Anthraxium is an evolved form of the virus Anthrax, commonly used in domestic terrorist attacks in the past. It was featured in the first PokeMongers video game, and was a driving part of the plot. Unlike past versions of the virus, Anthraxium was mutated by Silph Company to effect Pokémon as well as humans. After Chapter 20 of PokeMongers, the supplies of Anthraxium at Silph are all destroyed, although the ending hints that small strands of it are still active in some Pokémon.
Anthraxium is first mentioned in Chapter 2, where a television states that reports have appeared that a mutated form of Anthrax is being developed, but is likely a lie. It later appears in Chapter 5, when Isabelle overhears a discussion at Silph Company, where they discuss Anthraxium. Unfortuanatly, Isabelle doesn't tell any teachers or authorities due to the fact she believed it to be a code name for a new type of PokeTransfer. Later on, in Chapter 7, Principle Brown unknowingly opens a letter containing Anthraxium, and is confused by an otherwise empty letter.