Global warming or warning?

National Report

-- The plight of polar bears losing their food supply and habitat because of melting ice caps has been making news for some time, but could climate change really be causing a kitten boom? Will disease vectors on the move because of changes in their habitat cause outbreaks in companion animals?

There is a general awareness of the effects of climate change of wildlife in the face of deforestation, suburban sprawl and other human actions that deplete resources animals in certain parts of the world need to survive.

But some veterinarians are beginning to question the effect climate change can have on domesticated animals that don't depend on Mother Nature for food and shelter. They also wonder whether the effects of global warming as a threat to the health of companion animals also could cause a greater threat to human health.

"There's several categories where climate change is going to impact animal health in a big way," says Dr. Gwen Griffith, a veterinarian turned full-time conservationist adding that natural disasters often impact animal populations worse than humans, and the amount of high-impact disasters have increased in the last decade. Veterinarians might see more heat stress and trauma cases resulting from higher temperatures and natural disasters. Droughts are causing problems with starvation, Griffith says, pointing to the specific issue of horse starvation in certain areas. Disease is spreading quicker and farther than before, as well, sometimes moving from one region to another.

Areas that once were tropical are drying, and warmer climates are moving north. As a result, parasites, pathogens and disease vectors are increasing or changing their range, Griffith says.

"Their ranges are increasing and carrying disease into relatively nave populations," she says, citing the expansion of the heartworm larvae range into higher elevation areas like Denver and farther north than they used to be.

California already is seeing an increase of certain diseases in some regions, with a rise in West Nile Virus cases expected in Southern California this year, says David Jessup, senior wildlife veterinarian and supervisor for the California Department of Fish and Game. Jessup also serves on the American Veterinary Medical Associations Committee for Environmental Issues.

"The obvious thing in terms of vectors are clearly temperature and climate drive, and if global climate change is one toward warming, then that seems like a very realistic projection."

But how might this translate to what kinds of cases come into the average small-animal veterinary practice?

"I think what [veterinarians] might see is an increase in infectious diseases that will impact water quality. Outdoor pets drinking from local streams may pick up things from water that they didn't before," Griffith says. "I think the role that practitioners can play is to be that front line, to notice the changes and the trends and anticipate more zoonotics and how pets are affecting owners."

One hypothesis of how the effects of climate change can become visible in domesticated animals that has been questioned by a number of veterinarians has been posed by Dr. Julie Levy, DVM, Ph.D., DACVIM. Levy is an assistant professor at the University of Florida's College of Veterinary Medicine and works with the Maddie's Shelter Medicine Program there. She has pointed to climate change as a possible answer for the cat overpopulation problem despite long-time spay, neuter and re-homing efforts.

A cat's reproductive cycle is controlled by the "whim of planetary movements," Levy says. As a result, the low-daylight winter months cause a drop in pregnancies while high-daylight spring and summer months produce a wave of new kittens, she says. Other veterinarians have agreed that studies have shown how daylight hours can have an effect on a cat's breeding cycle, but vary on their opinions of how climate change has contributed to an increase in kittens.

The reproductive cycles of feral cats, who have less exposure to artificial lighting, have not changed in the last decade, Levy admits, but she thinks warmer weather could possibly cause puberty to occur sooner resulting in a more fertile cats comes breeding season.

"No, I do not believe that the breeding season has changed. Yes, I do believe that climate change could theoretically impact the phenomenon of kitten season," she says, adding that since cats evolved from African origins, climate change could be "mimicking their ancient origins and helping them reach their full reproductive potential."

Still, other veterinarians says no studies have been done to support a connection between climate change and a change in reproductive cycles. Instead, they offer other suggestions for the so-called kitten boom.

"The bottom line is we can't say it's a one-to-one correlation between the temperature and cats producing more," says Christine Peterson, an assistant professor at Iowa State's College of Veterinary Medicine. "It's not that having slightly raised temperatures is specifically leading to a direct increase in cat fertility ... [but] I do think [being] a little warmer overall makes it easier for them over winter."

A more likely theory is that less harsh winters make it easier for kittens and feral cats to survive, resulting in a larger population of adult cats during breeding season, says Peterson. This theory also was proposed by Levy, but Griffith says she wouldn't rule out Levy's first theory completely.

"I have not seen a good study on the effects on domestic cats as far as seasonal variations, but there are many good studies showing seasonal [reproductive] shifts in different wildlife species," says Griffith. "To me, it's not a stretch to think that would spread to domestic animals, as well."