An update of the role of the primordial reservoir in the biological cycle of the process of infection and contagion is made, using diseases of very frequent incidence at the present moment in the Mediterranean Area and the Iberian Peninsula. These diseases are, amongst others Severe and Acute Respiratory Syndrome (SARS), Rabies,
Lyme disease, African Horse Sickness, Blue Tongue, African Swine Fever, Ebola Hemorrhagic Fever, Hantavirosis, and Avian Influenza. The zoonoses classification proposed by the WHO Control Center in Athens in 1994 for the Mediterranean Area, based on the type of reservoir, the importance of the process and the type of transmission, and not focusing on the etiological agent, is very positively valued. Finally, the problem of Avian Influenza and the real risk posed by aquatic migratory birds in the diffusion and contagion of the present Avian Influence epidemics is reviewed.