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Prion Diseases

Prion diseases are a related group of rare, fatal brain diseases that affect animals and humans. Also known as transmissible spongiform encephalopathies (TSE). They include bovine spongiform encephalopathy (BSE, or "mad cow" disease) in cattle; Creutzfeldt-Jakob disease (CJD) in humans; scrapie in sheep; and chronic wasting disease (CWD) in deer and elk. The brain disorders are characterized by tiny holes that give the brain a "spongy" appearance. These holes can be seen when brain tissue is viewed under a microscope.

Types

BSE ("mad cow" disease)
BSE is a prion disease in cattle. In the United Kingdom, more than 184,000 cases of BSE have been confirmed, which peaked in January 1993 at almost 1,000 new cases per week. In the United States, the disease is rare. In 2003, 2005 and 2006, each year had a confirmed case.

Creutzfeldt-Jakob disease (CJD)
CJD is the most well-known of the human TSEs. It is a rare type of dementia that affects about one in every one million people each year.

Kuru
Kuru was identified in people of an isolated tribe in Papua New Guinea and has now almost disappeared.

Fatal familial insomnia (FFI)
Gerstmann-Straussler-Scheinker disease (GSS)
FFI and GSS are extremely rare hereditary diseases, found in just a few families around the world.

Variant CJD (vCJD)
It is a new type of CJD first described in 1996 and has been found in Great Britain and several other European countries. The initial symptoms of vCJD are different from those of classic CJD and the disorder typically occurs in younger patients. Research suggests that vCJD may have resulted from human consumption of beef from cattle with the BSE disease.

Causes

Research suggests that TSEs are caused by an abnormal version of a protein called a prion (prion is short for proteinaceous infectious particle). Prion proteins occur in both a normal form, which is a harmless protein found in the body's cells, and in an infectious form, which causes disease. The harmless and infectious forms of the prion protein are nearly identical, but the infectious form takes on a different folded shape from the normal protein.

Human TSEs can occur three ways: sporadically; as hereditary diseases; or through transmission from infected individuals. Sporadic TSEs may develop because some of a person's normal prions spontaneously change into the infectious form of the protein and then alter the prions in other cells in a chain reaction. Inherited cases arise from a change, or mutation, in the prion protein gene that causes the prions to be shaped in an abnormal way. This genetic change may be transmitted to an individual's offspring. Transmission of TSEs from infected individuals is relatively rare. TSEs cannot be transmitted through the air or through touching or most other forms of casual contact. However, they may be transmitted through contact with infected tissue, body fluids, or contaminated medical instruments. Normal sterilization procedures such as boiling or irradiating materials do not prevent transmission of TSEs.

Symptoms

Symptoms of TSEs vary, but they commonly include personality changes, psychiatric problems such as depression, lack of coordination, and/or an unsteady gait. Patients also may experience involuntary jerking movements called myoclonus, unusual sensations, insomnia, confusion, or memory problems. In the later stages of the disease, patients have severe mental impairment and lose the ability to move or speak.

Treatment

There is currently no treatment that can halt progression of any of the TSEs. Treatment is aimed at alleviating symptoms and making the patient as comfortable as possible.

 

Sources

National Institute of Neurological Disorders and Stroke, USA.

Centers for Disease Control and Prevention, USA.