The meandering Moei river marks the natural boundary between Thailand and Myanmar. Its muddy waters are at their fullest, but François Nosten still crosses them in just a minute, aboard a narrow, wooden boat. In the dry season, he could wade across. As he steps onto the western riverbank, in Myanmar, he passes no checkpoint and presents no passport.

The air is cool. After months of rain, the surrounding jungle pops with vivid lime and emerald hues. Nosten climbs a set of wooden slats that wind away from the bank, up a muddy slope. His pace, as ever, seems relaxed and out of kilter with his almost permanently grave expression and urgent purpose. Nosten, a rangy Frenchman with tousled brown hair and glasses, is one of the world’s leading experts on malaria. He is here to avert a looming disaster. At the top of the slope, he reaches a small village of simple wooden buildings with tin and thatch roofs. This is Hka Naw Tah, home to around 400 people and a testing ground for Nosten’s bold plan to completely stamp out malaria from this critical corner of the world.

François Nosten and colleagues on the Myanmar bank of the Moei river. © Ian Teh/Panos

Malaria is the work of the single-celled Plasmodium parasites, and Plasmodium falciparum chief among them. They spread between people through the bites of mosquitoes, invading first the liver, then the red blood cells. The first symptoms are generic and flu-like: fever, headache, sweats and chills, vomiting. At that point, the immune system usually curtails the infection. But if the parasites spread to the kidneys, lungs and brain, things go downhill quickly. Organs start failing. Infected red blood cells clog the brain’s blood vessels, depriving it of oxygen and leading to seizures, unconsciousness and death.

When Nosten first arrived in South-east Asia almost 30 years ago, malaria was the biggest killer in the region. Artemisinin changed everything. Spectacularly fast and effective, the drug arrived on the scene in 1994, when options for treating malaria were running out. Since then, “cases have just gone down, down, down,” says Nosten. “I’ve never seen so few in the rainy season – a few hundred this year compared to tens of thousands before.”

But he has no time for celebration. Artemisinin used to clear P. falciparum in a day; now, it can take several. The parasite has started to become resistant. The wonder drug is failing. It is the latest reprise of a decades-long theme: we attack malaria with a new drug, it mounts an evolutionary riposte.

© Alex Hedworth/Eye Candy

Back in his office, Nosten pulls up a map showing the current whereabouts of the resistant parasites. Three coloured bands highlight the borders between Cambodia and Vietnam, Cambodia and Thailand, and Thailand and Myanmar (Burma). Borders. Bold lines on maps, but invisible in reality. A river that can be crossed in a rickety boat is no barrier to a parasite that rides in the salivary glands of mosquitoes or the red blood cells of humans.

History tells us what happens next. Over the last century, almost every frontline antimalarial drug – chloroquine, sulfadoxine, pyrimethamine – has become obsolete because of defiant parasites that emerged from western Cambodia. From this cradle of resistance, the parasites gradually spread west to Africa, causing the deaths of millions. Malaria already kills around 660,000 people every year, and most of them are African kids. If artemisinin resistance reached that continent, it would be catastrophic, especially since there are no good replacement drugs on the immediate horizon.

Nosten thinks that without radical measures, resistance will spread to India and Bangladesh. Once that happens, it will be too late. Those countries are too big, too populous, too uneven in their health services to even dream about containing the resistant parasites. Once there, they will inevitably spread further. He thinks it will happen in three years, maybe four. “Look at the speed of change on this border. It’s exponential. It’s not going to take 10 or 15 years to reach Bangladesh. It’ll take just a few. We have to do something before it’s too late.”

Hundreds of scientists are developing innovative new ways of dealing with malaria, from potential vaccines to new drugs, genetically modified mosquitoes to lethal fungi. As Nosten sees it, none of these will be ready in time. The only way of stopping artemisinin resistance, he says, is to completely remove malaria from its cradle of resistance. “If you want to eliminate artemisinin resistance, you have to eliminate malaria,” says Nosten. Not control it, not contain it. Eliminate it.

That makes the Moei river more than a border between nations. It’s Stalingrad. It’s Thermopylae. It’s the last chance for halting the creeping obsolescence of our best remaining drug. What happens here will decide the fate of millions.