Vincent's agina

Vincent's agina, better known as trench mouth, was an infection of the Human gums, and led to inflammation, bleeding, deep ulceration, and necrotic gum tissue.

The infection was produced by two micro-organisms working in concert. While studying a disease that had infected a landing party from the USS Enterprise (NCC-1701) in 2266, Dr. Leonard McCoy noted similarities with Vincent's agina. (TOS novelization: )