Virological Trade: Screening Imported Wildlife for Emerging Microbes

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Martin Harvey

Monkeys that had been killed for food in Central Africa. A new study underscores the dangers of the illegal bushmeat trade.

Border customs agents are on the look out for many things: illegal drugs, stolen goods, smuggled liquor and sometimes even people. Add one more target: animal-borne viruses. In a new study published on Tuesday in the journal PLoS One, scientists from the Wildlife Conservation Society (WCS), the EcoHealth Alliance, the Centers for Disease Control (CDC) and other institutions reported on the first effort to identify new viruses in wildlife products that had been smuggled illegally into the U.S. And it turns out there may be a lot of bugs hitching a ride into the country along with dead wildlife—and that could have serious consequences for public health.

75% of the new emerging viruses in recent history started out in animals before jumping to human beings. Think SARS, avian flu, swine flu, Ebola—all of them began in animals before somehow mutating and spreading to people. “The global wildlife trade has historically contributed to disease emergence,” says Denise McAloose, chief pathologist for the WCS. “But we’ve never really looked at the trade in terms of what pathogens might be coming to the U.S.”

The CDC launched a pilot project to actually take a look at seized wildlife products coming into JFK airport and a few other U.S. ports and see what viruses they might be carrying. The wildlife products were mostly dead  animals—bushmeat, often of primates like monkeys—that were destined for human consumption before they were seized by customs agents. The trade isn’t small—an average of over 25 million kg of non-live wildlife enter the U.S. each year, and an estimated 273 tons of bushmeat are imported each year through Charles de Gaulle airport in Paris, often from Africa. The international trade of endangered bushmeat is illegal, but until this study, no one had attempted to see what viruses they might be carrying with them.

The results are worrisome. The researchers looked at 44 animals altogether—nine primates and 35 rats. They then used genetic techniques to essentially fish for viruses in the sampled meat, and found simian foamy virus, cytomegaloviruses, and lymphocryptoviruses, all of which can pose a threat to human beings. We don’t know how easily those viruses might have been able to jump to human beings if the meat hadn’t been interdicted, or how dangerous any of those zoonotic viruses really are. But the study confirms that wildlife—and the wildlife trade—is one more way a dangerous new microbe can be introduced into the human population.

The study underscores the need to police the boundary between human and veterinary health—something that scientists are just beginning to do. Dr. Nathan Wolfe, who runs Global Viral Forecasting, explained to me why that was so important when I visited him on a field trip to Cameroon this summer:

“On infectious disease, we’re where cardiology was in the 1950s,” he says. “We’re finally beginning to understand why pandemics happen instead of just reacting to them.” What’s needed is a global effort to scale up that kind of proactive work to ensure that every hot spot has surveillance running for new pathogens in animals and in human beings and that it has its own GVF-type group to do the work. Viruses don’t respect borders–whether between nations or between species–and in a world where airlines act like bloodlines, global health is only as strong as its weakest link. We got lucky with the relatively weak swine-flu pandemic in 2009, but history tells us our luck won’t last. “We sit here dodging bullets left and right, assuming we have an invisible shield,” says Wolfe. “But you can’t dodge bullets forever.”

Wolfe is right. But the PLoS study offers hope that we’re ready to start actively trying to stop those bullets—instead of waiting for one of them to hit us.