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.