Scientists race to eliminate malaria as ‘wonder drug’ loses its powers

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Continued from part 1

Why has a small corner of western Cambodia, no bigger than Wales or New Jersey, repeatedly given rise to drug-beating parasites?

White thinks that the most likely explanation is the region’s unregulated use of antimalarial drugs. China supplied artemisinin to the tyrannical Khmer Rouge in the late 1970s, giving Cambodians access to it almost two decades before White conceived of ACTs. Few used it correctly. Some got ineffective doses from counterfeit pills. Others took a couple of tablets and stopped once their fever disappeared. P. falciparum was regularly exposed to artemisinin without being completely wiped out, and the most resistant parasites survived to spread to new hosts. There is a saying among malariologists: “The last man standing is the most resistant.”

Genetic studies hint at other explanations. Early last year, Dominic Kwiatkowski from the University of Oxford showed that some P. falciparum strains from west Cambodia have mutations in genes that repair faults in their DNA, much like some cancer cells or antibiotic-resistant bacteria. In other words, they have mutations that make them prone to mutating. This might also explain why, in lab experiments, they develop drug resistance more quickly than strains from other parts of the world. Evolution is malaria’s greatest weapon, and these “hypermutators” evolve in fifth gear.

Kwiatkowski’s team also found that P. falciparum is spookily diverse in West Cambodia. It is home to three artemisinin-resistant populations that are genetically distinct, despite living in the same small area. That is bizarre. Without obvious barriers between them, the strains ought to regularly mate and share their genes. Instead, they seem to shun each other’s company. They are so inbred that they consist almost entirely of clones.

Kwiatkowski suspects that these parasites descended from some lucky genetic lottery winners that accumulated the right sets of mutations for evading artemisinin. When they mate with other strains, their winning tickets break up and their offspring are wiped out by the drug. Only their inbred progeny, which keep the right combinations, survive and spread.

It undoubtedly helps that Southeast Asia does not have much malaria. In West Africa, where transmission is high, a child might be infected with three to five P. falciparum strains at any time, giving them many opportunities to mate and shuffle their genes. A Cambodian child, however, usually sees one strain at a time, and is a poor hook-up spot for P. falciparum. The region’s infrastructure may also have helped to enforce the parasites’ isolation: local roads are poor, and people’s movements were long constrained by the Khmer Rouge.

West Cambodia, then, could be rife with P. falciparum strains that are especially prone to evolving resistance, that get many opportunities to do so because antimalarial drugs are abused, and that easily hold on to their drug-beating mutations once they get them.

These are plausible ideas, but hard to verify since we still know very little about how exactly the parasites resist a drug. Earlier cases of resistance were largely due to mutations in single genes – trump cards that immediately made for invincible parasites. A small tweak in the crt gene, and P. falciparum can suddenly pump chloroquine out of its cells. A few tweaks to dhps and dhfr, the genes targeted by sulfadoxine and pyrimethamine, and the drug can no longer stick to its targets.

Artemisinin seems to be a trickier enemy. Curiously, P. falciparum takes a long time to evolve resistance to artemisinin in lab experiments, much longer than in the wild. Those strains that do tend to be weak and unstable. “I suspect you need a complicated series of genetic changes to make a parasite that’s not lethally unfit in the presence of these drugs,” says White. “It would be unusual if this was a single mutation.”

Practices such as unregulated drug use and misuse may help encourage and accelerate the rate of such changes out in the field. Kwiatkowski’s study suggests that the parasites may have evolved artemisinin resistance several times over, perhaps through a different route each time. Several groups are racing to find the responsible mutations, with news of the first few breaking in December 2013. That’s the key to quickly identifying resistant parasites and treating patients more efficiently. (Currently, you can only tell if someone has artemisinin-resistant malaria by treating them and seeing how long they take to get better.) “We want to be able to track resistance using blood spots on filter paper,” says Chris Plowe at the University of Maryland School of Medicine, whose group is one of those in the race.

But time is running out. From its origins in Cambodia, resistance has reached the Thai–Myanmar border. Nosten has shown that the proportion of patients who are still infected after three days of ACT has increased from zero in 2000 to 28% in 2011. Most are still being cured, but as artemisinin becomes less effective, its partner drug will have to mop up more surviving parasites. Plasmodium will evolve resistance to the partner more quickly, driving both drugs towards uselessness.

This is already happening in western Cambodia, where ACTs are failing up to a quarter of the time and many people are still infected a month later. Long-lasting infections will provide parasites with more chances to jump into mosquitoes, and then into healthy humans. Malaria cases will rise. Deaths will follow. “This is the silence before the storm,” says Arjen Dondorp. “The threat is still slightly abstract and there’s still not that much malaria, which doesn’t help with a sense of urgency. If we suddenly see malaria exploding, then it’ll be a clear emergency, but it’ll also be too late.”

‘Appetite for change’

In his office at Mahidol University, Nick White is surrounded by yellowing monographs of old malaria research and overlooked by a wall-mounted mosaic of drug packets made by his daughter. He is now the chairman of the Mahidol–Oxford Tropical Medicine Research Unit and a mentor to the dozens of researchers within. He is gently ranting.

“Everything to do with change in malaria meets with huge resistance,” he says. He means political resistance, not the drug kind. He means the decade it took for the international community to endorse ACTs despite the evidence that they worked. He means the “treacle of bureaucracy” that he and Nosten swim through in their push to eliminate malaria.

“The global response to artemisinin resistance has been a bit pathetic. Everyone will tell you how important it is and there have been any number of bloody meetings. But there is little appetite for radical change.” He misses the old days when “you could drive a Land Rover across borders in your khaki shorts and spray things and do stuff.”

From the outside, things look rosier. Malaria is fashionable again, and international funding has gone up by 15 times in the last decade. Big organizations seem to be rallying behind the banner of elimination. In April, the World Health Organisation published a strategy called “The Emergency Response to Artemisinin Resistance…”

“It’s a marvelous plan,” he says drily. “It says all the right things, but we haven’t done anything.” It follows two other strategies that were published in 2011 and 2012, neither of which slowed the spread of artemisinin resistance. Elimination became a dirty word after the noisy failures of the 1950s and 60s, and the new strategies look like the same old tactics for controlling malaria, presented under the guise of eradicating it. “They’re prescriptions for inertia,” says White.

Worse, they are channeling funds into ineffective measures. Take insecticide-treated bednets, a mainstay of malaria control. “We’ve had meetings with WHO consultants who said, ‘We don’t want to hear a word against bednets. They always work.’ But how cost-effective are they, and what’s the evidence they work in this region? The mosquitoes here bite early in the evening. And who’s getting malaria? Young men. Are they all tucked up in their bednets by 6 o’clock? No. They’re in the fields and forests. Come on! It’s obvious.”

He says that resources could be better devoted to getting rid of fake drugs and monotherapies where artemisinin is not paired with a partner. That would preserve ACTs for as long as possible. The world also needs better surveillance for resistant parasites. White is helping with that by chairing the World-Wide Anti-Malarial Resistance Network – a global community of scientists who are rapidly collecting data on how quickly patients respond to drugs, the presence of resistance genes, the numbers of fake drugs, and more.

White also wants to know if artemisinin-resistant parasites from Southeast Asia can spread in African mosquitoes. Hundreds of mosquito species can transmit malaria, but P. falciparum is picky about its hosts. If resistant strains need time to adapt to new carriers, they might be slow to spread westwards. If they can immediately jump into far-off species, they are a plane ride away from Africa. “That changes your containment strategy,” says White, “but stupidly, it’s cut out of every research application we’ve ever made.”

He is pessimistic. “I’m pretty confident we won’t win but I think we should try a lot harder than we have been. If we didn’t pull out all the stops and kids start dying of artemisinin-resistant malaria, and we can trace the genetic origins of those parasites to Southeast Asia, we shouldn’t sleep easy in our beds.”

Hidden infections

When Nosten’s team first arrived at Hka Naw Tah in February, they slept and worked from the village’s unassuming temple. Using development funds from their grant, they put up a water tower and supplied electricity for the local school. In return, the villagers built them a clinic – a spacious, open-sided hut with a sloping tin roof, benches sitting on a dirt floor, a couple of tables holding boxes of drugs and diagnostic kits, treatment rooms, and a computer station. It took just two days to erect.

The Karen respect strong leadership but there is an easy-going camaraderie in the clinic. When we arrive, one of the research assistants is napping across a bench. Nosten walks over and sits on him. “You see, and I think this is a good sign, that it’s hard to tell who’s the boss and who’s the patient,” he says.

Most of the villagers don’t seem sick, but many of them have malaria nonetheless. Until recently, Nosten’s team had always searched for the parasites by examining a drop of blood under a microscope. If someone is sick, you can see and count the Plasmodium in their red blood cells. But in 2010, they started collecting milliliters of blood – a thousand times more than the usual drops – and searching for Plasmodium’s DNA. Suddenly, the proportion of infected people shot up from 10–20% to 60–80%. There are three, four, maybe six times as many infected people as he thought.

“We didn’t believe it at first,” says Nosten, “but we confirmed it and re-confirmed it.” Perhaps the tests were giving false positives, or picking up floating DNA from dead parasites? No such luck – when the team treated people with ACTs, the hidden parasites disappeared. They were real.

These “sub-microscopic infections” completely change the game for elimination. Treating the sick is no longer good enough because the disease could bounce back from the hordes of symptomless carriers. The strike will have to be swift and decisive. If it’s half-hearted, the most resistant parasites will survive and start afresh. In malarial zones, you need to treat almost everyone, clearing the parasites they didn’t even know they had. This is Nosten’s goal in the border villages like Hka Naw Tah. He has support from the Bill and Melinda Gates Foundation, one of the few large funders to have truly grasped the urgency of the situation and who are “very much in the mood for elimination.”

Killing the parasites is easy: it just involves three days of ACTs. Getting healthy people to turn up to a clinic and take their medicine is much harder. The team have spent months on engagement and education. The clinic is dotted with posters explaining the symptoms of malaria and the biology of mosquitoes. Earlier this morning, Honey Moon, a Karen woman who is one of Nosten’s oldest colleagues, knocked on the doors of all the absentees from the last round to persuade them to come for tests. As a result, 16 newcomers turned up for treatments, bringing the team closer to the full 393. Nosten is pleased. “In this village, I’m quite optimistic that most people will be free of the parasite,” he says.

Another village down the river is proving more difficult. They are more socially conservative and have a poorer understanding of healthcare. There are two factions of Karen there, one of which is refusing to take part to spite their rivals. “It’s a good lesson for us,” says Nosten. “These situations will be elsewhere.” Eliminating malaria is not just about having the right drug, the deadliest insecticide, or the most sensitive diagnostic test. It is about knowing people, from funders to villagers. “The most important component is getting people to agree and participate,” says Nosten. It matters that he has been working in the region for 30 years, that the Shoklo unit is a familiar and trusted name in these parts, that virtually all his team are Karen. These are the reasons that give Nosten hope, despite the lack of political will.

If the strategy looks like it is working after a year, they will start scaling up. Eventually, they hope to cover the entire sinuous border. I ask Nosten if he would ever consider leaving. He pauses. “Even if I wanted to go somewhere else, I’m more or less a prisoner of my own making,” he says. He would need to find a replacement first – a leader who would command respect among both the Karen and malaria researchers, and would be willing to relocate to a place as remote as Mae Sot. It is hard to imagine a second person who would tick all those boxes. Surrounded by airborne parasites, spreading resistance, and border-hopping refugees, Fran?ois Nosten is stuck. He would not have it any other way.

The Shoklo Malaria Research Unit and Dominic Kwiatkowski receive funding from the Wellcome Trust, which publishes Mosaic.