Rust

Rust is an extremely contagious viral condition that has been super-evolved by warp exposure, and is currently infecting several space marine chapters, Imperial Guard and other human worlds within the Imperium. It is belived to be the work of Nurgle, or the Hellforger by the Ordo Malleus, but the severe lack of information about the virus makes it hard to determine it's origin - or cure for that matter.

Stage I
The victim usually comes down with severe hallucunations, usually images of blooded eyes popping out of walls and staring at them, or gnashing mouths. This leads them to being driven mad.

Afterwards, the first physical symptoms appear, usually within 1-2 weeks. Crying tears of blood, worse hallucinations, vomiting strange black liquids constantly.

Stage II
The victim loses their hearing to the point where any noises are just static and muffled whines. Their hair falls out, along with with many patches of skin, exposing the muscular and inner organs, which have all gone black, and begin to seep more of this black liquid.

Stage III
The victim has reached the stage of being incurable. Their entire faces become holes lined with teeth, sometimes their arms or other limbs fall off dead, whilst others burst out of varying places to replace them, spider-like legs, writing arms, etc

Stage IV
The virus has reached full effect, the victim is now entirely mutated. Coming within a 10m radius of the mutant guarantees infection