ABC transport systems

A type of active transport including several proteins and several steps in which the molecule being transported is handed off from one protein to the next.

Abscess

A lesion that contains pus in a cavity hollowed out by tissue damage.

Acidophiles

Organisms that grow best in an environment with a pH of 4.0 to 5.4.

Active immunization

An immunization in which antigen representing the infectious agent is administered and confers immunity. This is used to increase herd immunity.

Active transport

The mechanism used to transport things from one side of a membrane to the other in a process that requires ATP.

Active viremia

Viruses replicating in the blood.

Acute congestion

A phenomenon that occurs where local capillaries become engorged with neutrophils.

Acute croup

Also known as laryngotracheitis. A severe infection of the larynx and trachea.

Acute disease

The opposite of chronic disease; one in which infection occurs quickly and lasts a short time.

Acute inflammatory colitis

Rapid inflammation of the colon.