Transmissible Spongiform Encephalopathies (TSFs)

Transmissible spongiform encephalopathies (TSEs) are a cluster of rare degenerative brain disorders. Also known as “prion” diseases, they leave their victims with tiny holes in the brain. The tiny holes give it a “spongy” appearance that can be seen under a microscope when a section of brain is dissected. Prion is short for proteinaceous infectious particle. The particle is a protein that occurs in a harmless normal form in the body's cells. However, deadly prion proteins are the proteins that can cause the disease. TSEs are transmissible because the deadly prion protein is acquired from an alien source. Researchers are examining the possibility that TSEs are also infectious. There are many forms of TSEs including Creutzfeldt-Jakob disease (CJD), Kuru (“laughing sickness”), fatal familial insomnia (FFI), and Gerstmann-Straussler-Scheinker disease (GSS).

In addition, a new type of CJD or a variant of it was first described in the United Kingdom and in several continental countries in 1996. The new TSE (designated as vCJD to mark it as a variant CJD) had symptoms that were different from classic CJD. Also, it afflicted much younger people. The cause of the disease may have been the consumption of beef that had a bovine form of spongiform encephalopathy (BSE). The name “mad cow disease” was used to label the new form of CJD.

Besides BSE, there are other forms of TSEs in animals. Since TSEs are transmissible, infected animals can spread the disease to other flocks if sold rather than being destroyed. In sheep and goats a fatal degenerative disease is known as scrapie. The disease causes loss of production and it prevents the sale of semen, embryos, or breeding stock to other countries. That elk and deer can be afflicted with TSE was discovered in the late 1960s. Chronic wasting [Page 1769]disease (CWD) is similar to mad cow diseases, but affects deer and elk populations. Herds in Colorado and Wyoming have been affected, and the disease is spreading. Feline spongiform encephalopathy (FSE) was found in cats in Great Britain in 1990. Since then it has been reported on the Continent as well. Transmissible mink encephalopathy (TME) was first diagnosed in 1947 in ranch-raised minks in the United States. TME affects the central nervous system. TME has been reported in Russia, Canada, Finland, and Germany.

Kuru was first identified in Papua New Guinea among the Fore people. With a Stone Age culture, they practiced ritualistic cannibalism. At funerary feasts they would eat the brains of deceased relatives, allowing infectious crystal protein to invade human cells. After the practice was outlawed in the 1970s, Kuru gradually disappeared. Fatal familial insomnia (FFI) is symptomatically similar to CJD. It is a hereditary prion disease that disrupts sleep, creating insomnia that lasts until death. The disease is due to a missense mutation at codon 178 of the prion protein gene on chromosome 20. The disease runs in families and is fatal in seven to 36 months after the onset of symptoms. Gerstmann-StrausslerScheinker (GSS) is a very rare TSE; most cases have been inherited. It usually strikes between ages 35 to 55. As the disease progresses, symptoms resemble Parkinson's disease with dysarthria, nystagmus, spasticity, disturbances in vision, or deafness.

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