A deadly form of malaria that has developed resistance to the most advanced drugs used to treat the disease is rapidly spiraling into new territory and putting the lives of millions of people around the world in danger, according to findings from two studies published in The Lancet and the journal Science.
Malaria is spread by mosquitos and is commonly caused by the Plasmodium falciparum parasite. The disease kills up to 1.2 million people every year, according to that latest estimates by the Institute of Health Metrics and Evaluation at the University of Washington in 2010.
Scientists have found resistant strains of the malaria parasite on the border between Thailand and Burma, 500 miles of where they originated in western Cambodia. Experts say that the strain is becoming increasingly more resistant the most effective drugs containing artemisinin, which acts faster and has fewer side-effects compared to other antimalarial drugs like chloroquine and mefloquine.
Researchers have known for some time of these resistant malaria strains when it was confirmed in 2006 that parasites in Cambodia have begun to grow resistant artemisinin, but they had hope the resistance wasn’t spreading.
However, the latest findings show that artemisinin treatment has become dramatically less potent in malaria cases in western Thailand. Lead author of one of the studies Standwell Nkhoma from the Texas Biomedical Research Institute said there could be a “public health disaster” if artemisinin resistance were to continue to spread to sub-Saharan Africa, where malaria resistance to the other existing treatments has already occurred.
Researchers from one of the studies published in the Lancet, which consisted of 3,202 patients from northwestern border of Thailand near Myanmar from 2001 to 2010, measured the time it took patients to clear malaria infections from their blood after treatment. They found that the number of slow-clearing infections increased from 0.6 percent of cases treated in 2001 to a fifth of all cases in 2010, indicating that the parasite in this region is steadily becoming resistant to standard treatment.
In western Cambodia, where the resistant parasite originated, 42 percent of all malaria cases involved resistant strains between 2007 and 2010, showing that the Thailand-Myanmar region was swiftly catching up to Cambodia's resistant rates.
"Genetically determined artemisinin resistance in P. falciparum emerged along the Thailand-Myanmar border at least eight years ago and has since increased substantially," the authors from The Lancet study wrote. "At this rate of increase, resistance will reach rates reported in western Cambodia in two to six years."
While scientists are still unsure of whether the diminished potency of artemisinin is due to the growing drug resistance in the malaria parasites themselves, they have identified a region of the malaria parasite genome which contains several potential genes that may be responsible for mutating resistance in order to survive.
Researchers from the study published in the journal Science linked a region on chromosome 13 of the parasite to drug resistance, and they estimated that this region accounts for at least a third of the heritable variation in treatment clearance rates.
Ian Cheeseman, a geneticist at the Texas Biomedical Research Institute in San Antonio, and his colleagues compared the genomes and clearance rates of malaria parasite samples from Cambodia, Thailand and Laos, where resistance to artemisinin-based drugs has not yet emerged.
Researchers found seven genes that may be responsible for making the parasite resistant to drugs. The findings may help scientists better understand the growing resistance in Southeast Asia by explaining how artemisinin interacts with the parasite, how resistance develops over time, and may even offer clues on how to revise treatment to fight off the resistant strains.
“Mapping the geographical spread of resistance can be particularly challenging using existing clinical and parasitological tools,” Texas Biomed’s Dr. Tim Anderson said in a statement. “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 importing for limiting further spread of resistance.”
"We have now seen the emergence of malaria resistant to our best drugs, and these resistant parasites are not confined to western Cambodia," said lead author of the Lancet study Francois Nosten, director of the Shoklo Malaria Research Unit that studies and treats malaria in the Thai-Myanmar region, said in a statement. "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."
Recently, the death toll from malaria has been rapidly declining in Africa mostly because of the increased use of artemisinin drugs and distribution insecticide-treated bed nets, and if strains resistance to the most effective artemisinin therapies reaches to the continent the results would be catastrophic.