Prions

Not all infectious diseases are transmitted by bacteria or viruses. Some neurological diseases, such as Creutzfeldt-Jakob disease (CJD) or mad cow disease is in fact caused by agents called Prions, which are of similar size to viruses but are made up of only protein. These diseases are can be called Prion diseases or transmissible spongiform encephalpathies (TSE).

Prions have these characteristics:

1. "The transmissible agent consists of aggregated forms of a specific protein".
2. These protein aggregates cannot be degraded by the agents that degrade most other proteins.
3. "The protein is largely or completely derived from a cellular protein called PrP, that is normally present in the brain".

So an aggregated form of a protein (that is already present in the brain) is the infectious agent in prion diseases.

The pathologic mechanism of prions is often associated with structural change. Exogenous prions cause the endogenous host proteins to undergo a structural change, rendering them functionless or harmful.

Prions size and structure enable them to resistance to:

• proteases
• heat (not in 100 celsius)
• radiation
• fixative treatments (formaldehyde)

If only the secondary, tertiary and quaternary structure destroys the prion can fold back to the prion after the influence of the substance.

examples of prion disease:

• scrapie - in sheep
• Bovie spongiform encephalopathy (BSE) mad cow disease
• Kuru (transmitted by ritual cannibalism)
• Creutzfeldt–Jakob disease (CJD)
• Chronic Wasting Disease (CWD) - in deer and elk