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By Phil Williams
pwilliam@franklin.uga.edu
Newly discovered infectious diseases of free-living wild animals may pose an increasing and significant threat to human health and to global biodiversity, according to a recently published report.
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,” says Peter Daszak of UGA’s Institute of Ecology and botany department. “The problem has largely been ignored by policy makers and the threat these wildlife diseases pose to humans, directly or indirectly, should be taken far more seriously.”
A report on the scope of the problem was published this past month in the journal Science. Daszak’s co-authors were Andrew Cunningham of the Zoological Society of London and Alex Hyatt of the Australian Animal Health Laboratory.
Human history is filled with the catastrophic consequences of emerging infectious diseases. The introduction of smallpox, typhus and measles by European colonizers in the 15th and 16th centuries resulted in a staggering 50 million deaths among native South Americans.
Despite suspicions that imported diseases may have had 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 neglect changed with the discovery that wild animals can act as natural reservoirs for diseases that can be extremely virulent among humans.
The report by Daszak and his colleagues points out that many emerging infectious diseases in wildlife result from the “spill-over” of pathogens from domestic animals to wildlife populations, from the translocation of host or parasites by human intervention, and also from 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,” says 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 both to wildlife and to domestic animals, Daszak says.
The translocation of wildlife species--the second method of spreading emerging infectious diseases--occurs when species are introduced in a new area for reasons of conservation, agriculture or hunting.
“The introduction of animals to new geographic regions and the co-introduction of their pathogens is a serious problem,” says 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.”
Infectious diseases that emerge without overt human involvement are among the thornier issues facing conservationists. For instance, weather patterns can cause changes in the prevalence of certain parasites that are deadly to some species of sheep. Further, researchers have found new diseases even in sites considered pristine. A newly discovered fungal disease has recently been identified as the cause of amphibian mortality in the Central American and Australian rain forests, areas scientists thought were beyond the reach of human environmental change.
Emerging infectious diseases have clear economic consequences. The post-exposure treatment of 655 people who had potential contact with a single rabid kitten in a New Hampshire pet store in 1994 cost $1.1 million. The costs of Lyme disease treatments in the United States 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,” says 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.”
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