AsianScientist (Apr. 9, 2012) – Two studies, reported in The Lancet and Science last week, places the spotlight on malarial resistance at the Thai-Myanmar border.
The studies, both funded by the Wellcome Trust and the U.S. National Institutes of Health, follow reports in 2009 of the emergence of Artemisinin-resistant malaria parasites in western Cambodia, 800 km away from the Thai-Myanmar border where the new cases of resistance have been observed.
According to the World Malaria Report 2011, malaria claimed an estimated 655,000 lives in 2010, mainly young children and pregnant women. The disease is caused by parasites that are injected into the bloodstream by infected mosquitoes.
The declining efficacy of Artemisinin drugs, currently the frontline treatment recommended by the World Health Organization (WHO) for the most deadly species of the malaria parasite, Plasmodium falciparum, raises concern that resistance might spread to India and then Africa, making elimination of the disease impossible.
The Lancet study was carried out over the ten years from 2001 to 2010 by researchers at the Shoklo Malaria Research Unit on the border of Thailand and Myanmar, part of the Wellcome Trust-Mahidol University-Oxford Tropical Medicine Research Program.
They measured how long it took to clear parasites from the bloodstream in 3,202 patients with falciparum malaria using oral Artesunate-containing medications.
Over the decade, the average time taken to reduce the number of parasites in the blood by a half, known as the ‘parasite clearance half-life,’ increased from 2.6 hours in 2001 to 3.7 hours in 2010, a clear sign that the drugs were becoming less effective.
Of greater concern, the proportion of infections that were slow-clearing, those with a half-life of more than 6.2 hours, increased over the decade from six in 1,000 to 200 in 1,000.
Compelling evidence that the decline in the parasite clearance rates was due to genetic changes in the parasites was found on examination of their genetic make-up.
“We have now seen the emergence of malaria resistant to our best drugs, and these resistant parasites are not confined to western Cambodia,” said Professor François Nosten, Director of the Shoklo Malaria Research Unit.
“This is very worrying indeed and suggests that we are in a race against time to control malaria in these regions before drug resistance worsens and develops and spreads further.”
The effect of that happening could be devastating, Nosten said, as malaria already kills hundreds of thousands of people a year. Should the drugs become ineffective, this figure will rise dramatically, he warned.
“If we can identify the genetic determinants of Artemisinin resistance, we should be able to confirm potential cases of resistance more rapidly,” said the leader of the genetics studies in both papers, Dr. Tim Anderson from the Texas Biomedical Research Institute.
The team has already identified the genome region that harbors a number of potential genes that may drive Artemisinin resistance. Finding the precise gene location for Artemisinin resistance could be critically important for limiting further spread of resistance, Anderson said.
The articles can be found at:
- Phyo et al. (2012) Emergence of artemisinin-resistant malaria on the western border of Thailand: a longitudinal study.
- Cheeseman IH et al. (2012) A major genome region underlying artemisinin resistance in malaria.
Source: Wellcome Trust.
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