S h a r a f a t A l i
Parasite and it's Classifications
1. What is parasites.
2. What is helminthes and classes of helminthes.
3. What is platyhelminthes:
– General morphological characters.
– General outline of the life cycle.
– On the basis of dependency.
A parasite is an organism that lives on or in a
host and gets its food from or at the expense of
There are three main classes of parasites that
can cause disease in humans:
Helminths are large, multicellular
organisms that are generally visible to the
naked eye in their adult stages.
Flatworms are unsegmented, bilaterally
symmetrical worms that lack a coelom
(acoelomate) but that do have three germ layers.
Flatworms have a cephalized nervous system
that consists of head ganglion.
Excretion and osmoregulation of flatworms is
controlled by "flame cells" located in
Has body cavity
Elongate and Cylindrical
Intestinal (Small and large
intestine and non-
Adult → egg →
larva → adult.
are viviparous (lay
larvae). Larva molts
its cuticle 3 times.
General morphological characters.
Ribbon-like flattened and bilaterally symmetrical.
There is neither body cavity nor digestive tract.
The body is formed of 3 parts:
Head (Scolex) which is provided by organs of attachment.
Neck is composed of actively dividing cells (stem cells) and it
is responsible for giving rise to new segments.
Body is composed of several segments (Immature, Mature
and Gravid segments).
Adult → egg → cysticercus
(the larval stage) → adult,
Except for D. latum, give
oval operculated egg
All cestodes require one
intermediate host (usually
D. latum requires two
H. nana does not require an
•Leaf-like, flattened and
•There is no body cavity.
Adult → egg → miracidium → sporocyst→ redia→ cercaria →
Egg is operculated, and should reach to a water source to
The first intermediate host is snail, and the second (if present)
is marine creature.
Except for Schistosoma, egg has a spine, no redia and no
On the basis of Dependency
1) Obligate parasites- These parasites can only
survive in a host and therefore go directly from
one host to another. This may involve complex
2) Temporary parasites- These parasites spend
only part of their lives as a parasite and another
part as free-living organism.
e.g. Fasciola hepatica (Liver fluke)
3) Facultative Parasite- These parasites which
can live in host if it is available, but capable of
living independently if it’s host is not available,
are known as facultative parasite.
Fungi such as Candida
(vaginal candidosis, athlete foot)
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