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New evidence for increasing resistance to malaria treatment

Gert van der Hoek

In Memoriam - Editor, Senior Moderator
5 April 2012

Resistance spread 'compromising' fight against malaria

By Matt McGrath
Science reporter, BBC World Service


Scientists have found new evidence that resistance to the front-line treatments for malaria is increasing.

They have confirmed that resistant strains of the malaria parasite on the border between Thailand and Burma, 500 miles (800km) away from previous sites.

Researchers say that the rise of resistance means the effort to eliminate malaria is "seriously compromised".

The details have been published in The Lancet medical journal.

For many years now the most effective drugs against malaria have been derived from the Chinese plant, Artemisia annua. It is also known as sweet wormwood.

In 2009 researchers found that the most deadly species of malaria parasites, spread by mosquitoes, were becoming more resistant to these drugs in parts of western Cambodia.

This new data confirms that these Plasmodium falciparum parasites that are infecting patients more than 500 miles away on the border between Thailand and Burma are growing steadily more resistant.

The researchers from the Shoklo Malaria Research Unit measured the time it took the artemisinin drugs to clear parasites from the bloodstreams of more than 3,000 patients. Over the nine years between 2001 and 2010, they found that drugs became less effective and the number of patients showing resistance rose to 20%.

Prof Francois Nosten, who is part of the research team that has carried out the latest work, says the development is very serious.

"It would certainly compromise the idea of eliminating malaria that's for sure and will probably translate into a resurgence of malaria in many places," he said.

'Untreatable malaria'

Another scientist involved with the study is Dr Standwell Nkhoma from the Texas Biomedical Research Institute.

"Spread of drug-resistant malaria parasites within South East Asia and overspill into sub-Saharan Africa, where most malaria deaths occur, would be a public health disaster resulting in millions of deaths."

Read more: BBBC News
 
Re: New evidence for increasing resistance to malaria treatment

[Source: The Lancet, full text: (LINK). Abstract, edited.]

The Lancet, Early Online Publication, 5 April 2012

doi:10.1016/S0140-6736(12)60484-X


Emergence of artemisinin-resistant malaria on the western border of Thailand: a longitudinal study


Original Text

Aung Pyae Phyo MD, Standwell Nkhoma PhD, Kasia Stepniewska PhD, Elizabeth A Ashley MD, Shalini Nair MSc, Rose McGready MD, Carit ler Moo, Salma Al-Saai MSc, Arjen M Dondorp MD, Khin Maung Lwin MD, Pratap Singhasivanon MD, Nicholas PJ Day FRCP, Nicholas J White FRS, Tim JC Anderson PhD, Prof Fran?ois Nosten MD



Summary

Background

Artemisinin-resistant falciparum malaria has arisen in western Cambodia. A concerted international effort is underway to contain artemisinin-resistant Plasmodium falciparum, but containment strategies are dependent on whether resistance has emerged elsewhere. We aimed to establish whether artemisinin resistance has spread or emerged on the Thailand?Myanmar (Burma) border.


Methods

In malaria clinics located along the northwestern border of Thailand, we measured six hourly parasite counts in patients with uncomplicated hyperparasitaemic falciparum malaria (≥4% infected red blood cells) who had been given various oral artesunate-containing regimens since 2001. Parasite clearance half-lives were estimated and parasites were genotyped for 93 single nucleotide polymorphisms.


Findings

3202 patients were studied between 2001 and 2010. Parasite clearance half-lives lengthened from a geometric mean of 2?6 h (95% CI 2?5?2?7) in 2001, to 3?7 h (3?6?3?8) in 2010, compared with a mean of 5?5 h (5?2?5?9) in 119 patients in western Cambodia measured between 2007 and 2010. The proportion of slow-clearing infections (half-life ≥6?2 h) increased from 0?6% in 2001, to 20% in 2010, compared with 42% in western Cambodia between 2007 and 2010. Of 1583 infections genotyped, 148 multilocus parasite genotypes were identified, each of which infected between two and 13 patients. The proportion of variation in parasite clearance attributable to parasite genetics increased from 30% between 2001 and 2004, to 66% between 2007 and 2010.


Interpretation

Genetically determined artemisinin resistance in P falciparum emerged along the Thailand?Myanmar border at least 8 years ago and has since increased substantially. At this rate of increase, resistance will reach rates reported in western Cambodia in 2?6 years.


Funding


The Wellcome Trust and National Institutes of Health.
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