Smithsonian National Zoological Park l Friends of the National Zoo



The Heart of the Matter

Cardiac problems are a leading killer for gorillas and other apes. Veterinary researchers are striving to learn why.

By Phyllis McIntosh

Veterinarians and great apes staff at the Smithsonian’s National Zoo still vividly remember the painful events of July 2006.

On July 1 of that year, 23-year-old Kuja, a male western lowland gorilla, lay on the operating table. He was desperately sick with a failing heart. Visiting surgeons from Alabama implanted an advanced pacemaker in his chest in an effort to control the rate and rhythm of his heart and restore cardiac function. But Kuja’s disease had progressed too far, and he died on the operating table.

Haloko, a western lowland gorilla

Haloko, a western lowland gorilla, lived at the Zoo for more than 20 years. (Jessie Cohen/NZP)

Two days later, the Zoo’s second silverback gorilla, 34-year-old Mopie, collapsed and died in the Great Ape House. Mopie too had been diagnosed with heart disease many years earlier, but his signs of disease were much less overt.

Both gorillas succumbed to the same illness, but it unfolded quite differently in each case. That added to the heartbreak and mystery surrounding this severe and increasingly prevalent ailment. And it galvanized the National Zoo to take a leading role in investigating heart disease in primates.

Kuja’s and Mopie’s deaths were not isolated tragedies. At zoos across the country, male gorillas’ hearts were giving out—and no one knew why. For the past decade, a dedicated group of veterinarians, pathologists, and cardiologists who treat human heart disease have painstakingly collected data on captive gorillas in hopes of finding answers. This research effort has evolved into the Great Ape Heart Project, which brings together experts to study heart disease in all four species of great apes: gorillas, chimpanzees, orangutans, and bonobos.

While the key to preventing heart disease in apes remains elusive, some important clues are emerging. In the meantime, specialists have made great strides in prolonging the lives of animals already diagnosed.


Uncovering an Epidemic

For decades, there had been scattered reports of gorillas dying from heart disease. But there are relatively few in captivity—about 360 in the United States. So there can be a significant lag time between diagnosing a few cases and recognizing a syndrome, says Suzan Murray, the Zoo’s chief veterinarian.

The first indication of a serious problem was a 1994 mortality report compiled by two advisors to the Association of Zoos and Aquariums’ Gorilla Species Survival Plan. Their findings were shocking: Heart disease was responsible for 41 percent of adult gorilla deaths in U.S. zoos. Of the animals that had died from heart disease, 70 percent were males. Unlike humans, these animals were not succumbing to atherosclerosis, in which fatty deposits clog the arteries. Something else had damaged their hearts.

gorilla mother with baby

(Jessie Cohen/NZP)

At about the same time, two National Zoo veterinarians, Yvonne Schulman and Richard Montali (then the Zoo’s head pathologist), published a study of cases they had reviewed. The gorillas had died from fibrosing  cardiomyopathy, in which fibrous material replaces healthy heart tissue and blocks electrical impulses that keep the heart beating normally.

Clearly, a systematic effort was needed to find out what was causing the condition and how to treat it. In 2000, two young women stepped up to the task and launched the Gorilla Cardiac Database. They were Hayley Murphy, now chief veterinarian at Zoo Atlanta, and Ilana Kutinsky, a cardiologist now based in Michigan.

The two doctors began asking zoos to include echocardiograms—ultrasounds of the heart—in their routine physical examinations and to submit results to the database. “In order to figure out what was going wrong, we needed to know what a normal heart of a gorilla looked like,” says Murphy. So far, they have collected usable images of about 330 animals. The National Zoo was an early contributor to this effort, providing valuable data from healthy gorillas as well as Kuja and Mopie. The Zoo’s contribution owed a great deal to the work of veterinary cardiologist Steven Rosenthal, a longtime collaborator.

Other research soon followed. The National Zoo began investigating BNP (brain natriuretic peptide), a hormone released from injured heart tissue. It is a marker for heart disease in gorillas, as it is in people. Suzan Murray receives and analyzes blood samples from apes across the country. Her team’s goal is to build a database of BNP levels for healthy gorillas, which will help clinicians identify sick animals.

When Murray detects an abnormal BNP level, she alerts the Great Ape Heart Project team. She and they review the blood work and echocardiogram results. They then contact the gorilla’s home zoo to recommend appropriate medication. If the animal has already been diagnosed and is on treatment, the BNP test can help monitor how well the meds are working.

“If we can diagnose this illness earlier and start treatment sooner, we’ll be better able to halt the progress of the disease and help these animals live a longer and healthier life,” Murray says. A lot of work has gone into the idea of trying not only to characterize the disease but also to create early warning systems.”


Looking for Causes

At Cleveland Metroparks Zoo, veterinary epidemiologist Pam Dennis looks for risk factors that might predispose apes to heart disease. “In the wild, gorillas eat high fiber, strictly vegetarian, low-calorie food, but in zoos we often provide a more calorie-dense, smaller-quantity diet, and they also move around less than in the wild,” Dennis says.

Fortunately for the National Zoo, the animal-care team plays a vital role in keeping gorillas healthy. Nutritionists ensure that the animals receive a balanced diet—full of fresh fruit and vegetables. Gorilla keepers then spread the food all around the enclosure, which helps the apes mimic natural, active foraging behavior. This is just one example of the Zoo’s collaborative approach to animal care.


(Jessie Cohen/NZP)

Five years ago, researchers decided that they needed general medical information on captive gorillas to really understand what was going on. The result was a broader initiative known as the Gorilla Health Project, which aims to collect complete birth-to-death records on as many animals as possible. Through this program, complete medical records were collected from zoos around the country. They are in the process of being analyzed. The project also helped boost awareness of heart disease, encouraging veterinary teams nationwide to engage in earlier and more advanced diagnostic screening.

Some of the most intense scrutiny apes receive comes after death. Linda Lowenstine, veterinary pathologist at the University of California at Davis and co-author of the 1994 report that first put numbers to the heart disease epidemic in gorillas, studies pathology reports and tissues of apes that have died. Recently, she began requesting and stockpiling whole hearts of all great apes that have died from any cause.


Treating Heart Disease

The good news is that, when diagnosed early, heart disease in apes is often treatable. With the help of medication, the National Zoo’s 44-year-old female gorilla Haloko lived comfortably for four months after being diagnosed with severe heart disease.

Currently, about 30 apes in the country are receiving heart medications. Kutinsky has found that two classes of drugs used in humans—ACE inhibitors and beta blockers, both of which relieve stress on the heart by controlling blood pressure—work well in apes. Not only can drugs stop the progression of disease if given early enough, but
in some animals there are indications they are actually improving the condition of the heart, Kutinsky says.

So far, drugs are the only treatment option. The advanced pacemaker that was being implanted in Kuja when he died has been used only on one other ape, a gorilla named Babec at the Birmingham Zoo in Alabama. He lived for several years with the device. Unfortunately, the pacemaker had drawbacks. It was very expensive, and installing it took several lengthy operations requiring highly skilled surgical teams. Babec also had to live apart from the rest of the gorilla group because any chest beating during a confrontation with another animal could damage the pacemaker.

The experts agree that the greatest challenge in preventing and treating heart disease in apes remains determining what is normal. Even though apes are so much like us, scientists still don’t know, for example, what is an ape’s normal blood pressure or body mass index or cholesterol level. It’s not uncommon for gorillas to have cholesterol in the range of 280 to 300, which in humans would warrant medication; yet the animals do not get atherosclerosis.

gorilla surrounded by foliage

(Jessie Cohen/NZP)

But it is the mass of data available on humans that is providing clues to heart disease in our closest cousins. “I find it ironic that early on we learned a lot about humans by studying primates,” says Pam Dennis. “Now, we’re delving into the human literature to try to help these nonhuman primates.”

Wherever sources enrich our knowledge of heart disease in apes, two things are sure. Veterinarians at the National Zoo will a key role in contributing to our understanding. And they will draw on that learning to help keep the Zoo’s magnificent apes healthy and happy.


—Freelance writer PHYLLIS MCINTOSH is a longtime Zoo volunteer.


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Smithsonian Zoogoer 40(6) 2011. Copyright 2011 Friends of the National Zoo. All rights reserved.