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Feature Emerging Diseases

Disease trackers

BMJ 2011; 343 doi: http://dx.doi.org/10.1136/bmj.d4117 (Published 05 July 2011) Cite this as: BMJ 2011;343:d4117
  1. Ed Yong, freelance journalist
  1. 1London, UK
  1. edyong209{at}googlemail.com

Why do many of the world’s emerging diseases, including SARS and H5N1 bird flu, originate from the same corner of South East Asia? Ed Yong investigates what’s special about the area and the international efforts to stop these deadly diseases in their tracks before they go global

The Mekong basin is teeming with life. Giant fish and crocodiles patrol the water, while thousands of birds fly through the air. The area’s biodiversity is among the richest in the world, and it is becoming more crowded. The basin stretches across 795 000 km2 of land, shared between China, Burma (Myanmar), Vietnam, Thailand, Laos, and Cambodia. It is home to an estimated 60-70 million people, mostly farmers, and this number is expected to increase to 120 million by 2025. These residents, and their livestock, are slowly encroaching into areas inhabited by wild animals—a clash of species that is turning the Mekong into a time bomb of disease. Within this throng of humans and animals, emerging infections can find plenty of hosts and vectors, and viruses and parasites can jump the species barrier into humans.

There have already been worrying precedents. In 2003, the coronavirus that caused SARS (severe acute respiratory syndrome) spread from a neighbouring province in southern China to 37 countries in a matter of weeks, killing a tenth of the people it infected. The virus was a new threat that had jumped into humans from bats and civets. In the same year, H5N1 influenza also emerged from southern China, spreading from poultry to humans, causing high death rates and spreading across South East Asia. Just this year, Chinese scientists identified a new tick-borne virus called SFTSV (severe fever with thrombocytopenia syndrome bunyavirus) that causes high fever and multiple organ failure and has killed 36 people. Since 1980, a new human disease has emerged somewhere around the world every eight months or so, but it’s not just the new ones that have people worried.1

The Mekong basin is a sanctuary where old diseases can gain a new lease of life. Drug resistant forms of malaria have a history of emerging from this region, and new strains that shrug off artemisenin, the most powerful weapon in our arsenal, have gained a foothold in Cambodia.

Animal connections

“There are innate fears that a disease will emerge that will cause something similar to the plague three or four hundred years ago—huge amounts of human death that can’t be controlled very quickly,” says Jonathan Rushton from the Royal Veterinary College. Such pandemics will probably start in other species. The US Institute of Medicine, an independent advisory body, estimates that three quarters of emerging infections are zoonotic (originating in animals). The health of animals and humans is inextricably linked, a concept enshrined by the One Health Initiative (www.onehealthinitiative.com), an international movement which seeks to unite doctors and veterinarians in efforts to control infectious diseases around the world. And there are few better places to start those efforts than the Mekong basin.

“The area is undergoing enormous change,” says Richard Coker, professor of public health at the London School of Hygiene and Tropical Medicine. Its population is booming and becoming increasingly urbanised, bringing people into closer proximity so that diseases can spread more easily. There is a substantial amount of migration; Thailand alone has millions of immigrants from its poorer neighbours, who often live in unsanitary and overcrowded conditions. “If you’d been to Bangkok 25 years ago and you went now, you wouldn’t recognise it,” says Professor Coker. “It’s an area that’s being transformed before our eyes.”

The crowded population is coming into increasing contact with animals, from bats to mosquitoes, and the diverse diseases they carry. Dr Rushton says, “We’re forcing ourselves into areas where we’re getting increased contact between wild animals, domestic animals, and humans.” As the region’s residents intrude into pristine habitats and develop more agricultural land, they set up opportunities for animal diseases to jump into new hosts. Every felled tree and every new rice paddy ratchets up the odds.

A thriving international trade in wildlife exacerbates this problem. Tens of millions of wild animals cross the Mekong’s borders every year, ending up in large trading centres and markets. After the SARS outbreak began in 2003, over 800 000 wild animals were confiscated from markets in Guangzhou, China. In a single Thai market, over 70 000 birds were reportedly sold in 25 weekends. Domestic animals are also on the rise. “We’ve had an explosion of livestock populations in pig and poultry,” says Dr Rushton. “This creates an environment where pathogens have an increased number of hosts,” and transfer to humans from these hosts is more likely because people are in close contact with them and eat them.

In conditions like these, new diseases are bound to emerge, and SARS and H5N1 were testament to that. These outbreaks were turning points for the Mekong. They highlighted the danger of zoonotic illnesses and showed how quickly local problems can turn into global ones. They acted as warning shots across the world’s bow, galvanising governments and funding agencies into action. “After the 2003 outbreak of SARS, everyone knew how important early detection is for controlling infectious diseases,” says Chun Cheng, a Chinese public health specialist.

United action

To control emerging infections, countries need good surveillance systems to predict outbreaks, spot their signs, and coordinate quick, concerted responses. The Mekong countries have prepared for future pandemics by setting up new public health institutions, diagnostic laboratories, and communication networks, supported by substantial funding from international donors. At the centre of this work lies the Mekong Basin Disease Surveillance initiative (MBDS), a partnership between the health ministries of the six Mekong countries. The initiative has been around since 1999, buoyed by funding from the Rockefeller Foundation, World Health Organization, and others. Its eyes and ears are pairs of surveillance sites dotted around the borders of the member states, where people work together to report and contain new cases of disease.

Collaboration is not easy among six nations with different languages, cultures, and political systems, not to mention big discrepancies in wealth. But the members of the MBDS have developed a sense of camaraderie that cuts through these clashes. “If you look at the resource differential between somewhere like Thailand and Laos, they’re very substantial,” says Professor Coker. “But academics and practitioners who work in infectious disease surveillance work pretty well together. They don’t tend to get caught up in the politics of the area.”

Before the MBDS existed, countries would find out about outbreaks in their neighbours from WHO. Now, people from one ministry will simply call their colleagues from another. “It makes the exchange of disease information much faster,” says Dr Cheng. “Several hours can save many lives.” Neighbours cooperate to control the disease in one country and prevent it from spreading into the other—a win-win situation. For example, in recent years, a Laotian man was found in Thailand with an H5N1 influenza infection, leading to a large investigation by public health officials and veterinarians from both countries. A similar response managed to trace and control a cholera outbreak in 2007. These are perfect examples of the One Health concept at work—teams of animal and human medics from different countries, working together to stop infections from spreading.

The MBDS is undoubtedly successful, but its much vaunted teamwork depends on finding infections of concern in the first place. As Dr Rushton explains: “The underlying aspect of surveillance is passive surveillance, where livestock keepers inform an authority about a problem that is then investigated.” But these reports can be hard to come by, especially when animals—and, therefore, people’s livelihoods—are involved. When H5N1 influenza spread through Asia in 2003 and 2004, governments responded by slaughtering poultry en masse. In Vietnam alone, 45 million birds were culled, resulting in a loss of almost $118m (£72m; €82m). Compensation rates were low, and only some farmers received it. “Many people were made poorer, and farmers and livestock keepers have become more worried about the consequences of reporting diseases,” says Dr Rushton. “You need systems that won’t disadvantage them, but they can’t be so good that people will deliberately infect their animals.”

The alternative to passive surveillance is to hunt for diseases. This is the approach taken by the Predict arm of the Emerging Pandemic Threats programme, an ambitious initiative launched in 2009 by the US Agency for International Development (USAID). “You can’t sample everything everywhere,” says Stephen Morse, professor of clinical epidemiology at Columbia University, who leads the project. “We target interfaces where humans are coming into increasing contact with species that they haven’t encountered before—wildlife trade, live animal markets.” They are training local communities to collect samples, store them appropriately, and analyse them. They focus on animals that are most likely to harbour zoonotic infections, such as bat, primates, and rodents. “The goal is to identify the next potential pandemic before it reaches the human population and prevent it from getting there.”

But this approach is a gamble. “The chances that you turn up on a particular day and sample a particular animal that is actually infectious are small,” says Dr Rushton. “These active systems aren’t actually that good at finding something that’s infectious.” There are exceptions. When Thailand experienced recurrence of H5N1 after the initial epidemic, it responded with a massive country-wide investigation. “They went out and knocked door to door asking if birds were sick, taking samples, and confirming if disease was present,” says Dr Rushton. “They stopped the disease, but doing this in a country the size of Thailand is not easy.”

Rapid response

Once cases are found, health workers need ways of rapidly spreading the word about potential threats. This is the province of ProMED-mail (the Program for Monitoring Emerging Diseases)—a web service that provides early warnings of outbreaks based on news stories, official reports, local observations, and more. Since 1994, the reports have been collated by volunteers, reviewed by expert panels, and sent to over 40 000 subscribers. In 2004, ProMED-mail launched PRO/MBDS, a service devoted to Mekong surveillance in partnership with the MBDS.

ProMED’s staff and subscribers include large numbers of vets, and the service has long championed the One Health concept, providing reports about animal and human health. This June alone, it has warned about two major threats—an outbreak of H5N1 among 1000 Vietnamese birds and a pig virus that is ravaging livestock in Burma and spreading to pets.

The service is known for its speed and transparency. On 10 February 2003, ProMED was the first to alert the world to the existence of SARS, with an email that read: “Have you heard of an epidemic in Guangzhou? An acquaintance of mine . . . reports that the hospitals there have been closed and people are dying.” This was a full month before the Chinese government’s official acknowledgment. On 19 November 2003, the service once again spread word of bird flu in Indonesia, three months before the official report arrived. These early warnings are invaluable for preventing baseless speculations while simultaneously catalysing formal investigations.

From its origins as an email list, ProMED has blossomed with new technology. Its reports are now plotted on an interactive health map, and it is active on Twitter and Facebook. Other programmes are turning to mobile phones to alert their colleagues about new risks.

An organisation called InSTEDD (Innovative Support to Emergencies, Diseases and Disasters) is working with the MBDS to bring the latest technology to the Mekong basin, speeding up the already impressive collaboration between the Mekong nations. Funded by Google and the Rockefeller Foundation, the tools include Geochat, a system that uses social media and geolocation to help health workers in the field. Workers can see where everyone in their group is on a map, read their updates in real time, and confer with them through emails sent via text message. It is a speedy way of sharing information on the ground without going through bureaucratic channels. “Typically, the village reports into the district, which reports into the province, which reports centrally,” says Dennis Israelski, chief executive of InSTEDD. “Then it goes back down, often not very effectively. You don’t need that up and down approach. You can go adjacent.”

In many ways, the Mekong basin is a testing ground for the One Health concept. It is an area where partnerships, technologies, and protocols have been put to the test by past epidemics and are being shaped to prevent future ones. “It’s an interesting test case for international cooperation,” says Professor Morse. The rest of the world is watching intently. Professor Coker adds, “People looked at the MBDS when planning disease surveillance in areas of conflict like Israel and Palestine, so it’s been a very successful model.”

Notes

Cite this as: BMJ 2011;343:d4117

Footnotes

  • Competing interests: The author has completed the ICJME unified disclosure form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declares no support from any organisation for the submitted work; no financial relationships with any organisation that might have an interest in the submitted work in the previous three years; and no other relationships or activities that could appear to have influenced the submitted work.

  • Provenance and peer review: Commissioned; not externally peer reviewed.

References