Scorched Plague

The Scorched Plague is caused by a fungus found underground in Appalachia in 2102.

Background
Research logs at Arktos Pharma seem to suggest that the Scorched plague was created by them before the war. Whether it was designed as a disease or accidently created as a byproduct is currently unknown.(source?)

The Scorched Plague is spread by a fungus found underground in Appalachia. It was spread to the surface by scorchbeasts and was influential in creating the Scorched, causing crystalline green growths in the latter.

The plague is responsible for the destruction in one way or another of every human faction that had existed in Appalachia, from the Responders and Free States to the Brotherhood and Raiders, even the Enclave sealed in their bunker beneath The Whitespring Resort succumbing to it.

Characteristics
The scorched plague is a highly contagious mutagenic virus that has infected almost all of West Virginia's human population, turning them into the scorched, intelligent yet feral ghouls capable of using weapons and armor to assault any uninfected humans unfortunate enough to cross their path.

The plague is also responsible for mutating the local pygmy bat population into scorchbeasts, giant bat creatures who, having overpopulated the underground caverns they lived in, spread the plague to the surface. The scorched plague has also infected other species of local wildlife, but hasn't mutated them anywhere near to the extent of the scorchbeasts.

At least in humans, the scorched plague continues to grow inside of the infected, causing green crystal like growths to cut through their skin, eventually overtaking the host and killing them.

Appearances
The Scorched Plague appears only in Fallout 76.