The Kagawa Virus was a type of synthetic virus.
The Kagawa Virus was synthesised from the poison sacs of the Kagawan lizard. It caused a feedback loop in the brain, occupying it completely, causing memory loss and eventually a coma. The victim would be conscious but unable to move. An antidote existed, though it became less effective over time and a complete cure would require the individual focusing on strong memories.
At some point, Kagawa Virus was found on Earth and collected by Alix, a dealer of alien artefacts. He used it on Joe Hirschman when he was caught selling alien artefacts on his own. He also sold it to Czisch's father for killing the members of Torchwood Three. (PROSE: Virus)