Chronic Wasting Disease – TSEs

by Vincent Racaniello, PhD

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    00:00 The other prions we are worried about are those in cervids.

    00:05 Cervids are wild animals like deer, elk and moose. They develop a prion disease called chronic wasting disease. On the left in this graph is a map of the US and Canada, those black and gray areas show you where prion diseases of cervids have been diagnosed in various herds, they're all over the US and Canada, they have also been found in South Korea. In the graph on the right shows you how the incidence of chronic wasting disease, CWD, has gone up over the years since 1965 to the present, so it is spreading, it is increasing. Why are we worried about this? So again cervids are moose, elk and deer.

    00:45 In standing herds, up to 90% of deer, so that's a deer on the left there and 60% of elk, that’s an elk on the right are positive for chronic wasting disease prions. That is a lot of animals.

    00:57 These are standing herds, you know, on a farm or something like that. However, in the wild cervids, it's pretty high too, 15%. And we don't know how it got there and it's obviously spreading, so we’re little bit worried about this. How do deer and other cervids pass this disease? Well they can shed it, it can sit in the environment for a while and go to another animal or it can be shed and spread directly to another deer. So let's explore how some of this works.

    01:26 Let's look at shedding first, how would deer shed prions? Well we know by studying deer in the laboratory, the velvet that covers their antlers can be contaminated, saliva, nasal secretions, skin, blood, milk, birthing matter, urine, feces, all of this can shed prion, it is pretty scary. The carcass, if a deer dies in the forest the carcass is infectious.

    01:51 Plenty of opportunities to shed the prion. How about the environment, what happens there? Lots of opportunities. There are hotspots where deers like to hang out, carcasses obviously, if there is a carcass, other animals are going to come and eat it. Scrapes and rubs, places where deer like to scrape themselves. Mineral licks, if you put out a block of salt, deer like to come and lick it. Wintering areas, captive facilities, these are all hotspots for transmission. How does the agent get moved? Does it go by water, dust, do scavengers pick it up, animals who eat the deer, predators, other insects, these are the things that are possible, but need to be examined. Soil, what happens if the prion is shed into the soil by deer feces or urine, does it stay there, does the infectivity change, does the stability change, does the soil matter. Very recently it was shown that you can put prions on plants and the plants will take it up and then you can feed them to another animal and they will get a prion disease. So plants take up deer prions, they remain infectious and they can be transmitted, that pretty scary. Finally the environment, what does it do? Is it oxidized, desiccated, freeze, does freeze, thawing make any difference, is it degraded in any way.

    03:03 So these are some issues that need to be addressed. And uptake, how would animals take up these prions? Well from deer to deer, it can go by oral lesions, it can be taken up into the nose, inhalation, oral ingesting, passing through the gut and absorption through the intestine and presumably other animals can take up these prions in a similar fashion.

    03:25 So we have shedding from a deer, either alive or dead, which can go to another animal by direct contact, saliva or mucus, or the deer can shed the prion into the environment and then it can be introduced in some way, perhaps via grass into deer, or into another animal.

    03:44 So what about the host range of cervid prions, let's do the experiment. Take a mouse; inject it with cervid PrPsc, what happens? No disease. That's good; there is a species barrier, so cervid PrP cannot infect the mouse at least. Let's take PrPsc and put it into a mouse that is transgenic for the cervid prnp gene, those mice then develop a TSE. Perfect so far, so the cervid PrPsc only works in animals that have the gene encoding the cervid prnp. Now what if you take a mouse and make it transgenic for a human prnp? So this is sort, we can't infect people with cervid prions right, so the next best thing is to take a mouse, give it the human prnp gene, inject the cervid PrPsc, no disease. That's a good sign. That suggests that people won’t be infected, at least directly by cervid prions, but this is a mouse and you know in animals, in experiments with animals you always have to worry, you can't always extrapolate the humans. So we still need to be careful. So it looks like cervid prions do not infect mice with a human prnp, but people worry about the possibility that cows may be infected with cervid prions in pastures. You can imagine a scenario where deer come to a cow pasture at night when the cows are gone, they can urinate and defecate or lick the grass and put prions on the grass and the next day the cows come and eat the prions and they will get infected and then the cow is put into the human food chain and we get cervid disease indirectly. So we can do an experiment to address this possibility.

    05:38 We take a cow and we inject it with deer prions and the answer is yes, the cows do develop deer prion disease. So again the species barrier doesn't exist between deer prions and cows, so theoretically, deer prions could get into cows, cause disease and get into the food supply. So obviously we need to develop drugs to cure these diseases and better diagnostics to make sure that this transmission doesn't occur. Meanwhile, even if you're not worried about chronic wasting disease, if you hunt, you should be careful and there is a website that you can go to that tells you all about how to take care of deer if you like to hunt them and bring them home to cook them, you shouldn't shoot or handle in any way a deer or an elk that is acting weird. You have to look at it, you can tell when they have overt scrapie or a prion disease, they walk weird and they look bad, their fur is matted and scraped away, leave those alone, don't shoot them because they're an easy target, because they might get you sick. If you do kill a healthy animal, when you take it apart in the field, which is the way you do this I'm told, I don't hunt so I don't know but I take their word for it, wear rubber gloves, don't use a saw to chop everything up, stay away from the spinal cord, don't open the spinal cord, don't open the vertebral column to get the spinal cord out, that's bad because that's where most of the prions are. Just take out the meat in the field and leave the rest there and stay away from brain, spinal cord, eyes, spleen, lymph nodes, these tend to have a lot of prions in them. Wash your hands when you're done and cook the meat well, even though as I said, it's not going to help to get rid of prions if they're already there. But it will protect you against other parasite diseases.

    About the Lecture

    The lecture Chronic Wasting Disease – TSEs by Vincent Racaniello, PhD is from the course Prions.

    Included Quiz Questions

    1. Hoof clippings
    2. Saliva
    3. Nasal secretions
    4. Skin
    5. Blood
    1. Humans
    2. Cows
    3. Moose
    4. Deer
    1. Spinal cord
    2. Striated muscle
    3. Smooth muscle
    4. Peritoneum
    5. Appendix

    Author of lecture Chronic Wasting Disease – TSEs

     Vincent Racaniello, PhD

    Vincent Racaniello, PhD

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