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THE CONCEPT OF EMERGING INFECTIOUS DISEASES
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Pathogenic organisms have been a constant companion of humans, their livestock, and their cultivated plants throughout evolution. Over the centuries, new organisms emerged as ecology changed or as humans managed to cross ecologic barriers such as oceans and mountains. Throughout history, there have been severe epidemics of infectious diseases, with devastating consequences to human populations over vast geographic regions. From the Plague of Justinian in Europe in the sixth century, to the Black Death in the fourteenth century, to the five cholera pandemics of the nineteenth century, to the 1918 Spanish influenza pandemic, to the current HIV/AIDS pandemic, the death toll in human populations has been enormous. The concept of emerging infectious diseases arose in the 1970s and 1980s with the recognition of several “new” diseases, such as legionellosis, HIV infection, Lyme disease, and toxic shock syndrome and was later expanded to include reemerging infectious diseases, such as tuberculosis. In 1991, the Institute of Medicine (IOM) convened a multidisciplinary committee to elucidate emerging microbial threats to health, with particular reference to the United States. In its report, the committee defined an emerging infectious disease as a disease “of infectious origin whose incidence in humans has either increased within the past two decades or threatens to increase in the near future.” In the year following the publication of the committee’s report, large outbreaks of Escherichia coli O157:H7 infection, cryptosporidiosis, and hantavirus pulmonary syndrome spurred the development of a national plan to recognize and interdict emerging and reemerging infectious disease threats by the Centers for Disease Control and Prevention (CDC). Since then, the list of emerging and reemerging viral, bacterial, fungal, and parasitic diseases has grown to include multiple infections and syndromes. Examples of emerging and reemerging infectious diseases, as of 2017, are shown in Table 461-1.
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The reasons for the emergence of previously unrecognized diseases and the reemergence of diseases that have previously been largely under control are legion. At its core, however, emergence has to ...