The document outlines the classification and characteristics of medically important parasites. It discusses the classification of parasites into helminths (trematodes, cestodes, nematodes) and protozoa. For each type of parasite, it describes morphological features, life cycles, important stages, habitats, and modes of infection. The objectives are to differentiate parasite types based on these characteristics and list examples of medically significant parasites.

1. Dr. Shahira Ahmed

2. Learning Objectives
1. Outline the classification of medically important parasites.
2. List types of medically important helminthes.
3. Differentiate between types of helminthes according to:
– General morphological characters.
– Organs of fixation.
– Habitat.
– General outline of the life cycle.
– Important stages in the life cycle.
4. List types of medically important protozoa.
5. List general characters of protozoa.
6. Differentiate between types of protozoa according to:
– Locomotororgans.
– Habitat.
– General outline of the life cycle and important stages.

3. • What makes parasites different from other
microorganisms?
•Multiple life stages
1.Different immune response.
2.Difficult to formulate vaccine.
3.Difficult to control

4. Outline the classification of
medically important parasites
•Classification of medically important parasites
–Helminthology.
–Protozoology.
–Entomology.

5. List types of medically
important helminthes
• Types of medically important helminthes
–Trematodes
–Cestodes
–Nematodes
•Intestinal nematodes
•Tissue nematodes

6. Differentiate between types of
helminthes
A-Trematodes (Flukes)
1-General morphological characters.
•Hermaphrodite except blood flukes (Unisexual)
•Leaf-like, flattened and bilaterally symmetrical
•There is no body cavity.
2-Organs of fixation:
Almost all have 2 suckers, oral (at the anterior end,
around the mouth) and ventral (on the ventral
surface).
 Heterophyes has its genital pore surrounded by a
muscular ring called genital sucker.

7. A-Trermatodes
3- Habitat:
They have different habitat; intestinal, hepatic, blood and
pulmonary flukes.
4-General outline of the life cycle.
•Adult → egg → miracidium → sporocyst→ redia→ cercaria →
metacercaria→ adult.
•Egg is operculated, and should reach to a water source to
hatch.
•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
metacercaria.

8. A-Trermatodes
5-Important stages in the life cycle.
•The diagnostic stage is the egg.
•The infective stage is the encysted
metacercaria except in Schistosoma, it is
the cercaria.
•The mode of infection is by ingestion of
food contaminated with the infective
stage except in Schistosoma, it is by skin
penetration of the cercaria.

9. B-Cestodes(tapeworms)
1-General morphological characters.
• Hermaphrodite.
• 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).

10. 2-Organs of fixation: 2 types:
•Suckers (4) with or without hooks that are arranged in
one or more circles on the apex of the scolex called
“rostellum”.
•Bothria (2) that take the form of grooves.
3-Habitat:
They all (without exception) are intestinal parasites.
B-Cestodes(tapeworms)

11. 4-General outline of the life cycle.
•Adult → egg → cysticercus (the larval stage) → adult,
Except for D. latum, give oval operculated egg
containing hexacanthembryo (coracidium).
•All cestodes require one intermediate host (usually
vertebrate), except
D. latum requires two intermediate hosts.
H. nana does not require an intermediate host.
B-Cestodes(tapeworms)

12. 5-Important stages in the life cycle.
•The diagnostic stage is the egg.
•The infective stage is the last larval stage which is
different according to:
No intermediate host (H. nana): Egg.
1 intermediate host (Other cestodes): Cysticercus
2 intermediate hosts (D. latum): Pleurocercoid.
•The mode of infection is by ingestion of food
contaminated with the infective stage.
B-Cestodes(tapeworms)

13. C-Nematodes (cylindrical worms)
1-General morphological characters.
 Bilateral symmetrical
 Has body cavity
 Separate sexes
 Elongate and cylindrical
2-Organs of fixation
are present in the mouth and buccal cavity as lancets and teeth.
3-Habitat: Intestinal (small and large) and
tissue nematodes.
4-General outline of the life cycle.
•Adult → egg → larva → adult.
•Tissue nematodes are viviparous (lay larvae). Larva molts its
cuticle 3 times.

14. C-Nematodes (cylindrical worms)
Intestinal
nematodes
Tissue
nematodes
Larva 2 rhabditiform
and filariform.
Larva called
Microfilaria
Intermediate host No intermediate
host
Essential to
complete life cycle
Egg Immature except
Entrobious
vermecularis
No egg

15. C-Nematodes (cylindrical worms)
Intestinal
nematodes
Tissue nematodes
Diagnostic stage Egg or Larva Microfilaria
Infective stage Egg containing larva
or filariform larva
Infective
microfilaria
Mode of infection Ingestion of food
contaminated with
the infective stage or
skin penetration
Ingestion or bite of
the infective vector
5-Important stages in the life cycle.

16. Types of medically important
protozoa
Pseudopodia.
Flagellates.
Ciliates.
Coccidia.

17. 1- General characters of protozoa
•Body is formed of cytoplasm and nucleus.
•Cytoplasm is differentiated into ectoplasm
and endoplasm.
•Nucleus contains karyosome and peripheral chromatin.

18. 1- Pseudopodia
 Locomotororgans: Pseudopodia.
 Habitat: Intestinal and free living.
 General outline of the life cycle and important stages:
Trophozoite and cyst.
2- Ciliates
 Locomotororgans: Cilia.
 Habitat: Intestinal.
 General outline of the life cycle and important stages:
Trophozoite and cyst.

19. 3- Flagellates
 General morphological characters: Flagella as Locomotororgans.
 Habitat:Intestinal, urogenitaland, blood.
 General outline of the life cycle and important
 stages:
•Intestinal and urogenitalflagellates: Trophozoite
and cyst.
•Blood flagellates:
•Leishmania: Amastigotes (in human) and promastigotes
(Vector).
• Trypanosoma:Trypomastigotes (human) and
Epimastigotes (Vector).

20. 4-Coccidia
 Locomotororgans:They are sporulated.
 They are members of Apicomplexa.
 Habitat: Intestinal, tissue and blood.
 General outline of the life cycle: Gametogony
(Sexual reproduction).
 Important stages in the life cycle:
Sporozoite, Schizont, merozoite, gametocytes, oocyst.

21. Thank you