The Fostossa virus was an epidemic on Bajor while Crell Moset, a Cardassian exobiologist, was practicing medicine during the Cardassian Occupation of Bajor.
The incident was recalled by Ensign Tabor of USS Voyager. Crell allegedly used inhumane practices, which he described as "procedures that never would have occurred to me under normal circumstances." According to Tabor, Moset infected hundreds of unaffected Bajorans, including Tabor's grandfather and brother, with the virus to produce a cure. Thousands of people allegedly died in his hospital, Tabor's relatives among them. On investigation into his activities during the Occupation, the Voyager crew found that he did not request any of the normal enzymes used in eliminating viruses. A more damning piece of evidence came when it was discovered that there had not been a single outbreak of Fostossa in the province in which he was practicing until his experiments began.
Moset's research did provide a cure, however, and Fostossa was eradicated sometime during the occupation. (VOY: "Nothing Human")