Scrapie – Prions

by Vincent Racaniello, PhD

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    00:00 Let's talk a little bit about the history of prion diseases so you can see how we began to understand them. The first TSE that was ever recognized was a disease called scrapie and it's a TSE of sheep. It was recognized initially by farmers who noticed many, many years ago, that the diseased sheep would rub themselves on fences; they would keep rubbing and rubbing until their hair was all removed, so they called the disease scrapie, from scraping themselves on the fences. The disease was not only associated with this scraping behavior but also motor disturbances, the sheep developed problems walking. They'd trembled, they had an uncontrolled trembling, also called tremblant du mouton in France, paralysis, weight loss and death, about 4 to 6 weeks after the initial onset of symptoms. Scrapie has been recognized as a disease of European sheep for over 250 years.

    01:06 In many countries in Europe it's endemic, for example in the United Kingdom scrapie affects about one percent of the sheep every year, so that's quite a few sheep, as you know sheep are raised for various purposes, so a lot of them still develop scrapie.

    01:21 Now, it was the sheep farmers who originally found that scrapie seemed to be an infectious disease, they noticed that if they had an infected sheep with the scraping phenotype of scraping against the fence, if they put that into a clean herd, that animal would transmit the infection to the other animals, so they learned right away if you had a scrapie sheep, you keep it away from the other sheep, otherwise it would transmit the disease. So anyway this said that there was some kind of infectious agent involved in the disease of scrapie.

    01:57 In 1939 it was found that you could take a brain from an animal with scrapie, you could grind it up and pass it through a filter and then you could take the material that went through the filter and inoculate another animal, and what went through the filter transmitted the disease. So these were the same filters that were used to separate bacteria and viruses, they would pass the virus through the filter. So people began to conclude, well scrapie must be a viral disease because it's passing through filters that hold back bacteria.

    02:31 But it soon became apparent that the scrapie agent was very different from a virus, for example, it was highly resistant to ultraviolet irradiation, ionizing radiation, and treatment with formaldehyde, these are all treatments which rapidly inactivate virus infectivity, but they had no effect on the infectivity of the scrapie agent. Finally an experiment was done that made it very clear that the scrapie agent was not a virus. On this graph I'm showing you the inactivation

    About the Lecture

    The lecture Scrapie – Prions by Vincent Racaniello, PhD is from the course Microbiology: Introduction.

    Included Quiz Questions

    1. Sheep
    2. Lizards
    3. Fruit flies
    4. Canines
    5. Cats
    1. 4-6 weeks
    2. 1-2 days
    3. 4-6 days
    4. 1-2 weeks
    5. 1-2 hours

    Author of lecture Scrapie – Prions

     Vincent Racaniello, PhD

    Vincent Racaniello, PhD

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