The time that elapses between the invasion of a susceptible host by an infectious agent and the onset of symptoms of the disease caused by that agent is called the incubation period. The term is also used to describe the comparable period in the life cycle of parasitic pathogens that have an intermediate host. In such cases the phase is sometimes referred to as an extrinsic incubation period; while this time period in a human host is called an intrinsic incubation period. The length of the incubation period varies greatly; it could be a few hours in the case of staphylococcal food poisoning, many months for a disease such as rabies, or even years for leprosy. The latent period in the mosquito intermediate host of the malaria parasite is temperature-dependent; some pathologens (including malaria parasites) can survive during the prolonged hibernation of the insect vector during the cool dry season.
JOHN M. LAST
(SEE ALSO: Latent Period)