The emergence of new virus diseases: An overview

From experience, we know that many different elements can contribute to the emergence of a new virus disease; these include virologic determinants [such as mutation, recombination, reassortment (drift and shift), natural selection, fitness adaptation, evolutionary progressional], natural influences (such as ecologic, environmental and zoonotic influences) and factors pertaining to human activity (such as behavioral, societal, transport, commercial and iatrogenic factors). In general, there is no way to predict when or where the next important new viral pathogen will emerge; neither is there any way to reliably predict the ultimate importance of a virus as it first emerges. Given this reality, initial investigation at the first sign of the emergence of a new virus disease must focus on characteristics such as mortality, severity of disease, transmissibility, and remote spread, all of which are important predictors of epidemic potential and societal threat. Clinical observations, pathologic examinations and preliminary virus identification and characterization often provide early clues, since new, emerging viruses often resemble their closest genetic relatives in regard to their epidemiologic and pathogenetic characteristics. Development of a global surveillance/diagnostics/communications network is needed, but this, in turn, must be linked to a global action network. This network must be designed to be flexible; capable, for example, in one instance of emphasizing local professional infrastructure development, and in the next of emphasizing global epidemic aid. Given the nature and magnitude of the threat represented by new and emerging virus diseases, the development of a global surveillance/action network is, indeed, a worthy goal for national and international public health authorities.