Glossary Section: Infectious disease biology and epidemiology

An infectious disease that can be transmitted between animals and humans.

Percentage of the population who have been diagnosed and have clinical symptoms of the disease.

Restricts movement and contact of potentially infected individuals (i.e., those who have had contact with an infected person) with individuals who are not infected.

An infected individual is no longer infectious; the pathogen has been eliminated.

A measure of a pathogen’s transmissibility. Reproduction Number is the average number of secondary cases arising from a Primary case in an entirely susceptible population (called basic Reproduction Number, R0), or the average number of secondary cases arising from a Primary case in a population comprised of both susceptible and non-susceptible individuals (called effective Reproduction…

The habitat where a pathogen normally resides and reproduces. This may include hosts such as humans and animals, and the environment (e.g., bodies of water).

Infection transmitted from an Index case in a circumscribed group such as a household or a dormitory.

An individual infected directly by the Primary case.

Time period between symptom onset of a Primary case and symptom onset of a Secondary case.

When a disease becomes extinct at random (by chance) in a geographic location even if Reproduction Number (R or R0) is greater than 1. This can take place in a small population or when the disease of interest is rare. Stochastic eradication/elimination (epidemic fade-out) may be modeled in stochastic models, not deterministic models.

An uninfected individual/population without sufficient immunity against a pathogen to prevent infection and is at risk of developing the disease with sufficient exposure (e.g., a Close contact).

A stage of illness where the infected individual has clinical symptoms of the disease.