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TRANSMISSIBLE SPONGIFORM ENCEPHALOPATHIES

Forty nine persons in United Kingdom have been diagnosed to be suffering from a new form of Creutzfeldt-Jakob Disease (CJD); a rare brain destroying disorder similar to the so called "mad cow disease" afflicting the British cattle herds. It is scientifically called as Bovine Spongiform Encephalopathy (BSE) and now redisignated as Transmissible Spongiform Encephalopathy (TSE). Although the researchers do not have direct evidence to link the cases of CJD to the exposure of BSE; they inferred that exposure to BSE agent is the most plausible reason. British Prime Minister announced that all the cattle above three years age would be exterminated to arrest the spread of CJD. This has caused great commotion in the scientific world and particularly so, to the beef producers, as there appear to be an element of zoonoses.

What is that agent causing BSE or CJD- is it a virus, bacteria, mycoplasma, rickettsia, parasite, protozoan? All these living organisms have got nucleic acid (RNA or DNA) in them. But the agent that produces BSE does not have chromosomes or RNA or DNA. Still it is capable of growing/ multiplying/ replicating /reproducing and increasing in quantity. Therefore it is an infection. Undoubtedly they are made up of protein and are infectious in nature.

Stanley B Prusiner coined the word 'prion' (Proteinaceous infectious particles) creating a new dimension in the nature of infection causing agents.

These are pronounced as "pree-ons". The term prion diseases gained majority over slow virus diseases with the inability to detect, till to day, nucleic acids to infectious material. The agents have properties, which are. Atypical of viruses as mentioned here under.

The infectivity is highly resistant to many physicochemical treatments such as heat and exposure to ionizing or ultraviolet radiation

The infection neither induces an immune response nor impairs the immunological responsiveness of the host to other infections

The combination of long incubation period, unusual stability and immunological neutrality explains why the agent has long been known as"unconventional slow virus"

There are several diseases in different species of animals and man where spongy form encephalopathic lesions are seen in the central nervous system. Naturally occurring prion diseases were recorded in sheep, goats, cattle, deer, mink and cats. Human prion diseases are obscure and they satisfy the Koch's postulates. CJD and Kuru have been transmitted to apes by 1968 itself. Prion diseases are fatal neurological diseases associated with the accumulation within the central nervous system of insoluble aggregates of a modified cell membrane protein called as prion protein.

Gerstmann-Straussler-Scheinker (GSS), is a familial spinocerebellar degeneration with dementia; long disease duration. Fatal Familial Insomnia (FFI) is autosomal dominant condition associated with untreatable insomnia, ataxia and dysutonomia and Familial Progressive Subcortical Gliosis (FPSG) has long disease duration with dementia, mutism and extrapyramidal signs. These three are human diseases, and are considered to be caused by prions.

Some of the prion diseases are mentioned here under

SCRAPIE

KURU (LAUGHING DEATH)

CHRONIC WASTING DISEASE (CWD)

BOVINE SPONGIFORM
ENCEPHALOPATHY (BSE)

TRANSMISSIBLE
MINK ENCEPHALOPATHY (TME)

CREUTZFELDT-JAKOB DISEASE (CJD)

Reference

PV Ramchandra Rao, P Anand Kumar, N Mrunalini, P Govardhan Reddy and PN Khanna (2000).

 
       
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