W. Nile Tests Show Dogs, Cats Readily Get Virus

July 20, 2003
By Diedtra Henderson, Denver Post Science Writer

Dogs and cats can readily get West Nile virus. And cats can carry enough virus, for brief periods, to pass infection to mosquitoes that bite them. The good news: Neither of the nation's most popular companion animals appears to shed virus in its saliva, meaning kisses from Fido and smooches from Fluffy carry no added West Nile bite.

Colorado State University veterinarians gave the mixed message to millions of pet owners on the opening day of the American Veterinary Medical Association annual convention.

Saturday's gathering at the Colorado Convention Center attracted thousands of veterinarians - from academics to those employed by the Department of Defense - and covered topics that ranged from kitties' problems with litter to effectively managing pain in pets and assessing lingering bioterror hazards in the former Soviet Union. Security was tightened in the complex where former New York Mayor Rudolph Giuliani was scheduled to speak, with guards checking passes in hallways and at the few unlocked doors.

West Nile virus sickened a wide range of wild animals last year, writing a new chapter in its behavior since its 1999 arrival in the United States. No worry has vexed 150 million dog and cat owners more than whether pets that share their homes might carry West Nile.

Unlike bats or pigs, domestic cats can ramp up high enough concentrations of the virus to, in theory, pass it to mosquitoes. But, the cats carry far less West Nile virus for much shorter times than birds, a main player in the relay of virus to mammals.

CSU studied 23 adult cats, male and female, all euthanized at the end of the study, said Laura Austgen, a doctoral student who worked with CSU professor Rich Bowen on the project.

Only a small number of cats ended up with a very high level of virus pulsing through their blood. The exact concentration they need to infect mosquitoes depends on the skeeter species and will be pursued in a follow-up study.

It doesn't take a swarm of mosquitoes to give a cat West Nile.

"In fact, one mosquito is enough," Austgen told the standing-room-only audience.

Most of the infected cats acted normally, with no visible signs of being sick after being bitten by two, six or nine tainted mosquitoes. A few cats ate less, had slight fevers and were lethargic.

Because cats stalk birds - which can carry huge amounts of West Nile - the group also looked at whether the kitties could eat their way into sickness.

They fed cats one to three West Nile-tainted mice. Or, at least, they tried to feed some cats. A few felines, accustomed to a far, far tamer food source, didn't eat the mice meals.

"They really don't recognize mice as a food source," she said of the pickier eaters.

Those that chowed down on the rodents - splintering bones and leaving no trace of the carnage - picked up West Nile and did so more quickly. The chewing releases more virus, she added.

In Colorado, Baca County reported one feline West Nile case last year. Nationwide, two cats with West Nile were reported in 2000 as was a single cat in 1999.

But since those infected pets carry few signs of illness, those numbers are thought to be low.

CSU researchers did similar work with four adult female hounds, letting nine to 11 mosquitoes feed on each dog.

"Dogs seem to really luck out," she said. They ate normally and didn't get fevers, and their immune systems kicked the virus out of their bodies by 4 1/2 days.

James Kile of the U.S. Department of Agriculture, leader of the largest study done yet on pets, found nearly six times more infected pooches than people in one of the nation's West Nile hot spots.

The study tested 580 dogs and cats taken to a vet's office as well as strays picked up in St. Tammany Parish, north of New Orleans.

The parish includes Slidell, where nearly 2 percent of the people were infected with the West Nile virus. That was eclipsed by an infection rate of 32.7 percent for the town's stray dogs.

Dogs were more likely to carry West Nile than cats. Not surprisingly, the animal's likelihood of being positive increased with the amount of time they spent outside.

One surprise: The odds of infection were 2.5 times greater in dogs that didn't get heartworm medication, Kile said.

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