Notes on the history of the prion diseases. Part II.

The protein-only theory of transmission of the prion diseases remains controversial. Other mechanisms such as the virus, virino, and viroid hypotheses are still under consideration. All these fit in the concept of 'slow' infections that had been proposed in 1954 by Bjorn Sigurdsson, an Icelandic pathologist. Regardless of the exact mode of infection, the presence of prions in the brain has served to unite Creutzfeldt-Jakob disease (CJD), the Gerstmann-Sträussler-Scheinker syndrome and fatal familial insomnia, as well as scrapie and a number of other animal diseases, into a single pathological entity, the transmissible spongiform encephalopathies. The appearance of bovine spongiform encephalopathy in the United Kingdom and its putative relationship to new variant CJD, have put a new and unpredictable light on these unusual and uncommon diseases.