Before the investigations of Louis Pasteur, Robert Koch or Julius Cohn, the origin, contagion and spread of infectious diseases were explained by curious and imaginative hypotheses that go back to the time of Hippocrates. Today, over the centuries and despite the progress in all areas of medicine, the importance of infectious diseases as a cause of death and suffering has not diminished a bit. In fact, in the XXI century, infectious diseases continue to be the leading cause of death in third world or developing countries, and the third in the first world, after cardiovascular diseases and cancer.

The epidemic of infection by the Human Immunodeficiency Virus (HIV) and its ultimate consequence, the Acquired Immune Deficiency Syndrome (AIDS) that caused millions of deaths in the last 2 decades of the 20th century.

The persistence of the global pandemic of tuberculosis or malaria, both with high mortality in third world countries; the increase in infections related to hospital care (nosocomial infections), the acquired resistance to antibiotics by common bacteria in our environment, the appearance of emerging viral pathogens (bird flu, coronavirus, hantavirus, Ebola)… they all recquire that this specialty of medicine constantly adapts and researches the challenges and threats of pathogenic microbes, in order to improve our tools for prevention, diagnosis and treatment.