A Cure for Euthanasia?
Science 18 Sep 2009:
Vol. 325, Issue 5947, pp. 1490-1493
(continued from page 1490)
That may be about to change, thanks to a U.S. billionaire named Gary Michelson, who has announced $75 million in grants and prize money for the development of a single-use, nonsurgical sterilant for dogs and cats. Suddenly, researchers who had abandoned this work are ramping up their efforts again. And those who had never considered the problem are starting to brainstorm novel approaches, such as genetically silencing brain pathways critical for fertility and developing toxins that specifically target sperm and eggs. This summer, Michelson’s foundation announced its first grantee, with more to follow. The scientific challenges are daunting, however, and some question whether such a product could actually solve the global dilemma of cat and dog overpopulation.
A walk on the wild side
The story of nonhuman contraception traces back to Billings, Montana, in 1971, when two cowboys walked into the office of a young Montana State University assistant professor named Jay Kirkpatrick. The U.S. Congress had just passed the Wild Free-Roaming Horses and Burros Act, which sought to prevent the oftenbrutal hunting of feral horses in the American West for pet food.
Although the cowboys applauded the principle of the legislation, they knew that without some sort of population control, wild horse numbers would soon explode. “They saw the train wreck coming years before it got here,” says Kirkpatrick, now the director of the Science and Conservation Center, a Billingsbased nonprof it dedicated to managing wildlife. “They came into my off ice—hats, boots, the whole 9 yards—and said, ‘Can you make horses stop reproducing?’” Kirkpatrick was dumbfounded but intrigued. “The concept of contracepting large wildlife was really off the screen,” he says. “It hadn’t been tried before.”
Kirkpatrick first turned to human contraception—specifically, “the pill,” a hormone-based approach introduced a decade earlier. Colleagues gave him a hard time. “I got laughed at a lot in the early days,” he says. “I couldn’t convince anybody that this was more than a harebrained idea.”
Things started to change in 1977, when the Bureau of Land Management granted Kirkpatrick $300,000 to test his hormone idea in western horses. “All these people who had been snickering before were suddenly interested in wildlife contraception,” he says. Over the next 10 years, Kirkpatrick showed that he could contracept wild horses with steroid shots that lasted through the breeding season. But catching the horses was expensive, and the hormones caused cancer in zoo animals. “The practicality wasn’t there,” he says.
So in 1988, Kirkpatrick says he “chucked everything out the window” and tried a new approach called immunocontraception. Originally developed for women, the idea was to administer a vaccine that would stimulate the production of antibodies against zona pellucida—the membrane that covers eggs—thereby preventing sperm from entering.
In humans, the approach proved less effective than the pill, but Kirkpatrick had great success in horses. He traveled to Assateague Island off the coast of Maryland and Virginia, which was dealing with its own impending horse overpopulation problem, and spent months wading through marshes and forests, darting mares with the zona pellucida vaccine. “A year later, not a single foal was born,” he says, and the vaccine showed no side effects. “The Assateague work changed everything.”
That’s when Kirkpatrick’s phone started ringing off the hook. For the past 2 decades, he and colleagues have used the zona pellucida vaccine to contracept everything from urban deer to sea lions. The vaccine was so effective in so many species that when researchers asked to try it in cats and dogs, Kirkpatrick was sure it would work. It didn’t.
Man’s best friends?
About the time that Kirkpatrick hit upon the immunocontraception approach, Julie Levy was witnessing the homeless pet problem for the first time. As a veterinary student at the University of California, Davis, in the late 1980s, she walked past sickly feral cats every day on her way to class. Occasionally, the campus’s public health and safety department would round them up and euthanize them. “As veterinary students who were trained to save animals, killing all of these cats seemed very contradictory to what we were on campus to do,” says Levy, now the director of a shelter medicine program at the University of Florida, Gainesville. So, with the faculty’s permission, Levy and a group of students began trapping and surgically sterilizing the cats. “By the time we graduated,” she says, “most of the cats on campus were neutered.”
Levy’s small program was part of a larger surgical sterilization movement begun in the 1970s. Estimates suggest that, by the beginning of that decade, U.S. shelters were euthanizing more than 20 million cats and dogs each year. At the time, most vets considered spay/neuter surgery “unwarranted mutilation” and performed it on only about 10% of dogs and cats, says Andrew Rowan, the chief scientific officer of the Humane Society of the United States. But as feral dogs posed an increasing public health risk, animal-welfare groups began pushing for surgical sterilization. Today, most U.S. shelters spay or neuter every animal that leaves their doors.
The surgical sterilization movement has had a dramatic impact. “Feral dogs are now, in large part, a thing of the past in the U.S.,” says Rowan, and rates of euthanasia have dropped precipitously. Yet U.S. shelters still euthanize nearly 4 million healthy dogs and cats every year, he says, and about 30 million feral cats still roam the streets. Feral cats are also a huge problem in Australia, where some environmentalists claim they have hunted endangered species to extinction.