Medical Parasitology PDF

MEDICAL
PARASITOLOGY
Samar N. El-Beshbishi
Professor of Medical Parasitology
Mansoura Faculty of Medicine
Introduction
Objectives
1.Types of parasites.
2.Types of hosts.
3. Host- parasite relationship.
4. Pathogenesis of parasitic diseases.
5. Zoonosis.
6. Classification of Medical Parasitology.
7. General characters of parasites.
Definitions
Medical Parasitology: is the study of parasites
of man and their medical consequences.
Parasites: are organisms which live on or

within its host (infestation & infection) , for
nourishment and physical protection.
Host: is an organism harbouring a parasite.

Types of parasites
1. Ectoparasite: lives on the surface or within
the superficial tissue of the host (e.g.
Pediculus, mites).
2. Endoparasite: lives within the host, (e.g.
Hookworms).
3. Temporary or intermittent parasite: visits

the host from time to time for food (e.g. soft
ticks).
4. Permanent or obligate parasite: depends
completely upon its host for its entire life (e.g.
Plasmodium, Enterobius).
5. Accidental parasites: free living organisms

which enter the human body by mistake (e.g.
larvae of house flies).
6. Facultative parasite: can exist in a free living or
parasitic state under unfavorable environmental
conditions (e.g. Strongyloides).
7. Specific parasite: affects only one species of
host (e.g. Enterobius).
8. Coprozoic or spurious parasites: foreign

parasites or stages of non human parasites
which have been swallowed and pass to feces
without causing infection (e.g. Fasciola).
Types of hosts
1. Definitive host (D.H.): harbors the adult stage
or sexually mature forms of the parasite e.g. man
for Taenia saginata.
2. Intermediate host (I.H.): harbors the larval
stages or asexually mature forms of the parasite
e.g. man for Plasmodium.
3. Reservoir host (R.H.): carries the adult stage
of parasite, and acts as a continuous source for
human infection e.g. cats for Heterophyes.
4. Amplifier host: is an I.H. in which asexual
multiplication takes place (e.g. snail ist I.H.).
5. Paratenic host (transport host): in which the
parasite doesn't undergo any multiplication or
developmental changes (e.g. fish 2nd I.H.).
6. Vector: is an arthropod which transmits the

parasites from one host to another (e.g. fleas
transmit Pasteurella from rodents to man).
Host-parasite relationship
Symbiosis: more or less permanent association
of two organisms of different species.
This relationship occurs in 4 forms:
a. Parasitism: one of the two organisms benefits,
on the expense of the other, that suffers from
such association (Schistosoma).
b. Commensalism: the parasite benefits without
harming the host (non-pathogenic ameoba).
c. Mutualism: the relationship is beneficial to
both associates (flagellates in the intestine of
ants that feed on wood).
d. Phoresis: in which the phoront is usually the
smaller organism and is mechanically
transmitted by the other which is usually large
(e.g. Dientameoba fragils on Entrobius egg).
Pathogenesis of parasitic infection
a)Pathogenic parasite: causes definite
pathological lesions (Ancylostoma).
b)Non-pathogenic (commensal) parasite:
derives food and protection from host without
causing pathological lesions (Entamoeba coli).
c) Opportunistic parasite: causes mild disease in
immunologically healthy individuals, and
severe pathological lesions in immuno-
deficient hosts (Cryptosporidium).
Zoonosis
Diseases and infections in which the causative
agents are transmitted from animals to man.
Anthroponosis: parasitic infection is found in
man alone as in trichomoniasis and entrobiasis.
Zooanthroponosis: parasitic infections mainly
affect man and animals become infected in life
cycle of parasite as in taeniasis.
Anthropozoonosis: parasitic infection is mainly
in animal and may be acquired by man as in
trichinosis.
Classification of zoonotic diseases:
1) According to the source of infection:
A-Feral or sylvatic zoonosis: source of infection
is a wild animal. Humans become infected
when population move to infected area or
become exposed during hunting as in
African trypanosomiasis.
B-Domestic zoonosis: these parasites
transmitted from man own domestic
animals as in hydatidosis.
2) According to the method of transmission:
A-Direct zoonosis: infection is directly
transmitted from the vertebrate R.H. to man
as in trichinosis.
B-Saprozoonosis: infection is transmitted via a
non developmental site as soil and water as
in visceral larva migrans (VLM) and Fasciola.
C-Metazoonosis: infection is transmitted from
the animal R.H. to man via an arthropod as in
leishmaniasis and trypanosomiasis.
Classification of Medical Parasitology
I. Helminthology (helminths):
1- Platyhelminths (flat worms)
- Class: Trematoda (Flat Worms or Flukes).
- Class: Cestoda (Tape worms).
2- Nemathelminths (round worms)
- Class: Nematoda (Round worms).
II. Protozology (protozoa).
III. Arthropods.
General characters of parasites
1. Trematodes: Un-segmented, leaf-shaped, and

hermaphrodite (except schistosomes), e.g.
Fasciola.
2. Cestodes: Long, segmented, tape-like and
hermaphrodite, e.g. Taenia saginata.
3. Nematodes: Elongated, cylindrical with
pointed ends and unisexual, e.g. Ascaris.
4. Protozoa: Unicellular microscopic parasites,
e.g. Giardia intestinalis..
Trematode Cestode Nematode
Protozoa Insect
Medical Helminthology
Platyhelminthes (flat worms)
Class : Trematoda (Flukes)
General characters:
1) Adults are leaf like, pear shaped or elongated
worms, flattened dorsoventrally.
2) Bilaterally symmetrical except schistosomes.
3) Size: varies, some are large fleshy (Fasciola)
others are just visible by naked eye
(Heterophyes).
4) Covered with protective cuticle that may be
smooth, spiny or tuberculated.
5) No body cavity, all organs are embedded in
loose connective tissue cells.
6) Suckers: for attachment, usually 2 in
number, in some there are 3
(Heterophyes heterophyes).
7) Digestive system:
- Starts by the mouth opening, found at the
bottom of the oral sucker.
- The mouth leads to a pharynx, then a short
oesophagus which bifurcates into two long
intestinal caeca.
- Caeca end blindly with no anus.
Digestive system
8) Excretory system
- Starts by a definite number of excretory cells
called (flame cells).
- Waste products pass from the cell excretory
tubules excretory duct excretory bladder
exceretory pore at the posterior end of the
fluke.
Flame cell
9) Nervous system: consists of a ring of nerve
ganglion around the pharynx, from which
nerve fibers arise.
10) Respiration and nutrition:
-Adult flukes are anaerobic.
-They feed on biliary secretion, intestinal
contents, tissue juices or blood according to
their habitat.
11) Genital (reproductive system):
-Nearly all trematodes are hermaphroditic with
exception (schistosomes).
The male reproductive organs consist of two
or more testes.
The female genital organs consist of a single
ovary situated in front of the two testes.
Genital system
ootype
Life cycle of trematodes:
- Eggs of trematodes should reach water in
order to develop.
- Alternation of generations in the life cycle of
trematodes:
Asexual cycle in the soft tissues of snail I.H.,
begins by miracidium and ends by cercaria
stage, passing through sporocyst and redia
stages (except for Schistosoma).
Sexual stage in tissue of D.H.
Trematode parasites (flukes) include:
Hepatic or liver flukes:
- Fasciola gigantica - Fasciola hepatica
- Opisthorchis viverrini
Intestinal flukes:
- Heterophyes heterophyes
Lung flukes:
-Paragonimus westermani
Blood flukes:
-Schistosoma haematobium, mansoni, japonicum and
intercalatum.
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MEDICAL

Parasites: are organisms which live on or

Host: is an organism harbouring a parasite.

3. Temporary or intermittent parasite: visits

5. Accidental parasites: free living organisms

8. Coprozoic or spurious parasites: foreign

6. Vector: is an arthropod which transmits the

1. Trematodes: Un-segmented, leaf-shaped, and

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