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Infectious Diseases

Author(s): Christine Herrmann, PhD

Types of Infectious Disease

Infectious diseases are classified by their duration and their location within the body, among other characteristics. “Acute,” “chronic,” and “latent” are terms used to describe the duration of a disease, how quickly the symptoms develop, and how long they last. The common cold is an acute disease; tuberculosis is a chronic disease; and herpes infections can produce latent infections with recurring attacks interspersed by periods with no symptoms (e.g. cold sores). 

“Local” and “systemic” refer to the location of a disease within the body. Pathogens that spread from a more localized site, enter the bloodstream and are carried to other tissues can produce a systemic infection.

“Primary” and “secondary” characterize the order of infection. A primary infection, usually an acute infection, occurs first in a previously healthy person. Sometimes, when a person is suffering from a primary infection and his or her immune system has been weakened by battling the primary infection, the person can succumb to a secondary infection caused by another agent. Thus, a person who has caught a cold due to a virus may then become ill with an ear infection caused by a bacterium because his/her immune system is incapable of fighting off another agent in its weakened state.