The virus mutates extremely rapidly, making the possibility of a cure seemingly impossible. It can be spread through water. The protoss were able to devise a nano-tech serum that could reverse the effects of infestation, and Confederate remnants developed a way to partially preserve the subject's sanity, but this was apparently no longer viable by the Second Great War. By then the Swarm had developed a particularly virulent strain of the virus which renders those infected vulnerable to UV radiation. Extreme mutation by the virus will turn a terran into an aberration.