The Saurian virus was a virus.

While on Dramia II in 2251, Dr McCoy treated a Dramian colonist named Kol-Tai, who was afflicted with a strain of the Saurian virus. Antibodies created to combat the Saurian virus were later discovered by McCoy to be the cure for the Dramian plague that afflicted the crew of the USS Enterprise. (TAS: "Albatross")