organization’s microtest (mark III) (between 1994 and 2002) and the histidine-rich protein-2 (HRP2)-based enzyme-linked immunosorbent assay (in 2010). Following World Health Organization protocol, at least 30 isolates were collected for each province and year represented in this study. Where possible, t-tests were used to test for significant differences.


There appears to be little variation across study sites with regard to parasite sensitivity to chloroquine. Quinine resistance appears to have been rising prior to 1997, but has subsequently decreased. Mefloquine sensitivity appears high across the provinces, especially along the north-western border with Myanmar and the eastern border with Cambodia. Finally, the data suggest that parasite sensitivity to artemisinin and its derivatives is significantly higher in provinces along the north-western border with Myanmar.


Parasite sensitivity to anti-malarials in Thailand is highly variable over time and largely mirrors official drug use policy. The findings with regard to reduced sensitivity to artemisinin derivatives are supported by recent reports of reduced parasite clearance associated with artemisinin. This trend is alarming since artemisinin is considered the last defence against malaria. Continued surveillance in Thailand, along with increased collaboration and surveillance across the entire Greater Mekong sub-region, is clearly warranted.

Plasmodium falciparum; Drug resistance; Artemisinin; Mefloquine; Thailand; The Greater Mekong subregion