Malaria shows signs of resisting best drug used to fight it

The frontline malaria medicine artemisinin shows gaps in effectiveness in Southeast Asia

WASHINGTON — Malaria that is resistant to the best available drug is more widespread in Southeast Asia than previously reported, new research shows. The worrisome finding poses a risk that travelers could carry this strain of the malaria parasite to other parts of the globe and unwittingly spread it, scientists reported November 19 at a meeting of the American Society of Tropical Medicine and Hygiene

The frontline drug in question is called artemisinin, the most potent medication currently in use against malaria. Signs of malarial resistance to artemisinin have surfaced over the past several years in Cambodia (SN: 11/22/08, p. 9). The new findings confirm that resistant malaria has now cropped up beyond a spot on the border of Thailand and Cambodia where it was initially detected. Now it has appeared in Vietnam and in two spots along the the borders of Myanmar (formerly called Burma) with Thailand and China.

“Things are changing. There’s no doubt the signs are concerning,” said Robert Newman, director of the Global Malaria Programme at the World Health Organization in Geneva. But he added that these signals are early and need further verification.

Patients in these areas take longer on average to overcome a malaria infection when given a standard combination of artemisinin and another antimalarial. This lag results from slower clearance of the malaria parasites from the blood, said WHO’s Pascal Ringwald, a medical officer who presented the update.

Patients who remain ill for longer stretches despite treatment need extra medication to recover from malaria and are also more likely to have severe or fatal cases, Ringwald said.

Malaria is caused by a single-celled parasite that infects the blood. Symptoms include fever, headache, chills, anemia and a swollen spleen. Of the more than 350 million people who come down with malaria worldwide each year, up to 1 million die. Mosquitoes spread the parasite from person to person.

Malaria has a history of becoming resistant to drugs, and artemisinin now risks becoming the most recent addition to that list. The new reports are disheartening to doctors because artemisinin normally packs a considerable wallop. Although artemisinin is a short-acting drug that gets cleared from the body in a few hours, it makes the most of its time — driving down parasite levels dramatically.

Using artemisinin alone invites resistance. So the standard therapy teams it with one of the longer-acting drugs, which perform mop-up duty on the remaining parasites, said Christopher King, a physician and epidemiologist at Case Western Reserve University in Cleveland.

The new flashes of resistance may have arisen because combination treatment isn’t always available. And since artemisinin can be bought over the counter in many parts of Asia, people seeking relief don’t always follow the WHO guidelines of pairing artemisinin with another drug, King said.

Also, taking artemisinin for a fever that isn’t caused by malaria can allow resistant strains of the parasite to take hold, Newman said.

In the past, malaria’s resistance to other drugs has been linked to specific genetic changes in the parasite. The precise mechanism underlying resistance to artemisinin is still unsolved, King said.

Artemisinin is derived from extracts of the sweet wormwood bush. The bush’s leaves have been used as a folk remedy against fevers for roughly 2,000 years in Asia but fell out of use in the 20th century with the introduction of modern antimalarial drugs such as chloroquine.

During the Vietnam War, North Vietnamese leader Ho Chi Minh appealed to China for traditional remedies for soldiers who had malaria. Tea made from sweet wormwood leaves worked and ultimately became the basis for artemisinin drugs. It’s not clear whether parasites in Southeast Asia are the first to become resistant because they have had a long history with artemisinin, or if other factors are involved, Newman said.

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