Necrotic Bite Fever

Every survivor knows the rule: get the wound cleaned. Do not wait. Do not shrug it off. Do not tell yourself it is just a scratch. Necrotic Bite Fever exists to remind those who forget.
  NBF is a fast-acting infectious disease triggered when virulent necrotoxins enter the bloodstream through a bite, sting, or poisoned weapon. The source varies: a Zombie carrying the strain, a Critter whose venom has been altered by the Infection, a Raider's blade coated in harvested toxin. The entry point matters less than the speed of what follows. The Infection within the body reacts violently to the foreign agent, accelerating localized tissue decay and spreading necrosis outward from the wound site. Within minutes to hours, the area reddens, burns intensely, and begins to swell. Then it turns black.
  The disease cannot spread through air, proximity, or casual contact. It requires a wound, a break in the skin through which the necrotoxin can enter the bloodstream. Some Raiders have learned to exploit this deliberately, coating ammunition and blades with venom harvested from NBF-carrying creatures. The disease remains localized as long as the Infection can contain it, sacrificing sections of tissue to wall off the toxin. When containment fails, necrosis spreads through the bloodstream toward vital organs.
  Symptom progression is rapid by wasteland standards: hourly, not monthly. The wound site swells and blackens. Fever and chills set in alongside extreme pain. Darkened veins trace visible lines from the wound toward the heart, mapping the toxin's advance through the body. Blood thickens as the Infection tries to slow the spread, causing dizziness and disorientation. The flesh around the wound turns foul, leaking discharge that smells of chemical rot.
  In advanced stages, necrosis reaches deep tissue and organs. The skin turns ashen and cold. The body emits a faint odor, something between rotting citrus and chemical burn, that lingers in enclosed spaces. Movement slows. Breath comes shallow. The Infection continues its losing battle, digesting the host from within in a desperate attempt at containment. Without intervention, death follows from sepsis or cardiac failure.
  What separates NBF from slower diseases is the treatment window. At Stage 1, simple wound care from any capable medic is enough. At Stage 2, blood transfusion and cleaning. By Stage 3, the work requires a master physician replacing skin and muscle with Infection material. Stage 4 demands morgue-level surgery, the Living Experiment, and Resolve. Stage 5 pushes further still, requiring Mortis Extract and Grave Flesh. The escalation is steep and deliberate: every hour of neglect adds complexity, cost, and pain to the cure.
  Death before the terminal stage cures the disease entirely. At terminal stage, the next Body damage the afflicted takes kills them instantly, and they return from the Mortis at Stage 2 with the original wound still evident. The disease does not forget where it started.
  Survivors of early intervention carry the marks: scarring at the wound site, loss of sensation or movement in affected limbs. The Infection saved what it could, but the cost of that salvation is written in dead nerves and rigid tissue. Sometimes the cure is as cruel as the rot it stopped.