Fan Casting Left 4 Dead

The Green Flu,[1][2] commonly referred to as the Infection, is the name given to the unknown virus which caused the current in-universe epidemic. The virus turns the afflicted into a zombie-like being, making them incredibly homicidal. In rare cases, the infected will not turn and instead become "Carriers." Biologically, the "flu" seems to be a rabies-like pathogen, and CEDA's designation of the virus as a form of influenza appears to be nothing more than a cover-up to avoid mass panic. The origin of the virus is unknown, although it is speculated to be from biochemical weapon experiments. In terms of containment, the Green Flu is likely bio-hazard level 4.