A variant of the viruses that cause prion damage in the brain, such as CJD and BSE, that has been engineering to work considerably faster and to be far more contagious.
There have two test firings of dispersal devices designed to spread the virus. The first was successful, leading to a severe outbreak of the virus. The second was prevented by freelancers. The first test firing caused dozens of casualties, with the victims losing a significant amount of higher brain function within the space of about 36 hours. Freelancers ended up killing them all in an extended firefight.
As yet unknown.
A first attempt at a vaccine has been completed, doses need to be synthesised and tested.