Phyrox plague

From Memory Alpha, the free Star Trek reference

The Phyrox plague was a deadly disease that infected the population of Cor Caroli V in 2366.

The plague was finally eradicated on stardate 43714.1 with the assistance of the crew of the USS Enterprise-D, where the crew put their lives at at stake for others. Following its eradication, Starfleet classified the Cor Caroli V plague as "secret." (TNG: "Allegiance")