From:    Karen Claxon 
Subject: U.S. News Are humans and beasts too close for comfort (5-22-00)

U.S. News: Are humans and beasts too close for comfort? (5/22/00)
U.S. News and World Report
 http://www.usnews.com/usnews/issue/000522/animals.htm


Science & Ideas 5/22/00


Germs and sickness in a shrinking world
Are humans and beasts too close for comfort?
By Laura Tangley
Bird-watchers aren't the only ones keeping close tabs on feathered
migrants this spring. Public-health officials, fearing a resurgence
of the imported virus that gave both birds and people West Nile fever
last summer, are scanning the skies for signs of avian ill health.
But biologists warn that sickly birds, beyond being harbingers of
human disease, warrant concern in their own right. Last year's West
Nile outbreak, which killed seven elderly people, also felled 5,000
to 10,000 native birds=96mostly crows but 19 species in all, including
robins, blue jays, herons, hawks, and kingfishers.
That's not surprising. Just as measles and smallpox carried to the
New World by Spanish conquistadors took a devastating toll on Native
Americans who had never been exposed to the germs, transporting
domestic and wild animals from one place to another introduces native
creatures to new, and often deadly, infectious diseases. As
globalization shuffles more people, animals, and
pathogen-contaminated products around the world, biologists say such
infections are increasing. According to Peter Daszak of the
University of Georgia's Institute of Ecology in Athens, "There is
probably no place on Earth that is free from pathogen pollution."
In a report published last winter in Science, Daszak documents dozens
of "emerging" wildlife diseases=96from elk stricken with bovine
tuberculosis to Antarctic penguins who show signs of exposure to a
chicken virus. He believes such diseases pose a significant, yet
largely unrecognized, threat to global biodiversity. And the spread
of some wildlife infections also endangers human health. In last
week's Science, researchers warn that seals just discovered to be
infected with influenza B could spawn a new flu epidemic among
humans.
Like predators, pathogens are natural components of ecosystems that
help regulate wildlife populations. But humans cook up host-pathogen
combinations that could never occur in nature. One early example was
the introduction of cattle to Africa in the late 1800s, which sparked
an epidemic of a virus called rinderpest among native buffalo,
wildebeest, and other grazers. So many of these animals died that
large swaths of natural savanna turned into scrubby forest.
Unnatural. Indeed, spillover of pathogens from domestic livestock and
pets may be the leading cause of emerging wildlife diseases,
especially as humans encroach increasingly on wild-animal habitat. In
the western United States, the black-footed ferret was nearly wiped
out by distemper, a deadly viral disease of domestic dogs. African
wild dogs in the Serengeti did die out after exposure to canine
distemper. Today Africa's endangered mountain gorillas are threatened
by several diseases, from measles to the common cold, that they catch
directly from human tourists.
Sometimes, this process reverses itself in what Daszek calls "spill
back." A disease known as brucellosis, for example, was probably
introduced to North America along with cattle. But infected bison
roaming Yellowstone National Park are now considered a threat to
livestock, and are often shot by ranchers when they wander outside
park boundaries.
Destroying habitat is another way humans spawn disease outbreaks. The
loss of U.S. wetlands has crowded ducks, geese, and other waterfowl
into smaller bodies of water, sparking epidemics of cholera and
botulism that kill tens of thousands of birds at a time. According to
Robert McLean, director of the U.S. Geological Survey National
Wildlife Health Center, "Shrinking habitat is also deteriorating,
which promotes growth of bacteria and other pathogens."
Deadly mix. Occasionally, the culprit behind an emerging wildlife
illness is a mystery. In 1998, biologists identified a new fungal
disease that was killing huge numbers of frogs in remote upland rain
forests of Australia and Central America. Since then, the same fungus
has been fingered in die-offs of boreal toads in the Colorado
Rockies. But even in these cases, Daszak suspects people are
ultimately to blame. One possibility is that global warming, which
has increased the number of dry days in tropical cloud forests,
concentrated water-loving frogs in too small a habitat, sparking
disease outbreaks similar to those rampant among waterfowl.
Whatever the cause, biologists are seriously worried about massive
frog die-offs, as well as the threat infectious diseases pose to
biodiversity as a whole. Though scientists only recently began
considering the possibility, disease is now thought to have played a
role in many previous extinctions, including the disappearance of
several Hawaiian birds, the passenger pigeon, and even woolly
mammoths. Recently, researchers documented the first proven
"extinction by infection" when the last of a species of Polynesian
tree snail was killed by a parasitic disease.
The human species has its own welfare to worry about as well. Many
wildlife diseases=96from plague and flu to emerging infections like
Ebola, hantavirus, and West Nile fever=96also infect people. That's a
sobering thought as mosquitoes and birds set off on their springtime
migrations.



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