Decades of research at Tanzania’s Gombe National Park have identified two major threats facing the park’s chimpanzees: habitat loss and disease.

The two factors are linked, with human incursions into chimpanzee habitat increasing the risk of exposure to disease.

Given the close genetic relationship between chimps and humans, diseases can flow both ways.

Established 15 years ago, the Gombe Ecosystem Health Project aims to improve the health of chimps, humans and the wider ecosystem in the Gombe area.

Chimpanzees’ health is not just an issue of concern for conservationists or animal rights activists.

Great apes can spread plagues of biblical proportions — the human immunodeficiency virus (HIV) first crossed from chimps to humans in what is now the Democratic Republic of Congo and eventually killed 35 million people.

More than 60 percent of emerging infectious diseases originated in animals. And due to their similarity with humans, primates are a particularly potent reservoir or amplifier for pathogens that pose a risk to humans.

Infectious outbreaks can be devastating for the environment as well, wiping out entire communities of wildlife.

The good news is that for more than 15 years, a group of committed scientists has been working hard to understand how the health of humans, animals and ecosystems affect each other. Their living laboratory is Tanzania’s Gombe National Park, a 52-square-kilometer (20-square-mile) nature reserve that has for half a century played a pivotal role in chimpanzee (Pan troglodytes) conservation.

Increasing opportunities for exposure

Gombe is a fragile strip of grassland, woodland and tropical rainforest that straddles the steep slopes and river valleys on the shores of Lake Tanganyika in western Tanzania. It was here that Jane Goodall began her primate research in 1960, making groundbreaking discoveries about chimpanzees’ tool use, hunting, and complex social relationships. (Editor’s note: Jane Goodall is a member of Mongabay’s advisory board.)

Research continues to this day, making Gombe the site of the world’s longest-running chimpanzee study. Decades of data have given a clear diagnosis for the greatest threats to Gombe’s chimpanzee population: disease and habitat loss outside the park.

These two factors are related, says Dominic Travis, a veterinary epidemiologist and associate professor at the University of Minnesota’s College of Veterinary Medicine. As people move into chimpanzee habitat, interactions between humans, livestock and apes increase, resulting in more opportunities for apes to be exposed to human diseases.

“Contact between apes and humans has increased in the so-called Anthropocene,” Travis says. “Human decisions about land use, travel and tourism, natural resource extraction, and even what protein source we choose — or have to eat to survive — all affect the level of contact between us, and hence the risk of potential transmission.”

Despite the potential for devastating outbreaks, relatively little is known about endemic (normal) infectious disease rates in wild apes, let alone the factors influencing the risk of the introduction and spread of diseases among apes, humans and livestock.

From Goodall’s time on, researchers in Gombe have observed that disease has a major impact on the park’s chimpanzees, Travis says. For example, primatologists observed clinical signs of illnesses like simian immunodeficiency viruses, an AIDS-like syndrome. But researchers did not historically perform necropsies to conclusively determine why the animals were dying.

“There is a need to build scientifically sound wildlife ‘public health’ systems that can detect and monitor disease and health of these populations,” Travis told Mongabay by email.

Getting started

A chance meeting led to the 2003 establishment of an initiative that aims to fill this gap: the Gombe Ecosystem Health Project.

The project was born at Chicago’s Lincoln Park Zoo. Travis, who was then consulting with the Mountain Gorilla Veterinary Project, met primatologist Elizabeth Lonsdorf, now an associate professor at Franklin & Marshall College’s Department of Psychology.

“It became clear that we could partner our respective expertise to try to find out more about health in the Gombe chimpanzees,” Lonsdorf told Mongabay by email. They worked with the Tanzanian National Parks Authority and the Jane Goodall Institute to bring the project to life.

They were soon joined by disease ecologist Thomas Gillespie (now a professor at Emory University) who brought his expertise in infectious diseases among primates to the team. The trio then joined forces with a parallel effort, led by Beatrice Hahn, the virologist who first traced the HIV back to primates, who was examining simian immunodeficiency virus in the Gombe chimps. Since then, the team has expanded to include pathology (Karen Terio, University of Illinois), endocrinology (Rachel Santymire, Lincoln Park Zoo), as well as a host of other specialties.

‘One Health’

Core to the project is the “One Health” approach, a view that acknowledges that the majority of emerging pathogens are zoonotic, i.e. able to jump between species, and works to improve global health, veterinary health and biodiversity conservation by studying how ecology, animal behavior, human behavior and environmental change affect diseases.

The Gombe Ecosystem Health Project thus aims both to prevent outbreaks and to be prepared to respond when they do happen. The goal is to help conserve animals and humans in and around Gombe, while also developing and evaluating methods that can help other teams do the same.

Efforts to understand and control diseases also have a broader impact on the ecosystem as a whole, ecologist Gillespie told Mongabay by email. “Insights over the past three decades have clarified how the health and persistence of tropical forest systems depend on critical ecosystem services provided by wildlife,” he says.

Wildlife shape ecosystems in a number of ways, such as by spreading pollen or dispersing or preying on seeds. But many of the species that play these critical roles are in decline. Habitat loss and unsustainable hunting are major factors, Gillespie said. But disease plays a role too.

For example, the western lowland gorilla (Gorilla gorilla gorilla), a seed disperser, declined due to Ebola. Pollinators like the honeycreeper (Cyanerpes sp.) declined in Hawaii due to the introduction of malaria, while indicator species such as frogs have declined and eventually gone extinct due to the chytrid fungus.

Collecting data

To better understand the effects of disease in Gombe, researchers began by building what they describe as “a minimally invasive nonhuman primate surveillance system.” Both researchers and park authorities were uncomfortable with the risks involved in trapping and testing chimps, Travis says. In any case, few diagnostic tests have been validated for use on the animals. Instead, researchers focused on collecting syndromic health data: they systematically record standardized information on symptoms noted in chimps and categorized according to health problems associated with them. Over the years, researchers have studied trends in signs of ailments like respiratory, gastrointestinal and skin disorders among chimps, as well as the illnesses and deaths associated with these health problems.

They also collected feces and carcasses for laboratory analysis. In recent years, technological advancements have allowed researchers to make great strides in understanding how infectious diseases may threaten endangered species. For example, modern tests can use fecal samples to detect respiratory or blood-borne pathogens like malaria and immunodeficiency viruses.

“Similarly, an exciting innovation that’s just taking off is letting mosquitos, leeches, and carrion flies do the work for us,” says Gillespie. These invertebrates, he explains, seek out wildlife for a meal. By trapping them and analyzing their gut contents, researchers can determine which wildlife species they fed on, and in some cases, the pathogens that infected those individuals.

This is especially interesting when it comes to carrion flies, which feed more or less indiscriminately on dead or dying animals. This “could provide an inventory of faunal and pathogen diversity including data on the presence or absence of cryptic species,” Gillespie says, pointing out that screening large numbers of carrion flies gives researchers a picture of the diversity of wildlife in a forest and the pathogens affecting those wildlife. Moreover, because carrion flies feed on dead animals, an increase in the DNA of a particular species can alert wildlife authorities to a spike in deaths of that species.

Related projects

The baboon project at Gombe is part of this “One Health” effort. It began 1967, as a parallel study to the chimpanzee research, since the two species share the same habitat and resources. They’re competitors, but chimps also prey on young baboons (Papio anubis).

On top of that, they can share many pathogens. Transmission can happen via branches or feces, or directly. “Juvenile chimps and baboons sometimes play together, with wrestling and mounting, etc.,” Anthony Collins, director of the Baboon Research Project at Gombe Stream Research Centre, told Mongabay via email. “There has been at least one case of sexual contact between a young male chimp and an adolescent female baboon.”

More broadly, the Jane Goodall Institute at Gombe has a long history of using innovative technologies for monitoring chimpanzee health, says Lilian Pintea, the institute’s vice president of conservation science. In the 1980s and 1990s it was an early adopter of video, DNA sequencing and genomics technologies. Since 2000, the institute has also been using very high-resolution satellite imagery, geographic information systems (GIS) and GPS technologies to study the relationships between chimpanzees, habitats and disease vectors in Gombe and nearby communities.

The institute is continuing that tradition; today, it works with Microsoft Research, the Tanzania Wildlife Research Institute and the Tanzania National Parks Authority to explore the potential of new tools like robotic mosquito traps, artificial intelligence, and cloud metagenomics — the study of microbes in their natural living environment.

Looking to the future

Sixteen years since the founding of the Gombe Ecosystem Health Project, researchers are now working to summarize what they know. They aim to use this knowledge to help the park authorities and local health workers manage or prevent disease in wildlife, livestock and human populations.

“When we started, we knew relatively little other than the chimps would periodically ‘look sick’ and outbreaks of these clinical signs would occur,” Lonsdorf says, highlighting they have now made good progress on identifying some of the pathogens that put chimpanzees at risk.

“I guess it’s an iterative circle — we have asked a bunch of questions, to which we now have at least partial answers,” Travis says. “So, next steps are to integrate this into current management strategies and outline the next set of questions.”

Gillespie says data on infectious diseases in tropical wildlife used to be limited due to costs, logistical challenges and the technological restrictions of non-invasive sampling. However, expanded sample gathering, paired with recent improvements in sample preservation and diagnostic capacity are rapidly improving researchers’ understanding of the epidemiology and threat of various pathogens to tropical wildlife and people.

“When we talk about sustainable and resilient populations we must take an inclusive approach to the problem, including areas adjacent to the park, as well as the human and animal populations that live there,” Travis says. “We have learned that chimpanzees do not live in isolation, even when they have preserved habitats.”

Banner image: Gremlin carries her son Grendel in Gombe National Park. Image © the Jane Goodall Institute / By Bill Wallauer.

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