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Transmissible Spongiform Encephalopathies

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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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6
        “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)
                                            7
• 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.

                                           8
          Early Symptoms

•   Confusion
•   Depression
•   Behavioral Changes
•   Impaired Vision
•   Impaired Coordination



                            9
         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.

                                                10
     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.

                                           11
            Human TSE’s
• Kuru
• Creutzfeldt-Jakob disease (CJD)
• Gerstmann-Straussler-Scheinker
  Syndrome (GSS)
• Fatal Familial Insomnia (FFI)
• New variant CJD (nvCJD)


                                    12
             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
                                                   13
              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

                                              14
15
                  Prions
• Identified in 1982 by American scientist
  Stanley Prusiner
• “Proteinaceous infectious particles”
• Nobel Prize in 1997




                                             16
          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



                                              17
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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.


                                              19
• 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



                                               20
              Transmission
•   Eating infected material
•   IV or IM injections
•   Tissue transplants
•   Contaminated surgical instruments
•   Blood???




                                        21
           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.




                                              22
              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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            Treatment
No 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.

                                             24
              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.

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