Latency and Incubation Period

Most organisms need some time from the moment they infect a new host until they can become infectious and be spread further.   The latent period is the period of time between when the host is infected to when he or she becomes infectious.   This period can vary from a few days in the case of influenza, to several weeks for hepatitis A.

A closely related concept is the incubation period. The incubation period is the time interval from the time an agent enters the host to the time the agent starts to cause disease.

The interplay between these 2 periods is crucial for disease control efforts.   For many diseases, the latent period is slightly shorter than the incubation period, meaning that people can be contagious before showing any symptoms of illness and isolating people once they become ill will not necessarily prevent transmission.   This is true with many respiratory viruses and with hepatitis A.   These characteristics help the agent to continue to survive and move to new hosts.