Lions Bound Back From an Epidemic

Four years after a distemper epidemic roared through Serengeti National Park, killing at least a third of its famed lions, researchers say the beasts seem to be making a remarkable comeback.

In recent weeks, it has been relatively easy to spot lions throughout the park. Camera-toting tourists have been particularly captivated by six cubs scampering about in the tall grass by the Seronera River. Researchers have named them Mickey, Babe, Alannis, Gwyneth, Horny and Lizzie.

The sight of frisky cubs is welcome on various fronts--for the sake of the lions, as well as for researchers, visitors and the governments of Tanzania and Kenya, which are in chronic need of foreign currency from tourists.

Long-term, however, researchers say the watchword is caution. The distemper outbreak offers a revealing lesson in the connections among people, domesticated dogs and the wild cats of the Serengeti.

In February 1994, tourists drifting over the park in a hot-air balloon saw a gruesome sight: a dark-maned lion flailing, jerking, unable to stand. The seizures continued throughout the day; that night, the animal died.

Scientists recognized the damning signs of canine distemper, which causes encephalitis and pneumonia.

As the months went by, other lions were stricken. The virus spread into the far western reaches of the Serengeti, then north into Kenya’s Masai Mara Reserve.

In the southeastern Serengeti, where Craig Packer of the University of Minnesota has been studying the wild cats for 20 years, the lion population fell from 256 to 146 in 1994.

Assuming a comparable mortality rate throughout the Serengeti ecosystem, which includes the Masai Mara, Packer and other researchers estimate that between 1,000 and 1,200 lions died during 1994.

Scientists were puzzled over how the disease was being spread.

Canine distemper is an airborne disease typically transmitted by sneezing. Lions rarely venture into towns or villages. Tanzanian villagers value fierceness in their dogs--and thus give them names such as Simba, Scud and Sadaam--but even the fiercest dog would not take on a lion.

It was known that a strain of distemper had raged among dogs in the area west of the park in the early 1990s. Blood samples later showed that the same strain had made its way to the lions.

Between 50,000 and 100,000 dogs live to the west, between the park boundary and Lake Victoria, said Sarah Cleaveland, a veterinary epidemiologist based in Edinburgh, Scotland, whose doctoral thesis was about the dogs of Tanzania. The Tanzanian dog population, she said, grows about 10% each year; the average domesticated dog in the region lives only two to three years.

The human population around the park also is growing, about 3% a year.

More villagers and more dogs, researchers surmise, meant more opportunity for hyenas and jackals, which scavenge near village compounds for food, as well as for leopards, which eat dogs.

The lions, researchers believe, contracted the virus from one of these other animals. Lions come into contact with hyenas, for example, at kills.

One sick lion can quickly infect an entire pride. And sick lions tend to wander, thus infecting other prides.

The solution: vaccination. But not the lions--the dogs.

Dubbed Project Life Lion, the vaccination program has inoculated about 20,000 dogs since 1996 against distemper, rabies and parvo virus. Cleaveland said there has been no evidence since of distemper among the dogs.

But, she said, there are so many new puppies that the same villages have to be visited every eight or nine months. In addition, with the program’s scope limited by finances to the area west of the park, “we can’t guarantee it hasn’t come in [to the Serengeti] from somewhere else,” she said.

And there now may be enough dogs to make up “a reservoir of disease with a much greater impact on wildlife than happened before,” Packer said.

For now, though, the lion population is rebounding--up to 234, for instance, in the southeastern Serengeti.

“We’re all really surprised at how fast they’ve come back,” Packer said. “But they did.”