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BOX 3-1Factors in Emergence
1992
Microbial adaptation and change
Economic development and land use
Human demographics and behavior
International travel and commerce
Technology and industry
Breakdown of public health measures
2003
Microbial adaptation and change
Human susceptibility to infection
Climate and weather
Changing ecosystems
Human demographics and behavior
Economic development and land use
International travel and commerce
Technology and industry
Breakdown of public health measures
Poverty and social inequality
War and famine
Lack of political will
Intent to harm
niches that occur as we continue to alter the environment and extend our contact with the microbial world. Most of the microbes that live on or inside humans or exist in the environment do not cause disease in humans (see Box 3-2). These microbes may appear to be unimportant. However, they are often crucial to the human ecosystem. Moreover, microbes that have heretofore not affected humans directly may still represent a potent threat. Microbes that are pathogenic to the animals and plants on which we depend for survival, for example, are an indirect threat to human health. Other microbes live in apparent harmony with animals but can be pathogenic for humans, as evidenced by the number of emerging zoonotic diseases that are transmitted to humans from animals. Microbes are also adept at adaptation and change under selective pressures for survival and replication, including the use of antimicrobials by humans. Microbial adaptation and change continually challenge our responses to disease control and prevention. For example, the influenza virus is renowned for its ability to continually evolve so that new strains emerge each year, giving rise to
