00:01
Alright so that's our second opportunistic
fungal infection. Here's another one and this
one is called aspergillosis. It's called by the
species Aspergillus. These are again environmental
filamentous fungi; they are not part of our
normal flora. So if you recall the first yeast
that we talked about, Candida are normal flora
in humans, it's only when our immune system
is perturbed in some way, they become pathogenic,
but aspergilli are not members of our normal
flora. Aspergilli are normal inhabitants of
the environment. Most people breathe aspergillus
spores every day. I'm probably breathing some
right now and so are you, but we're fine breathing
these, we don't get sick. Some of us may have
an allergic reaction, it's only when we are
either neutropenic, again we have low levels
of neutrophils which are important for combating
a lot of these fungal infections, or if on
corticosteroids or if we're transplant recipient
and we're being immunosuppressed to prevent
rejection of the organ, in those cases then
an aspergillus inhalation of spores can lead
to severe disease. Now aspergillus, we inhale
the spores initially and when they go into
our lungs, they germinate and they start to
grow as hyphae. So here's a case where initially
the spores become hyphae and these are invasive.
01:37
They can go from the lung tissues into the
blood vessels, through the blood vessel walls
and then they can spread elsewhere from there.
They can destroy the blood vessel as a result
of this mycelial growth. They can cause hemorrhaging
and destruction or necrosis of the vessels
and surrounding tissues. So the hyphal growth
in a tissue is associated with particularly
nasty effects.
02:01
Neutrophils as you might guess and macrophages
are the main host defense against aspergillosis.
02:05
And I suspect that in most of us with a healthy
immune system, as soon as we inhale a spore,
our lung is full of phagocytic cells, macrophage
cells that can take up spores, but they can't
take up the hyphae. So if the spores germinate
and get to the point where they start to develop
hyphae and a mycelium, the macrophages can't
handle that, but the neutrophils can take
care of that. Again in an immunocompetent
individual, neutrophils secrete reactive oxygen
species that will kill the hyphae. So even
in you or I who are immunocompetent, if a
few of the spores germinate and form hyphae
the neutrophils can take care of them. Again
it's only in people with compromised immune
systems, these cells are not functional and
the hyphal growth continues unabated. Inhalation
of spores and growth is initially accompanied
by pulmonary or sinus infections, which may
be mistaken for a flu-like illness or allergies,
but then again, if the immune system is defective,
you will get hemorrhagic infarctions as the
hyphae invade various tissues and this can
happen in many parts of the body as well as
the brain. When we have pulmonary invasion
by the hyphae, this is called invasive pulmonary
aspergillosis, it's associated with fever,
chest pain, cough and shortness of breath
or dyspnea. The growth of the fungus not only
invades the brain, in immunocompromised people
can cause brain abscesses, but can also cause
necrotic skin lesions, which are typical of
the infection.
03:48
How do we diagnose and treat aspergillosis? It's
easy to culture Aspergillus in the laboratory,
but because the spores are everywhere, it's
very important to differentiate contamination
in the lab from actual infection. So because
again, it's so pervasive, this is not easy
to do even in a clean laboratory. We can take
biopsies of various tissues to document invasion
and we can see the typical cellular forms
or the hyphal forms of the Aspergillus and
then when confirmed, we can then treat with
voriconazole, amphotericin B and caspofungin.
04:28
So that's aspergillosis. That's a common environmental
fungus. That again, it's opportunistic because
it causes problems in immunosuppressed individuals.