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Prion Diseases

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Transmissible Mink Encephalopathies (TME)- mink. Animal TSE's and ... TME- found in ranched mink so has an impact on fur sales. More TSE's and Animals. Scrapie ... – PowerPoint PPT presentation

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Title: Prion Diseases


1
Prion Diseases
  • Microbes and Society
  • Fall 2007

2
What is a Prion?
  • Prion- small proteinaceous infectious particles
    which resist inactivation by procedures that
    modify nucleic acids
  • Disease causing prion is a modified form of a
    normal cellular protein known as PrPc. This
    normal form is protease sensitive so it does not
    accumulate.
  • The modified prion is known as PrPsc (for
    scrapie) which is relatively resistant to
    proteases and accumulates in cytoplasmic vesicles
    of diseased individuals.
  • Appears that the acquisition of PrPsc allows for
    conversion of PrPc into PrPsc and that leads to
    disease.

3
Transmissible Spongiform Encephalopathies
  • TSEs are a family of rare progressive
    neurodegenerative disorders that affect both
    humans and animals. They are distinguished by
    long incubation periods, characteristic
    spongiform changes associated with neuronal loss,
    and a failure to induce inflammatory response.
    (CDC)

4
TSEs in Animals
  • Scapie- sheep, first known TSE been around for
    100s of years. Sheep get it by ingestion off of
    pasture or transplacental transmission
  • Mad Cow Disease or BSE- cows. First cases may
    have occurred by feeding scrapie infected tissue
    to cows
  • Chronic Wasting Disease (CWD)- deer, elk
  • Transmissible Mink Encephalopathies (TME)- mink

5
Animal TSEs and Society
  • BSE in Great Britain cost millions of dollars,
    loss of life, a crash in the beef industry and
    fostered mistrust of the government. Others?
  • CWD- Mostly scared hunters. However has the
    added cost of monitoring which cost
  • TME- found in ranched mink so has an impact on
    fur sales

6
More TSEs and Animals
  • Scrapie-
  • Packers and producers have had difficulty finding
    options for disposal of sheep offal and dead
    sheep causing packers and producers to incur
    significant increases in disposal costs.
  • Other countries have expressed concerns and
    have indicated that they may prohibit or restrict
    certain ruminant products because the United
    States has scrapie.
  • Domestic and international markets for U.S.
    sheepderived meat and bone meal have been
    adversely affected.
  • The combination of all of these factors has led
    to the decision to develop a strong scrapie
    eradication program in the United States

7
TSEs and Humans
  • Creutzfeldt-Jakob Disease (CJD)
  • Variant Creutzfeldt-Jakob Disease (vCJD)
  • Gerstmann-Straussler-Scheinker Syndrome
  • Fatal Familial Insomnia
  • Kuru

8
Classic CJD
  • Classic CJD has been recognized since the early
    1920s. The most common form of classic CJD is
    believed to occur sporadically, caused by the
    spontaneous transformation of normal prion
    proteins into abnormal prions. This sporadic
    disease occurs worldwide, including the United
    States, at a rate of approximately one case per 1
    million population per year, although rates of up
    to two cases per million are not unusual.

9
vCJD
  • There is now strong scientific evidence that the
    agent responsible for the outbreak of prion
    disease in cows, BSE, is the same agent
    responsible for the outbreak of vCJD in humans.
    Both disorders are invariably fatal brain
    diseases with unusually long incubation periods
    measured in years, and are caused by an
    unconventional transmissible agent.
  • However, risk of acquiring vCJD through infected
    cow meat is still low. Why?

10
Comparison of classic CJD and vCJD
  • The median age at death for vCJD patients is 28
    years, compared with 68 years for patients with
    classic CJD.
  • The median duration of illness for vCJD is 14
    months, compared to 5 months for classic CJD.

11
Kuru
  • Kuru is a rare and fatal brain disorder that
    occurred at epidemic levels during the 1950s-60s
    among the Fore people in the highlands of New
    Guinea.
  • The disease was the result of the practice of
    ritualistic cannibalism among the Fore, in which
    relatives prepared and consumed the tissues
    (including brain) of deceased family members.
  • Brain tissue from individuals with kuru was
    highly infectious, and the disease was
    transmitted either through eating or by contact
    with open sores or wounds.

12
(No Transcript)
13
Inherited Human TSEs
  • Gerstmann-Straussler-Scheinker Syndrome- a rare
    inherited dementia that presents in the later
    years.
  • Fatal Familial Insomnia- an extremely rare
    inherited prion disease that is characterized by
    insomnia and ultimately death.

14
Treatment
  • Nothing yet, but immune cells may be what carries
    the protein to the lymph nodes and eventually the
    brain.
  • Prevention- food animals have strict diets which
    limit or prevent animals from ingesting CNS
    material that may contain prions.
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