When an intense fever overcame 50-year-old Daw Cho Cho last spring, she took the same steps as when she last had malaria.

Wary of village medicine and aware of the well-funded clinic across the border, she crossed into Thailand from her Burma village and came to the malaria centre for treatment. Seven years ago, her malaria was cured within a day. This time, it took much longer.

Within three days, medication had killed the parasites in her blood and Daw Cho Cho felt normal, her symptoms gone. But a month later, the malaria came back. The drugs were unable to kill all the parasites in her blood, and they multiplied.

Dr François Nosten has studied malaria on the Thai-Burma border for 30 years. Photograph: Kathleen E McLaughlin for the Guardian

She is among the thousands who have been infected with an insidiously evolving drug-resistant parasite that may account for 80% of the malaria on this section of the Thai-Burma border. The mosquito-borne illness is becoming resistant to the last anti-malaria drug standing – artemisinin – largely because of counterfeit medicines and incorrect usage.

A leading researcher at the Shoklo Malaria Research Unit (SMRU), a research centre based on the border and funded primarily by the Wellcome Trust, is taking radical measures to stop the spread of the new strain before it becomes uncontrollable. Dr François Nosten, SMRU's director, has studied malaria in this border region, near where the disease first became drug resistant, for three decades. He believes that in order to stop it spreading to India, then Africa, where the vast majority of the world's malaria cases occur, it's essential to chase the parasite into Burma's forests and pre-emptively treat even people who may not be ill.

"If we don't do anything, we think that we know what's going to happen," said Nosten, explaining that as malaria rates decline, the strongest and most resistant strains of the parasite survive and spread. "It has always happened like this in the past, there's no reason to think this time will be any different."

The level of alarm Nosten and other scientists express over drug-resistant malaria contrasts with how it manifests in people, in these early stages. It acts just the same as any malaria, but is more difficult to cure. The number of cases creeps up slowly, spreads, then explodes.

"The thing about resistance to anything – drugs, antibacterials – is that it rises exponentially," said Nick White, a professor with the Oxford Tropical Medicine Research Programme who works with Nosten on this issue. "There's a long period where it doesn't appear to be rising – and then it's rising."

People who have had the new strain of malaria report that it feels no different to the disease cured in a day by artemisinin combination therapy just a few years ago. That may change, but for now, the malaria itself doesn't cause new symptoms or more complications – it's just becoming much more difficult to destroy.

Daw Cho Cho, 50, was treated for malaria but the parasites returned a month later Photograph: Kathleen E McLaughlin for the Guardian

My Yee Thaung, whose nine-year-old son recently had malaria thought to be drug-resistant, said he recovered, slowly, "but he's still not eating very well."

These patients are among thousands participating in a nine-week study of their blood. The clinic, one of five malaria centres for Burmese refugees in Thailand run by SMRU, pays their transportation fees and a nominal amount to cover lost wages, and the patients return to give blood samples once a week.

The number of malaria cases has shrunk in this region dramatically in the past 30 years, since Nosten and his team began to contain and eradicate it. When Nosten started the first border clinic, the parasite was a major killer, infecting tens of thousands of people each rainy season. Today, there are a few thousand cases each year. But those that remain are more likely to contain a wilier parasite, one that is evolving to evade what was first touted as a miracle drug.

The global implications of artemisinin losing its edge on malaria are alarming. Worldwide, the WHO estimates there were 207 million malaria cases in 2012 and more than 600,000 deaths, and says malaria rates dropped 25% worldwide during 2000-2012. The Institute for Health Metrics and Evaluation uses a different methodology for tallying malaria deaths and says the global death toll could be double what the WHO reports.

In either case, malaria numbers have dropped dramatically in the past decade. But what remains is even more dangerous, and Nosten warns of a potential complacency that could allow drug-resistant malaria to erupt.

Scientists in Mae Sot's border clinics study malaria parasites and new drugs that might be used to destroy them. Photograph: Kathleen E McLaughlin for the Guardian

"It is an emergency. Everyone is spending their time in meetings, giving advice, not acting quickly enough," he said. "It looks like this time we are going to lose."

The march of drug-resistant malaria westward has begun. Cases are cropping up further west in Burma, and may have entered Bangladesh. If that's the case, and history repeats itself, this dangerous and potentially deadly parasite could move further west into India, then drop south to Africa. It has happened twice before with the world's best malaria drugs and researchers such as Nosten fear a third wave is under way, negating a frontline treatment for a killer of millions, with nothing new on the shelf to take its place.

Starting this summer and backed by the Global Fund and others, Nosten's team is going on the offensive against malaria in Burma. His teams will establish 800 village health stations inside Burma, treating people who have the illness and pre-emptively giving medication to entire villages where a high percentage of people carry the malaria parasite. He believes containment – the strategy of choice thus far – has been too limited, though malaria rates have dropped dramatically. Elimination is now necessary.

Artemisinin-based malaria drugs have few side-effects and most people require only a three-day course to get rid of the parasites. Nosten faced early opposition to his plan, but says time and options have run out, and the downsides are minimal.

"It's already spread from the border into Myanmar [Burma]," he said. "We should have done this three or four years ago. Now I'm afraid it could be a bit too late."

Changing resistance



Malaria is forever outrunning its attackers, shifting its shape to survive the drugs invented to eradicate the parasite.

Chloroquine was widely effective around the world, but began to lose its grip on malaria after mass dosing in endemic areas. Malaria grew resistant to the drug by the 1950s. Sulfadoxine-pyrimethamine, commonly sold as Fansidar, came next and proved effective until the end of the last century, when resistance proved common.

Artemisinin, derived from sweet wormwood, followed. China's People's Liberation Army at the behest of the Communist party leader, Mao Zedong, developed the drug as part of a secretive project during the Vietnam war. The highly effective drug was kept out of the global marketplace by China but also because of global pharmaceutical spats. In 2006, it became the world's frontline malaria treatment.

Today, artemisinin still works within a combination drug. Because of a global abundance of fake drugs (many made in China) and bad dosing, however, its days are numbered.