Resistance to key malaria drug emerges

Biting back: Plasmodium falciparum, carried by mosquitoes, is showing signs of resistance Copyright: Flickr/trebol-a

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The parasite responsible for the deadliest form of malaria is showing the first signs of resistance to artemisinin — the drug hailed as the biggest hope for eradicating the disease.

The cases of resistance in Plasmodium falciparum were detected on the Thai-Cambodian border, in the same area that drug-resistant strains of the malaria parasite have developed in the past, most notably to chloroquine in the 1950s.

"We feel that we not only have to beat the drum but shake the cage: guys, this is significant," R. Timothy Ziemer, head of the President’s Malaria Initiative, who visited the area to assess the resistance problem, told the International Herald Tribune.

The reports of resistance, one of which was recently published in the New England Journal of Medicine, confirm fears that artemisinin — extracted from a plant used in traditional Chinese medicine — is losing its effectiveness in the area.

Global health authorities try to ensure that artemisinin is sold only in combination with other longer-lasting antimalarials that can ‘mop up’ any remaining parasites resistant to artemisinin. The two most recent tests that found resistance were not carried out using a combination drug.

The studies have found only the early signs of resistance, and patients with resistant forms have been cured.

It took chloroquine resistance decades to spread, so it is likely that artemisinin-based drugs will be used for many years. But if the resistance spreads sooner, there are no drugs in the pipeline to replace artemisinin combinations.

Efforts are now focused on preventing the spread of the parasites. A malaria monitoring centre will be set up in Myanmar and The Bill and Melinda Gates Foundation is donating US$14 million to the Cambodian and Thai governments to help contain resistant parasites.

They are providing mosquito nets and screening programmes with follow-up visits to assess the effectiveness of antimalarial drugs, and in Thailand ‘motorcycle microscopists’ are carrying out on the spot tests and distributing drugs.

Speaking to the International Herald Tribune, Pascal Ringwald, malaria coordinator at the WHO said: "This could spread in any direction — we have to make sure it doesn’t."

Link to full paper in the New England Journal of Medicine


N Engl J Med 359, 2619 (2008)