SUMMARY

Until the 20th Century, infectious diseases played a major part in the history of Mankind by controlling population growth. Epidemics periodically devastated countries and decimated populations.

An improvement in living conditions, coupled with the development of vaccines and antimicrobials, have led to a higher level of wellbeing and greater economic development and, therefore, longer life expectancy. While bacterial infections have been controlled and the risk of cholera or plague pandemics has disappeared, viral infections still present a real and permanent threat. Only a handful of viral infections, such as small pox, polio or measles, have been controlled to date. Most of them are still out of control due mainly to their animal reservoirs and their ability to mutate, which produces continuous changes in their antigenic composition, rendering the possibility of developing an effective vaccine unattainable. Also included in this category are those viruses that use Nature as their reservoir, such as those transmitted by mosquitoes - dengue or encephalitis caused by the West Nile virus.

Another aspect covered in this paper is the appearance of emerging infections or the re-appearance, and prevalence, of infections such as tuberculosis.

Finally, the risks of bioterrorism will be analysed, along with the agents that could represent a real danger for the population.