The parasite that causes malaria is growing increasingly resistant to the drugs commonly used to fight it, according to new surveillance reports. But several new drugs are in development, and at least one in early clinical trials may offer new hope against this global killer.
"Although there has been considerable progress in malaria control in the past decade, the battle against malaria is far from won, and there is still much more to do," said Dr. Brian Greenwood, professor of tropical medicine at London School of Hygiene and Tropical Medicine, who wrote a commentary accompanying the new research.
Especially worrisome is the growing power of malaria parasites to survive the drugs that are designed to kill them, Greenwood said. One study reported widespread resistance to the drug artemisinin across mainland Southeast Asia. A second study found resistance to a drug combination -- dihydroartemisinin-piperaquine -- in Cambodia. Resistance to this drug is particularly concerning because this combination is often used in the most difficult-to-treat malaria infections.
Fortunately, even those who show resistance may get well when given longer courses of medication.
"Many of these patients will get better eventually if they are treated for many days or treated with an additional effective drug," Greenwood said.
All of the new research, along with Greenwood's editorial, appears in the July 31 issue of The New England Journal of Medicine.
Malaria is an infection caused by the parasite plasmodium, according to the World Health Organization (WHO). It is transmitted through the bites of infected mosquitoes.
It's estimated that more than 200 million cases of malaria occur every year, according to the WHO. The annual death toll from malaria around the world has fallen from 1 million 20 years ago to about 650,000, mostly children in Africa, according to Greenwood.
The decline, he said, is due to better funding for treatment and prevention from international donors and national governments in malaria-stricken areas.
Greenwood said researchers are still trying to figure out if the same type of resistance seen in Southeast Asia is happening in India and Africa. The surveillance study on artemisinin resistance did include several sites in India and Africa, but Greenwood pointed out in his editorial that there just wasn't enough sampling from those areas to definitively say whether or not resistance is developing.
"There is a major concern that artemisinin-resistant parasites will spread to or emerge in sub-Saharan Africa, where the main burden of malaria is found," he said. "This would be a major catastrophe, but this could be curtailed if alternative drugs can be found."
One potential alternative medication is known as KAE609, from a class of drugs known as spiroindolones. In another new report, this one funded by the drug company Novartis, scientists report that they successfully treated malaria in 21 patients from Thailand with the medication.
The drug "appears to rapidly clear the blood of the two most common species of the malaria parasite," said study co-author Thierry Diagana, head of the Novartis Institute for Tropical Diseases in Singapore. It may also prevent transmission of malaria, Diagana said.
However, it's still too early to know if the drug is a success. The study represents the second phase of three stages of research required of new drugs.
The study was too small to determine if there are any significant side effects, according to Diagana. It's also too early to know the potential cost of the drug. More studies are needed in the second phase of research for the new drug, Diagana noted.
Greenwood said that the focus must remain on controlling the spread of malaria, treating those who are sick with existing medications, and developing new drugs to control the disease.