Urodelan flu was a relatively harmless viral disease. Symptoms included blurred vision, dizziness, palpitations, and a stinging sensation in the lower spine. Urodelan flu was characterized by a slightly irregular K-3 cell count, elevated intravascular pressure, and heightened electrophoretic activity. Some of these symptoms were similar enough to those of Terellian Death Syndrome that the medically inexperienced may confuse one for the other.
Most Humans were naturally immune to Urodelan flu. An exception was Reginald Barclay, who contracted it in 2370. Dr. Beverly Crusher attempted to cure it by activating the immunity gene with a synthetic T-cell, inadvertently causing a condition later known as Barclay's Protomorphosis Syndrome. (TNG: "Genesis")