The incubation period is the time during which an infectious disease develops, from the point when the infecting organism enters the body until the appearance of the first symptoms. This can be as short as a few hours for cholera or as long as a decade in the case of leprosy. See also incubation.

One of the problems in establishing quarantine protocols to minimize the risk of back-contamination is the uncertainty about what relationship might exist between an alien pathogen and a terrestrial host.