Cholera was a bacterial disease that affected Humans. It was prevalent on Earth in the 19th centuries. It was spread by contaminated water. Though lethal, it typically did not kill large numbers of people at a time, as it was not virulent enough to do so.
According to the Star Trek Encyclopedia (4th ed., vol. 1, p. 140), cholera was an acute infectious enteritis and was common on 20th century Earth, as well. Cholera was caused by the organism Vibrio cholerae.