Why are gorillas in zoos dying from heart disease?

April 7, 2008 5:22:32 AM PDT

April 7, 2008 --

He had a healthy appetite (he'd put away 7 pounds of food daily) and Mopie was no couch gorilla, either: He'd nimbly scale the mesh of his enclosures at the National Zoo in Washington, D.C., playfully chase the younger gorillas, and perch himself high in an outdoor maple, as if to show the world he was the king of the Great Ape House.

"The unique thing about Mopie was how extremely handsome he was," says Lisa Stevens, curator of primates and giant pandas at the National Zoo, and whenever the silverback sat, proudly, in the exhibit's trees, "it just added to his impressiveness."

Which is why Stevens and the zoo's staff were so stunned when, on the afternoon of July 3, 2006, this prized western lowland gorilla suddenly collapsed after playing with some newly introduced mates. By the time the keepers cleared out the other gorillas and tried CPR on Mopie, the gentle, 430-pound giant was lifeless - a victim of heart failure at 34.

Like his father, who had died the same way at the zoo in the early 1990s, Mopie had previously been diagnosed with an unexplained form of heart disease known as fibrosing cardiomyopathy, in which healthy heart muscle turns into fibrous bands unable to pump blood. And yet, he had not shown any outward symptoms, and his diet and behavior were normal.

"There was nothing to indicate he was feeling poorly or under the weather," recalls Stevens. "That's what made it even more of a shock."

No less troubling, two days earlier the National Zoo had lost its only other male group leader, a silverback named Kuja. Diagnosed just a month earlier with congestive heart failure related to cardiomyopathy, Kuja died while undergoing surgery to receive an advanced pacemaker. He was 23.

Sadly, Mopie and Kuja were not alone.

Gorillas in zoos around the nation, particularly males and those in their 20s and 30s, have been falling ill - and sometimes dying suddenly - from progressive heart ailments ranging from aneurisms to valvular disease to cardiomyopathy.

Just two months before the deaths at the National Zoo, the San Francisco Zoo had lost a lowland gorilla named Pogo to heart disease. A week before that, the Memphis Zoo lost one named Tumai the same way. And in previous years, there were others: Akbar at the Toledo Zoo in 2005, and in 2000 both Sam at the Knoxville Zoo and Michael at the Gorilla Foundation in California.

Now zookeepers are scrambling to understand what factors may be causing the illnesses and what might be done to save the 368 lowland gorillas that currently reside in 52 zoos across North America.

A 1994 study of 74 captive gorilla deaths, published by veterinarians Tom Meehan of the Brookfield Zoo in Chicago and Linda Lowenstine of the University of California at Davis, found that 41 percent - and 70 percent of males older than 30 - were from heart disease, mainly fibrosing cardiomyopathy.

"That study was a wake up call," says Meehan, now the vice president for veterinary services at the Chicago Zoological Society. It showed the need to "go to the next level of evaluating the animals and figuring out how their lifestyle related to their health."

In the mid-1990s, when the study was published, about 100,000 western lowland gorillas roamed freely within vast forests in Cameroon, the Central African Republic, the Republic of Congo, Equatorial Guinea, Gabon, Angola and Nigeria. Far less endangered than their relatives, the mountain gorillas, these apes were officially considered only as "vulnerable."

Since then, however, lowland gorillas in the wild have been dying at an accelerating rate. Poaching, logging, a dramatic expansion in the trade of bushmeat, and outbreaks of Ebola have reduced their numbers to roughly 30,000 - and in September, the species was reclassified as "critically endangered." At their current rate of decline, the gorillas are projected to disappear from the wild by 2050.

"Soon, these great apes may only exist in captivity," says Haley Murphy, director of veterinary services at Zoo New England, which runs Boston's Franklin Park Zoo and the Stone Zoo in Stoneham, Mass. The zoos are home to seven western lowland gorillas, the only species kept in captivity.

In 2000, Murphy, together with Dr. Ilana Kutinsky, a cardiologist with the Michigan Heart Group, began reviewing cardiac ultrasounds of zoo gorillas in hopes of discovering why the animals were at risk for heart trouble. It was part of a broad, veterinary detective effort to help save what Murphy calls "our closest living relatives, evolutionarily."

Problem was, no one had defined how a normal gorilla heart operated.

But as ultrasound information was entered into a database and compared to necropsy reports on deceased gorillas, clues began to appear. "We started noticing that some gorilla hearts were grossly abnormal from others," Kutinsky says. "The abnormal ones were mildly enlarged, very thick, and weren't pumping as much blood."

The findings raised more questions: Were the heart abnormalities the result of genetic differences? The gorilla's sex? Did climate play a role? How big a factor was diet? Were the gorillas getting enough exercise in their enclosures? Or too much? Was heart disease being caused by bacterial or viral infections?

Some even asked: Were gorillas developing heart disease because of the way they were reared or socially grouped at the zoos?

As the scope of the mystery widened, the number of cases of apes developing heart problems steadily climbed.

One was Babec, a 24-year-old lowland gorilla at the Birmingham Zoo in Alabama. Male gorillas in zoos have lived to age 54, and median life expectancy is 30; so when Babec started coughing, eating less and clutching at his chest in early 2003, the staff veterinarians examined him, and identified his nemesis: cardiomyopathy.

Although the gorilla was given medications for heart disease in humans, his condition kept deteriorating. He lost 80 pounds (20 percent of his body weight), was accumulating fluid in his abdomen. And by the summer of 2004, his heart pumped just 10 percent of the blood his body needed.

With Babec in the final stage of heart failure, the zoo risked a procedure never before attempted on a gorilla: the implantation in Babec's chest of an advanced pacemaker that corrects the heart's electrical circuitry and restores its ability to contract properly.

Today, Babec's prognosis is excellent. He's dropped the excess water weight, his heart and other organs work more efficiently, and his heart and pacemaker are continuously monitored.

Neal Kay, a cardiologist at the University of Alabama at Birmingham's Heart and Vascular Center who volunteered to perform the operation, later remarked that the only reason Babec still greets visitors to the Birmingham Zoo is that "we got to him in time."

Such intervention could save individuals like Babec - but still largely unaddressed were questions of why gorillas develop heart disease in the first place, and how to halt the disease's progression.

That's why in November 2006 - three months after Mopie and Kuja died at the National Zoo - ape experts, human cardiologists, and zoo epidemiologists, pathologists and managers from around the country gathered at the Brookfield Zoo in Chicago to establish what they called the "Gorilla Health Project."

Their first task: To build a National Gorilla Cardiac Database. With it, veterinarians could track rates of heart disease and death and try to learn why scar tissue was replacing cardiac muscle in apes.

To Kristen Lukas, chair of the Gorilla Species Survival Plan for the Association of Zoos and Aquariums, the project marks "a sea change" in how zoos will care not only for gorillas, but a host of other endangered species in captivity.

This level of networking between veterinary and human medical experts from universities, hospitals and animals rights groups "just never happened before," she says.

Meehan, the Chicago veterinarian who has worked with gorillas since 1979, expects the initiative to bring animal care forward a quantum leap from, say, the 1960s, when gorillas were originally brought to North American zoos and staff struggled just to keep the captive population alive.

Gathering new data will present challenges, of course. One is the need for echocardiograms of apes. To do the test, a gorilla must be anesthetized, "which carries a certain amount of risk," says cardiologist David Liang of Stanford University, a consultant to the Gorilla Foundation in California.

Another option, some experts say, might be to perform biopsies on affected gorillas to obtain tiny samples of heart muscle. This, too, would require anesthesia.

Many primatologists and veterinarians consider diet a prime suspect of heart disease in captive animals. And exploring that may require extensive study of the mortality of western lowland gorillas in the wild, they say - which, for many reasons, is tricky.

Gorillas in the wild tend to die younger, meaning not as many live long enough for age-related disorders to show up. Moreover, male silverbacks - the king of gorilla society - often hide symptoms of illness because they fear they may be challenged by younger males.

Still, research in the wild has paid off before. Not long ago, for example, it was learned that lowland gorillas, which are primarily herbivores, wade into swampy lake areas and eat vegetation growing underwater.

"There was no way of knowing that sort of thing was happening until somebody went out there to Africa and noticed what the gorillas were doing," says primatologist Joseph Erwin of the Foundation for Comparative and Conservation Biology in Needmore, Pa.

Ellen Dierenfeld, a gorilla nutritionist at the St. Louis Zoo, says that a member of the ginger family, Aframomum melegueta, is a staple food of western lowland gorillas in their native environments.

Some scientists say Aframomum is a powerful antibacterial, antiviral, antifungal and anti-inflammatory "natural drug," which may serve as a preventive medicine for the gorillas. But this and other native African plants are often not part of zoo gorillas' daily diets.

The Gorilla Health Project's diet and other data should be gathered by early 2009, analyzed and shared later that year, says Pam Dennis, a veterinarian in charge of analyzing the information.

"The important thing is that we're now working to prevent the diseases in the first place," says Dennis, an epidemiologist with the Cleveland Metroparks Zoo and Ohio State University.

"We started out trying to figure out human health by studying animals. Now we're turning to our findings in humans to figure out how to treat animals," she says with a chuckle. "It's come full circle, which is sort of a beautiful thing."