[Emerging and reemerging viral diseases].

Recent decades have witnessed previously unknown viruses like HIV, along with other previously controlled viruses like dengue. The most important mechanisms have been the emergence of new viral strains by genetic alterations, the breakdown of species barriers by viruses, and viral spread from ecological niches. The main factors facilitating such mechanisms have been demographic pressure, with the expansion of the agricultural frontier, social behavior patterns, intensive air traffic, transporting both vectors and infected humans, importation of animals carrying the viruses, large-scale ecological alterations like dam- and road-building, and the widespread transformation of health systems, with a reduction in resources and infrastructure for disease control activities. Discussions on an international scale have recommended investments in the areas of Epidemiological Surveillance, Research Applied to Public Health, an emphasis on disease prevention and vector control measures, and infrastructure improvements in the health sector at the local, State, and federal level to reduce the impact of these viral diseases.