The Ornaran plague was a disease that struck Ornara in the 22nd century. The only cure was felicium, a drug refined from a plant indigenous to the planet Brekka. The plague was completely cured by the felicium, however, the drug's addictive nature obscured this to the Ornarans, and they believed they still carried it. However, the Brekkians knew it had been cured, and took advantage of that. All attempts to cultivate the plant on Ornara failed, leading to a trade agreement between the Ornarans and Brekkians that lasted at least two centuries. (TNG: "Symbiosis" )