Terellian Death Syndrome was a deadly disease which caused cellular decay. Its initial symptoms were somewhat similar to that of Urodelan flu, and included blurred vision, dizziness, palpitations, and a stinging sensation in the lower spine.
After consulting the Starfleet Medical Database, Lieutenant Reginald Barclay incorrectly diagnosed himself with Terellian Death Syndrome in 2370. (TNG: "Genesis")
Captain Carol Freeman came down with Terellian Death Syndrome in 2381, which was cured by Ensign Escher. According to Ensign Sam Rutherford, Escher "was in the right place with the right hypospray." (LD: "We'll Always Have Tom Paris")