Health researchers and wildlife biologists say the number of infectious diseases that have jumped the boundary from animals to humans and between animal species is on the rise. Scientists believe the increase may be a result of more frequent contact between humans and wild animals, as well as the growing trade in wild animals, both legal and illegal.
Towards the end of the 1990s, several Asian countries lived one of their worst health nightmares. A new, highly pathogenic, strain of Avian Influenza known as H5N1 killed hundreds of people. Over the next years, more than 9-million chickens were destroyed in an effort to stem the epidemic. Scientists believe the H5N1 virus was transmitted from wild birds to domestic poultry and pigs, which then passed it to humans. H5N1 is just the latest of various influenza strains that have killed up to 100 million people over the last century.
Now scientists are concerned about the appearance of new illnesses. Jonathan Sleeman is the director of the National Wildlife Health Center at the U.S. Geological Survey.
"Human health, wildlife health and domestic animal health are all interconnect within the context of the environment," said Sleeman. "And environmental changes and changes in environmental quality will have negative impacts in all 3 groups."
Experts say there are many causes: the increasingly rapid movement of people and animals around the world, increasing human contact with and consumption of wildlife, and the legal and illegal trade in wild animals.
"It's no longer a wildlife conservation issue, it's no longer a separate human issue. It's a combination. It's both a conservation and human health issue," added said Sleeman.
Scientists from a variety of disciplines met recently in Washington to share their concerns about pathogens spreading from animals to humans.
It's not a new problem. The AIDS virus, HIV, is now known to have originated from a similar virus in African chimpanzees. An estimated 30-million people have died of AIDS since the early 1980s. Other human diseases with animal origins include SARS, Ebola hemorrhagic fever and West Nile encephalitis.
New animal illnesses generally originate in invasive species. Zebra mussels that have spread throughout the U.S. Great Lake introduced a type of botulism that has killed some 100,000 birds in the last decade. A fungus spread by the trade in amphibians has led to the extinction of about 120 species of frogs around the world.
Many other imported, exotic animals escape or are released into local ecosystems. They disrupt native ecologies, out-compete native species and potentially spread new diseases.
Jonathan Epstein, with the EcoHealth Alliance, says 13 million animals have been confiscated in the past few decades, as part of the illegal trade in exotic species.
"The global illegal wildlife trade is second only to the trade in narcotics and weapons," said Epstein. "Just between 2000 and 2006, we had about 1.5 billion animals imported into the U.S."
Experts say more attention must be paid to the human disruption of wildlife and ecosystems to avoid the emergence of other infectious diseases with deeper and even more severe consequences.