Virus is an extremely sinister form of Black Magic which allows the user to create a virus anywhere in the opponent's body, eating at the victim from the inside. The spell can be utilized to affect any living creature, including Celestial Spirits. The user can also target multiple enemies at a time. The effects are dependent on the organs affected; it can cause anything from severe intestinal distress to brain death. The effects appear to be absolute unless the user cancels the casting of their Magic or unless the virus itself is removed from a person's body by Magic that allows one to do so, such as Sky Dragon Slayer Magic.
- Fairy Tail Manga: Chapter 432, Pages 5-8