PRION BASICS Animal Diseases

Prion diseases are caused by the misfolding of normal cellular prion protein into an abnormal infectious form. These diseases are transmissible from host to host of a single species and sometimes from one species to another. They destroy brain tissue giving it a spongy appearance. For these reasons, prion diseases are also called transmissible spongiform encephalopathies (TSEs). Prion diseases affect mammals, including cattle, sheep, goats and cervids (elk, deer and moose). Some prion diseases are infectious, and all are fatal.


Bovine Spongiform Encephalopathy (BSE or commonly known as mad cow disease)

  • Affects cattle;
  • Spread is caused by feed containing meat and bone meals from infected cattle and sheep. This practice has been banned in Canada since 2004; 
  • Can cross the animal-human barrier; and
  • The World Organisation for Animal Health (OIE – historically Office international des épizooties) has three risk categories for BSE: negligible risk, controlled risk and undetermined risk. Canada is currently classified as being a controlled risk.


  • Affects goats and sheep; and
  • There is currently no evidence to suggest scrapie can cross the animal-human barrier.

Chronic Wasting Disease (CWD)

  • Affects cervids (deer, elk and moose);
  • Spread through animal-to-animal contact and contact with infected material such as soil; and
  • So far there is no evidence to suggest CWD can cross the animal-human barrier.

We do not know why or how prions and other proteins misfold or what mechanism causes the nerve cells in which they collect to die. We do know that diseases caused by abnormal prions can have substantial social and economic costs. Thus far, we cannot vaccinate against, treat or cure these diseases.