Epidemic of Crossover Diseases Threatens Biodiversity, Human Health
1/21/00
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RELAYED TEXT STARTS HERE:
Title: Epidemic of Crossover Diseases Threatens Biodiversity,
Human Health
Source: Environment News Service
Status: Copyright 2000, contact source for permission to reprint
Date: January 21, 2000
Byline: Cat Lazaroff
ATHENS, Georgia, January 21, 2000 (ENS) - Newly discovered infectious
diseases in wildlife may pose an increasing and significant threat to
human health and to global biodiversity, a new international study
reveals. The report urges wildlife and medical experts to look for
evidence of crossover diseases that can jump from species to species
- even to humans.
While emerging human diseases such as Ebola have grabbed headlines in
recent years, similar diseases in wildlife have been understudied,
and few regulations concerning exotic disease threats to wild animals
or systems for surveillance are in place to prevent their spread.
"With a new wave of globalization on an unprecedented level, we don't
even know what the greatest threats are in terms of emerging
infectious diseases of wildlife," said Dr. Peter Daszak of the
University of Georgia's Institute of Ecology and department of
botany. "The problem has largely been ignored by policy makers and
the threat that these wildlife pose to human, directly or indirectly,
should be taken far more seriously."
Daszak's report on the scope of the problem, cowritten with Dr.
Andrew Cunningham of the Zoological Society of London and Dr. Alex
Hyatt of the Australian Animal Health Laboratory, was published
Thursday in the journal "Science."
Human history is filled with the catastrophic consequences of
emerging infectious diseases. The introduction of smallpox, typhus
and measles by the Spanish conquistadores in the 15th and 16th
centuries resulted in 50 million deaths among native South Americans.
Despite suspicions that disease may have caused similar effects on
wildlife, systematic studies of emerging infectious diseases of wild
animals and their effect on human populations have been few and far
between.
That all changed with the discovery that wild animals can act as
natural reservoirs for diseases that can be extremely virulent among
humans. The influenza virus, for example, causes pandemics in humans
following the periodic exchange of genes between the viruses of wild
and domestic birds, pigs and humans.
The report by Daszak and his colleagues points out that many emerging
infectious diseases of wildlife are associated with the spill-over of
pathogens from domestic animals to wildlife populations; with the
translocation of host or parasites by human intervention; and with
events that have no human or domestic animal involvement, such as
global warming or floods. Whatever the reason, these diseases have
spread just as human diseases did.
"In the same way that Spanish conquistadores introduced smallpox and
measles to the Americas, the movement of domestic and other animals
during colonization introduced their own pathogens," said Daszak.
The first major method of animal disease transmission, "spill-over,"
refers to the spread of infectious agents from reservoir animal
species - often domestic animals - to wildlife. Outbreaks of spill-
over diseases represent a serious threat to wildlife and domestic
animals, Daszak said.
For instance, a disease called brucellosis that causes pregnant
animals to abort was probably co-introduced to America with cattle.
So the presence of the disease in bison of Yellowstone National Park
is considered a potential threat to domesticated cattle grazing at
the park's boundaries. The problem has led to tension between
conservationists and cattlemen, and the shooting by the Montanta
Department of Livestock of bison that graze the same areas as
domesticated herds, even though there is little evidence of cattle
becoming infected, Daszak says.
The relocation of wildlife species - the second method of spreading
emerging infectious diseases - occurs often in conservation efforts
or for agriculture or hunting.
"The introduction of animals to new geographic regions and the co-
introduction of their pathogens is a serious problem," said Daszak.
"For example, avian malaria on Hawaii is thought to have caused the
extinction of a number of native species and was originally
introduced with exotic, alien birds."
The emergence of infectious diseases without overt human involvement
is among the thornier issues facing conservationists. For instance,
weather patterns can cause changes in the abundance of certain
parasites that are deadly to some species of sheep.
Researchers are finding new diseases even in sites considered
pristine. A newly discovered fungal disease has recently been
identified as the cause of death in frogs, toads and salamanders of
the Central American and Australian rain forests, areas scientists
thought were beyond the reach of human environmental change.
Whatever the source of infectious wildlife diseases, both human
health and global biodiversity are being increasingly threatened, the
authors argue.
Recent genetic analyses have shown that avian influenza can be
transmitted directly from birds to humans. Potential non-human
primate reservoirs for human immunodeficiency viruses - HIV-1 and
HIV-2 - have also been found. Daszak said that natural reservoir
hosts for such feared disease as Ebola have been more elusive, though
bats and some small forest dwelling mammals have been tentatively
implicated.
Researchers involved with human health have begun to search for new
animal diseases as part of a strategy to control emerging disease
threats to humans, but far too little is known about potential
threats at this point, the authors say.
While potential human disease outbreaks can be linked to animal
disease, just as troubling is the role of animal disease in the loss
of global biodiversity. While there are numerous examples of disease
emergence following the introduction of pathogens to a population,
"there undoubtedly are many more that have not been identified as
such."
The international movement of food crops, timber, agricultural
materials and domesticated animals, as well as landfill wastes and
ship ballast water, combine to cause global threats. The authors say
that even such remote protected areas as the Gal pagos Islands and
Antarctica are not exempt.
Just how science can offset the effects of emerging infectious
diseases in wildlife is still unclear, but the scope of the problem
is becoming increasingly obvious, said Daszak. The problems involved
have clear economic consequences. In 1994, 655 people who had
potential contact with a single rabid kitten in a New Hampshire pet
store were given post exposure treatment at a cost of $1.1 million,
the authors point out. The costs of Lyme disease treatments spreak by
ticks in the U.S. may be as much as $500 million a year.
"Current measures for the detection and control of emerging
infectious diseases in humans and livestock are inadequate for the
identification of similar threats in wildlife," said Daszak. "The
conservation community has drawn up guidelines to prevent the release
of animals carrying exotic pathogens to new areas, but these
recommendations are now under used. We need an integrated approach,
using traditional and cutting-edge techniques, to investigate
outbreaks as they occur in wildlife."
Techniques now used to help control emerging diseases in humans and
domestic animals - including satellite imaging, Internet news groups,
outbreak investigations and large-scale vaccinations - may well work
in certain populations of wild animals. Until then, these diseases in
wildlife will likely continue to cause serious and growing problems
for human health and biodiversity.