1 transmissible spongiform encephalopathies. 2 kuru since the early 1900’s the fore people of new...
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Transmissible Spongiform Encephalopathies
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Kuru
• Since the early 1900’s the Fore people of New Guinea have honored their dead by cooking and consuming the bodies of the deceased.
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Kuru• In the 1920’s a new disease appeared. It
killed primarily children and adult females.
• Symptoms were:– Lack of coordination, staggering and slurred
speech– Uncontrollable shivering– Mood changes: euphoria to indifference– Paralysis and death in a few months to a year
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• By 1950’s kuru had become an epidemic
• Not a psychological disease
• Not a bacterial disease
• Not a viral disease
• Not a genetic disease
• Not heavy metal or other poisoning
• Not a vitamin deficiency
• Brains full of sponge-like holes and abnormal deposits of protein
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“Mad Cow Disease”• Between 1984 and 1986 dairy cows in
England developed strange neurological symptoms:– Aggressive or apprehensive– Muscle tremors– Lost weight and coordination– Fatal after a few months to a year– Brains had holes and protein deposits
• Bovine spongiform encephalopathy (BSE)
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• BSE became an epidemic over the next 6 years, with 180,000 confirmed cases by the year 2000.
• Cattle were being fed rendered cattle, sheep and goats as a cheap source of protein.
• More than 120 people have contracted new variant Creutzfeldt-Jakob disease from eating infected beef.
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• Confusion• Depression• Behavioral Changes• Impaired Vision• Impaired Coordination
Early Symptoms
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Later Symptoms• Dementia: confusion and disorientation,
memory loss, personality loss, agitation, and restlessness
• Neuromuscular symptoms include wasting, myoclonus, athetosis
• Coma and increased susceptibility to repiratory infections can occur.
• Death can result within a year of symptom onset.
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Transmissible Spongiform Encephalopathies
• Long incubation periods
• No inflammatory response
• No antibody production
• Sponge-like holes in brain and protein deposits called plaques.
• Lose motor function, become demented and die.
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Human TSE’s
• Kuru
• Creutzfeldt-Jakob disease (CJD)
• Gerstmann-Straussler-Scheinker Syndrome (GSS)
• Fatal Familial Insomnia (FFI)
• New variant CJD (nvCJD)
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CJD Facts
No definitive diagnosis w/o brain biopsy or autopsy
1/million affected: 250 - 300 new cases a year
Sporadic or classical (sCJD) - 85% of cases: no known cause
Hereditary or familial - 15% of cases; autosomal dominant
Aquired (aCJD) - contamination through medical procedure
Variant (vCJD) - Beef tainted with BSE
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Animal TSE’s
• Scrapie in sheep
• Bovine Spongiform Encephalopathy
• Transmissible Mink Encephalopathy
• Feline Spongiform Encephalopathy
• Chronic Wasting Disease in deer and elk
• Exotic Ungulate Encephalopathy –kudu, orynx and nyala
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Prions• Identified in 1982 by American scientist
Stanley Prusiner
• “Proteinaceous infectious particles”
• Nobel Prize in 1997
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Prion Hypothesis
• Normal nerve cells contain the normal prion protein, a glycoprotein called PrPc
formed by the Prnp gene.
• TSE-infected cells contain the abnormal form of the protein, called PrPsc. This differs from the normal protein by having beta-sheets instead of alpha-helices
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Prion hypothesis
• PrPsc interacts with PrPc, converting it into another PrPsc
• Infectious PrPsc can come from inside or outside the host.– Taken in by injection or ingestion– Random event, or mutation of Prnp gene that
makes protein susceptible to mis-folding.
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• Usually transmitted inefficiently between species– May be due to difference in amino acid
sequence in proteins
• Species barrier may be broken if passed through an intermediate host.
• Mutations of Prnp gene linked to inherited TSE’s
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Transmission
• Eating infected material
• IV or IM injections
• Tissue transplants
• Contaminated surgical instruments
• Blood???
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Decontamination
• Must be subjected to dry heat at least 600oC for one hour.
• Or be treated for one hour in a bleach solution containing at least 2% chlorine.
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Restrictions
• On decontamination procedures for surgical instruments
• Blood donations
• 200 patients world wide contracted CJD through organ transplants and pituitary gland extracts.
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TreatmentNo cure
Opiate drugs can help relieve pain
Clonazepam and Sodium Valproate relieves involunatary muscle jerks
Later stage involves catheter use, intravenous fluid, feeding tubes
Pentosan Polysulphate (blood-thinning and anti-inflammatory drug) - as of Dec 2004, 1 cure.
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Blood Test
• August 29, 2005 scientists developed a blood test for vCJD.
• Could protect those receiving blood transfusions and organ transplants
• Predict the size of future vCJD epidemics
• Test all the cows in the herd instead of destroying them.