Malaria remains one of the world’s great unnecessary killers. More than 650,000 people succumb to the disease each year — that’s more than one per minute — mostly in the poor nations of sub-Saharan Africa, but as deadly as malaria is, it doesn’t have to kill. Prevention and better treatment can stop the progression of the disease, and death tends to be a matter of extreme poverty.
Indeed, in recent years great progress has been made in controlling malaria, with deaths down 30% over the past decade. That’s thanks largely to more effective treatment regimens that make use of artemisinin, a plant-derived antimalarial drug originally developed in China. Artemisinin is the closest thing we have to a miracle drug for malaria.
That’s what makes the results of two studies out this week in the Lancet and Science so disturbing. Health officials have known for a while that some malaria parasites in the Southeast Asian nation of Cambodia have begun to develop resistance to artemisinin, but they hoped the resistance wasn’t spreading. Now researchers in the region have shown that artemisinin is becoming dramatically less potent in malaria cases in western Thailand, and they know it’s due to growing drug resistance in the malaria parasites themselves. If resistance to artemisinin were to spread to sub-Saharan Africa, the result could be a “public health disaster,” in the words of lead Lancet author Standwell Nkhoma of the Texas Biomedical Research Institute.
Artemisinin-resistant malaria parasites first emerged in Cambodia in 2006, which led to an international effort to control malaria and contain resistant strains there. But scientists in the Lancet study looked at more than 3,000 patients who were treated at malaria clinics in northwestern Thailand between 2001 and 2010. The researchers — including staff from Texas Biomed, Mahidol University in Bangkok and the Centre for Tropical Medicine at Oxford — found that it took longer and longer for malaria parasites to be cleared during treatment, a sign of growing resistance.
Molecular analysis of the malaria parasites showed that this resistance to treatment was due to a genetic trait — the parasites were adapting to artemisinin, just as they had in Cambodia. “Genetically determined artemisinin resistance in [the parasite] emerged along the Thailand-Myanmar [Burma] border at least eight years ago and has since increased substantially,” the authors wrote in the Lancet paper. “At this rate of increase, resistance will reach rates reported in western Cambodia in two to six years.”
In another study published in Science, researchers at Texas Biomed and their colleagues managed to get close to isolating the genes in the malaria parasite that convey resistance to artemisinin. That will help scientists understand how artemisinin interacts with the parasite, and how resistance takes place over time. In the future, it may even offer clues on how to alter treatment to cancel out resistance — to adapt to the parasite’s adaptation. “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.”
Drug resistance is inevitable — the more a treatment is used, the faster resistance will often develop, and the fact is that there are some 250 million cases of malaria a year. The only hope is to try to root out resistant-malaria where it occurs, and stop the chain of resistant transmission. That was hard enough in Cambodia, but with drug-resistant malaria spreading to Thailand and likely Burma as well — a desperately poor nation with a threadbare medical system — it will only get tougher. And if resistant malaria spreads to Africa, where the disease is still a catastrophe, perhaps millions more could die, as Francois Nosten of the Shoklo Malaria Research Unit in Thailand put it:
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. Malaria already kills hundreds of thousands of people a year — if our drugs become ineffective, this figure will rise dramatically.
The struggle against malaria really is a war — and it’s far from over.