Spillover is literally the transmission of a virus from one “reservoir” species, in which it habitually circulates, to a new “host” species, in which it can die or adapt and possibly even trigger an epidemic. Examples include SARS-CoV-2, Ebola, HIV, measles and seasonal flu viruses. The jump from an animal to a human requires three distinct phases: contact, infection and transmission.

To find out in detail how a spillover works, watch this video produced by the Istitituto Zooprofilattico Sperimentale delle Venezie (IZSVe), an Italian health authority and research organization in the fields of animal health, food safety and zoonoses.