Tarellian plague

From Memory Alpha, the free Star Trek reference.

The Tarellian plague was a deadly disease that struck the Tarellian race in the 24th century. By the early 2360s, the plague had all but wiped out the species.

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")

It is suggested in the ENT: "Future Tense" that Miller may have been successful in finding a cure as genetic evidence of the race survives into the 31st century.