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American Zoos Concerned Over Gorilla Deaths

April 6, 2008

At Washington D.C.’s National Zoo, the staff were puzzled and stunned when Mopie, a strong, muscular, healthy-looking western lowland gorilla able to put away 7 pounds of food a day, suddenly collapsed the afternoon of July 3, 2006 after playing with some newly introduced mates.

By the time the keepers cleared out the other gorillas and performed CPR on Mopie, the gentle, 430-pound gorilla was lifeless, a victim of heart failure at age 34.

Lisa Stevens, curator of primates and giant pandas at the National Zoo, said the prized gorilla looked the picture of ape fitness, with broad, imposing shoulders and energetic enough to chase around the younger gorilla and nimbly scale the mesh of his enclosures.

“The unique thing about Mopie was how extremely handsome he was,” Stevens told the Associated Press, “it just added to his impressiveness.”

Like his father, who had died in the same manner 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.  Yet in Mopie’s case, he had not shown any outward symptoms of the disease, and his behavior and diet were normal.

“There was nothing to indicate he was feeling poorly or under the weather,”  Stevens recalled. “That’s what made it even more of a shock.”

Two days earlier the National Zoo had lost its only other male group leader, a silverback named Kuja, who had been diagnosed a month earlier with congestive heart failure related to cardiomyopathy.   Kuja died at age 23 while undergoing surgery to receive an advanced pacemaker.  But sadly, Mopie and Kuja were not alone.

Throughout the country’s zoos, Gorillas, particularly males and those in their 20s and 30s, have been falling ill, many times experiencing sudden death, from progressive heart ailments ranging from aneurisms to valvular disease to cardiomyopathy.

Just two months before Mopie and Kuja died at the National Zoo, the San Francisco Zoo lost a lowland gorilla named Pogo, also to heart disease.   A week prior, the Memphis Zoo lost one named Tumai in the same way.   In previous years, Akbar died in 2005 at the Toledo Zoo, and in 2000 both Sam at the Knoxville Zoo and Michael at the Gorilla Foundation in California died suddenly.

The situation has zookeepers scrambling to understand the factors causing the illnesses, and what steps can be taken to save the 368 lowland gorillas that currently reside in 52 zoos across the continent.

A study conducted in 1994 examining the deaths of 74 captive gorillas found that 41 percent,  70 percent of males over the age of 30, were from heart disease, mainly fibrosing cardiomyopathy.   The study was published by veterinarians Tom Meehan of the Brookfield Zoo in Chicago and Linda Lowenstine of the University of California at Davis.  

“That study was a wake up call,”  Meehan, now the vice president for veterinary services at the Chicago Zoological Society, told the AP, adding that the results showed the need to “go to the next level of evaluating the animals and figuring out how their lifestyle related to their health.”

When the study was published in the mid 1990s, about 100,000 western lowland gorillas roamed freely in the forests of Cameroon, the Republic of Congo, the Central African Republic, Nigeria, Equatorial Guinea, Gabon, and Angola.  These gorillas were far less endangered than their relatives, the mountain gorillas, and were officially only considered as “vulnerable”.

However, since that time lowland gorillas in the wild have been dying at an increasing rate, with poaching, logging, a dramatic expansion in the trade of bushmeat, and outbreaks of Ebola all contributing to the reduction in their numbers to roughly 30,000.  In September, the species was officially reclassified as “critically endangered”.

At their current rate of decline, the gorillas are expected to disappear entirely from the wild by the year 2050.

“Soon, these great apes may only exist in captivity,” Haley Murphy, director of veterinary services at Zoo New England, which runs Boston’s Franklin Park Zoo and the Stone Zoo in Stoneham, Mass, told the AP.

The zoos house seven western lowland gorillas, the only species kept in captivity.  In 2000, Murphy and Dr. Ilana Kutinsky, a cardiologist with the Michigan Heart Group, began examining cardiac ultrasounds of zoo gorillas with the goal of discovering why the animals were at risk for heart trouble.  The study was part of a broad detective effort to help save what Murphy called “our closest living relatives, evolutionarily.”

The researchers were challenged in that no one had defined how a normal gorilla heart operated.  But after 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 additional questions, such as whether or not the heart abnormalities were due to genetic differences, or perhaps the gorilla’s sex.  Other questions remained as well, such as how big a role climate and diet played, or whether or not the gorillas were getting enough, or even too much, exercise.   Perhaps the illness was being caused by bacterial or viral infections.

Some even questioned if the gorillas were developing heart disease due to the way they were raised or socially grouped at the zoos.    As the questions mounted, the number of cases of gorillas developing heart disease also continued to rise.

One, Babec, a 24-year-old lowland gorilla at the Birmingham Zoo in Alabama, began coughing, eating less and clutching at his chest in early 2003.  After the staff veterinarians examined him, Babec was diagnosed with cardiomyopathy.

Male gorillas in zoos have lived up to age 54, and median life expectancy is 30.

Although Babec 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.

The zoo decided to perform a risky procedure, a first for any gorilla, and implanted an advanced pacemaker in Babec’s chest that would correct his heart’s electrical circuitry and restore its ability to contract properly.

The procedure was a success, and 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.

Cardiologist Neal Kay of the University of Alabama at Birmingham’s Heart and Vascular Center had volunteered to perform the operation.  He later said the only reason Babec is still alive is that “we got to him in time.”

While such procedures could save gorillas like Babec, the underlying issue of why gorillas develop heart disease in the first place, and how to halt the disease’s progression, is still unanswered. 

As a result, in November 2006 ape experts, human cardiologists, zoo epidemiologists, pathologists and managers from around the country gathered at the Brookfield Zoo in Chicago to establish the “Gorilla Health Project.”

The project’s first task is to build a National Gorilla Cardiac Database that allows veterinarians to track rates of heart disease and death, and  to learn why scar tissue was replacing cardiac muscle in apes.

Kristen Lukas, chair of the Gorilla Species Survival Plan for the Association of Zoos and Aquariums, said the project marks a sea change in how zoos will care for gorillas and other endangered species in captivity.

This level of coordination between veterinary and human medical experts from hospitals, universities, and animals rights groups “just never happened before,” she told the AP.

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

The new project will not be without its challenges, however.  One is the need for echocardiograms of apes, which require the gorillas to be anesthetized.  The procedure “carries a certain amount of risk,” said cardiologist David Liang of Stanford University, a consultant to the Gorilla Foundation in California.

Some experts say another option might be to perform biopsies on affected gorillas to obtain tiny samples of heart muscle.  However, this would also require anesthesia.

Many veterinarians and primatologists consider diet a primary factor of heart disease in captive animals.   They said exploring that might require extensive study of the mortality of western lowland gorillas in the wild, which for many reasons would be challenging.   Gorillas in the wild tend to die younger and not live long enough for age-related disorders to appear.  Additionally, male silverbacks, the king of gorilla society, often hide symptoms of illness in fear of being challenged by younger males.

But previous research on animals in the wild has shown tremendous benefits.  For example, not long ago 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,” said Joseph Erwin, a primatologist at the Foundation for Comparative and Conservation Biology in Needmore, Pa.

Ellen Dierenfeld, a gorilla nutritionist at the St. Louis Zoo, told the AP that Aframomum melegueta, a member of the ginger family, is a staple food of western lowland gorillas in their native environments.   Some experts say Aframomum is a powerful antibacterial, antiviral, antifungal and anti-inflammatory “natural drug,” which may serve as preventive medicine for the gorillas.  

However, this and other native African plants are not typically part of zoo gorillas’ daily diets.

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

“The important thing is that we’re now working to prevent the diseases in the first place,” Dennis, an epidemiologist with the Cleveland Metroparks Zoo and Ohio State University, told the AP.

“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 said.  

“It’s come full circle, which is sort of a beautiful thing.”




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