Deaths of Large Cats From Virus Stump Experts : Animals: The outbreak of canine distemper at a shelter has only affected exotic felines, adding to the mystery.

In a case described as a scientific and medical anomaly, an illness common to dogs has jumped species and killed 16 African lions and other large cats at the Wildlife Waystation, an animal shelter in Angeles National Forest in the foothills above Lake View Terrace.

Veterinary experts said the recent siege of canine distemper--which has killed lions, tigers, leopards and jaguars over the past several months--is the largest outbreak of the illness ever reported in cats. They said only two or three cases were previously recorded, and that these involved small numbers of animals.

Adding to the mystery of a dog disease in cats is the puzzle of why only exotic cats seem affected. None of the way station’s native felines--four bobcats and 22 mountain lions--have become sick.

“What is happening in California is exceptionally unusual,” said Brian Summers, an associate professor of pathology at the New York State College of Veterinary Medicine at Cornell University, part of a team that isolated the canine distemper virus in the felines’ tissue. “There is . . . precedent for it, although in very low numbers,” he said.

Despite isolated cases in the past, this “is the first actual outbreak of this type of disease in big cats that I know of,” said Eric Hughes, a veterinarian in charge of disease investigations for the Los Angeles County Department of Health.

Martine Colette, president and founder of the way station, described the cat deaths as the most “devastating” event in the history of the refuge, which has been taking in injured and abandoned animals since 1976.

“This is a very rough time for the people here as well as the animals,” she said. “It’s very hard to lose magnificent animals that you have come to know as unique personalities.”

Colette said the last death occurred in late November, when a tiger named Vanaja died. Only a single tiger remains ill, raising hope that the disease has run its course.

But the 160-acre refuge in Little Tujunga Canyon--which houses 750 animals, including 74 cats--remains under quarantine. Twice monthly public tours have been temporarily halted because of concern over visitors carrying the virus on shoes or clothing.

Among other precautions, Colette said, refuge staff members are disinfecting their boots and tools. Moreover, she said, the health center for sick animals has been moved from its location among the big cats to an area about an eighth of a mile away.

Colette and Hughes speculated that it was spread by infected raccoons brought to the health center, although they said this would not explain why the virus affected the cats.

Distemper normally afflicts dogs, wolves, coyotes and other canines. But raccoons are also susceptible--and the way station has seen an unusual number of raccoons with distemper in recent months, Colette said.

Still, the refuge in the past had treated raccoons with distemper with no effect on cats. If raccoons were the carriers, “one of the . . . questions we have been asking--including the experts--is why now?” Colette said.

Summers theorized that a particularly virulent strain may be responsible, or that some other ailment weakened the cats’ immune systems, making them susceptible to the distemper virus.

The canine distemper virus, which spreads through the air, attacks the respiratory, gastrointestinal, immune and central nervous systems. Dogs routinely are vaccinated against it. Once it strikes them, however, the disease is fatal more than half the time, and surviving animals may suffer neurological damage.

The recent plague began in August, when M’Toto, a young African lion, fell ill and began having seizures.

Extensive tests, including a CAT scan and spinal tap, failed to disclose the problem. Tests of soil, leaves and wood chips did not reveal an environmental cause.

Then M’Toto, who had been on life support, began to recover. But in early September, Brutus, a leopard, was stricken and died in a matter of days. Soon, other cats began suffering diarrhea, respiratory distress, listlessness and in some cases seizures.

Way station veterinarians summoned experts from UC Davis, who performed a necropsy on a lioness named Doris. Working with colleagues at Cornell--including Summers and Dr. Max Appel, a professor of virology and an authority on distemper--the researchers identified the dog disease as the cause.

There is no vaccine to protect cats against canine distemper because there has never been a need for one. However, Colette said the way station recently began inoculating its cats with a canine distemper vaccine. Colette said it may not be effective, but is worth a try.

Summers said the outbreak is sure to be discussed in professional veterinary journals. “Unwillingly and unwittingly,” Colette said, “we’re going to be a major contributor” to knowledge in the area.

Although its occurrence in cats has been rare, canine distemper has crossed the barrier into other species. Along with raccoons, it has been reported in pandas and ferrets, and was found to be killing javelinas--a type of wild pig--in Arizona a couple of years ago.

It was also found to have caused the deaths of thousands of seals in Lake Baikal in the former Soviet Union a few years ago.

In the late 1980s, canine distemper was also blamed for the deaths of thousands of seals in the North and Bering seas and of dolphins in the Mediterranean. Scientists concluded that phocine distemper, caused by a closely related and previously unreported virus, was the culprit.

Summers said that in a reverse of the latest case, an illness common to cats, known as panleukopenia, crossed over to domestic dogs about a decade ago, causing many deaths.