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- (Narrator) When dealing
with the human body,

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you have to talk about the immune system.

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So first off, it's your
body's defense mechanisms.

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You have barriers.

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Just flat out stops things from coming in.

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Your skin is a great physical barrier.

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Stomach acid, tears are
great chemical barriers.

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Your stomach has a very, very low pH.

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A pH of maybe 2, or so.
So it's very acidic.

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It will simply destroy a lot of bacteria.

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Tears, you're going to have
different defensive mechanisms

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in your tears that help
to destroy bacteria.

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Vomiting. You're saying,
well hold on...vomiting?

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A lot of times vomiting
is caused by something

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that is in the stomach,
or in the GI tract,

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the upper GI tract, that
is going to be irritating.

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It could be a toxin.
It could be a bacteria.

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But something your body
wants to get out of there.

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Then you have these
things called non-specific

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defense mechanisms.

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Non-specific because it does
not matter what triggers it.

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Anything that causes a
problem can trigger it.

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Phagocytosis. That's when
you have your defensive cells

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eating other cells or particles.

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So, phagocytosis is a cell eating.

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Inflammation. If you ever
had a cut, a bruise, a bump;

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you know it swells up.

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Inflammation is your body's
defense mechanism to try

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to help limit further
injury or further infection.

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But then we have some that
are very, very specific.

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You have antibodies and T cells.

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Well, T cells are a
derivative of one of your

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white blood cells, they're
coming from your lymphocytes.

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The T cells are meant to
cause an immune response.

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They're meant to attack,
destroy foreign particles.

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Well antibodies, they're also
coming from the lymphocyte.

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Now it's not a direct path,

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there's something else between.

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But, the idea is, these antibodies

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coming from the lymphocytes indirectly

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are going to be able to
recognize foreign objects.

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Could be foreign pathogens,
like bacteria or virus.

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Could be foreign cells that
just shouldn't be there.

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So we have our antibodies and T cells.

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They are specific because
they only recognize

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what they're programmed for.

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The example for antibodies,
think about...chicken pox.

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If you ever had chicken
pox, or if you didn't.

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You might have had the
chicken pox vaccine.

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Well, once you've either had
the vaccine or had chicken pox;

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How often do you get it a second time?

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Not typically, I mean some
people will get it a second time.

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But more often than not,
once you get it, that's it.

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It's because your body
has recognized that virus.

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Your body made antibodies
to recognize the virus

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and then it fights off the
virus anytime it sees it.

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These diseases could be
caused by either living

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or non-living organisms.

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Now, these living organisms,

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like bacteria, fungi, parasites,

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any of those can cause
a pathogenic infection.

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Now bacteria, you've probably heard of.

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They're one celled prokaryotes,

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very basic, very simple
organisms, things like Ecoli.

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Fungi, or fungus,

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unicellular and multicellular,

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that means they could be
one cell or many cells.

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But they're eukaryotes,
a little more complex.

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Could be a parasite or
parasites even, plural.

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Again, unicellular, one
cell or multicellular, many.

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So any of these. bacteria, fungi,

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or parasites can cause infection.

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But there's also nonliving particles.

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You have viruses and prions.

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Now a virus is not living,
because without a host,

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a virus cannot survive.

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The way a virus typically
replicates, or duplicates,

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is by injecting its
DNA into a living cell,

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letting the living cell
perform the action.

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Prions, well they're even
smaller than viruses.

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They're tiny particles

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that when ingested into the system,

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either eaten, it can be
have a drink, it could be

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simply inhaled, unfortunately.

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They potentially could cause
pretty severe infections.

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So we have both living and nonliving

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that can both cause a
pathogenic infection.

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Here's looking at the left
hand side is a eukaryotic cell.

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If you notice, a eukaryotic
cell has a nucleus.

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It has all these different
particles around it:

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your endoplasmic reticulum,
your golgi apparatus,

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your mitochondria.

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All the organelles.

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But in comparison, look how small

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the bacterium is next
to the eukaryotic cell.

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And the bacteria, all you're seeing:

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cell wall, DNA, ribosome,

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plasma membrane.

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It's pretty small and pretty basic.

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But even smaller and more
basic, are going to be a virus.

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So for the virus, it's a tiny little dot

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in comparison to a
larger, eukaryotic cell.

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So we have our viruses,

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bacteria that are typical animal

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cells with a eukaryotic cell.

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All right, so back to these bacteria.

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We mentioned they're
prokaryotic, single-celled.

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Just one cell. You might found
a clump of thousands of them.

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But each one is its own organism,

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with a ton of different
ways to grow and reproduce.

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You can find bacteria living in

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thermal vents in the bottom of the ocean.

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You kind find them living in the coldest

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reaches of a mountain peak.

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You can find them pretty much anywhere.

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It adapted to live in
almost any environment.

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Now infections, we're
looking at pneumonia,

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tonsillitis, tuberculosis, botulism,

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toxic shock syndrome,

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syphilis, Lyme disease, and
the list goes on and on.

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None of these are overly pleasant.

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Probably, of course
this sounds really bad,

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but one of the more mild
versions here is tonsillitis.

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Any of the rest of them
can get pretty severe,

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pretty quickly.

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All by these tiny, single-celled bacteria.

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More often than not, though, all of these

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can be treated by antibiotics.

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Now the trick with antibiotics is to

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one, make sure it is a bacteria.

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Because a virus, antibiotics
doesn't make a difference.

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But two, it'd be great
if they could figure out,

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okay which antibiotic will be functional

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against this particular bacteria.

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So you know that the antibiotic will work,

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not just kill off all your normal flora

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or your normal bacteria,
leaving the pathogenic one

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to get larger and proliferate.

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Well, if you think about
antibiotics and viruses

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don't forget they usually don't work.

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They're very, very small.

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Tiny little thing, much
smaller than a bacteria.

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Now I put them under the
nonliving category earlier

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but there technically is debate

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of whether they're living or non.

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The reason that it goes non usually,

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not living, is because it cannot

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reproduce without a host cell.

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That means a virus by itself
cannot make more viruses.

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Also, a virus will not have
any metabolic activity.

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So living, nonliving? It's up for debate.

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A lot of them are heading more toward

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the nonliving currently.

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Structure of viruses, DNA or RNA?

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You will not have both.

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And this DNA, or the RNA, within a virus

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is surrounded by this protein coat,

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it's meant to keep it safe

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and keep it contained
all in the one place.

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Viruses can cause things
like AIDS, HIV- AIDS.

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Hepatitis, encephalitis, rabies,

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influenza,

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colds, warts, chicken pox

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and there's more than that.

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What all these share in common, though,

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is they all can be confected
and caused by a virus.



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How about these prions?

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Now prions, a lot of time
you've never heard of.

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They pop up every so often,
but more often than not,

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they're not really talked about.

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Prions are actually just protein.

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Its normal brain proteins

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that just don't quite fold properly.

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So they turn into these
little, tiny particles.

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And once they're misfolded
or turned the wrong way,

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then it become self-propagating.

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So once there's a couple of them

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they make more and more and more.

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Now all this protein that's
around is not helping anything.

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This excess protein debris

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can actually fill, disable,

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and potentially destroy any
cell it comes in contact with.

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And here's the scariest part...

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Prions cannot be cooked
away. You can't kill them.

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Freezing. Doesn't do a thing.

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They just stay there
because they are nonliving.

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Drying. You can try to dry out

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the particles as much as you want.

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But it's not living.
No metabolic activity.

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So really drying, freezing, cooking.

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None of these have any impact
on getting rid of prions.

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So bovine spongiform encephalitis,

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better known as "mad cow
disease", is caused by a prion.

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That's why countries are being so

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cautious when they go through
the whole buy process.

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If you're buying beef from a country

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that has found to contain prions,

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a lot of times they'll shut
down all sales in that country.

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Visible fact they're
not wanting to introduce

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the prions into the current market.

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This goes for Canada, the US,
Britain, any of the countries.

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We also have Creutzfeldt-Jakob disease.

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Another prionic-based disease.

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So both these are based
on those mutant proteins

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just building up and causing problems.

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Now that we've gone through the

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different types of pathogens,

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let's figure out how they are transmitted,

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how they pass along.

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Well transmitability is
how easy that pathogen

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can go from person-to-person.

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It could be in a handshake.

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It could be someone sneezing and

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the particles are floating around.

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So there's different
types of transmission.

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There's respiratory, your breathing.

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When you sneeze, you
cough and all of a sudden,

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the particles are floating around.

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It could be fecal to oral transmission.

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You're thinking, hold
on, that's just wrong.

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Well, fecal to oral.

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How do you know where all the
fecal matter is in the world?

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The fecal matter has to be
filtered out at some point.

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It goes back into the ground
and is reused as nitrogen.

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So it's not saying
direct fecal necessarily,

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but it could be in some roundabout way.

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It could've been from some animal

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that decided to have a
problem right in your garden.

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So this whole fecal-oral
sounds disgusting.

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But, it's one of the biggest reasons

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why you wash your hands
after going to the bathroom.

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Testing doorknobs and bathrooms,

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you'd be amazed at how much it shows up

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on those doorknobs what's there.

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Body fluids. These are things from

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tears, to blood, to saliva,

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to any other fluid coming
forth from the body.

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Virulence is the damage it can infect.

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Some of the high virulence means

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it'll influct a lot of
damage, very quickly.

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An example is the Ebola virus

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The Ebola virus

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can inflict a ton of damage

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within the first 24 hours,

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if not potentially kill the
person within the 24 hours.

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Something with a lower virulence
could be the common cold.

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You might have it for a day or two

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and not even know it,
until it builds up enough.

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Once it builds up, a couple of days later,

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a lot of times, you're back up and moving.

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No major problems.

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So transmitability, mode of transmission

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and virulence.