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PUBLIC HEALTH PREVENTING THE NEXT PANDEMIC An international network for monitoring the fl ow of viruses from animals to humans might help scientists head off global epidemics By Nathan Wolfe weat streamed down my back, thorny As the chimps feasted on the monkey’s raw KEY CONCEPTS shrubs cut my arms, and we were losing fl esh and entrails, I thought about how this them again. The wild chimpanzees my scene contained all the elements of a perfect ■ Most human infectious S colleagues and I had been following for nearly storm for allowing microorganisms to jump diseases originated in animals. fi ve hours had stopped their grunting, hooting from one species to the next, akin to space trav- and screeching. Usually these calls helped us elers leaping at warp speed from one galaxy to ■ Historically, epidemiolo- follow the animals through Uganda’s Kibale another. Any disease-causing agent present in gists have focused on Forest. For three large males to quiet abruptly that monkey now had the ideal conditions un- domestic animals as the surely meant trouble. Suddenly, as we ap- der which to enter a new type of host: the chimps source of these scourges. But wild animals, too, have proached a small clearing, we spotted them were handling and consuming fresh organs; transmitted many diseas- standing below a massive fi g tree and looking their hands were covered with blood, saliva and es to us, including HIV. up at a troop of red colobus monkeys eating and feces, all of which can carry pathogens; blood playing in the treetop. and other fl uids splattered into their eyes and ■ To address the threat The monkeys carried on with their morning noses. Any sores or cuts on the hunters’ bodies ) posed by wild animals, researchers are studying meal, oblivious to the three apes below. After could provide a bug with direct entry into the the microbes of these appearing for a moment to confer with one an- bloodstream. Indeed, work conducted by my creatures and the people other, the chimps split up. While the leader crept group and others has shown that hunting, by photoillustration who come into frequent toward the fi g tree, his compatriots made their animals such as chimpanzees as well as by hu- contact with them. way up two neighboring trees in silence. Then, mans, does provide a bridge allowing viruses to ■ Such monitoring may in an instant, the leader rushed up his tree jump from prey to predator. The pandemic form enable scientists to spot screaming. Leaves showered down as the mon- of HI V began in this way, by moving from mon- ( CHRISTIANSEN JEN emerging infectious keys frantically tried to evade their attacker. But keys into chimpanzees and, later, from chim- diseases early enough the chimp had calculated his bluster well: al- panzees into humans. Getty Images; to prevent them from though he failed to capture a monkey himself, Today HIV is so pervasive that it is hard to becoming pandemics. one of his partners grabbed a juvenile and made imagine the world without it. But a global pan- —The Editors his way down to the forest fl oor with the young demic was not inevitable. If scientists had been monkey in tow, ready to share his catch . looking for signs of new kinds of infections in SCIENTIFIC OXFORD 76 SCIENTIFIC AMERICAN April 2009 DANGER: Wild animals can carry pathogens capable of jumping into humans— the fi rst step toward be- coming a major infectious killer—so a new plan for avoiding pandemics begins with them. www.SciAm.com SCIENTIFIC AMERICAN 77 Africans back in the 1960s and 1970s, they [THE AUTHOR] do on their farm during deer season, in prepa- could have known about it long before it had af- ration for their annual venison dinner party. Nathan Wolfe is Lorry I. Lokey fl icted millions of people. With a head start like Visiting Professor in Human Biolo- The only differences, perhaps, are that the Cen- that, epidemiologists might well have been able gy at Stanford University and tral African hunter relies on this food for his to intervene and mitigate the virus’s spread. HIV director of the Global Viral Fore- own survival and that of his family and that his is not alone in having emerged from an animal casting Initiative. He earned a primate quarry is more likely to transfer its vi- doctorate in immunology and reservoir. More than half of human infectious infectious diseases from Harvard ruses and other microorganisms to the hunter diseases, past and present, originated in ani- University in 1998. A recipient of than is a deer, which is related to humans much mals, including infl uenza, SARS, dengue and the National Institutes of Health more distantly. Ebola, to name a few. And today the vast inter- Director’s Pioneer Award and the Persuading the villagers to cooperate with us connectedness of human populations, linked so National Geographic Society’s on this project was not easy. Many feared that Emerging Explorer Award, Wolfe extensively by road and air travel, allows new currently has active research and we were going to seize their game. Only after diseases to become pandemic more quickly, public health projects in 11 coun- gaining their trust could we begin collecting whether they come directly from wild animals, tries in Africa and Asia. data. Their cooperation was essential: in addi- as did HIV, or indirectly, by passing from wild tion to drawing samples of their blood for study animals to domestic ones and then to us, as in and peppering them with questions about their the case of Japanese encephalitis virus and some health and hunting activities, we needed blood strains of infl uenza. In response to these threats, samples from their prey. We relied on them to my colleagues and I recently developed a bold obtain these samples by using pieces of fi lter pa- new plan to monitor wild animals and the peo- per we gave them. ple who come into frequent contact with them Our analyses of the blood from the hunters for signs of new microorganisms or changes in and the hunted revealed several animal viruses the bugs’ activity. We believe such eavesdrop- not previously seen in humans. One agent, which ping may provide the early warning needed to we fi rst reported in a paper published in 2004 in stop pandemics before they start. Lancet, is known as simian foamy virus (SFV), and it is a member of the same family of virus- Stalking Viruses es—the so-called retroviruses—to which HIV Our surveillance vision grew out of research we belongs. SFV is native to most primates, includ- began 10 years ago, when we initiated a study ing guenon monkeys, mandrills and gorillas, of viruses in rural villagers in the Central Afri- and each of these primate species harbors its can country of Cameroon who hunt and butch- own genetically distinctive variant of the bug. ) er wild animals, as well as keep them as pets. We We found that all three variants had entered the Wolfe were trying to determine whether new strains of hunter populations. In one particularly telling HIV were entering into human populations, example, a 45-year-old man who reported hav- and we suspected that these people would be at ing hunted and butchered gorillas—animals particularly high risk of infection. rarely pursued by subsistence hunters—had con- To understand why we thought these Central tracted gorilla SFV. ( CLYNES TOM OF COURTESY African populations are vulnerable, consider a typical bushmeat hunter going about his day. The hunter wears only simple cotton shorts as he [CONTEXT] walks barefoot along a forest path, carrying on DISEASE SOURCE his back a 50-pound baboon. He has transport- AIDS Chimpanzees ed the animal for some miles and still has more Infectious Hepatitis B Apes to go before he reaches his village. As the hunter Diseases from Infl uenza A Wild birds travels, the blood from his prey mingles with his Plague Rodents own sweat and drips down his leg, fl owing into Wild Animals Dengue fever Old World primates open cuts along the way. Any infectious agents in the baboon’s blood now have access to the Many of the major infectious diseases East African Wild and domestic of humans are believed to have come sleeping sickness ruminants hunter’s circulatory system and tissues. from wild animals. This fact under- If the hunter had his choice, he and his fellow Vivax malaria Asian macaques scores the need to monitor the mi- villagers might very well prefer pork or beef to West African Wild and domestic crobes of wild creatures, in addition sleeping sickness ruminants monkey. But those forms of animal protein are to those of livestock. The table Yellow fever African primates rare here. And so he does what humans through- at the right lists 10 such diseases Many wild and domestic out the world have done for millennia: he hunts and the animals from which they Chagas’ disease the local fauna, just as my friends in New Jersey likely emerged. mammals 78 SCIENTIFIC AMERICAN April 2009 [STAGES TO WATCH] From Animal Microbe to Human Pathogen The process by which a pathogen of animals evolves into one exclusive to humans occurs in fi ve stages. Agents can become stuck in any of these stages. Those in early stages may be very deadly (Ebola, for example), but they claim few lives overall because they cannot spread freely among humans. The better able a virus is to propagate in humans, the more likely it is to become a pandemic.

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