Drug-resistant malaria spreads across Thailand

MALARIA parasites in west Thailand are becoming resistant to artemisinins - the world's most effective antimalarial drugs. The march of increasingly drug-resistant malaria across the country has sparked fears that it could reach Africa, where 90 per cent of all malaria deaths occur.

Increasing resistance to artemisinins was first identified in Cambodia in 2006, and is now common along its border with eastern Thailand.

Nicholas White of Mahidol University in Bangkok, Thailand, and colleagues looked for signs of resistance in 3200 patients from clinics on Thailand's western border. They did so by measuring how long it takes for the number of malaria parasites in a person's blood to halve. With artemisinin treatment, this should take around 2 hours. In Cambodia, it now takes around 5.5 hours.

On Thailand's western border, this figure rose from 2.6 hours in 2001 to 3.7 hours in 2010. The percentage of infections that clear very slowly - 6.2 hours or more - soared from 0.6 per cent of all patients in 2001 to 20 per cent in 2010 (The Lancet, DOI: 10.1016/S0140-6736(12)60484-X). "If it carries on, we will lose the use of these drugs," says White.

There are several factors behind the increasing resistance, including the sale of diluted artemisinin treatments. Parasites in Cambodia also appear to have enhanced genetic resistance to the drug compared with resistant parasites in other parts of the world. The most important tool needed to contain resistance is finding a genetic marker for it, says White.

The World Health Organization agrees that the search for a reliable marker is paramount. Without this tool, "it's not possible to establish where strains have spread or emerged anew", says Pascal Ringwald, resistance coordinator at the WHO's global malaria programme in Geneva, Switzerland.

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