Richter's Syndrome was a contagious and fatal disease. It could become airborne or could be passed through contact.
The first symptoms were cramps, fatigue and fever, followed by excruciating agony. They would say it was like being boiled alive due to the fact that every nerve cell in the body would be screaming out in agony. It was not unusual for victims to beg for death. This was followed by an uncontrollable, primal fury and eventually death. (AUDIO: Cobwebs)
The virus eventually mutated, making any ordinary vaccine ineffective against it. The cure for Richter's Syndrome was discovered by Nyssa and Adric Traken, who adapted a vaccine that Nyssa had created with data for how the virus mutates calculated by Adric over 25 years. (AUDIO: Prisoners of Fate)