prion diseases

-AN OVERVIEW
Prince. C.P
Department of Microbiology
Mother Theresa Institute of Health Sciences
Puducherry

Infectious diseases are caused by microorganisms like bacteria, viruses, fungi, protozoan parasites and helminthic parasites.
Recent research by Stanley.B.Prusiner and others discovered the existence of a new group of infectious agents which are responsible for some rare fatal diseases. These agents do not belong to any of the classical pathogens, as they do not posses a nucleic acid (RNA/DNA) and are just infectious protein molecules. They are called as Prions.
Prions are small Self replicating proteinaceous infectious particles which can resist inactivation procedures like sterilization and can modify nucleic acids.
Prions are resistant to denaturation by proteases, heat, radiation, and formalin treatments, although their infectivity can be reduced by such treatments.
are often called Transmissible Spongiform Encephalopathies because of the post mortem appearance of the brain with large vacuoles in the cortex and cerebellum.
have Common features like long incubation periods (years), characteristic spongiform changes associated with neuronal loss and failure to induce inflammatory response-no antibodies are produced against prions.
in animals
Scrapie: sheep
TME (transmissible mink encephalopathy): mink
CWD (chronic wasting disease): mule -deer, elk
BSE (bovine spongiform encephalopathy): cows
in man
CJD: Creutzfeld-Jacob Disease
GSS: Gerstmann-Straussler-Scheinker syndrome
FFI: Fatal familial Insomnia
Kuru
Alpers Syndrome

These diseases are characterized by loss of motor control, dementia, paralysis, wasting and eventually death, typically following pneumonia.
The first Prion disease identified was Kuru, which was found among the Fore tribe of Papua New Guinea. .Kuru is transmitted among this tribe due to their practice of cannibalism .They eat their relative’s dead body.
Prion proteins induce abnormal folding of normal cellular Prion proteins (PrP) in the brain, leading to brain damage. When infectious PrP-sc enters into nervous tissues it interacts with normal PrP-c of the brain cells and converts them into Prp-sc. This leads into the accumulation of PrP-sc in brain cells.
Diagnosis is mainly based on symptoms. Other useful methods are 1.Electroencephalography — often has characteristic triphasic spikes
2. Cerebrospinal fluid analysis for 14-3-3 protein
3. MRI of the brain
No treatment is available today. The search for viable treatment is going on. Preventive measures like strict quarantine laws and mass slaughtering of infected animals are useful to control the spread of infection.
Prion research in future may provide the clarification for the doubts about origin of life and pathogenesis of diseases like Alzhmer’s and Parkinsonism.

-------------------------------------------------------------------------------------------------Posted bymedical microbiologyat10:32 AM