The Telepath virus was an affliction designed by Edgars Industries in order to control the Telepath population. An infected telepath would die painfully if he or she did not receive a regular dose of the antidote, effectively enslaving them to whoever held the cure.
Following the sacking of Edgars' headquarters, Alfred Bester took custody of the vials containing the virus itself and the cure. He destroyed the virus, but kept the cure just to be absolutely safe. It's possible that the virus is at least in part Shadow Technology.