By Ben Hirschler

LONDON, Feb 12 (Reuters) - Scientists and police have exposed a major Asian trade in life-threatening fake malaria drugs, resulting in the seizure of hundreds of thousands of tablets and the arrest of a dealer in southern China.

Details of the unique collaboration, made public on Tuesday, highlight the growing threat posed by the trade in counterfeit medicines and the difficulty of tracing the suppliers.

The problem is acute in Southeast Asia, where researchers have identified counterfeit versions of the malaria drug artesunate as a problem since 1998.

An investigation coordinated by Interpol, with input from international researchers, found as many as half of the malaria tablets sampled in Vietnam, Cambodia, Laos, Myanmar and on the Thai/Myanmar border were counterfeit.

They were disguised with authentic-looking packaging, including 16 different types of fake holograms.

Artesunate forms an essential part of artemisinin-based combination therapy, recommended as the mainstay of malaria treatment by the World Health Organisation (WHO) since 2001.

Most of the counterfeits examined contained no active drug and some had potentially toxic ingredients, including banned pharmaceuticals and even the raw material for making ecstasy.

Worryingly, some tablets also contained small amounts of artesunate, possibly to foil screening tests.

The doses were too low to be effective but high enough to contribute to the development of resistance in malaria parasites, adding to the problems of fighting the mosquito-borne disease, which still claims more than a million lives a year. Writing in the Public Library of Science journal PLoS Medicine, scientists said they traced the origin of the bogus medicines using pollen traces and chemical analysis.

At least some of the counterfeit supply came from southern China, leading Chinese authorities to arrest a suspect in Yunnan Province in 2006.

He is alleged to have traded 240,000 blisterpacks, each with 12 tablets, although only a tenth of this stash was seized.

Dr Paul Newton of the Wellcome Trust-University of Oxford SE Asian Tropical Medicine Research Programme, the main author of the PLoS report, fears this case is just the tip of the iceberg.

"There are probably other similar problems with other life-saving medicines we are unaware of," he said in a telephone interview. (Editing by Will Waterman)

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