Arish University
Faculty of Medicine
Parasitology department
Parasitology Introduction & Classification
By
Dr. Wafaa Mohammed Zaki
Assistant Professor
Medical parasitology department
Faculty of Medicine
Suez Canal University
Objectives
CLASSIFICATION OF MEDICALLY IMPORTANT
PARASITES.
GENERAL CHARACTERS OF MEDICALLY
IMPORTANT PARASITES.
LIST THE COMMON TECHNIQUES USED FOR THE
DETECTION OF PARASITES IN FECAL AND
BLOOD SPECIMENS.
THE BASIC STRATEGY FOR PREVENTION AND
CONTROL OF PARASITIC INFECTIONS.
Classification of parasites
Helmint Protozoa Arthropo
hs ds
Trematode Amoebas Insecta
s
Flagellates Arachnida
Cestodes
Ciliates Crustacea
Nematodes
Sporozoa
Filariae
Microspor
ea
General characters of helminths
A-Trematodes (Flukes)
1-General morphological characters.
•Hermaphrodite except blood flukes
•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.
3- Habitat:
They have different habitat; intestinal, hepatic, blood
and pulmonary flukes.
4-General outline of the life cycle:
•Adult → egg → miracidium → sporocyst→ 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.
5-Important stages in the life cycle.
• Thediagnostic 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.
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).
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 are intestinal parasites In man.
Only E. granulosus and cysticercus of Taenia solium can
present in tissue
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.
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.
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.
Intestinal Tissue
nematodes nematodes
Larva 2 rhabditiform Larva called
and filariform. Microfilaria
Intermediate host No intermediate Essential to
host complete life cycle
Egg Immature except No egg
Entrobious
vermecularis
5-Important stages in the life cycle.
Intestinal Tissue
nematodes nematodes
Diagnostic stage Egg or Larva Microfilaria
Infective stage Egg containing Infective
larva or filariform microfilaria
larva
Mode of infection Ingestion of food Ingestion or bite of
contaminated with the infective vector
the infective stage
or skin penetration
Enterobius
vermicularis
egg
Anchylostoma doudenale
egg
Ascaris lumbircoides
egg
Tricuris tricura egg
