Drug-Resistant Malaria Casts A Growing Shadow in Asia

By webadmin on 10:00 pm May 01, 2012
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Bangkok. Resistance to an anti-malaria drug, artemisinin, is suspected along the Thailand-Burma border and in southern Vietnam, but scientists are hoping that it can be contained. Artemisinin resistance emerged on the Thailand-Cambodia border around eight years ago.

Resistance — the ability of the malaria parasite to survive drugs intended to kill it quickly — to chloroquine, an antimalarial previously widely used, forced treatment to change in the early 1970s and also originated in what is known as the Greater Mekong subregion, which includes Cambodia, the southern provinces of China, Laos, Burma, Thailand and Vietnam.

Chloroquine resistance spread to India and then to sub-Saharan Africa, which has the world’s highest burden of the disease.

Decades later, faced with another bout of resistance, officials are cautiously optimistic about preventing the spread of resistance to artemisinin.

“So far, we haven’t found any artemisinin resistance outside the Mekong region. … I think we have good chances to keep it in the Mekong region,” Pascal Ringwald, coordinator of the global malaria program for the World Health Organization, told a meeting of experts on antimalarial drug resistance in Bangkok.

He noted that the suspected cases of drug resistance along the two Thai borders appeared to be “totally independent, and it raises a concern that it could emerge anywhere.”

Roots of resistance

Resistance to artemisinin is not necessarily fatal for patients because partner drugs can boost its efficacy when it falters, but treatment may take longer and be more expensive.

Studies published earlier in April, covering more than 3,200 patients along the northwestern border of Thailand near Burma from 2001 to 2010, indicated a steady increase in drug resistance, from 0.6 percent of surveyed patients to 20 percent after a decade.

Scientists are still searching for the exact causes of the resistance, but link it to the widespread use of monotherapies, in which only artemisinin is prescribed.

Despite an international resolution addressing the danger of monotherapies, 25 countries and 28 pharmaceutical companies continue to market them.

Monotherapies are easier and less expensive to manufacture and market than combination therapies, which pair artemisinin with other drugs (artemisinin combination therapies, or ACTs), but they speed the development of resistance to artemisinin in malaria parasites.

According to the WHO, the parasite is highly unlikely to become drug resistant to ACTs.

Other possible factors in resistance are parasite biology, human behavior (like not taking the correct dosage or type of antimalaria drugs) and counterfeit drugs.

Where?

The four countries most affected thus far by artemisinin resistance are Cambodia, Thailand, Vietnam and Burma, which is the most affected.

Poor data has made it difficult to get a clear picture of the threat in Burma, where conflict zones are still largely off-limits to aid workers.

A national malaria containment project, implemented in 2011, has started yielding important data, but the WHO notes that a lack of funding is stunting its rollout.

“We are starting to get more baseline data to better map the situation,” Ringwald said.

While there are several national and regional plans to fight resistance to malaria, there is no regional coordination and a lack of cross-border collaboration to contain it, according to WHO experts trying to get the issue on the agenda of a meeting from July 2-6 of Asean health ministers.

In 2010, there were about 216 million malaria cases globally, and an estimated 655,000 deaths.

IRIN