August 01, 2014
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Artemisinin resistance spreading through Southeast Asia

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Artemisinin resistance has developed in Plasmodium falciparum in border regions of Southeast Asia, according to a report in The New England Journal of Medicine.

The same region, the Cambodia-Thailand border, is where resistance to other first-line malaria drugs first emerged, according to the report. However, there was no sign of artemisinin resistance in the three sites in Africa involved in the study.

“It may still be possible to prevent the spread of artemisinin-resistant malaria parasites across Asia and then to Africa by eliminating them, but that window of opportunity is closing fast,” Nicholas White, FRS, of the Mahidol Oxford Tropical Medicine Research Unit and professor of tropical medicine at the University of Oxford, said in a press release. “Conventional malaria control approaches won’t be enough. We will need to take more radical action and make this a global public health priority, without delay.”

As part of the Tracking Resistance to Artemisinin Collaboration (TRAC), White and colleagues analyzed blood samples from 1,241 adults and children with acute, uncomplicated falciparum malaria who enrolled in an open-label trial from May 2011 to April 2013. The patients received artesunate for 3 days, followed by a 3-day course of artemisinin-based combination therapy. The researchers evaluated the parasite counts in the blood samples and determined the clearance half-lives.

The study took place at 15 sites in 10 countries: seven in Asia and three in Africa. The median parasite clearance half-lives varied, ranging from 1.8 hours in the Democratic Republic of Congo to 7 hours at the Thailand-Cambodia border. Slow-clearing infections were associated with a mutation on the P. falciparum kelch 13 gene, which was detected from southern Vietnam up to central Myanmar. Those with slow parasite clearance also had higher incidence of pre- and post-treatment gametocytemia, and thus more transmission potential.

However, a 6-day course of malaria therapy was associated with a cure rate of 97.7% at 42 days in western Cambodia, one of the areas where artemisinin resistance was found.

“Frontline artemisinin combination treatments are still very effective at curing the majority of patients,” Elizabeth Ashley, MBBS, PhD, the TRAC study lead scientist and a clinical researcher at the Mahidol Oxford Tropical Medicine Research Unit, said in the press release. “But we need to be vigilant as cure rates have fallen in areas where artemisinin resistance is established. Action is needed to prevent the spread of resistance from Myanmar into neighboring Bangladesh and India.”

Disclosure: The researchers report no relevant financial disclosures.