The Tarellian plague was a deadly disease that struck the Tarellian race at an unknown date. By the early 2360s, the plague had all but wiped out the species. The plague was a Biological weapon, a product of Tarellian biotechnology, and was used in the Tarellian Civil War.
In 2364, a Tarellian plague ship approached the planet Haven, as its crew believed the planet contained a cure for the plague. The group was successfully turned away from settling on Haven after meeting the USS Enterprise-D in orbit. During the encounter, Dr. Wyatt Miller beamed over to the plague ship with medical supplies from the Enterprise, believing it was his purpose to find a cure for the plague. (TNG: "Haven")