Mechanisms of viral emergence

Domingo, Esteban

A viral emergence is generally defined as the appearance of a new pathogen for a host, such as human immunideficiency virus (HIV)-1 for humans in the twentieth century. Viral re-emergence often refers to the reappearance of a viral pathogen after a period of absence, such as the periodic human influenza epidemics or pandemics. Three major steps have been distinguished in the processes of viral disease emergence or re-emergence: (1) introduction of a viral pathogen into a new host species, (2) establishment of the pathogen in the new host, and (3) dissemination of the pathogen among a large number of individuals of the new host species to bring about outbreaks, epidemics or pandemics. Viral genome adaptability has been listed as one of 13 major influences that determine the emergence of infectious disease [1, 55, 69, 77] . The influences cited by Smolinski et al. include modifications of climate, weather and ecosystems, human demographics and behavior, international travel and commerce, poverty, social inequality, war and famine, and lack of political will. Peters has emphasized the role of viral variation by expressing viral emergence in the following terms: (viral variation) + (changing ecology) + (travel and transport) = (increased opportunities for viral emergence) [69] .