Parasites: Protozoa (classification, structure, life cycle)

Assalam Alaikom everyone welcome again! In this video we’ll talk about important basics of parasites including its different
classifications and their life cycle. So what is a parasite? A parasite is
basically an organism that derives all its benefits from another organism while
harming that organism in the process. Therefore, there are different
classifications for the parasitic association with the host. It can be
either an obligate parasite: which can only survive in a host, a
facultative parasite: which can survive with or without the host. And then they
can be either an endo-parasite which is a parasite that only lives inside the
organism or an ecto-parasite which is a parasite that lives on the body surface on
the outside. Endo means inside and ecto means outside.
tThe parasites can be divided into two major groups: the protozoa and the
helminths. Is in this video we’ll just talk about the protozoa and hopefully in the
future we’ll make a video on helminths. (Just to mention the helminths are simply
worms.) So first of all we’re going to discuss the structure of the protozoa.
The protozoa are single-cell eukaryotes, and they don’t have cell
walls. They can also form double membranes or cysts to become more
resistant. During the life cycle of each parasite
it goes through two medically important stages: the first one is the infective
stage, and the second one is the diagnostic stage. The infective stage is
when the parasite invades the host and causes the infection, and the diagnostic
stage is when we as doctors can realize that the patient is infected with that
parasite. There are several ways in which we can
classify protozoa: either to their site of infection, or to their type of
movement. The major classification of protozoa is according to their type of
movement; thus, we divide them into four major categories: the first one is
amoebas, and they’re parasites moving with pseudopods or cytoplasmic
projections (pseudo means lying’s or pseudopods fake legs, let’s say). And then
we have flagellates, and there are parasites with two or more flagella. And
then we have the ciliates which are parasites with cilia. And then we have
the sporozoa, which are non motile and therefore they are obligate
intracellular parasites because they can’t move. Now we’re going to discuss
the important medical protozoa of each type. The first one belongs to the
amoebas and it’s called entamoeba and it’s mainly transmitted via the feco-oral route (feco means feces and oral means through the mouth).
So basically you ingest either contaminated water or contaminated food.
The entamoeba has different species that affect humans, however; we’re concerned
with the entamoeba histolytica due to its pathogenic characteristics. It’s
very important to be able to differentiate it from the other species
such as: entamoeba coli, because it’s non-pathogenic, so it doesn’t affect us
negatively. Basically e.coli and e. histolytica can be differentiated according
to the number of the nuclei in the cysts so if it’s more than four nuclei then
it’s considered as a coli and if it’s less than four then it’s considered as
E. histolytica. Next we’re going to move on to the
flagellates, and in the flagellates we have three major types: Giardia lamblia
trichomonas vaginalis, and Leishmania Giardia lamblia life cycle starts with an
infection via the fecal-oral route, which is like I mentioned before through the
ingestion of contaminated food or water. Then they released the trophozoite which
is binucleated, so two nuclei, in the small intestine, and then they multiplied
by binary fission. After that the trophozoite moves to the colon where
the cyst formation occurs. Therefore Giardia lamblia has two life
cycle stages: the trophozoite and the cysts.
On the other hand trichomonas vaginalis is transmitted via sexual contact and replicates its trophozoite without forming any cysts. they usually
resides in the female genital tract and the male urethra and prostate. Thirdly we
have Leishmanias. Leishmanias are usually transmitted via sand flies, and
it resides in animals such as rodents or dogs. So the vector of transmission are
the sand flies and the reservoir of the parasite are the rodents and dogs. The
infected sand fly has the promastigote form of the Leishmania: which is
flagellated, and then it infects the host through the blood and it grows in the
macrophages in the form of amastigote, which means it doesn’t have a flagellum,
This is the diagnostic stage of Leishmania. There are several disease
manifestations accompanying the infection with Leishmania, such as:
cutaneous ulcers and kala azar. Kala azar is simply a severe form of that
infection, and this symptoms usually are enlargement of the liver and the spleen,
so it’s pretty life-threatening! Lastly is an important type of sporozoa
which is Plasmodium. plasmodia are the main causative agents for malaria, which
is a really serious disease. The life cycle starts with the female mosquito where sexual reproduction takes place between the male and female gametocytes. After
that the mosquito bites and injects the sporozoites into the host. these sporozoites migrate to the liver and this is referred to as the exo-erythrocytic
cycle because the sporozoites hasn’t invaded the red blood cells yet. Then
the sporozoites mature into schizonts inside the liver.
After that the schizonts rupture and release merozoites into the blood to
invade the red blood cells. At this stage it’s known as the erythrocytic cycle, because it’s in the red blood cells. Now after that the merozoites have
two pathways to follow: some of the merozoites will grow into schizonts again and
then they rupture and then they release more merozoites more invasion of red
blood cells, and then the cycle repeats. However some of the merozoites will
develop into the sexual forms of male and female gametocytes, which will then
be taken by the mosquito and then sexual reproduction takes place, and the cycle
repeats. So for entamoba histolytica the infective
stage is the cyst and the diagnostic stage is the cyst and trophozoite. For
Giardia lamblia the infective stage is the cyst and the diagnostic stage is also
cysts and trophozoite. For trichomonas, however; remember we didn’t have a cyst
so the infective stage and the diagnostic stage is the trophozoite. Then we have Plasmodium and the infective stage is the sporozoites, when it’s on the
female mosquito, and the diagnostic stage is when it’s during the erythrocytic cycle
inside the red blood cells. Lastly we have theLeishmania, the infective stage is
the promastigote when it has the flagella, and then the diagnostic stage
is the amastigote when it loses the flagella and it’s inside the macrophage.
And we’re pretty much done with the parasites. Hope you enjoyed! Please give
us your feedback so we can improve in the next videos and don’t forget to Like
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86 thoughts on “Parasites: Protozoa (classification, structure, life cycle)

  1. very nice, I'm trying to learn more about these parasites seeing as I'm currently infected with Giardia….yuck

  2. Hey, I'm from Brazil and I loved the video. Amazing animation and content.Thank you very much, it was really helpful.

  3. Machaa Allah , a really helpful video ,
     so glad to see these "beautiful" names in such professional work , God bless you all 🙂

  4. Salam ailikoum I like yr explanation is so helpful please i did not find video about helminths I want it thank you

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