An epidemic on Deep Space 9 caused by a virus that the Bajoran resistance had hidden in the station's replicators years earlier, which left its victims unable to speak or understand language.
In the Deep Space Nine episode Babel, an overworked Miles O'Brien repairs a faulty replicator and soon begins talking in jumbled words. Others follow, and Bashir identifies an engineered virus that scrambles the brain's handling of language and later brings fever and death. It mutates and becomes airborne, and Sisko quarantines the station.
The device that released it dates from the Occupation, when the station was still Terok Nor: a Bajoran act of sabotage that was never triggered. Its creator, Dekon Elig, is long dead. Kira tracks down his former assistant, Surmak Ren, now a physician, and when he refuses to help she beams him aboard so that he is infected too.
With nearly all of the senior staff stricken, Odo and Quark keep the station running and stop a freighter captain, Jaheel, from tearing loose from his docking clamps. Surmak finds the antidote.