The Wither Sickness is inflicted if a person remains in contact with the Wither Storm's tractor beam or its tentacles for too long.
When a person is inflicted with Wither Sickness, he/she slowly gets weaker, and the affected part of the body slowly turns purple. The disease then slowly spreads to the whole body, and the person slowly "withers" away, causing inability to think or move.
Sometimes, a person inflicted with Wither Sickness does not get any aforementioned symptoms of the disease, but instead also starts to suffer from amnesia, and loses his/her memory. It still, however, causes the person's skin to turn darker, as well as changes their pupils to red.
Unlike the regular Wither Effect, Wither Sickness does not wear off over time and is more lethal. The only known treatment for Wither Sickness is to destroy the source, i.e. The Wither Storm. It's unknown if anything else can cure Wither Sickness.
- Most citizens who were trapped inside the Wither Storm were completely withered away, thus, they could not move or think though they were still alive.
- At one point in Episode 1, both Petra and Gabriel the Warrior will get caught in the Wither Storm's tractor beam, but the player will only be able to rescue one of them. Whoever gets rescued will get away from the Wither Storm, and catch up with the group in the middle of Episode 2, but will get infected with the first variant of the Wither Sickness. Whoever doesn't get rescued will be released from the Wither Storm at the end of Episode 3, but will suffer from the second variant. Both are cured at the end of Episode 4.
- Interestingly, Gabriel/Petra (whoever Jesse chose to save in Episode 1) was infected with a strong Wither Sickness for being caught in the tractor beam for only a relatively short time, and Jesse, who was caught in tractor beams and touched the Wither Storm's tentacles several times, was never infected with Wither Sickness.
- Gabriel mentioned in "Assembly Required" (determinant) that he had contracted Wither Sickness before in his travels, but it "always wears off."