"There are probably hundreds, if not thousands -- maybe even millions -- of viruses out there"

...said Robert G. Webster, a virologist at the St. Jude Children's Research Hospital in Memphis to Rob Stein of The Washington Post. "We don't even know they're there until we disturb them. SARS is probably just a gentle breeze of what one of these big ones is going to do someday."

Stein is writing about the increasing outbreaks of exotic diseases, like monkeypox, that are showing up. These are "zoonotic diseases" passed from animals to humans. While this has been going on for centuries (plague, smallpox, influenza), the process has accelerated in the last few decades.

This transfer is happening at an alarming rate because of a combination of several overlapping factors:

- people are moving around the world into areas that were previously wilderness, putting us into contact with new species carrying unknown or little-understood infectious diseases;

- climatic changes are driving birds, mosquitoes and other disease-carrying creatures into new living areas that include humans;

- exotic animals are being taken from former wilderness places as pets and food;

- worldwide transportation allows people to become infected in one area and quickly travel to another, infecting hundreds or thousands of people on their way;

- industrialized food production techniques are distributing contaminated food products to more people scattered over a wider area than ever before.

These new outbreaks of highly infectious and lethal diseases, combined with the growing threat of bioterrorism, is leading to the introduction of increasingly sophisticated networks and policies for reporting and tracking the spread of new diseases worldwide.