Gorillas & Heart Disease: Cleveland Metroparks Zoo Leads Fight For Treatment & Prevention

On a warm spring day, 30-year-old Mokolo chows down on specially chosen leafy greens at Cleveland Metroparks Zoo, seemingly undisturbed by a crowd of kids and adults who eagerly watch him – snapping pictures, wide-eyed in awe at his size and his laid-back personality.

He’s one of four western lowland gorillas, a species native to Western Africa, at the Cleveland Metroparks Zoo. And he’s the only male.

“I think the exciting thing for people is seeing our group interact with each other,” says Tad Schoffner, the zoo’s animal curator. He has a special interest in the group’s interaction, as he facilitated the introduction of Nneka, the zoo’s third female gorilla, from San Francisco just last month.

“We had a very quick integration and quarantine and got her into our group of four now,” says Schoffner. “I’ve been here for quite a while, and I've been mostly used to our bachelor gorilla group that we had for 20 some years and getting females back was really exciting.”

The troupe’s makeup changed in early 2017, following the death of Mokolo’s longtime partner, Bebac. The 32-year old male suffered from heart disease. He had lived alongside Mokolo since the younger gorilla’s birth, the duo arriving in Cleveland together from Chicago, in 1994.

A color-coded chart arrayed with dots and squares occupies the largest part of one wall in Kristen Lukas’ office. We’re inside the zoo’s Sarah Allison Steffee Center for Zoological Medicine, and the old-school chart is critical to the breeding and transfer recommendations for 350 gorillas housed at zoos across North America.

In addition to her role as the Director of Conservation and Science at Cleveland Metroparks Zoo, Lukas leads the gorilla species survival plan for the Association of Zoos and Aquariums, a consortium of more than 230 wildlife preserves in America and around the world.

“Each year we look at the entire population and try to make the best decisions for the longevity of the population so that it's sustainable,” Lukas explains. “We're looking out 100 years in the future, to make sure that we have a genetically fit population and one that will carry on for many years and then also looking out for individual animal welfare.”

Lukas and her team have been on a mission of discovery over the past decade, culling data to determine why heart disease is so prevalent among captive gorillas, especially compared to their wild counterparts. More than 45 percent of gorillas in captivity are known to have heart disease, and it is the leading cause of death among males.

“Across the AZA population we had this knowledge that adult males tend to get heart disease,” says Pam Dennis, a veterinary epidemiologist with the zoo. But Dennis says research hit a roadblock, due to the difficulties surrounding diagnosis. Institutions feared putting their gorillas under anesthesia, concerned the animal might have complications or even die.   

“Mokolo hadn't had an exam for many years,” says Dennis. “You know we looked at him, we did physical exams, but we didn't have him under anesthesia until there was this big invigoration of people to say let's look at this.”

When they did, Dennis, Lukas and the rest of the staff in Cleveland received confirmation: Mokolo too had heart disease.

“Once we knew he had heart disease, then we could manage it,” Dennis says. “We needed the information not only to get the diagnosis on him, but to define heart disease in a living animal versus on pathology. We have to be able to study it and measure it to demonstrate whether the changes that we make, actually make a difference.”

Since Mokolo’s diagnosis nearly 10 years ago, staffers in Cleveland have trained the 400 pound animal to stand still while they perform cardiac ultrasounds, which give far more accurate readings. That data is then shared with other institutions, by way of the Great Ape Heart Project, a national collaboration investigating cardiovascular disease.

In their journey to better understand heart disease, staff in Cleveland, led by Elena Less, a Case Western Reserve University Ph.D. student at the time, started with the gut -- looking at the influence of a captive gorilla’s diet on overall health.

 “The gorilla diet previously was based primarily on a biscuit and if you imagine what dog food is like -- it's formulated so that it provides the animal with all of its essential vitamins nutrients,” says Lukas. “We've learned both in human nutrition as well as in wildlife management in zoos that oftentimes processed diets are not in the best interest of all the animals. We were curious to know if we replace that biscuit with other food items that might provide the same nutrients, but feed a gorilla more like a gorilla should be fed both internally and also behaviorally. We worked with veterinarians and nutritionists from all over the country for well over a year to formulate a diet that we felt would work and that could be acceptable to the animals here at Cleveland Metroparks Zoo.”

 The gorillas’ new diet included leafy greens, high in fiber. The team noticed changes almost immediately. Longer feeding times, comparable to the amount of time they would spend eating in the wild, allowed for more natural gorilla behavior.  

“Gorillas at many zoos regurgitate their food after they're finished and that behavior has always stumped me,” Lukas says. “Why are they doing this? What was amazing was that as soon as we transitioned to this new diet, that behavior completely stopped in our gorillas. We knew we were onto something. We learned how to completely eliminate this behavior that had been an issue for many zoos for many years.”

The diet change also allowed zoo staff to feed the gorillas more in quantity, but with fewer calories. That in turn requires the gorillas to be on the move, as they look for and consume different plant material.

With regurgitation eliminated, Dennis hopes that by studying gorillas’ digestive tracts, scientists might be able to gather more clues. That’s done by looking at microbiomes – an ecological community of sorts, found in the animal’s feces.

“What it reflects is what’s going on in the GI tract, and in human health and in veterinary medicine, we’re really just starting to get a handle on this,” Dennis says of the science. “What we found, and this is why I'm particularly excited about it, is that if you look at the low starch high fiber diet compared to the standard zoo diet, that roughly mimics the gut microbiome from humans healthy versus diabetic. And one of the questions that I have is insulin resistance, which is essentially the body not responding to insulin that's being produced -- it's sort of a pre diabetic state -- could be an underlying cause of heart disease in gorillas.”

The next step, according to Dennis, is to use that information as a starting point for a multi-year study across a larger population.

“This is a tiny little grain of information that gets us one tiny, little baby step closer to figuring out how all of this interacts,” Dennis says.

Zoo Executive Director Chris Kuhar says because of the work here, an increasing number of zoos are coming to Cleveland for answers -- and ideas.

“A lot of the research that we’re implementing here, folks are watching,” he says. “They’re looking to see what the success is and they’re taking those ideas and holding Cleveland as a model for how they can manage their gorillas moving forward.”

The hope, according to the team in Cleveland, is to make a difference for individual animals, but also, indirectly, for the entire population.

“We want there to be future generations of gorillas. We want them to be healthy,” Dennis says when asked about the impact of her research. “They're in our care. For us to know they have heart disease and not figure it out… we can't do that.”

The zoo recently introduced an updated outdoor gorilla habitat, adding climbing structures and significantly increasing the square footage, allowing more room for activity. Considerations about conservation and the health of the animals are included in each update to exhibits throughout the zoo.

“A lot of people still have that vision of what zoos are in their heads. And quite honestly it's changed drastically,” says Kuhar. We've gone from being a consumer of wildlife -- extracting wildlife from the wild -- to organizations that strive for sustainable animal populations and are actually doing a lot of work, we're actually putting resources back into the communities that we were once withdrawing them from. We've become conservation organizations, and we're just in the process now of really telling that story in a better way to our visiting public.”

A public that is also on a learning curve – not just regarding the critically endangered mountain gorilla, but about other species. And with that education, stressed by members of the Association of Zoos and Aquariums, comes hope.

“Conservation isn't a long term strategy. Conservation is an emergency strategy at this point,” explains Kuhar. “We've got to do something right now. What we want to do is empower people, help people understand what they can do. Give them a reason to participate and inspire them to participate. Part of that is changing our exhibits.”

Changing exhibits is one measure – changing minds, is another. But the shift is coming, albeit slowly. Latest census findings indicate the mountain gorilla population increasing, with Cleveland intimately involved in the effort through a longstanding relationship with the Dian Fossey Fund, which operates in Rwanda and the Democratic Republic of Congo.

Lukas makes regular trips to Rwanda, helping train university students there to become future conservationists. While here at home, she works to share her passion and commitment with the next generation.

“My dream,” says Lukas, “is that as the gorillas grow up, and we are able to provide the most healthy food environment, physical environment and social environment for them, then they will continue to inspire our kids… my own kids and others, to understand what gorillas are and why they are so special and significant.”