Prion Diseases

Primary reference(s)

CDC, no date. Prion Diseases. Centres for Disease Control and Prevention (CDC). Accessed 14 September 2020.

Additional scientific description

Prion diseases are a group of rare transmissible disorders characterised by long incubation periods, characteristic spongiform changes associated with neuronal loss, and a failure to induce inflammatory response. They are often difficult to diagnose, untreatable, and ultimately fatal (CDC, no date).

Prion diseases involve accumulation of an abnormal prion protein in the central nervous system with no specific immunological response. Human prion diseases include sporadic, familial, and variant Creutzfeldt-Jakob disease (CJD). Sporadic CJD is the most common, representing an estimated 85% of cases and thought to affect approximately 1 person per million worldwide each year. Sporadic CJD is caused by the spontaneous transformation of normal prions into abnormal ones. Familial CJD is inherited as a result of genetic mutations and counts for 10–15% of cases worldwide. The remaining cases are iatrogenic and variant CJD (WHO, no date).

Bovine spongiform encephalopathy (BSE) is a transmissible spongiform encephalopathy found in cattle. Variant Creutzfeldt- Jakob disease (vCJD), found in humans, is believed to be a zoonotic disease caused by the BSE agent. The route of transmission of vCJD is through exposure to food contaminated by the bovine spongiform encephalopathy agent (WHO, no date).

Scrapie, another animal prion disease is endemic in some sheep and goat flocks of Europe, Asia and North America, with the exception of a small number of countries. Recently other animal prion diseases have been found in elk and deer (chronic wasting disease), mink (transmissible mink encephalopathy) and felines (feline spongiform encephalopathy) (WHO, no date).

The World Health Organization (WHO) has published guidance on case classification and surveillance standards for vCJD and other human-transmissible prion diseases (WHO, 2003).

Metrics and numeric limits

Not applicable.

Examples of drivers, outcomes and risk management

Acquired human prion diseases are rare. In these instances, the most common outside sources are either medical procedures, where an individual may be exposed to the abnormal prion protein via contaminated equipment or certain transplanted human tissues, or via ingestion of meat from cattle infected with BSE (linked to vCJD). Other prion diseases such as scrapie and chronic wasting disease can be transmitted between animals, however transmission from animals to humans has only been observed in BSE/vCJD (WHO, 2003).

Over 180,000 cases of BSE were confirmed in cattle in the United Kingdom between 1986 and October 2004. The disease was also found in several other countries. This epidemic peaked in 1992, with almost 1000 new cases diagnosed each week. Control measures, including restrictions on ruminant feed, have now greatly decreased its prevalence, and cases have become uncommon or rare in many areas. Many countries have also passed new regulations to prevent BSE-containing tissues from entering human food supplies (OIE, 2016).

In some countries, certain prion diseases such as CJD and vCJD may be classified as a routine notifiable disease (WHO, 2003).