Craig Packer, who has studied the lions of the Serengeti for more than a decade, remembers getting the bad news in the spring of 1990. The report came from his collaborator Stephen O’Brien of the National Cancer Institute. Many of Packer’s kingly beasts, O’Brien had just learned, were infected with a feline equivalent of the virus that causes AIDS in humans. All I could think was ‘Whoa, not my guys!’ says Packer, a behavioral ecologist at the University of Minnesota. Feline immunodeficiency virus, or FIV, was new. It had been discovered only three years earlier in domestic cats, and in them it was often lethal. Alarmed by the possibility that his lions might be on the threshold of death, Packer alerted his field assistants in the Serengeti to watch for warning symptoms.
Today, after five years of close scrutiny, Packer and O’Brien are cautiously hopeful. Although O’Brien has now shown that 84 percent of the Serengeti lions harbor the virus, there is as yet no evidence that the animals develop AIDS. As far as we can tell, says O’Brien, there seems to be a balance between the host and the virus.
To O’Brien, the lions’ apparent resistance to AIDS means that these infected cats may hold a key to fighting the epidemic in humans. At the very least, the cats are giving us an unprecedented understanding of how immunodeficiency viruses evolve. FIV, O’Brien’s team has now shown, has infected 25 species of cats around the world, from the lions of the Serengeti to the cougars of Wyoming, the snow leopards of the Himalayas, and the Pallas’s cats of the Siberian steppes. So far
O’Brien has studied four of these species closely--the lion, puma, leopard, and domestic cat--and has determined that each is infected with its own particular strain of FIV. He wouldn’t be surprised, he says, if that holds true for the other cat species also. That degree of variety and prevalence, coupled with the cats’ seeming good health, has important implications.
It basically means that FIV is an old virus, explains O’Brien. And to me, an old virus is a good virus. It hasn’t killed off its host, or it wouldn’t be here. And so it gives us a beautiful model for understanding these coevolutionary events.
