Multiphasic Prion
From Star Trek : Freedom's Wiki
The multiphasic prion is a pathogen that infects Humans and can be potentially life-threatening. The prions initially attach themselves to the mitochondrial wall, and later migrate to the cell membranes and rupture them. One of the early symptoms of infection is a slight elevation in body temperature.
Crewman William Telfer, a hypochondriac, thought he had a multiphasic prion infection before his first away mission in 2376. (VOY: "Good Shepherd")