1. Persistant viral infections of the central nervous system

2. Persistant viral infections of the central nervous system
Genomes either integrate or persist as episoms
Mechanism of persistance is not yet understood
Avoid detection and elimination by the host
Progresive
Conventional viruses
prions

3. Conventional viruses
Subacute Sclerosing panencephalitis (SSPE): Measles
Rubella
JC virus
Enterovirus

4. Prion (Unconventional Diseases)
Humans
Creutzfeld-Jacob, variant CJD
Gertsmann-Straüssler-Scheinker Disease
Kuru
Fatal Familial insomnia
Animals
Scrapie(sheep)
Bovine spongioform encephalopaty (BSE:cows)

5. Basic properties of prions
Progresisive without remission
No inflamatory disease
No alteration in pathogenesis by immunosuppresion or immunopotentiation
Size estimated 5-100nm
No virionlike structure by elctronmicroscopy
Transmissible to experimental animals
No interferon production or interferans by viruses
Unusual resistance to UV irradiation, alohol,boiling,proteases
Can be inactivated by prolonged exposure to steam autoclaving or 1N or 2 N NaoH

6. Nobel Prize for Medicine 1997
Stanley Prusiner
Identified the role of prions in disease
Acuolar changes in cortex and cerebellum
Spongiophorm encephalopathy
Prion : small proteinaceous particle
No nucleic acid
Prion protien is encoded by normal cellular gene PrP in the brain.

7. Proposed mechanism

8. Prevention No contact with the infected tissue 1h with 2 N NAOH
60-90 min autoclave
Genetically engineered growth hormone