ABSTRACT
The inevitable, but unpredictable, appearance of new diseases has been recognized for millennia, well before the discovery of causative infectious agents. Today, however, despite extraordinary advances in the development of countermeasures (diagnostics, therapeutics, and vaccines), the ease of world travel and increased global interdependence have added layers of complexity to containing these infectious diseases that affect not only the health but the economic stability of societies. One example of disease emergence includes SARS, which emerged from bats and spread into humans fi rst by person-to-person transmission in confi ned spaces, then within hospitals, and fi nally by human movement between international air hubs. Nipah virus also emerged from bats and caused an epizootic in herds of intensively bred pigs, which in turn served as the animal reservoir from which the virus was passed on to humans. In, 2009 H1N1 pandemic infl uenza virus emerged from pigs as well, but only after complex exchanges of human, swine, and avian infl uenza genes (Morens et al., 2009). H5N1 infl uenza emerged from wild birds to cause epizootics that amplifi ed
virus transmission in domestic poultry, precipitating dead-end viral transmission to poultry-exposed humans. On the contrary a good example of re-emerging diseases is cholera, which has repeatedly re-emerged over more than two centuries in association with global travel, changing seasons, war, natural disasters, and conditions that lead to inadequate sanitation, poverty, and social disruption. Each of these diseases has caused global societal and economic impact related to unexpected illnesses and deaths, as well as interference with travel, business, and many normal life activities.
