00:01
The first opportunistic infection we'll consider
is candidiasis. Now opportunistic signifies
that in most people, these fungi do not cause
disease, it's only when there's an opportunity,
such as immunosuppression, do they cause problems.
And candidiasis may be caused by three different
species of candida; Candida albicans, Candida
glabrata and Candida parapsiloses. And these
pictures of candida show the typical fluffy
white appearance of the colonies on an agar
plate, that's the picture on the left and
on the right is in the microscope, you can
see the single cells of Candida. So this can
assume a yeast configuration, it can also
assume a mycelial configuration. Candida species
are normal inhabitants of our skin and our
mucosal surfaces, such as our mouth and the
genital tract. So here's a case where everybody
has these bacteria, excuse me, everybody has
these fungi, but in only certain situations
do they cause disease. So, when is candidiasis
a problem? Those individuals at risk for this
disease include: the immunosuppressed, if
you're having an organ transplant and you
need to have drugs to reduce the risk of rejection
of the organ, patients in intensive care units,
the use of broad-spectrum antibiotics that
can alter the normal microbial flora and allow
certain species to overgrow, people who have kidney
failure and they require dialysis and needles
need to be inserted into these individuals
repeatedly, that can introduce the candida
below the surface of the skin, which is where
it normally inhabits. Central intravenous
catheters, people with catheters for example,
people with catheters in the main veins of
the chest who need them for various reasons,
these can introduce bacteria and Candida into
that region. Those people receiving nutrition
by means other than by the mouth, that's what
parenteral means, so for example by intravenous
feeding, or people with AIDS, because they
are immunosuppressed. These fungi don't cause
infection unless the normal flora is disrupted.
02:29
So all the conditions we just talked about
may lead to the disruption of the normal flora
or introduction of candida, where it shouldn't
be, so you may have a skin maceration which
inadvertently pushes the Candida species where
they shouldn't be and that can cause infection.
02:48
So alteration of the flora by medical procedures,
or disruption of the skin. These procedures
cause the Candida to get into the bloodstream.
So for example chemotherapeutic agents that
destroy the mucosal gut barrier, these are
normal inhabitants of the gut as well.
03:04
If you're taking drugs that change that barrier,
many anticancer drugs do that, can allow
the Candida to come in and as I said before
central venous catheters that deliver medications
to the major veins and arteries of the body,
these are at risk for introducing microorganisms,
because they are not only inside the body,
they come outside as well and the organisms
can get in that way.
03:31
Normally the Candida species on our mucosal
surfaces are held in check by our immune response
and specifically for Candida this is T cell-mediated
immunity. So the Candida is living in places
in our body, we presumably derive some benefit
from that and the balance of the two is mediated
by T cells. When that's disrupted, then the
Candida can overgrow. AIDS patients in particular
are at risk because they have reduction in
their T cell efficacy as a result of virus
infection. So they frequently develop oral
pharyngeal and vaginal candidiasis, it's a
very typical outcome of AIDS infections, that
among the other opportunistic infections that
these individuals acquire, one of them is
candidiasis, which is very obvious because
it presents, at least partially in the mouth,
as a white coating as the fungi grows on the
tongue.
04:36
Neutrophils are the main host defense against
invasion and dissemination. These cells prevent
the candida from normally invading beyond
the mucosal and skin layers where they normally
inhabit, but again, any kind of procedure
that disturbs the immune balance and particularly
neutrophils, will allow Candida to get inside
of us. There are a number of people who are
what we call neutropenic, they have low levels
of neutrophil, as a variety of reasons.
05:08
It could be infection or drug treatment. In these
individuals the candida is not properly controlled
and it frequently spreads via the blood to
other organs, such as the eyes, the kidneys,
the heart, brain, the liver, the spleen and
there the Candida can multiply and cause extensive
problems. Candidiasis manifests itself visually
by a white coating of thick cells on the mucosal
surfaces of the mouth, of the reproductive
organs and this is often called thrush. And
this is very common in babies who are born
vaginally, by a vaginal delivery. Females have
Candida in the vaginal tract as a normal flora,
and some women have higher levels than
others, some babies may be slightly more immunosuppressed
than others, but it's a very common occurrence
within a few days of birth for babies to develop
a white coating on their tongue called thrush,
which then can be treated without any
further effects.
06:09
There is another form of candidiasis called
Intertriginous candidiasis. This is when the
fungus grows in the warm and moist areas of
the skin, such as the groin, so babies often
get a diaper rash and it can involve Candida.
This is because, of course, the diaper is
holding the moisture in, especially modern
diapers that are very sealed against fluid
leakage, they can keep in the moisture and
the heat, the Candida can grow there. These
individuals are not necessarily immunosuppressed,
although babies’ immune systems are not
as good as older individuals’ immune system.
And there's also Candida which may grow
underneath breast tissue. This is actually
a good reason to wear a bra, because if you
have breasts that press against the chest,
there will be a region of skin under them
that is dark and moist and if you have any
immune issue whatsoever, Candida can grow
under there. So these are called intertriginous
candidiasis.
07:11
When Candida goes beyond the mucosal and skin
surfaces, we call it a disseminated infection,
this can then bring the yeast to many other
organs. It can infect the brain, leading to
meningitis. It can infect the eye, in particular
the retina and the membranes just on top of
the retina, this is called Chorioretinitis.
It can cause abscesses in the spleen and in
the liver, Hepatosplenic abscesses. It may
involve the vertebral column and called vertebral
osteomyelitis. And finally it can cause heart
infections, especially if you have an artificial
valve, a prosthetic valve, it can cause endocarditis
at that site. So the yeast can go from its
normal site on mucosal surfaces in the skin
to many other regions when we have problems.