The Other The Enemy Within - The Sentient Flesh Eating Bacteria

Prying curiosity means death.

H.P. Lovecraft

"The Rats in the Walls"

Necrotizing fasciitis was a rare bacterial infection that can destroy skin and the soft tissues beneath it, including fat and the tissue. By the 3rd Human Empire the bacteria had been re engineered into an anti aging cosmetic treatment for the rich. Things went horribly wrong when the "treatment" encountered the sentient alien organisms of  Necrono 3 & the two merged into one horrible organism. Slowly but surely the infection has spread through four systems. The disease has only communicated twice with authorities & simply referred to humanoid life forms as food. There have been been 2 known cases where the infections have been spread by freeze dried worms simply called "rot grubs"
  The disease has a sort of hive mind that often takes over the victim before the latter stages can set in. The intelligence of the disease is in direct influence by the number of victims that it infects. The more infected there are the smart it gets until an entire world is overcome. The disease then has one overriding instinct to spread.
  In some rare cases the disease may create a secondary means of spreading by taking on liquid form. This form is rarely seen but a former victim's features may be taken on for short periods of  time. When the disease knows it will be seen. As soon as approached the disease will explode the shape causing the victim to be coated with a layer of blood & tissue.  The only known cure for this disease is the advanced science of  The Great Race Of Yith Some forms of  super science may slow it down for a time until it begins to talk with you.

There are those who insist that the Sensibilis uicesimum dicendum quod comedere carnem Bacteria has an alien agenda for human evolution itself.