New Research: Increased Animal Disease A Hidden Cost Of Deforestation

July 28, 2004

GAINESVILLE, Fla. — Add another item to the list of ills caused by deforestation: It can make animals sick.

In the first study of its kind, a team of University of Florida scientists has found that cutting down swaths of African forest worsens parasite infections in the endangered red colobus monkey. That likely makes it more difficult for monkeys to survive the loss of habitat and food being caused by rampant forest fragmentation in Africa, where more than two-thirds of the original sub-Saharan forest has been lost, and about 70 percent of the continent’s colobine, or leaf-eating, monkeys are endangered, rare or extinct.

“It probably has an impact in combination with other things,” said UF zoology professor Colin Chapman. “If the monkeys are already nutritionally stressed (from deforestation) and they pick up more of these parasites, then it becomes a problem.”

Chapman and Thomas Gillespie, a UF zoology doctoral student and the lead researcher on the project, will present the results of the study Friday at the Society for Conservation Biology’s annual meeting at Columbia University in New York City.

Many scientists have studied the transmission of diseases between wild animals and people, but few have examined how deforestation alone affects disease outbreaks, Gillespie said. The UF research is one of the first such studies and the only one yet to address primates, experts said.

“To the best of my knowledge, this is the first demonstration of a link between fragmentation and primate disease,” said Michael Huffman, an associate professor in the Primate Research Institute at Japan’s Kyoto University. “It is very exciting news and an important breakthrough for conservation medicine, biology and the growing field of eco-parasitology.”

The research may also point to a wider trend, said Tony Goldberg, an assistant professor of epidemiology at the University of Illinois College of Veterinary Medicine in Urbana.

“It is likely that the phenomenon that Tom documented is a very general one,” Goldberg said. “I suspect that fragmentation alters the dynamics of infectious disease transmission not only for primates, but for the diversity of animals” that live in fragmented habitats.

Gillespie gathered data on gastrointestinal parasite infections among red and black-and-white colobus monkeys from 1999 through 2003 in two areas: about 700 acres of undisturbed forest in

Uganda’s 190,000-acre Kibale National Park and a fragmented forest adjacent to the park. The latter area – which is rapidly being deforested by local residents clearing it for farmland – consisted when the study started of 22 forest patches ranging from about three acres to about 22 acres.

To gauge the prevalence of parasite infection among the resident monkeys, the researchers

collected and analyzed the monkeys’ feces. To understand how fragmentation also might increase the monkeys’ risk of infections, the researchers analyzed the concentrations of parasites on tree leaves and ground-level vegetation where the animals are thought to be exposed. In all, the researchers examined 1,400 stool samples and 42 roughly 8-square-foot vegetation plots, including ones high in trees that could be accessed only through special tree-climbing techniques.

The researchers found higher concentrations of the parasites in the fragmented forests than the undistributed forests, meaning the monkeys living in the fragmented areas had a greater risk of infection, Gillespie said. Although red colobus monkeys in the fragmented areas had more frequent infections than those in undisturbed forest, the infection rates among black-and-white colobus monkeys were the same in both areas.

“This suggests that red colobus are more susceptible to infection,” Gillespie said, adding that black-and-white colobus eat a wider variety of foods, which may make them less susceptible.

Why fragmentation causes higher risk for and numbers of infections in red colobus isn’t clear, Chapman said. “It could be that the animals are all basically stuck in a small area. It could also be that there are fewer feeding trees, so they end up feeding in a tree longer” and becoming exposed to more parasites, he said.

From 2000 to 2003, nearly half the original forest fragments in the study site were cleared. The number of red colobus monkeys in the fragments that survived fell 20 percent, from 163 to 131, while the numbers of black-and-whites increased slightly from 91 to 101. Numbers remained stable for both species in the undisturbed park. The increased frequency of parasite infections likely is just one of several factors that contributed to the red colobus’ decline, Gillespie said.

“Forest fragmentation results in a suite of alterations that may increase susceptibility to infection and infection risks in resident populations,” he said. For example, “more frequent interactions with humans may reduce immunity and elevate susceptibility to infection.”

Huffman, the Kyoto University scientist, said fragmentation also may expose people to animal diseases.

“Problems now seen with the transmission of diseases between wild animals and companion animals, and as an extension to humans, is an emerging issue due to fragmentation,” he said

Chapman said the research has the potential to help Ugandan officials as they seek to preserve and restore ecological areas across the country.

“It gives us one more piece of information we need to say, ‘These are the problems and this is how we might solve them,’” he said.