Big Cat Questions continued . . .


Munson is best known for her work with cheetahs, lions, tigers, jaguars, and leopards. She helped identify the disease that in 1994 suddenly began killing lions in Africa's Serengeti park. About one-third of the approximately 1,000 Serengeti lions died in just a few months.

"Many of the lions just disappeared," Munson says. "Some of the sick animals were videotaped by tourists. They were going into horrible, repeated convulsions."

A tour guide alerted one of the park's wildlife veterinarians, who called Munson. "She knew that I was working with other researchers to survey major diseases in African cats," Munson says.

The UT researcher studied cells from some of the infected Serengeti lions and saw signs of a viral infection. "I recognized the disease problem, but then I brought in geneticists and virologists to try to determine exactly what the organism was," she explains. The culprit turned out to be canine distemper virus. Researchers think spotted hyenas, who sometimes venture into human habitat near the Serengeti, contracted the disease from domestic dogs and brought it back to the lions.

The drama of the Serengeti saga reinforces what Munson says is often the popular impression of pathologists: "Many people think of us as `Quincy' types." However, she spends a lot more time examining tissues under a microscope than dead bodies in the field. The key to identifying and understanding diseases, Munson explains, is an intimate and extensive knowledge of how cells are affected by various types of disease processes.

For example, since 1988 Munson has been investigating two problems that affect the survival of cheetahs in United States zoos.

"Throughout the 1980s, it was becoming apparent that cheetahs did very poorly in captivity. Many of the cubs died shortly after birth and many of the adults didn't live beyond six or seven years old. Other species of zoo cats usually live to about 14 or 16 years old.

"The captive cheetahs were also not very reproductively active. There are about 300 cheetahs in captivity, and less than 10 percent of those were breeding," she says. Munson and other researchers thought that perhaps a single disease was causing the cheetahs to die young as well as making them infertile.

Linda Munson, right, tracks the health of cheetahs in U.S. zoos and in the wild in Africa.


In 1988 the researchers formed the Cheetah Research Council to look for answers. "Because of my experience with big cat pathology, I was asked to serve as the council's pathologist. We designed a surveillance program for all the cheetahs in captivity in the United States." For the next five years, every time a cheetah died in the U.S., zoo veterinarians sent Munson tissue samples and she analyzed them and put the results into a database.

The killers were two very rare diseases of the kidney and liver.

"We spent the next several years looking at toxins the cheetahs could have been exposed to or infectious diseases that might have caused the problem," she says.

The researchers also took biopsies from more than 80 captive cheetahs who showed no outward signs of being infected. "Their tissues also showed early signs of the disease. So we were left with the problem of `Do cheetahs acquire these diseases because of their genetic background or because of captive management?' " Munson and her colleagues meanwhile had determined that the diseases didn't cause the captive cheetahs' infertility. So what did?

"Based on the results of this study, UT in 1993 supported a grant for me to go to southern Africa, which has the largest free-ranging cheetah population in the world, to try to determine if these diseases are inherent in all cheetahs," Munson says.

Geneticist Steve O'Brien of the National Cancer Institute had already determined that there was very little genetic diversity in the cheetah population.

"They appear to be inbred," Munson says. "The reason for this isn't known other than at sometime in the past, the African population became miniscule due to climactic change or disease. The whole modern population emerged from those few animals, so they are very similar genetically, like sisters and brothers. It was thought that with such a low amount of genetic diversity, maybe all cheetahs are predisposed to get these diseases," Munson says.

Munson spent six weeks setting up a surveillance program for the South African native wild cheetahs. "I also went to Namibia to work with the Cheetah Conservation Fund. The farmers in Namibia consider the cheetah a pest and capture cheetahs just as American farmers capture coyotes. So the Cheetah Conservation Fund tries to move the pest animals, either to another location in the wild or, if that's not possible, to one of the wildlife parks in southern Africa.

"From that process we've gotten blood samples and an enormous amount of information on the wild cheetah. We have tissues from about 12 wild cheetahs that have never been in captivity. We have learned that cheetahs in the wild have none of the kidney or liver diseases, nor do cheetahs in the big wildlife parks with lots of space. However, cheetahs in small zoos in Africa tend to have the same diseases as those in zoos in the United States. There's something in captive management that appears to be causing these diseases, so what we're looking at now is how cheetahs respond to stress," Munson says.

Stress also seems to be the reason that captive cheetahs aren't reproducing, Munson says. "Animals who aren't in an optimal environment, even if they have no diseases and are capable of normal hormonal functioning, can just shut down the reproductive tracts," she says.

Stress in captive cheetahs will be tracked over the next few years by a new, non-invasive method that measures the level of stress hormone in feces. "As soon as cheetahs are translocated or placed in zoos, we're going to start measuring the stress hormones in their feces and see if we can correlate the level of stress over time," Munson says. If she and her colleagues can pinpoint the sources of stress, zoo veterinarians should be better able to prevent the diseases plaguing captive cheetahs.

Munson monitors other species as well.

"We have a major problem with captive lions and wild lions in South Africa.

A lot of the lions carry antibodies to the virus called FIV [feline immunodeficiency virus], the cat equivalent of HIV. However, we have no evidence yet that it causes a significant disease in this species. We don't have enough long-term information about what diseases lions have in general, and we certainly wouldn't be able to pick up subtle changes that are caused by this immunodeficiency virus." The researchers have created a program to identify diseases that occur in captive lions in the U.S. and diseases seen in the African wild population. "By putting that information together, we hope to determine if there's any correlation between an animal being FIV positive and a particular high prevalence of the disease," she says.

Closer to home, Munson has surveyed the red wolf population in the Great Smoky Mountains National Park since 1989. "That's when there were enough in captivity to start releasing them. I've been following the disease problems they've had, not just what causes death but what diseases are being seen in captive animals," she says. She's found that red wolves are prone to parvo virus and other infectious diseases common to domestic dogs, and alerted the program managers to the problem.

She's also involved in monitoring disease problems associated with surgically implanted contraceptives. "Zoos were using contraceptives in big cats and finding that certain diseases kept showing up. So I helped start a national monitoring program to determine what diseases were occurring. We've been analyzing tissues and placing results in a database, trying to determine if these diseases are associated with a species, with an age group, with exposure to a particular drug, or some other factor. We've learned that there are several problems associated with contraceptives zoos have been using. So here at UT, researchers have been running clinical trials using the domestic cat as a model for zoo cats. They hope to develop new, safer contraceptives that can be used in zoo conservation programs," Munson says.

Such work doesn't bring overnight or easy solutions. "To be in this profession you have to be a little eccentric and a great optimist," Munson admits. "It's all teamwork, like any other form of research. We all add little bits to the puzzle to move the big picture along.

"The impact we hope to make is in preventive medicine. We're the ones who try to keep disasters from happening."