 They have also proposed that individuals having contracted CJD in the early 1990s represent a distinct genetic subpopulation, with unusually short incubation periods for bovine spongiform encephalopathy (BSE).This means that there may be many more people with vCJD with longer incubation periods, which may surface many years later.Prion protein is detectable in lymphoid and appendix tissue up to two years before the onset of neurological symptoms in vCJD.