Right: A greater coucal trapped in rural Vietnam could be dinner for the hunter’s family or could be sold into the country’s bustling wild bird trade [Photo: Rachel Nuwer]

The hunter is in luck. Caught in his snare trap—a homemade contraption fashioned from bamboo twigs and some rope—is a greater coucal, its neck tightly lassoed. About the size of a Chihuahua, coucals often make their home around forest fringes surrounding farmland in southern Vietnam, and their haunting, deep call is sometimes associated with omens in Asian culture. The bird’s blood-red eyes flash as it struggles to free itself; its fate, however, is sealed. The hunter claims the illegal prize.

I ask the hunter what he will do with the bird. It’s still early in the day; he’s not sure how his luck will go, so the coucal’s verdict depends on how many animals the hunter eventually bags. We’re in the U Minh peat swamp forests of southern Vietnam, a hot, boggy stretch of flat plains, twisted melaleuca trees, and dark canals, mostly inhabited by rural poor living on the forest’s fringes. Life here is hard, and people like this hunter will seize the opportunity to supplement their meager farming income and diet by trapping animals.

The hunter shrugs. He may opt to bring the bird home, where it will be caged side-by-side with his flock of free-range chickens and ducks before making a tasty addition to his family’s supper. Or it may enter the complex network of Vietnam’s illegal wildlife trade. In that case, it could travel by boat, motorbike, and car, making its way north from village to town to city. The terminal stop could be on a plate in a chic wildmeat restaurant in Ho Chi Minh City or at a prestigious songbird contest in Hanoi, or even in a traditional medicine shop in China. For now, though, the bird still pants and struggles in the hunter’s firm grasp.

The unfortunate bird is not the only player facing danger in this interaction, however. The hunter is not completely in control of the situation, for there could be another player—an unseen presence—also exploiting opportunity in this jungle encounter.

Zoonoses, or infectious diseases originating from animals, are increasingly finding their way to the top of health officials’ risk lists. And wildlife trade is a major platform for introducing animals and people, and thus to the possibility of disease. The worldwide trade in wildlife—both legal and illegal—gives platform to this disease risk at every stage: from the animal’s initial capture, when the hunter is exposed, to the transportation, when the traders are exposed and the zoonotic organisms is moved to new geographic areas, to the final purchase by consumers, who may be looking for food, pets, medicine, or trophies. At each stage of this complex trade network, an opportunistic zoonotic pathogen could seize the chance to jump species and infect the humans it comes into contact with.

Left: Wild-caught birds of all shapes and sizes being held at a rural Vietnamese house. [Photo: Rachel Nuwer]

These days, most emerging pathogens in humans have an animal component, says Andrés Gómez, a veterinarian and ecologist at the American Museum of Natural History’s Center for Biodiversity and Conservation. This all comes down to something called the taxonomic transmission rule, Gómez explains. This rule predicts that, the closer two species are related, the higher the probability of a pathogen crossing from one species to another. In other words, it’s more likely that we can catch something from a monkey than from a bird, from a bird than from a fish, from a fish than from a fern.

These diseases aren’t just hypothetical, either. Zoonoses include some of the most fearsome diseases known: HIV, Ebola, rabies, West Nile, and SARS—the list goes on. The general scientific consensus is that HIV originated from human-monkey interactions, most likely during the butchering and consumption of primates. The 2002 SARS outbreak claimed approximately 800 human lives and the slaughter of a countless number of civets in Chinese markets and farms before the disease was contained.

Though zoonotic pathogens can be viral, bacterial, or fungal, there’s a big bias in what we’re looking for, says Sergios-Orestis Kolokotronis, an evolutionary biologist at the American Museum of Natural History’s Sackler Institute for Comparative Genomics. Because viruses evolve quickly, they can diversify faster than fungi or bacteria. They also tend to be more lethal, Kolokotronis says. For these reasons, viruses are usually the focus of zoonotic disease research.

People are becoming more mobile, both within nations and between countries, says Kelly Edmunds, a conservation ecology doctoral candidate at the University of East Anglia in Norwich, England, who studies the relationship between bird trade and disease in Southeast Asia. As people venture further afield in their search for resources and work, opportunities for human-wildlife interaction are created that previously did not exist. Because of our widespread dispersal around the planet and our increasing mobility, “if a pathogen wanted to leave a place and go somewhere,” Kolokotronis adds, “humans would be the absolute perfect vehicles.”

This introduces another key factor contributing to the spread of emerging infectious diseases: naïve human populations that have never before encountered the pathogen and thus have no natural resistance. During the SARS outbreak, for example, people working in animal markets in Asia were found to have antibodies for the disease at the onset, says Diana Bell, a conservation biologist at the University of East Anglia who supervises Edmunds’ research. This indicates that they had been exposed to a SARS-like virus before. But for those who had not spent time around the markets, their unexposed immune systems provided an open invitation for infection. This point also came to light when the first case of highly pathogenic avian influenza H5N1 struck Europe in 2004. Infected birds smuggled into Belgium on a plane from Thailand were to blame, paving the way for an international outbreak amongst the naïve populations of Europe and beyond.

Following this lead, Edmunds used Vietnam’s bird trade as an investigative window into disease transmission, publishing her findings in August in the journal EcoHealth. In market surveys, she found that about 25 percent of the 36,584 birds of 43 species are known to be susceptible to highly pathogenic avian influenza H5N1, and their frequent mingling with poultry species makes this risk even higher.

An estimated four million live birds enter the wildlife trade market annually, according to the Wildlife Conservation Society. Since the early 1990s, the number of bird markets in Vietnam and other Southeast Asian countries has been on the rise. Vietnam’s expanding economy provided more and more middle class people with access to luxuries—like songbird contests and exotic pets—previously prohibited by expense. With the 2005 outbreak of H5N1, the Vietnamese government announced a ban on the transportation and sale of all wild birds across Vietnam’s urban areas.

Despite this legislation, Edmunds found that during a two-year period—from May 2007 to January 2009—the tally of individual birds on sale increased by 387 percent, and Edmunds thinks this is an underestimation of the overall number of birds extracted from the wild since it doesn’t take into account those birds that die before reaching the markets and those that are shipped out of Vietnam. The types of birds on sale, however, didn’t change much from 2007 to 2009; the number of species increased by only five percent. Interviews with 20 bird vendors in Hanoi revealed that 95 percent were not aware of any bans on bird sales. The vendors involved in the study “showed remarkably little knowledge about H5N1,” says Bell, co-author of the study.

Bird and other animal trade in Vietnam creates a particularly risky scenario for the emergence of novel pathogens. First, where there are more wildlife species, there is a higher risk. Vietnam falls in the tropics; the mix of humidity, mosquitoes (often the go-betweens for human/animal diseases—think West Nile), and dense populations is “the perfect recipe for something bad to happen,” says Gómez.

The conditions animals encounter in the wildlife trade are also an ideal setup for a dormant pathogen to make its move. When an animal is stressed out, its immune system suffers a blow, Gómez explains, so any pathogen it may be carrying could cause an outbreak. Like in humans, stress can cause the immune system suppression, so an animal could be more susceptible to pathogen attack under the manic, crowded circumstances often encountered in the trade.

Right: Though all appears neat and orderly at this Hanoi bird shop, a peak around back often reveals stacks upon stacks of filthy, crowded cages [Credit: Rachel Nuwer]

And if the wildlife trade is anything for an animal, it’s stressful. Imprisoned in the shops, “birds don’t get to see any light,” Edmunds says, recalling Hanoi vendors who stack cages upon cages filled with wild-caught birds in the back of dusty stalls. “When you go into the shop you would hold your breath,” she said, “it just reeked.” Overcrowded conditions of mixed species, little air circulation, and lack of ample food and water create the perfect breeding ground for pathogen emergence amongst the imprisoned birds.

Around the world, and especially in Asia, humans have a long history of exploiting birds for food and entertainment. Birds are “a bit like dogs” in that a range of traditional venues of contact with people exists, says Bell, from songbird contests to pets to cockfighting. In the Buddhist cultural framework, the releasing of a trapped animal is seen as pleasing the gods, Edmunds says, so birds are often used for religious merit releases. In a seemingly altruistic gesture, customers purchase caged birds from one of the many vendors set up around Buddhist temples to give the birds their freedom. But the animals are usually re-captured almost as soon as they’ve been set free. In terms of religious merit release “they think what they do is good,” Edmunds says. Especially because of the deep-rooted cultural associations surrounding birds, she says, “it’s really difficult to tell people to stop doing that.”

As Vietnam’s failed attempt to control the bird trade showed, curtailing the spread of disease is not as easy as simply passing a law. Though officials visited bird traders initially, follow-up visits and action against violators was basically nonexistent. The laws are “completely ignored,” Edmunds says, and they’re “just not very detailed.” Lawbreakers tend to be either completely ignorant that they’re breaking the law, as Edmunds’ study found, or else they scoff at the ease of evading detection, like stuffing live birds inside of empty noodle boxes to avoid police detection. And at an estimated annual profit of US$92,000 for birds surveyed in Hanoi alone, Vietnam’s avian trade will need more than laws on paper before it’s shut down.

From a local perspective, small steps could greatly improve the situation. Basic hygiene could be a starting point. For example, in Hong Kong’s bird markets, Edmunds found that conditions for the animals are much nicer. Birds are placed outside, and the market has facilities for the safe disposal of dead birds. Hand sanitizer is even provided for vendors.

General education would also be a plus, though it should be carefully thought out. People can easily misconstrue animals as the problem rather than recognizing the fact that humans have penetrated into wildlife areas, Kolokotronis says, which can fuel retaliation. For example, a mysterious outbreak in 1999 causing inflammation of the brain claimed over 100 lives in Malaysia. Flying foxes—the world’s largest bat—were found to be the natural host of the disease, eventually dubbed Nipah virus. Panic induced a mass slaughter of flying foxes, though scientists argued that farmers had encroached on the bat’s territory and that prevention measures could easily be carried out. People need to be made aware of health risks without relying on scare tactics, Gómez says, since scaring people can have conservation repercussions for animals.

But what’s really needed is research and collaboration. It’s impossible for people sitting in offices in developed countries to know what’s going on in the field, Kolokotronis says, we need in-country collaborations between local specialists, veterinarians, ecologists, and law enforcement. And the reins should be tightened on controlling animals and animal products that find their way through the cracks of the import controls of developed nations. While it’s easy to point fingers of blame at developing countries, Kolokotronis says, “if you’ve been in a country like that you can understand that it’s very difficult because it’s not exactly the first priority—livelihoods are, and should be.”

Even in the U.S., though, it’s not easy to get a handle on illegal animal imports. For the New York City—the largest port of entry for both legal and illegal animals in the country—the Bureau of Environmental Crimes Investigation typically has only 25 officers working in a city of over 8 million. This branch of the New York State Department of Environmental Conservation is responsible for everything from exotic birds for the pet trade to illegal lobsters for the food trade to crocodile handbags for the fashion trade, says John Fitzpatrick, a lieutenant at the Bureau. “It’s very difficult,” Fitzpatrick says of the practicalities of policing such a large area and scope of problems, and he doesn’t have any illusions that he and his officers are managing to tackle every case of illegal animal importation.

New York’s Wild Bird Law now prevents the importation and sale of any wild-caught birds without a permit. The Fish and Wildlife Service evaluated 869 cases of international bird imports (totaling 83,823 animals) into New York City alone from January 2005 to June 2011. Of these cases, about 44 percent were taken from the wild but only four percent were refused entry into the country and either seized or re-exported. In the United States as a whole, 1,382,781 birds from 7,948 cases entered U.S. ports between the same dates. Of those cases, just five percent were refused entry, while 22 percent of the birds were taken from the wild. Of 289 total bird species, the top imports were parrots (1,166 cases), finches (831 cases), canaries (587 cases), and parakeets (478 cases).

Despite the high number of bird imports, Fitzpatrick says his agents aren’t trained to deal with zoonotic diseases entering the U.S. via international animal imports, so though there may be disease issues with some of the animals he handles, it’s not their area of specialty. The Centers for Disease Control prohibits the importation of species known to frequently carry disease, like some bats, but that doesn’t mean that disease couldn’t sneak in under the radar, as with H5N1 in Belgium. There’s no international organization in charge of monitoring illegal animal trafficking and the diseases that could accompany the trade, Fitzpatrick says, so basically individual countries are on their own when it comes to enforcement.

For now, at the very least we should keep a close eye on diseases emerging from wildlife trade. “Wildlife trade itself will almost certainly play a role in a major emerging infectious disease in the future,” Edmunds says. But what that disease will be, or where it will originate, is yet to be seen. “We know very little about most things on earth,” Gómez says, “the first action would be to understand what’s out there.”

As for the greater coucal, it forfeited its freedom the moment it stepped foot into the snare trap. Anyone working in Vietnam understands that until wildlife trade’s plethora of cultural drivers are addressed—from the country’s rural poor needing livelihoods, to lax law enforcement, to urbanites’ demand for wildmeat—animals like the coucal will continue to be exploited, regardless of health risks. The hunter told me he didn’t know what he’d do with the coucal, but chuckled at his good luck as he tossed the bird into a small cage alongside a wild duck and an egret he’d snared earlier that day.