Hanging by a Thread

Thomas Gillespie’s parents and teachers always wanted him to go into medicine.

“Growing up in Rockford, Illinois, if you were smart and interested in biology, you were supposed to be a doctor,” he says.

Gillespie, meanwhile, was always more interested in primates. In seventh grade, he phoned animal psychologist Penny Patterson, famous for teaching the gorilla Koko how to use sign language, and interviewed the scientist about Koko’s diet while punching out notes on a typewriter. He was premed at the University of Illinois, but spent his internship at the Brookfield Zoo in Chicago, working in the “Tropic World” primate exhibit. His favorite undergrad course was biological anthropology, the study of biological and behavioral aspects of humans and nonhuman primates, looking at our closest relatives to better understand ourselves.

Gillespie eventually took a year off before graduate school to work with primate communities in the Peruvian Amazon. The apes finally won out—Gillespie would choose a doctorate in zoology over medical school.

But it wasn’t long before the two fields of study collided. While monitoring the group behavior of colobine monkeys in Africa, Gillespie observed that some of the animals were eating bark from the African cherry tree— not a typical food source for them. When he dug deeper, Gillespie learned that human doctors in the region used that same bark to treat parasites in their patients. The monkeys, he realized, were self-medicating.

“That discovery in these monkeys brought me back toward the health science side of biology,” says Gillespie.

Reality Check Gillespie has studied Madagascar as a microcosm of the environmental destruction that is threatening health around the globe; in related work, Brian Hare (above) observes great apes in the Congo.

Courtesy of Brian Hare

Gillespie’s return to a medical approach to zoology came not a moment too soon—for the sake of the primates and maybe even all of humankind. As an associate professor in Emory’s Department of Environmental Sciences specializing in the disease ecology of primates, Gillespie and his team of researchers have helped uncover a crisis among our nearest taxonomic neighbors. According to an article coauthored by Gillespie and thirty other experts and published in the journal Science Advances, 75 percent of the world’s five-hundred-plus primate species are declining in population, and a whopping 60 percent face extinction, largely due to human encroachment.

This is not just deforestation—which leads to habitat loss—and poaching, both of which are rampant. Scientists also have discovered the spread of pathogens from human hunters, farmers, loggers, and ecotourists to the nonhuman primates. The foreign germs morph into viruses that can wipe out communities of primates with no prior exposure or immunity. The diseases can also mutate into ailments that can be passed back to humans—and the next form of Ebola or West Nile virus could emerge from the jungle in a pandemic that could put our own existence in jeopardy.

“Yellow fever kills monkeys,” says Gillespie. “When people see that, they think monkeys are the source. But in reality, they are just the sentinels.”

It's the Little Things

Germs have long been history’s stealth killers. Generations of schoolchildren have been taught that the Native Americans were overcome by the guns and steel blades of European settlers, when in reality, around 90 percent of native populations were erased by smallpox, flu, measles, and other diseases unwittingly delivered by the white interlopers. The American buffalo was said to have been hunted to the brink of extinction, but there’s evidence that there were ten buffalo for every bullet available on the Great Plains, and that it was more likely the introduction of cattle disease that did the great beasts in.

Gillespie and his colleagues are exposing the same misconception about primate populations all over the globe. For instance, in East Africa, Gillespie and his team observed widespread deforestation— logging and clearcutting for farming and development—that has greatly diminished gorilla habitats. Forest fragmentation, or turning one big forest into smaller copses of trees, has left the apes with limited food and resources. But rather than dying from malnutrition, many of the gorillas leave the forest and wander into the open, even into farmers’ fields, where they come into contact with human remnants and those of domesticated animals, dogs, and livestock. The apes then carry those pathogens back to their vulnerable shrewdness—oddly enough, the term for a group of apes.

Previously, this link was difficult to prove—scientists couldn’t be sure that the diseases they were seeing were being directly transmitted nor from whom to whom. Now, through DNA fingerprinting, researchers like Gillespie have changed the game by tracking the movement of bacteria, like E. coli and associated antibacterial resistance.

“The beauty of this is we can actually track whether or not we’re seeing similarity in the bacteria between individuals,” says Gillespie. “We looked at the bacteria of monkeys, people, and domestic animals and found that the degradation equaled similarity. The proximity could lead to bacterial transmission.”

This scenario is playing out in microcosm on the island of Madagascar. Once a paradise of flora and fauna diversity, there is hardly any natural habitat left on the island due to human development, including deforestation from slashand- burn agriculture. Gillespie says he can leave the capital of Antananarivo and drive eight hours without seeing a native plant. When he flies over the country, he notes that there’s so much sediment floating out into the ocean from all of the erosion, what’s left of the landscape resembles the surface of the moon.

But the few pockets of habitat remaining are filled with a wondrous diversity of species that would defy imagination—and that’s part of the problem. Tourists and guides traipse into those last-standing rain forests, leaving germs as a souvenir for the wild residents.

Gillespie and his team have journeyed into the roadless island jungles to trap mouse lemurs—the world’s smallest primates and one species that isn’t critically endangered. The scientists bait traps with bananas, hang them in trees, and almost always return a few hours later to find a tiny, very angry lemur. They do a quick health screening, collect fecal samples, and microchip the creature before releasing it so that its health can be monitored.

“We’re finding that where we have tourism, lemurs are getting hammered with human pathogens,” says Gillespie.

The researchers also visit the neighboring villages, where diarrheal disease is widespread and deadly, especially among children. There they have collected human fecal matter from the villagers to compare with the lemurs’.

“When these positive samples are sequenced, we will have a better idea of whether the pathogens are originating from humans or from other lemurs,” says Lydia Rautman 18C, who, along with fellow Emory environmental science grad student Kelsey Shaw 23PhD, works with Gillespie in Madagascar. “At this point, it seems unlikely that the lemurs are a source of disease for humans, but past research has suggested we may find that giardia in lemurs is associated with proximity to humans.”

All this work is based on what Gillespie calls the “one health” concept— the growing understanding in the broad scientific community and beyond that the threat of disease knows no boundaries, and that efforts to push back will need to cross the lines between fields of expertise as well.

“The goal is to consider human health issues in light of the health of animals and the environment,” says Rautman. “In our lab we have a number of projects involving many different taxa, including bats, rodents, ticks, and, of course, primates. My focus is the small wildlife component of a larger study that also considers rodents, livestock, and human behavior as influencing factors in human disease. Being surrounded by such interdisciplinary projects has furthered my understanding of disease ecology and the complex relationships among humans, animals, and the environment.”

Spreading the Word

Brian Hare 98C, an associate professor of evolutionary anthropology at Duke University, says he has seen the impact of the one health approach in his own work with great apes in the central Congo basin. Although that’s far west of Gillespie’s studies in East Africa, their common interests keep the two following one another’s research projects and comparing notes.

In the Congo, Hare explains, there is plenty of untouched forest for gorillas, chimps, and bonobos. Unfortunately, due to the lack of farmland, human residents resort to illegally hunting apes for food. Gorilla meat also fetches a pretty penny on the black market, attracting bands of poachers. The concern is not so much the pathogens that the hunters carry into the wild, but orphaned gorillas of the hunted who, without human intervention, would perish and further diminish an already shrinking population.

Hare works at sanctuaries where he and his colleagues nurture and raise these orphaned apes into adulthood. The problem is that the babies have never before been exposed to humans—or their diseases. Now they have both encountered hunters and are living in close quarters with scientists.

“Their immune system doesn’t have any way to defend them,” says Hare. “We’re exposing them to all these viruses and bacteria. We’re racing to try to understand how we can better take care of them.”

Once the gorillas reach adulthood and are ready for release back into the wild, the pathogen transfer concern is reversed. What if the newly freed orphan carries a human germ back to into the wild?

“The fear is they might come into contact with wild ape populations and infect them,” says Hare. “And that could cause an epidemic that we’re not even aware of. There’s a need for this type of research if we are going to save our closest relatives.”

Sanctuaries serve an important function at the interface of animal welfare and species conservation, Gillespie says. “Both animal welfare and conservation are ethical imperatives, but what promotes one does not inevitably benefit the other. That’s just one of the many things that we’re learning as we work to conserve and care for chimpanzees.”

The growing field of study known variously as one health, ecohealth, planetary health, and conservation medicine has made it clear that there is also a need for action on the part of governments and the public.

“We’ve always known that wildlife is affected by habitat loss and poaching,” Gillespie says. “But we now know that the threat of disease is actually a conservation issue as well. That’s been a big shift.”

The path forward, according to Gillespie, will require not only the protection of primates from hunting and habitat destruction, but also the broader promotion and support of human health. For instance, most endangered primates live close to impoverished villages and communities with scant access to clean water, which means behavior change—such as improved sanitation practices—is an important part of the solution.

“The most effective interventions involve empowering community members to teach others,” says Rautman, “and the most successful research will take an interdisciplinary approach.”

And experts must continue to build awareness that protecting primate populations isn’t about saving the “monkeys” seen at the zoo or on TV. If pathogens can pass from humans to apes, the inverse is also true—contagion is a two-way street.

“Zoonosis is the origin of HIV, malaria, Ebola, all sorts of scary things,” says Hare. “This isn’t altruism; this is mutualism. That’s why Tom’s work is so important—not just to protect the great apes, but to protect ourselves.”