Anchilles fever

Anchilles fever was a highly contagious and virulent disease that was capable of infecting and killing millions. While vaccines for the disease were available, the were often rare to find and couldn't be easily synthesized.

In 2364, the planet Styris IV suffered an outbreak of the fever which led to the crew USS Enterprise-D to negotiate for a rare vaccine that was discovered on Ligon II. (TNG episode: "Code of Honor")

At the same time in one continuity of the mirror universe, an outbreak also occured on that reality's Styris IV. In order to obtain the vaccine from Ligon II, Captain $𝜇$ had the planet's southern continent subjected to gamma-fission radiation. (TNG novel: Dark Mirror)