Levodian Flu was an illness harmless to most humanoids involving fever, chills, and the sniffles.

The Levodian Flu virus was easily adapted as a way to spread bioengineered plagues such as The Change. By the mid 23rd century it had been in use within the Klingon Empire for biological projects for over 100 years.

A Trill colony was once infected by the Levoidan Flu virus, causing them ot develop facial ridges and lose the spotting that the vast majority of Trill possessed. (TLE novel: Excelsior: Forged in Fire)