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Drug-resistant malaria on the Cambodian border: a new health challenge
Malaria programmes have seen death rates plummet in south-east Asia, but some experts warn radical action is needed to protect the world from an emerging strain. Sophie McBain All day long, rickety wooden boats cross the muddy Moie river that separates Burma and Thailand. They deliver the sick to Wang Pha clinic, a whitewashed bungalow on the Thai riverbank - and one of the few clinics in Mae Sot offering free healthcare to Burmese people living on both sides of the border. Many of Wang Pha's patients are invisible to national governments: some are stateless; others are undocumented illegal migrants, internally displaced people or refugees marooned for decades. Now, however, they find themselves at the centre of a battle to contain a new form of malaria, a mosquito-borne disease that the World Health Organisation (WHO) estimates kills 660,000 people a year. Last year researchers at the Shoklo Malaria Research Unit (SMRU), which runs Wang Pha, analysed 3,000 patient blood samples taken between 2001 and 2010. They noticed that artemisinin, the most effective antimalarial drug to date, was taking ever longer to clear malaria parasites from infected patients. "This is the hallmark of drug resistance," says Professor Francois Nosten, SMRU's director. "We don't know how bad this will become, but if it continues to worsen then maybe one day the drug will become completely ineffective. "We're worried that this resistance can spread to other parts of the world, especially to Africa, where the transmission of malaria is much higher," he adds. This has happened before. In the late 1950s, resistance to the antimalarial drug chloroquine was first discovered in south-east Asia. It eventually spread to Africa and, according to a 2001 study reported in the Lancet, the numbers of malaria deaths and hospital admissions doubled or trebled as a result. Experts at the World Malaria Conference 2012 predicted that if artemisinin resistance is left to follow a similar path, global malaria deaths will increase by 25%. At Wang Pha, Burmese farmer Sow Htun Haung has been diagnosed with Plasmodium falciparum, the most deadly malaria strain. He waited eight days to seek help and he looks jaundiced. Doctors hope he'll stay for three days so they can monitor his treatment, but every day Sow doesn't work, he won't get paid. Ensuring people consult medical professionals, access the correct drugs and complete their course of treatment is essential to combating drug resistance - but among mobile, cross-border populations, this is a challenge. Over the past three years, the Thai government has allocated between £6-10m to treat migrants, but this isn't just a funding issue. Some migrants fear arrest or deportation if they go to public hospitals. For Nosten, the emergence of artemisinin resistance in Mae Sot is a sign that efforts to contain drug-resistant malaria have already "failed". Resistance was first discovered in 2006 in the Cambodian town of Pailin, which borders Thailand. Scientists aren't yet certain whether it spread or emerged in Mae Sot independently. In Pailin at least, efforts to contain drug resistant malaria, supported by international NGO Malaria Consortium, are intensifying. In 2011 Hun Sen, the Cambodian prime minister, announced his intention to eliminate malaria in Cambodia by 2025. This, together with increased international funding, acted as a catalyst for new containment projects. By 2012, village malaria workers had been trained in 1,600 Cambodian villages. Their role is to educate the community about malaria, and to diagnose and treat simple malaria cases, thereby shortening the window for malaria transmission. In artemisinin-resistance hotspots, drug inspectors are also ensuring that antimalarials are no longer available in the private sector to try to crack down on inferior drugs that could hamper treatment and increase resistance.  | A village health worker tests a woman for malaria in Pailin as part of Malaria Consortium's Malaria
Eradication Scientific Alliance (MESA) project. Photograph: Patrick Brown |
High stakes Overall, the number of cases has fallen, and no one has died from malaria in Pailin since 2009, but artemisinin resistance has continued to rise. Drugs have become so ineffective here that P Falciparum patients are now treated with the top-of-the-range medicine Malarone. This costs $55 per course, compared to just $1-2 for artemisinin-based treatments. Some experts believe the risks are so high that it's time to take drastic action. "At the moment, the strategy seems to be for everyone to just try harder at what they're already doing," argues Dr Nick White, professor of tropical medicine at Bangkok's Mahidol University. "We need to take risks. Imagine bird flu was coming to England and killing people - we wouldn't just say 'oh carry on chaps,' we'd do something rather more about it." He wants WHO to investigate radical interventions, like mass-treating the population with antimalarials or screening for malaria at all borders and airports. Malaria Consortium and partners are piloting one such initiative in Pailin, Stung Treng and Ratanakiri provinces, carrying out tests for malaria at official and unofficial border crossings. "Intensifying screening activities and identifying asymptomatic cases becomes key in the malaria elimination context. We've been actively finding these cases with some success," says Arantxa Roca-Feltrer, an epidemiologist and technical co-ordinator for Malaria Consortium in Cambodia. Dr Pascal Ringwald, head of WHO's drug-resistance and containment unit, says WHO is researching some of these options, but sees no reason for alarm. "We don't know how artemisinin resistance will spread. We think [it] might have appeared in south-east Asia in 2001 and till now it has only reached Myanmar [Burma]. In 12 years chloroquine resistance spread from east to west Africa." But, if artemisinin resistance emerged in 2001, this means it took five years to detect. "This is what happens with resistance: it's under your nose for a long time before it becomes obvious," says White. Projects like Tracking Resistance to Artemisinin Collaboration (TRAC), funded by the UK government Department for International Development (DfID), are monitoring 15 sites, including three in Africa, and have so far found no evidence of artemisinin resistance beyond south-east Asia. But the scope of such projects is limited. Scientists can't rule out that artemisinin resistance has already spread to Africa. Increased air travel only augments the risks. Theoretically one person with artemisinin-resistant malaria travelling from Thailand to Africa could be enough to spread the disease, so the most robust response would be international. At Wang Pha, doctors will continue treating boatloads of the poor and displaced, and monitoring artemisinin resistance, but Nosten already sounds resigned. Perhaps when artemisinin resistance is found beyond south-east Asia the world will take radical action, he suggests. "But then it will be too late."
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