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West Nile Specie Impact*


West Nile's Widening Toll

Impact on North American Wildlife Far Worse Than on Humans

By Rick Weiss

Washington Post Staff Writer

Saturday, December 28, 2002; Page A01

First there was the silence of the crows.

Then the horses fell ill -- more than 14,000 this past summer alone -- along with squirrels, chipmunks and mountain goats. Even mighty raptors -- eagles, hawks and great horned owls -- dropped from the sky.

Now scientists are beginning to taking stock of West Nile virus's North American invasion, and they are taken aback by the scale and sweep of its ecological impact. While the human toll dominated the nation's attention this year -- the virus killed at least 241 people and infected many thousands more -- the effects on wildlife were far worse.

The virus swept westward with alarming rapidity this year, appearing in almost every state in the nation -- an astonishing expansion for a bug that had never been seen in the Western Hemisphere until three years ago. Equally unexpected, nearly 200 species of birds, reptiles and mammals fell ill from West Nile this year, including rabbits and reindeer, pelicans and bats, even a few dogs and cats. The virus also slammed dozens of exotic species in about 100 U.S. zoos, killing cockatiels, emus, seals, flamingos and penguins. Florida alligator farms lost more than 200 of the reptiles.

"In my years of working, I've never seen a mosquito-borne virus spread so quickly," said Robert G. McLean with the Agriculture Department's National Wildlife Research Center in Fort Collins, Colo.

Indeed, the epidemic has so resembled a bioterrorism attack that the nation's zoos -- which spearheaded an effort to track West Nile's march and mount emergency vaccinations -- could end up with potentially important roles in the emerging arena of homeland security. Just last month, in a hastily organized effort reminiscent of President Bush's smallpox plan, officials at two California zoos inoculated their endangered California condors with an experimental vaccine that may be the animals' only hope for survival.

West Nile is not fatal in all animals, and over time some species are expected to adapt. But even partial dropoffs in key populations could have serious consequences. Rodent populations could blossom in areas where raptors are dying, and pest birds such as house sparrows may be increasing where crows are absent.

The worst is still ahead, scientists say. Come spring, West Nile is expected to complete its push to the West Coast, home to endangered whooping cranes and economically important flocks of domestic geese. The virus is also poised to leap to the subtropics, where rare birds and other vulnerable creatures already face formidable threats to their survival.

"Once it gets to the tropics, where you've got species already stressed by habitat destruction and you have the potential for year-round mosquito transmission, some of those populations are not going to make it," said Peter Marra, an animal ecologist and West Nile specialist at the Smithsonian Environmental Research Center in Edgewater, Md. "I'm concerned about parrots and hummingbird populations. There's not that many of them left."

North American Debut

West Nile made its North American debut in the fall of 1999, discovered in a dead New York crow. Scientists don't know how the virus reached U.S. shores perhaps it hid inside a single infected bird imported from the Middle East. But one thing is certain, said Stephen Ostroff of the Centers for Disease Control and Prevention (CDC) in Atlanta: "There's no way that West Nile is going to go away."

The virus appears no more virulent in Americans than in other people around the world, and scientists suspect that the population will gradually gain immunity through low-level exposures. That is the situation today in countries where the virus has been active for many years. Most people in those countries have antibodies to the virus from early childhood, and serious complications or death from West Nile are rare.

But in North American wildlife, the virus has proven to be unusually aggressive and capable of infecting a surprisingly diverse array of animals.

"Most viruses tend to be rather host-specific, but that's not the case with what we were seeing," said Tracey McNamara, chief of pathology for the Wildlife Conservation Society, which has its headquarters at the Bronx Zoo, where the first infected crow was found.

It is still unclear how many of the 200 or so species struck by West Nile infection have suffered significant population declines. But a consensus is emerging that among birds, in particular, far more species are being hurt than scientists had predicted -- not just the crows, ravens and jays that were known to be especially vulnerable.

"There's been a huge die-off of raptors," said McLean of the agriculture department's Fort Collins lab.

The experience of the University of Minnesota's Raptor Center, which rehabilitates sick and injured raptors, was typical. "In mid-August, we had our first case: a great horned owl," said spokeswoman Sue Kirchoff. "In September and October, we were just inundated."

The center took in 70 ailing birds of prey, including great horned owls, eagles and red-tailed hawks. Officials there presume that if that many were found and brought to the center, countless others died in the wild, with potentially far-ranging repercussions.

"From a biological standpoint, raptors take longer to mature and have fewer offspring" than smaller birds, said Patti Bright of the American Bird Conservancy. "Whether they'll be able to rebound, well, we just don't know." It will take a while longer, Bright and others said, before it is known whether rodent populations are taking advantage of West Nile's impact on birds of prey.

The evidence for declines in songbirds and other small avian species is less direct, in part because they are so much less visible. "We're simply not going to know for a while with the smaller birds, because we're not going to find the bodies," said David S. Wilcove, a professor of ecology at Princeton University who has been studying West Nile.

Still, researchers this year found more than 140 bird species sickened or dead with West Nile, including chickadees, doves, grackles, gulls, herons, kingfishers, pelicans, sparrows, swans, turkeys, warblers, woodpeckers and wrens. And while most of those species will probably pull through as resistant individuals mate and pass their antiviral vigor to their offspring, ornithologists expect that others will not be so lucky.

They point to the experience in Hawaii, where the arrival of avian pox virus in the 1890s and avian malaria in the 1930s drove dozens of species to extinction or close to it. "Those viruses just hammered Hawaiian forest birds," Wilcove said. "That illustrates the potential for harm when a disease organism encounters a naïve population."

Bird-to-Bird Infection

Several unexpected aspects of the epidemic have fed Wilcove's and others' pessimism.

One surprise is that the virus can be transmitted directly from bird to bird, not only via mosquitoes. Raptors can acquire the virus by eating infected prey, and some birds can apparently spread the virus in their droppings. There's also evidence that some birds can pass the virus directly to their chicks while they're still inside the egg.

Another surprise is that West Nile virus can be transmitted directly from adult mosquitoes to their eggs, so that newly hatched aquatic larvae are born infected. That could make insecticides, which typically kill only adults, less effective.

Scientists have also been surprised to learn that the virus can persevere through the winter, even in many Northern states. Researchers are not sure which animals are serving as the virus's winter host, but the phenomenon is allowing the disease to spread year round and is giving the summer viral eruption an earlier start each year.

Yet another surprise is the number of mosquito species -- 36 at last count - that carry the virus. "This is a virus that's never seen a mosquito it doesn't like," said Ostroff of the CDC. "That's not typical for most pathogenic viruses."

If that weren't enough, some researchers suspect that West Nile might be capable of mixing its genetic material with that of a closely related virus, such as the one that causes St. Louis encephalitis, if both viruses were to infect a single animal. Other viruses have periodically produced such hybrids, creating in the process an entirely new and dangerous bug.

"This virus is amazing," said CDC virologist Robert S. Lanciotti. "I've been in this field almost 20 years, and I've never seen anything like it."

Neither has the state of California, but it is about to, experts say.

"It's going to spread to the West Coast big time by next year, no question," USDA's McLean said. "Each habitat is different, but California seems to be an area that has all the factors you need for a major spread. I think they're going to be facing major problems in humans, horses, birds and other animals. I just don't see any barriers."

Such predictions have a particularly ominous ring for researchers on the California Condor Recovery Team, who have been struggling to bring the ungainly bird back from the brink of extinction. They knew that this summer's experimental inoculations of zoo birds with the horse vaccine -- the only West Nile vaccine approved for marketing in this country -- had been disappointing, with many birds failing to develop protective antibodies. So in November, veterinarians at the Los Angeles and San Diego zoos injected into the thighs of their condors an experimental vaccine to try to confer immunity before the spring egg-laying season.

"We had absolutely zero negative effects," said Cynthia Stringfield, veterinarian of the Los Angeles Zoo, and preliminary blood tests suggested that the birds "had a fantastic immune response."

If further tests show that the vaccine works, the team will try to vaccinate all 128 captive California condors and the approximately 70 birds now living in the wild.

What Zoos Do

Zoos may take the lead in the fight against West Nile in more ways than that. More than 100 U.S. zoos and wildlife parks have joined a newly created information-sharing network, which has its headquarters at Chicago's Lincoln Park Zoo, to track West Nile and other emerging infections in exotic animals.

Some scientists suspect the network may even prove useful in the cause of homeland security, by providing a sensitive, nationwide "sentinel system" for detecting the first hints of a bioterrorism attack. After all, zoo officials noted, New York crows were dying in droves in the fall of 1999, but no one figured out that West Nile was the culprit -- or that the deaths were related to a spate of unusual human illnesses -- until a crow died on the grounds of the Bronx Zoo.

Zoos, it turns out, take every death seriously -- even those of non-zoo animals on zoo grounds -- because any death can mark the start of a devastating epidemic. "Every dead animal is picked up and immediately necropsied," said McNamara, the Bronx Zoo pathologist. "That's not true in Central Park."

When the Bronx crow was found to be teeming with West Nile, it was the first evidence that the Old World virus had leaped the Atlantic -- and the beginning of the recognition that an epidemic was already underway in humans. With a system in place, McNamara said, a zoo vet could be the first to know if terrorists have released a human or animal pathogen. The consortium is seeking federal funding.

Still, some scientists fear that the nation may soon become less able to prevent outbreaks such as that of West Nile -- whether accidental or intentional. They said the U.S. system for screening incoming animal, plant and microbial life -- a patchwork of more than 20 agencies -- has long been undervalued and underfunded. Now the largest component, the Agriculture Department's Animal and Plant Health Inspection Service, is to become part of the new Homeland Security Department. That's leading many ecologists to fear that it will narrow its focus to classical bioterrorism pathogens such as anthrax, leaving the nation more vulnerable to civilian bugs such as West Nile.

"I have a feeling that beetles in imported wood packaging are not going to be at the top of the list," said Faith T. Campbell, director of the invasive species program at the American Lands Alliance in Washington. Yet the recent U.S. invasion by Asian longhorned beetles, which arrived in wood packaging from China, is expected to cost the nation as much as $669 billion in insect-destroyed trees in urban areas alone in coming decades, Campbell said.

Whether West Nile ends up decimating many animal populations or settling in as a mere high-grade ecological disturbance, the epidemic should be a wake-up call to beef up the nation's surveillance and quarantine network, said Princeton's Wilcove.

"We may be lucky this time and get by with minimal losses of human life and minimal losses of wildlife, but this is not going to be the last disease to get into this country," he said. "One of these days we're going to draw the short straw."

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