Primary and Secondary TB - Medical Video Lecture - MBBS

Let's say that these are your lungs.
This is your right lung.
This is your left lung.
We're just going to label them
upper and this will be lower.
This will be the middle lobe.
You're minding your own business and
somebody coughs,
and they get TB in your lungs.
That TB gets inhaled,
you breathe it in,
and the location that
the TB likes to go to,
it's actually a pretty interesting thing,
is it likes to go along these
fissures that I'm drawing out here.
These are the fissures;
They separate the lobes of the lungs.
They are kind of like the boundaries.
The TB bacteria like to
go near those fissures.
They also actually like to go sub-pleural.
Pleural indicates the
outside layer of the lung.
So, if it's sub, it's right underneath
that outside layer.
They like to go somewhere
along the fissure
and somewhere in the sub-pleural space;
right on the edge.
They're going to jump into some alveoli.
Let me just draw it out for you here.
You know, you've got
millions of these guys;
I'm going to draw a few more,
just to make it really
clear that these things
are in packs.
What's going to happen is,
of course, you're going to have an immune
response right away to this bacterium
that's in there.
You might have a macrophage
coming along like that.
This macrophage is going to pick up
the bacteria that's now landed inside
of that air sac,
and it's going to take a journey
through the tissue of the lung.
It's going to go and drain down to a
local lymph node.
This is a local lymph node;
a neighborhood lymph node.
Let me label it right here; lymph node.
That's the journey that the macrophage
is going to take;
not every single one, but some of them
are going to go to the lymph node.
What they do by doing that is,
they actually carry with them
the micro bacterium.
This little bacterium is now
carried along, 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.
I should've 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.
What's going to happen is,
there's going to be a reaction.
The micro bacterium and the macrophages
are going to start warring.
They're going to fight.
You're going to get this entire area
turned into literally a battlefield,
with dead micro bacterium and some
dead macrophages.
Some of your own cells are going
to be part of this,
but a lot of it is just going to be
the bacteria.
You're going to get some of this
battlefield going on over here as well,
in this lymph node.
That's what it's going to turn into;
a giant battlefield.
If you look under a microscope,
it actually looks like,
well we call it a granuloma.
That's the description that a
pathologist might use
for what we are actually
describing here.
The 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 erase the center out,
if you were to peek inside,
let's say I was to cut it open,
what you would see is,
inside of this granuloma
is literally this mess;
this goo that somebody
at some point,
thought looked like cheese.
I'm not sure how they came up
with that conclusion,
but it kind of stuck.
So, we call this caseous necrosis.
Caseous literally refers to cheese.
This is the same kind of cheese that
might go on your crackers.
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.
Let me fix that with a little hyphen.
So, cheesy death.
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.
Ghon Focus is what we call this thing.
It's termed a granuloma,
and specifically here because it's a
granuloma, which is more a 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;
it's the other name for it.
Both of these,
if you're trying 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; Ghon complex.
That just refers to both of the
areas of disease.
This is how disease starts,
but what happens after time passes?
Let me just slide this over a little bit.
If we then take a little bit of
passage of time.
Let's say there are three options.
Time has passed.
What are the different possibilities?
Well, let me actually go through and
talk about micro bacterium;
micro bacterium tuberculosis from the
standpoint of 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 lower case t.
Micro bacterium
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 lying in wait.
The third option is that it's
multiplying like crazy;
it's actually going and dividing
and dividing and dividing.
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 diseased tissue,
not normal tissue.
You might even see some large
diseased lymph nodes.
That's what it'd look
like on a chest x-ray.
These other two, on a chest x-ray,
basically would look normal.
If you were to look at 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.
Actually, this is helpful,
because remember,
these two together,
we call these,
both situations we call 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.
If you had some super ability
to actually zoom in;
let's say you looked under a microscope,
you would notice one key difference
between these two.
This is not something you can see
on a chest x-ray,
you can see only if you had amazing vision
and 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.
In the case where you
have dormant bacteria,
you would actually see
some bacteria there;
some red, live bacteria.
That's the key difference between these
two situations.
Again, both of them we call
latent TB infection.
In this scenario,
the bottom one, is going to be called
progressive because things are
slowly but surely getting worse;
you can see more disease
on the chest x-ray.
Primary, with a 1 and a
degree sign, infection;
this is the name for this,
progressive primary infection.
It sounds a lot like what we had
named that 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, or drew this out, earlier.
Let's say more time is passing, of course.
Maybe years have gone by.
This person has had live bacteria
in their lungs for years and years;
nothing has happened.
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 going to come out with a vengeance.
There's going to be a cavity
that forms; usually in the upper lobes.
A cavity that forms up here.
It's going to be packed full of
TB bacteria.
This person, you could imagine,
if they coughed, they're
going to be coughing
out lots and lots of these little
bacteria that i'm drawing.
Around that area there's a lot of disease;
a lot of disease in this area and it's
very, very distinct.
If you see cavities, and you see lots and
lots of disease, you're really going to be
worried that this person might have
what we call progressive
secondary infection.
The reason I'm saying
secondary is because,
again, this is happening separate from
that primary infection; this is happening
sometimes years later.
Another way you can
actually have this happen
is through what we call
a secondary infection.
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.
You can also think that
this is re-infection,
because you basically got re-infected with
the same bug.
The thing that ties
reactivation together with
re-infection is that in both situations
your immune system has at some point
in the past been exposed to TB.
We think 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?
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 that they
got the first infection with TB,
or secondary which could be years later.