Malaria remains a huge problem in much of the world, but over the past decade the number of people getting sick and dying from the disease has gone down dramatically.
Health workers attribute much of this progress to the widespread use of artemisinin-based drugs. The problem now is that resistance to these drugs is starting to develop in Southeast Asia.
One place where this resistance was first found is along the border between Thailand and Myanmar, also known as Burma.
At the small Whampa health clinic on the Thai side of the Moi River, Dr. Aun Pyae Phyo is treating a 5-year-old Burmese boy with severe malaria. The boy had been carried to the clinic three days earlier.
"On that day, he couldn't even move his limbs," the doctor says of the boy. "So we need to start intravenous anti-malarial drugs, and we also need to transfuse him with blood."
If the boy's mother had waited even a day longer to come to the clinic, the doctor says, the child probably would have died. But the boy responded well to an initial dose of intravenous artemisinin drugs. The staff followed that with a three-day regimen of pills including artemisinin.
This is what these drugs have done so well around the world — a child is on the verge of death, and a quick course of artemisinin brings him back to health.
But over the past couple of years, doctors have started to see that some cases of malaria don't respond in the same way to these powerful anti-malarial medications.
"If the parasite strain inside that kid turned out to be resistant," Dr. Aun Pyae Phyo says shaking his head, "the scenario would turn out to be quite disastrous."
He says the boy's first day at the clinic was critical. If the parasite hadn't responded to the initial treatment and had continued to multiply in the boy's body, the infection could have been fatal.
So far, the cracks in artemisinin's armor are minor. Sometimes the drugs just take longer to work. But it's clear that the malaria parasite is evolving, shifting, learning how to outwit the drugs that were designed to kill it.
Francois Nosten, the head of the Shoklo Malaria Research Unit, which runs this clinic on the Thai-Burma border, says drug-resistant malaria is still the exception rather than the rule here, but it's a major concern.
"Clearly it's very worrying," Nosten says. "These drugs have been very effective."
If artemisinins aren't part of the medical staff's arsenal at this clinic, there are few other options.
Malaria has developed resistance to most of the other major drugs thrown at it. Chloroquine and Fansidar, which were once leading malaria treatments, are now useless against the parasite in many parts of the world. The expectation among researchers is that this will also happen eventually with artemisinins.
Some new drugs are being developed, but they probably won't be available for at least five years.
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