The pathogen of Andronesian encephalitis.
Andronesian encephalitis is an unpleasant, but not life-threatening, disease transmitted by airborne particles that is common in Federation space due to the transmission of the particles via space travel.
In 2152, when Phlox insisted on examining Travis Mayweather, he reasoned this with the possibility, that he could suffer a seizure at the helm due to Andronesian encephalitis. (ENT: "Singularity")
In 2154, a sample of this disease's pathogen was stored at Cold Station 12. (ENT: "Cold Station 12")
Although the disease was easily treated and regarded as a minor condition by 2365, Anya, the guardian of the Dauphin of Daled IV, regarded it as a threat and requested that the person infected be terminated. (TNG: "The Dauphin")