

In the past 30 years, more than 40 viral infections have been diagnosed among the human population in the United States. These and other viruses have infected people in other places in the world. Some, such as the Ebola virus, are associated with a high mortality rate but rarely are encountered in humans outside specific geographic areas. Others, such as the hepatitis C virus, have infected millions of people worldwide, including approximately 1.5 percent of all Americans, but are associated with a less dramatic course.

Most emerging diseases are zoonotic in nature: they are found initially in animals and, through various modes of transmission and genetic transformations, infect and cause disease in humans. A zoonotically transmitted virus that initially attracted a lot of attention in the lay press still is causing a great deal of suffering, but it no longer is the "disease of the day" and has mostly disappeared from the front pages. Yet, this mosquito-borne virus, the West Nile virus, has in the past five years spread across the country from its original U.S. port of entry, New York City, to California and the western parts of Canada. In 2004 alone, there were 2,470 reported cases of West Nile virus infection and 88 related deaths in the United States.

Other infections, such as HIV disease, still are causing great concern. This viral infection first was brought to our attention in 1981 and has since ravaged the world, infecting more than 60 million people, including almost 1.5 million Americans. In its wake, social advances and economic growth, as well as hard-fought improvements in public health, have crumbled. This pandemic still endures almost unabated, with almost one new infection every six seconds.

A more recent example of an emerging disease is severe acute respiratory syndrome (SARS). This viral infection first was recognized in Hong Kong in the fall of 2002 and spread quickly to other countries. In an unprecedented demonstration of rapid international collaboration among public health officials, h