[Emerging viral diseases].

In the last few years an increasing rise of new infectious diseases or of other diseases considered to be under control has been observed. The so called emerging and reemerging diseases are those new infections that have come up in a population or those existing diseases which incidence and geographic extension are on a rapid increase. Factors such as social and economic situations, medical assistance, food production, changes in human behaviours, environmental changes, health systems deterioration, and adaptation and changes of microorganisms are related with the emergence or reemergence of a number of entities. This paper sets forth an analysis of the emergence and reemergence of viral diseases and of those factors that have had an impact on this situation.