Something to think about - to what extent are human activities
contributing to the spread of diseases in wildlife? Consider the
following item from the washington post.
_______________________________________________________________
http://www.washingtonpost.com/wp-dyn/articles/A23844-2001Mar18.html
Rapid Spread of Infections Puts Wildlife at Risk
By Cheryl Lyn Dybas
Special to The Washington Post
Monday, March 19, 2001; Page A07
Soon, some biologists say, Florida manatees may be as rare as mermaids,
the fabled creatures for which manatees are named.
The manatees are on a growing list of animals affected in recent years
by new infectious diseases. That list includes certain species of
dolphins, sea otters, seals, corals, prairie dogs, ferrets, amphibians,
birds, and a host of other creatures.
While an epidemic of foot-and-mouth disease is causing panic in Europe
as it spreads among domesticated livestock, less well-known outbreaks of
infectious diseases have been occurring in recent years among wildlife
around the world.
In the same way that Spanish conquistadors centuries ago introduced
smallpox, measles and other diseases to the Americas, the movement of
disease-carrying domestic and wild animals is introducing new pathogens
to previously uninfected areas.
Some biologists, like wildlife disease researcher Peter Daszak of the
Consortium for Conservation Medicine in New York, call this new threat
to wildlife "pathogen pollution." Pathogens that might not have caused
harm before are turning out to be killers when released among unexposed
animals, he said. Or microbes that had been inactive in an area are
suddenly on the scene with a vengeance.
"Considering the speed with which things move around the globe these
days, who knows what microbes are being transferred into regions in
which the animals are what we call 'naive,' that is, they have not been
exposed to these microbes before and hence often have no immune system
protection against them," Daszak said. "Some of these microorganisms
have caused epizootics" -- epidemics of disease in animals other than
humans.
Outbreaks of infectious diseases among wildlife may also be caused by
ecosystem alterations such as global climate change, habitat
degradation, pollutant inputs and over-fertilization of rivers, bays and
the sea with nitrogen and phosphorus from agricultural runoff, said
Cheryl Woodley of the National Oceanic and Atmospheric Administration's
Center for Coastal Environmental Health and Biomolecular Research in
Charleston, S.C.
"These environmental changes may stress an animal, compromising its
immune system and leaving it open to infections," she said.
In many cases, said Daszak, "when we look at emerging diseases in
wildlife, we find that the pathogens are almost identical to those that
cause human diseases."
That's the case with the manatees. "Papillomavirus, the virus
responsible for cervical cancer in women, for the first time has
infected manatees," said Gregory Bossart, a marine mammal veterinarian
at the Harbor Branch Oceanographic Institution in Fort Pierce, Fla. In
manatees, the virus results in skin lesions of unknown seriousness, and
it has necessitated the quarantine of these graceful "sea cows" near
Florida's Homosassa Springs State Park. Papillomavirus also has been
found in killer whales and dolphins.
"The virus may have been present in these animals' environment for some
time, but something has recently caused it to surface," Bossart said.
In a similar case in the Chesapeake Bay, a new microbe that has infected
one of the bay's prized fish, the striped bass, closely resembles the
bacterium that causes tuberculosis in people. Like the human disease,
this fish infection covers the internal organs of its victims with
bacteria-filled nodules, according to veterinarians Robert Heckert and
Ana Baya of the Virginia-Maryland Regional College of Veterinary
Medicine in College Park.
The Nipah virus from Malaysia is new to both people and animals. This
virus is transmitted among fruit bats, domesticated pigs and pig
farmers. Similarly, an insect that lives on palm trees in Brazil carries
a microbe, Trypanosoma cruzi, that has made the jump from palm trees to
insects to humans. As palm trees are cut down for economic reasons,
Brazilian scientists have found, the insects disperse and more human
cases of the infection occur. "Things that impact sentinel species can
also impact us. We need to look hard at what's happening that's
fostering the emergence of these infectious diseases," Bossart said.
Scientists are also investigating recent deaths in one of the last
remaining populations of endangered boreal toads in the Rocky Mountains,
linked to a fungus called a chytrid fungus. Sick and dying toads in this
Colorado population were first discovered in May 1999. Since then, dead
toads have been found every month. "We have no idea why this fungus is
affecting Colorado's boreal toads at this particular time," said Bob
McLean, director of the U.S. Geological Survey's National Wildlife
Health Center in Madison, Wis.
What makes figuring out the connections so difficult, said veterinarian
Beth Thomas of the University of Wyoming at Laramie, "is that one thing
may be connected to something else, and pretty soon you have a long
chain of events that has resulted in a particular disease."
Thomas's experience is with endangered black-footed ferrets in Wyoming
and other western states. "A decade ago, we lost most of the last
free-ranging colony of black-footed ferrets to canine distemper virus.
Canine distemper is transmitted by contact with infected animals, which
are not always dogs. In this case, it was probably badgers or coyotes,
although how they contracted the disease, we're still not sure."
Canine distemper is one of several morbilliviruses, viruses that have
been referred to as the kudzu or zebra mussels of the microbial world.
Morbilliviruses are able to adapt to almost any conditions. Thanks to
effective vaccines, these viruses no longer threaten domesticated
animals. But they're rapidly transmitted from one animal to another in
wild populations, or from a domesticated animal to a wild one. A case in
point is that of Caspian seals, which live only in the Caspian Sea.
Canine distemper virus killed more than 10,000 of these seals during the
spring of 2000. The virus's origin is unknown, but there are reports of
contact between seals and dogs, possibly virus-infected, that roam the
shoreline in this region.
Scientists hope there may be ways to limit the spread of the pathogens
responsible. "We certainly need to better screen animals before they're
transported across borders," Daszak said.
"What's really essential is an understanding of how infectious diseases
spread in wildlife," McLean said. "We need to monitor wildlife diseases,
and develop a baseline knowledge of what's happening. When bodies of
wild animals are found, it's crucial to discover how and why they died.
"You never know when any of these pathogens might make the next jump --
to humans."
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