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
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