To avoid detection, the virus disguised itself as a memory engram – normally a memory so traumatic that the host suppressed it into the subconscious. In Tuvok's case, the memory was of a girl falling from a cliff. The virus was discovered and destroyed in 2373 by The Doctor aboard the USS Voyager, using thoron radiation. (VOY: "Flashback") As evidenced by the first draft script of "Flashback", what ultimately became the memory virus was originally to have been commonly referred to as an alien parasite instead, with no mention of it as a virus.