Animals sick, dying in greater numbers from West Nile virus

Chicago Tribune via
The Charlotte Observer


DENVER - (KRT) - Winkie Dink, an 8-year-old wolf, was the first resident at the Denver Zoo to drop dead last month. Then, Tracey, an 11-year-old reindeer, expired, followed by an unnamed goose and swan and Toola, a baby camel.

All five animals had West Nile virus.

Fifty miles away, Penny and Mark Miller were stunned when two alpacas collapsed and couldn't get up at their ranch in Loveland, Co. A week later, a third alpaca went from running in the pasture to stumbling aimlessly, her head swinging from side to side, in the course of a morning. Within a day, she too was dead, the latest to be struck down by the viral disease.

This is the emerging reality as West Nile marches across the continental U.S. and into the Caribbean and Mexico: more mammals and birds are sick or dying as the virus reaches deeper into the animal kingdom.

Hundreds of thousands of animals will die this year, scientists say, and little can be done to protect them. Most at risk are endangered or threatened species where the numbers of animals are limited to begin with and even a few deaths could make a difference, such as California condors or whooping cranes.

"As the virus spreads into new regions, more and more species are being infected," says Nicholas Komar, a research biologist and West Nile expert with the Center for Disease Control's mosquito-borne diseases branch, based in Ft. Collins, Colo.

"The more we look for the impact on (birds and animals), the more we are finding."

After a wet spring and hotter-than-average summer, Colorado is epicenter of the epidemic this year. As of Friday, 11 people had died in the state out of 884 recorded cases.

Nationally, 21 people have succumbed to West Nile so far this year, out of 1,442 cases reported by late August. The season is far from over - September traditionally is the worst month in terms of people.

However frightening West Nile may be to people, its devastation on birds and animals is far worse.

"Hundreds of thousands of wild birds are dying (of West Nile) each year," said Robert McLean, research program manager at the U.S. Agriculture Department's National Wildlife Research Center, in Ft. Collins. McLean co-chaired the first national summit on West Nile's impact on wildlife earlier this year, with representatives of the Smithsonian Education Research Center and the National Audubon Society. There was widespread agreement on the need for more research, but funding is limited and the work is difficult. Wildlife is hard to track, and animals tend to die far from population centers.

One vulnerable target are America's wild horses, known to be susceptible to West Nile, researchers note. Last year alone, the virus infected more than 15,000 horses across the U.S., and the death rate for sick horses tops 30 percent.

An equine vaccine is available, but most of the 37,000 wild horses overseen by the U.S. Bureau of Land Management will not get injections, said Don Glenn, wild horse and burro program specialist for the bureau in Washington.

Rounding up the horses from wild lands in Wyoming, Nevada and other western states and giving them the shots would be too expensive, given the risk of infection, Glenn said.

Animals in California, may be at risk sooner than anyone had thought. Mosquitoes carrying the virus were discovered for the first time a few weeks ago near California's Salton Sea, a major stopping point for migratory birds, which are suspected of carrying the virus cross-country.

If West Nile were to hopscotch to Hawaii, where species such as Hawaiian crows and Hawaiian honeycreepers, a brightly colored bird, have already been decimated by other factors, it could cause multiple species extinctions, said Peter Marra, West Nile specialist at the Smithsonian Environmental Research Center in Edgewater, Md.

Some researchers say the initial wildlife damage from West Nile is similar to the devastation of smallpox on Native American populations when Europeans first came America, because wildlife is unprotected by previous exposures. Survivors eventually will develop antibodies and species will adapt, they predict.

In the meantime, however, owls, hawks, and eagles are being struck down in significant numbers this year. At the Air Force Academy in Colorado Springs, four falcons who are school mascots contracted West Nile and a fifth falcon died.

For the first time this year, there are also reports of mule deer and white tailed deer being infected. They join a growing list of mammals known to have contracted West Nile, including cows, goats, sheep, dogs, cats, skunks, pandas, seals, squirrels, chipmunks, lamas, rabbits, donkeys, elephants, mules and others.

Based on preliminary evidence, many of these mammals - especially common farm animals and pets such dogs and cats - do not appear to become seriously ill in great numbers.

Meanwhile, the unknowns about how this illness affects animals _Does it cause pregnant animals to abort? Can it be passed from mother to child? - far outweigh what is known.

In addition, no one has a good grasp on the role West Nile infections in animals play in spreading the virus.

For instance, experts now suspect that infected rodents may carry sufficiently high levels of West Nile to serve as "reservoirs" of the virus, capable of passing it on to mosquitoes, according to Chris Brand, head of field research at the National Wildlife Health Center in Madison, Wis., a unit of the U.S. Geological Survey.

Even if the rodents don't die from West Nile in large numbers, they may play an important role in keeping the virus circulating in an area.

Until recently, only birds such as crows and blue jays were known to transmit the West Nile virus to mosquitoes. Now, other common birds such as cardinals are suspected of transmitting the disease.

As for zoos, they have been breaking new ground by cooperating nationally with public health authorities to supply surveillance data about the spread of West Nile. According to unpublished results from 2002, last year zoo animals got "hammered" by West Nile much worse than they did the year before.

"There were far more deaths, mainly at zoos in the middle of the country, and a far wider variety of animals were affected," said Dominic Travis, veterinary epidemiologist at Chicago's Lincoln Park Zoo and co-coordinator of the National Zoological West Nile Virus Surveillance Working Group. Among the animals hit for the first time: seals, antelope, reindeers, he said.

The trend continues this year, with even more species being infected by West Nile, though the numbers of animals affected are slightly down, perhaps because there are fewer zoos in the Plains states where the virus is concentrated this year.


© 2003, Chicago Tribune.


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