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or country. Where a country or region finds itself on the spectrum will change over time with these factors as well. However, because of rapid changes in transportation and movement of humans and animals, we are clearly all impacted by any major event or outbreak anywhere in the world.

Global Emerging Infectious Disease Risk: In December 1979 the World Health Organization declared smallpox eradicated from the globe. After this enormous victory over disease, accomplished by a serious joint effort between Russian, U.S., and collaborating public health leaders from around the globe, the infectious disease community felt good about its ability to control biological risks. Some even speculated that we would now move on from smallpox to polio, malaria, and other important scourges, until we made the world free from infectious disease. It was not to be. In 1992 the Institute of Medicine of the U.S. National Academies published a report authored by Professors Lederberg, Shope, and Oaks entitled Emerging Infections: Microbial Threats to Health in the United States. The report, while making several important recommendations for the future, stated, “Disease-causing microbes have threatened human health for centuries. The Institute of Medicine’s Committee on Emerging Microbial Threats to Health believes that this threat will continue and may even intensify in coming years.”1 Those words proved to be prophetic.

An Important Lesson in the United States: In late June 1999 an unusual number of dead birds were reported in the borough of Queens, New York City. Six to 8 weeks later, an unusual number of human cases of encephalitis were noted in hospitals in the area. The human disease was soon diagnosed as St. Louis encephalitis, a mosquito-borne viral encephalitis, the causative agent of which does not kill birds. Approximately 2 weeks after the first human cases, the “St. Louis” outbreak was announced and mosquito control was begun. Then, 2 or 3 weeks later, animal disease data and human disease data were integrated, and the true causative agent, West Nile virus, was implicated in both the bird and the human deaths. We will never know if, or exactly how many, lives and dollars might have been saved by knowing 6 weeks earlier that a new, deadly zoonotic arbovirus had been introduced to North America, but experts agree days—and sometimes even hours—make a real difference when dealing with infectious outbreaks. Had we been thinking in terms of disease—wherever it occurs—rather than just human disease, we might have done better. The origin of the virus in North American birds or mosquitoes is unknown, but there is little doubt that it came from outside the borders of the United States.

Discovering Disease Early: Whether a disease is introduced naturally, accidentally, or intentionally, one of the most important factors is discovering it as early as possible and understanding its spread through the population. Because many diseases of concern to humans are first seen in animals—West Nile encephalitis, SARS, monkey pox, and H5N1 influenza are recent examples—it is critical that we seek to discover disease in the species of origin. Finding evidence of a zoonotic disease first in animals will very likely allow preventive or prophylactic

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