Hey everyone, this lesson is on amebiasis, otherwise known as intestinal amebiasis (amoebic dysentery)
so in this lesson, we're going to talk about specifically an infection with entamoeba
histolytica we're also going to talk about how we can get infected with this
type of amoeba what is the pathogenesis how this amoeba can cause the
signs and symptoms that it does. We're also going to talk about those signs and
symptoms and we're also going to talk about how we can treat it so intestinal
amebiasis is an invasive intestinal infection with amoeba of the genus
entamoeba so entamoeba you can remember the word entamoeba by it's the suffix
amoeba so that's easy and then we can think of Ent so "Ent", "Int", "INTestinal" so
that's how we can remember this type of genus of amoeba now it's a estimated
that about 50 million individuals are infected worldwide annually with this
type of infection and there are actually four different types of amoeba species
that can cause intestinal neaby aces these include entamoeba histolytica
entamoeba dispar and entamoeba moshkovskii and entamoeba Bangladeshi and again
we're gonna specifically talk about entamoeba histolytica because this is
the most common cause of intestinal amebiasis so how do we get infected
with this amoeba? Well there's a cyst stage of infection that's the infective
stage, and then there's also the trophozoite stage which is the stage of the
amoeba that actually causes the invasive disease so we get an infection from
ingestion of the amoebic cysts so the amoeba during their cyst stage that is
the infective stage we can get this from contaminated water or food we can also
get it from fecal oral route as well so if an individual has an infection with
entamoeba histolytica they will actually release mature cysts in their feces and
then if another individual comes along and actually ingests contaminated food
or water that has been contaminated with these cysts they're going to get
infected themselves so surprisingly cysts can actually survive in the environment
for weeks to months so they're very resilient and there are several stages
of infection so again the cysts are the infective stage they
are what we ingest from the environment and when these cysts pass through the
stomach they will transform into trophozoites in the small
intestine this is what is the cause of the invasive disease so the trophozoites
themselves will invade into the mucosa of large intestine so they pass
through all the in small intestine they make it to the large intestine and then
they start to wreak havoc so they start to cause damage to the tissue causing
increased secretions and eventual bloody diarrhea so they basically burrow into
the mucosa of the large intestine this causes damage to those tissues the
tissues begin to become inflamed and ademma tiss causing increased secretions
and you're gonna get blood as a result of all that damage so what does the
entamoeba histolytica specifically do to cause this pathogenic scenario well
entamoeba histolytica for one they secrete proteinases that destroy protein
so they will secrete these enzymes proteinases that destroy proteins of the
host so they can go in release these proteinases
and can actually destroy proteins in the large intestinal mucosa another thing
they can do is they can destroy intestinal cells through a direct
contact mechanism so they can get against the cells and they can actually
destroy the cells through direct contact they can also form what we call an
amoeba pore which forms pores in lipid bilayers of infected cells this will
basically lyse the cells and to cause them to become injured and destroyed and
another pathogenic mechanism by which entamoeba histolytica can cause tissue
damage is through disrupting tight Junction proteins eventually result in
increased intestinal permeability so with all these mechanisms they can lead
to destruction of intestinal tissue leading to a bloody diarrhea and also
increased secretions increased intestinal permeability so they can do a
lot of damage so what are some of the clinical features of intestinal amebiasis
we already talked about several so some of the other ones
include the following you can actually have an asymptomatic pitcher so if you
have a very good immune system if you're exposed to these amoeba you might not
even have these symptoms if you're able to clear the infection
the other one is amoebic dysentery so we've talked about this in length the de
century again involves abdominal pain and colitis they can get bloody diarrhea
from this and again the bloody diarrhea is due to local tissue damage and
destruction and in addition to amoebic dysentery you may also get amoebic
abscesses and these abscesses will commonly occur in the liver so here's an
image a CT scan of amoebic abscesses within the liver and these are due to
hematologic spread so if you get an infection in your GI system they can
actually spread hematological e to the liver and set up shop there and you're
gonna get hepatomegaly, right upper quadrant pain, weight loss, and fever and
these abscesses can also occur in other sites less commonly than the liver but
you can also get them in the lungs in the brain so this is can be very
significant so again these abscesses are most common in the liver but can also
call occur in the lungs in the brain so these are the three clinical scenarios
with an infection of entamoeba histolytica one you may be completely
asymptomatic if you have a very good immune system you may be that clear this
infection with no issues the second you may have amoebic dysentery so you
might have abdominal pain colitis you may have bloody diarrhea due to that
tissue damage we talked about before and the third you may get these amoebic
abscesses and these abscesses most commonly occur in the liver but can also
occur in the lungs in the brain so how do the clinical features of intestinal
amebiasis well we can think about the species entamoeba histolytica so int
entamoeba you can think of nth for intestinal so that might clue you into
the de century and you can think of histo lytic lytic that component of the
word lytic lytic means destruction so you can think of lytic as destroying
abdominal tissue so that's you can think of that in relation to the bloody
diarrhea or another way to remember these clinical features is the mnemonic
"Ame" ordered BLOOD LABS
so Amy spelled ame so that will
clue you into amoeba ordered blood labs blood this will help you remember bloody
diarrhea and labs L for liver and abs for abscess so you can just think of a maybe
a physician whose name is Amy she's ordering blood labs and that may help
you remember that amoeba or entamoeba histolytica cause bloody diarrhea and L for
liver and abs for abscess so they cause bloody diarrhea and liver
abscess so hopefully that helps you remember some of the clinical features
of Amebiasis so how do we make the diagnosis and how do we treat intestinal
amebiasis so investigations and diagnosis include the following so we
can do serology we can look for antibodies against entamoeba histolytica
we can do antigen testing we can do stool sampling looking for those
trophozoites always we talked about before and we may need to do a biopsy of the
colon because these amoeba can burrow into the intestinal mucosa you might
have to actually take a piece of the colon to actually look at it under
microscope to see these organisms so once you've made the diagnosis how do
you treat it so treatment involves a use of metronidazole so if we got intestinal
maybe aces just the GI symptoms of amoeba amoeba infection we can use
metronidazole to help clear that infection if we have you know more an
invasive picture more systemic illness perhaps cysts perhaps more an invasive
disease we might have to use Iodoquinol or paramycin so again these are for
cysts and for invasive disease so this can be effective treatments for amebiasis
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