Prion diseases occur in sheep, goats, cattle, elk, deer, minks, and cats. Depending on the disease, they can be transmitted from one species to another when an animal does the following:

• Eats an infected animal

• Comes in contact with an infected animal's body fluids or waste

• Comes in contact with soil contaminated by infected animals

• Is housed with infected animals

Like people with Creutzfeldt-Jakob disease, affected animals gradually become uncoordinated and behave in abnormal ways as brain function deteriorates.

Scrapie, the prion disease in sheep, is so named because the sheep tend to scrape themselves against fence posts or other structures and tear their wool off.

In elk and deer, prion disease is called chronic wasting disease. In most US states, South Korea, Canada, Norway, Finland, and Sweden, there is concern that chronic wasting disease may be transmitted to people who hunt, butcher, or eat affected animals. However, there have been no reports of chronic wasting disease or sheep scrapie causing prion disease in people. Researchers are studying whether chronic wasting disease can be transmitted to people.

Mad cow disease (bovine spongiform encephalopathy) is so named because the cattle become noticeably agitated. The disease was likely initially transmitted from sheep to cattle by feeding cattle scrapie-infected sheep parts.

Eating contaminated beef or beef products causes a form of Creutzfeldt-Jakob disease in a small percentage of people. First described in 1996, this form is called variant Creutzfeldt-Jakob disease (sometimes also called the human version of mad cow disease). Variant Creutzfeldt-Jakob disease differs in many ways from other forms of Creutzfeldt-Jakob disease:

• It causes different changes in brain tissue (seen under a microscope).

• The first symptoms tend to be psychiatric symptoms (such as anxiety or depression), rather than the memory loss and loss of coordination that occur in people who have other forms of Creutzfeldt-Jakob disease.

Variant Creutzfeldt-Jakob disease was very rare, even at its peak. As of May 7, 2022, there have been 178 cases in the United Kingdom, and there have been 55 in other countries, for a total of 233 worldwide. In the United Kingdom, the number of new cases occurring each year peaked in 2000. Since then, the number has steadily declined. In the United States, the disease has been diagnosed in four people. All of them probably acquired the disease in a foreign country.