Prion Diseases: What They Are and How They Spread

Prion diseases happen when proteins normally found in the body misfold, causing brain damage and other symptoms. They are rare. Symptoms can take years to appear, but once they do the disease moves fast, and prion diseases always lead to death, within months to years. There is no treatment and no vaccine.

Some prion diseases affect people and some affect animals. There is not always a known reason someone gets one, but people can sometimes be infected by:

• eating or handling meat contaminated with prions;
• organ transplants, or exposure to contaminated equipment during surgery.

In people

The most common human prion disease is Creutzfeldt-Jakob disease (CJD). Others include variant CJD, kuru, variably protease-sensitive prionopathy, sporadic fatal insomnia, and inherited forms caused by genetic mutations.

Classic CJD

CJD makes the brain break down or stop working normally. It progresses quickly once symptoms begin and is always fatal, usually within a year. Called "classic CJD" to set it apart from the variant form, it mostly affects older people and usually appears sporadically, with no known cause. A smaller number of cases occur in people who inherited genetic changes that make them prone to it, and occasionally people have been infected by prion-contaminated surgical equipment or other products.

Variant CJD (vCJD)

Variant CJD is a different, much rarer disease linked to eating beef from cattle with bovine spongiform encephalopathy (BSE). First identified in the United Kingdom in 1996, it often strikes people in their 20s or younger, causing neurological symptoms, behavioral changes and pain when touching things (dysesthesia). Only four cases have been reported in the United States, all in people probably exposed to BSE abroad.

In animals

Animal prion diseases are also very rare. The two best known in the United States are BSE and chronic wasting disease.

Bovine spongiform encephalopathy (BSE)

• BSE affects cattle. The first cases were identified in the mid-1980s, and a major outbreak in the United Kingdom in the late 1980s and 1990s affected millions of cows. By 2005, 24 countries, nearly all in Europe, had reported BSE in native cattle.
• In North America, the first case was reported in 1993 in a cow imported into Canada from the United Kingdom; more Canadian cases followed from 2003. Later that year a cow in Washington state tested positive — imported from a Canadian farm and probably exposed there. It remains the only classic BSE case found in the United States, though atypical cases have been found.
• The cause: experts concluded that BSE spread through feeding cattle meat and bone meal from other cattle with prion disease. Those practices have since changed.

Chronic wasting disease (CWD)

CWD affects deer, elk, moose and reindeer. It has been found in the United States, Canada, Norway, Finland and Sweden, with imported cases reported in South Korea. First recognized in Colorado in the late 1960s, it has now been identified in 32 U.S. states.

No human cases of CWD have been found, but experts think it may be possible, because CWD is related to BSE, which has caused human disease. If it could spread to people, hunters and people who eat meat from infected animals would likely be at greatest risk.

Sources

• Centers for Disease Control and Prevention: "About Prion Diseases."
• The source spells the term for painful touch as "dyesthesiasis"; this page uses dysesthesia.