Researchers have found that there is increasing resistance to the front-line treatments for malaria. A pair of studies published in The Lancet and the journal Science showed how the disease is moving fast into new territory and identified a region of the parasite's genome that may be responsible for mutating in order to survive.
They have confirmed the presence of resistant strains of the malaria parasite on the border between Thailand and Burma, 500 miles 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. Artemisinin is rarely used on its own, usually being combined with older drugs to help fight the rise of resistance. These artemisinin based combination therapies are now recommended by the World Health Organization as the first-line treatment and have contributed substantially to the recent decline in malaria cases in many regions. 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.
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.
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.”
“Either the resistance has moved and it will continue to move and will eventually reach Africa. Or if it has emerged, now that artemisinin is the standard therapy worldwide then it means it could emerge anywhere,” Prof Nosten told the BBC. “If we were to lose artemisinin then we don't have any new drugs in the pipeline to replace them. We could be going back 15 years to where cases were very difficult to treat because of the lack of an efficacious drug.”
Prof Nosten says the current spread of resistance could be similar to what happened in the 1970s with chloroquine, a drug that was once a front-line treatment against the disease. “When chloroquine resistance reached Africa in the middle of the 1970s it translated into a large increase in the number of cases and the number of children who died increased dramatically.”
In a separate paper published in the journal Science researchers have identified a region of the malaria parasite genome that is linked to resistance to artemisinin.
The research focused on what was making these parasites different, and found that a region on chromosome 13 of the parasite was strongly associated with slow clearance of infection. They sequenced the genomes of 91 P. falciparum parasites from Cambodia and western Thailand and compared them to parasites from Laos, where resistance to the latest artemisinin-based drugs has not yet emerged. They found seven genes that may be responsible for making the parasite resistant to drugs, and which may explain up to 35 percent of the growing resistance in southeast Asia.
Dr Tim Anderson, from Texas Biomed who led this study, says that while mapping the geographical spread of resistance can be challenging it may be hugely beneficial. “If we can identify the genetic determinants of artemisinin resistance we should be able to confirm potential cases of resistance more rapidly. This could be critically important for limiting the further spread of resistance,” he said.
Malaria is a mosquito-borne disease commonly caused by a parasite, Plasmodium falciparum, that kills up to 1.2 million people a year, according to 2010 estimates by the Institute of Health Metrics and Evaluation at the University of Washington, Seattle. According to the World Malaria Report 2011 malaria was responsible for killing an estimated 655,000 people in 2010 - more than one every minute. A majority of these were young children and pregnant women.
The two studies were funded by the Wellcome Trust and the US National Institutes of Health, and included scientists from Mahidol University, Bangkok; the Centre for Tropical Medicine at Britain's Oxford University; and the Texas Biomedical Research Institute in the United States.
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