Abstract
Emergent viral infections are defined as those the incidence of which has increased over the last 20 years. These infections concern human but also animal viruses affecting wild or tame animals. In humans, emergent viruses are of zoonotic origin and often due to crossing of species barrier. This inter-species crossing is promoted by various circumstances: environmental and climatic variations, bioterrorism, evolutive potential of the virus, etc. Screening for the animal reservoir is extremely important to prevent re-emergence and to eradicate the disease. The emergential success of some viruses has had serious consequences on human public health: flu pandemics, AIDS pandemic, hemorrhagic fever, and more recently SARS.