Slithering Sickness

The Slithering Sickness is a nasty disease casused by a parasitic worm that enters the victim's body and then multiplies rapidly, eventually killing the host and using its body to spread the infection further. The initial symptoms of the infection are mild: stomachache, fever, and weakness. As the disease progresses, the patient suffers excrutiating pain and begins to lose control of bodily functions as the rapidly-growing worm population feeds on internal organs and muscles. As the worms multiply, their movements become visible beneath the surface of the victim's skin, which usually means that most of the the vicitm's innards have been hollowed out and replaced by worms.
Once the worms have occupied most of the body, they work as a unit to manipulate the body in a clumsy and stilted approximation of human locomotion and go out hunting for new victims. The most horrific aspect of the disease--seen on the horror-stricken faces of the worm-controlled bodies--is that the worms seem to have no interest in the brain, or in fact anything above the victim's tongue. As a result, the victim remains fully aware until the worms finally leave the body, causing the brain to die as well. 
The Slithering Sickness can be cured if it's caught before the worms have mulitiplied enough to cause major damage. Imperial Law states that those whose infection has reached the uncurable stage should be killed by fire and there are severe penalties for harboring a known incurable victim of the condition.