A malaria treatment considered the most effective weapon against drug-resistant strains of the lethal disease may be losing potency in Asia, doctors say.
Sensitivity to treatments based on artemisinin is declining in the border area between Thailand and Cambodia, the epicenter of emerging malaria drug resistance since the 1970s, the World Health Organization said. The Plasmodium falciparum parasite, which is carried by mosquitoes and causes the disease, may have mutated to evade yet another drug, the agency said in a report.
Artemisinin is the basis for all WHO-recommended falciparum treatments. Health officials are worried a potentially resistant strain of the parasite could spread to Africa, where malaria kills about 800,000 children aged 5 years and younger every year. Annual funding for malaria has risen more than 10 times, to at least $600 million, since 2004.
``It would be a pity if that kind of parasite is jumping to Africa and hijacking previous efforts,'' said Charles Delacollette, coordinator of the Mekong Malaria Program, a WHO- led group fighting the disease. ``This is what the concern is.''
Delacollette and colleagues are studying the susceptibility of artemisinin in the region and its effectiveness when combined with other medicines. They plan to release a report on their findings within three months.
So far, no resistance to artemisinin has been found, Delacollette said in an interview from Bangkok yesterday. The declining sensitivity may have occurred because some patients weren't taking enough of the medicine to clear the parasite, he said.
Artemisinin is derived from the sweet wormwood plant and has been used as a remedy in China for hundreds of years. An intravenous treatment containing the drug was approved by U.S. regulators in August.
Artemisinin combined with the drug mefloquine has been the first-line treatment for most falciparum infections since 1995 in Thailand and 2000 in Cambodia, the WHO said in its Oct. 12 Weekly Epidemiological Record.
Monitoring the emergence of new malaria strains for resistance is crucial, said Brian Greenwood, a professor at the U.K.'s London School of Hygiene & Tropical Medicine. The possibility of artemisinin-resistant malaria is ``very concerning,'' he said. ``It would be disastrous.''
``If it comes to Africa in 20 years, we'll have new drugs by then,'' Greenwood said in an interview yesterday in Seattle, where he was attending a Gates Foundation-sponsored meeting. ``If we see it in five years, we won't.''
Malaria is spread by mosquitoes in 103 countries, where it kills between 1 million and 3 million people each year. Most victims are children in Sub-Saharan Africa. The disease is estimated to rob Africa of $12 billion in gross domestic product annually and cost the average household a quarter of its income.
Malaria has made a career out of developing resistance to the most powerful drugs man has developed against it. Chloroquine, artemisinin's predecessor, blocks an essential process in the parasite's attack, the formation of long-chain molecules from blood proteins.
Yet malaria has learned to block the drug or rid it from infected cells, said Dyann Wirth, a Harvard School of Public Health malaria researcher, in an interview at the Seattle meeting. Those resistant strains probably also emerged in Southeast Asia.
``All the nasty resistances came from that area and if it's there it will spread out of the area,'' she said.