- [Instructor] Let's say that these are your lungs.
This is your right lung,
and this is your left lung,
and I'm just gonna label them upper,
and this will be lower.
And this'll be the middle lobe.
And you're minding your own business
and somebody coughs,
and they get TB in your lungs.
So that TB gets inhaled,
you breath it in,
and the location that the TB likes to go to
is actually a pretty interesting thing,
is it likes to go along these fissures
that I'm drawing out here.
So these are the fissures,
they separate the lobes of the lung, right?
They're kinda like the boundaries,
and so they like,
the TB bacteria they like to go near those fissures,
and they also actually like to go sub-pleural.
Pleural kinda of indicates the outside layer of the lung,
so if it's sub it's right underneath that outside layer.
So they like to go somewhere along the fissure
and somewhere in the sub-pleural space,
kind of right on the edge.
So they're gonna jump into some alveoli.
Let me just draw it out for you here.
And you know you've got millions of these guys,
so I'm gonna draw a few more
just to make it really clear that
you know these things are in packs.
And what's gonna happen is that of course
you're gonna have an immune response right away
to this bacteria that's in there.
So you might have a macrophage coming along like that,
and this macrophage is gonna pick up the bacteria
that's now landed inside of that air sac,
and it's gonna take a journey
through the tissue of the lung,
and it's gonna go and drain down to a local lymph node.
So this is a local lymph node,
kind of a neighborhood lymph node.
Let me label it right here lymph node.
So that's the journey that the macrophage is gonna make.
Not every single one, but some of them are gonna go
to the lymph node.
And what they do by doing that
is they actually carry with them
the Mycobacterium right,
so this little bacterium is now carried long
going for the ride,
and now the bacteria is in two spots.
It's in the original spot where it landed in the lungs,
but it's also in the lymph node
because it got carried there by the macrophage.
And I should have mentioned this earlier,
but let's assume that this is your primary infection.
In other words this is the first time
that this person, or I guess it could be you or me,
is breathing in the TB bacteria.
So what's gonna happen is that there's gonna be a reaction.
The Mycobacterium and the macrophages
are gonna start warring, they're gonna fight.
And you're gonna get this entire area
turn into literally like a battlefield
with dead Mycobacterium
and some dead macrophages.
So some of your own cells are gonna be part of this,
but a lot of it is just gonna be
the bacteria, right?
And you're gonna get some of this battlefield
going on over here as well
in this lymph node.
So that's what it's gonna turn into,
giant battlefield,
and if you look under a microscope,
it actually looks like what we called it a granuloma.
That's the description that a pathologist might use
for what we're actually describing here.
And same thing is true for the lymph node,
there's a little granuloma in there as well.
If you were to peek inside of this granuloma,
let's just actually kinda erase the center out,
if you were to peek inside
or let's say I was to cut it open,
what you would see is inside of this granuloma
is literally like this mess, this goo,
that somebody at some point thought looked like cheese.
And I'm not sure how they came up with that conclusion,
but it kinda stuck,
and so we call this caseous necrosis.
And caseous literally refers to cheese.
And this is the same kind of cheese
that might go on your crackers.
So cheese and you can think of it almost like
cheesy death I guess, cheesy death for the necrosis part.
I think I added an extra e there by accident,
but let me just fix that with a little hyphen.
So cheesy death.
And because I'm naming things,
let me go ahead and give you a couple more names.
Ghon Focus, what the heck does that mean?
Ghon Focus, actually named after Dr. Ghon,
but Ghon Focus is what we call this thing.
So it's termed a granuloma,
and specifically here because this granuloma,
which is the more broad term,
is in the sub-pleural space we said,
and it's close to a fissure and we suspect it's from TB,
we would call it a Ghon Focus actually,
that's the other name for it.
And both of these if you were to try to name both
of these together,
the lymph node that has a granuloma
and the Ghon Focus together make up what we call the
Ghon Complex.
So that just refers to both of the areas of disease.
So this is how disease starts.
But what happens after time passes?
Let me actually just slide this over a little bit.
If we then take a little bit of passage of time,
and let's say there are three options, right.
Time has passed.
What are the different possibilities?
Well let me actually go through and talk about
Mycobacterium tuberculosis from the standpoint of the bug
what is going on.
Actually I just noticed I have in the past
made the mistake of using a capital t,
but it should be a lowercase t.
So Mycobacterium tuberculosis, three options.
One option is that the bacterium may be dead,
you may have killed it with your macrophages.
Another option is that the bacterium is dormant,
it's just kinda lying in wait.
And the third option is that it's multiplying like crazy,
it's actually going and dividing and dividing and dividing.
And the last one actually
is going to look if you looked on a chest x-ray like this,
you see lots of disease.
This red indicates disease tissue,
not normal tissue,
and you might even see some large diseased lymph nodes.
So that's what it'd look like on a chest x-ray.
And these other two on a chest x-ray basically
would look normal.
So if you were to look on a chest x-ray
this is what the three options would look like.
The first two would look normal,
and the third one would look like
something is wrong.
And actually this is helpful because remember,
these two together we called these,
both situations we called them latent TB infection.
Remember we can't really easily distinguish the two
because in both situations you've had prior exposure to TB,
and in both situations the x-ray looks normal.
But if you had some super ability
to actually zoom in,
let's say you could look under a microscope,
you would notice one key difference between these two.
And this is not something you can see
on a chest x-ray,
but you could see only kind of
if you had amazing vision and you could look down
at the microscopic level at somebody's lungs.
You'd see macrophages,
and in the top case where there are dead bacteria,
the macrophages would look healthy and happy.
And in the case where you have dormant bacteria,
you could actually see some
bacteria there, some red live bacteria.
So that's the key difference
between these two situations.
But again, both of them we call latent TB infection,
and this scenario the bottom is gonna be called
progressive because things are slowly but surely
getting worse.
You can see more disease on the chest x-ray.
Primary with a one and a degree sign infection.
This is the name for this,
progressive primary infection.
So it sounds a lot like what we had named out here
with primary infection,
but the word progressive tells us that things
are actually getting worse,
the disease is getting more nasty.
Now, let's actually play out the rest of this.
Let's think about what will happen
with the dormant situation.
I wrote out, drew this out earlier.
And let's say more time is passing of course,
maybe years have gone by,
and this person has had live bacteria in their lungs
for years and years,
nothing has happened.
And now, they have what we call reactivation.
Maybe it's because their immune system
is not working properly,
or maybe they have another disease.
Who knows why, but all of a sudden,
now the bacteria, the TB bacteria,
are gonna come out with a vengeance.
And there's gonna be a cavity that forms,
usually in the upper lobes,
cavity that forms up here,
and it's gonna be packed full of TB bacteria.
So this person you can imagine if they cough,
they're gonna be coughing out lots and lots
of these little bacteria that I'm drawing.
And around that area there's a lot of disease,
so a lot of disease in this area,
and it's very very distinct.
So if you see cavities and you see lots and lots of disease,
you're really gonna be worried
that this person might have what we call
progressive, progressive,
secondary infection.
And the reason I'm saying secondary
is because again this is happening
separate from the primary infection.
This is happening sometimes years later.
Another way you can actually have this happen
is through what we call secondary infection.
So maybe you actually literally get more TB,
maybe you're on a bus or a boat,
and a second person decides to cough,
and TB gets into your lungs through breathing it in.
That's another way to actually get progressive
secondary infection.
So you can also think this is reinfection
because you basically got reinfected
with the same bug, right?
So the thing that ties reactivation together
with reinfection is that in both situations
your immune system has at some point in the past
been exposed to TB.
And we think that that's the main reason
why you see these cavities,
and you see so much disease.
That's a really horrible infection to get.
So thinking about this a little bit more broadly then,
both the progressive primary infection
and the progressive secondary infection,
who are the folks that you'd be most worried
getting these diseases?
Well I always worry about HIV patients
before any other group because we know
that HIV and TB is a really really bad combination.
They're at high risk for getting progressive disease,
both primary which is at the time they got the first
infection with TB,
or secondary which could be years later.