and “a whole range of other disease agents enter the United States multiple times each year.” Arrival of the agent does not automatically mean emergence of the disease, since this is contingent on interactions among the agent, host, and the environment. “Because agents, host characteristics, and the environment are constantly changing, there are always new opportunities for diseases to emerge,” he said.

Hueston also described key trends in demographics, agriculture, and the environment that can help one predict where and when diseases are likely to emerge or re-emerge. Population growth in cities and suburbs is causing increasing encroachment of suburban areas on “what heretofore have been wilderness or wildlife areas,” he said, noting that this has led to more interactions between humans and wildlife. He cited as an example problems caused by the overabundance of deer in the suburbs of Washington, DC, and many other cities. Hueston said that it is within these “ecoclines,” or locations where ecosystems meet, that new diseases are most likely to emerge. He recommended expanded surveillance in these areas, especially where humans, domestic animals, and wildlife interface. He also argued for more integration of the animal health and human health infrastructures. “Remember, diseases work both ways, from humans to animals and from animals to humans, and I think it is a dynamic interface.”

Diseases are also likely to emerge in high-population agricultural areas with large animal populations, where demographics are changing the most, and where there is pressure to intensify production. Environmental changes caused by changing weather patterns and human interventions, such as the draining of wetlands, construction, and landscaping, also increase our vulnerability to new diseases. “As the environment changes, it creates new ecologic niches,” he noted.

On the issue of public policy, Hueston noted what he referred to as the “conundrum of prevention”: As countries attain a higher health status, they tend to reduce their investment in animal health infrastructure. This is because governments get credit for solving problems, but not for preventing them. “If we are successful in preventing a disease, we will be condemned for having wasted money for something that never occurred. If, on the other hand, we fail to prevent disease, then we will be condemned for not taking more aggressive actions and spending more money.”

Hueston concluded that “anticipating and responding to the next major animal disease threats is going to require an integrated and coordinated interdisciplinary approach.” Hueston added that this approach would require flexibility and broader use of resources in public and animal health, civilian agencies, and the military.

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