Biology: Parasitology

University of Duhok
College of Health Sciences
Dep. of Medical Laboratories & Anesthesia
Biology/1st Stage
Lecture 10
Dr.: Shameeran S. Ismael
BVM & S, M.Sc Medical Microbiology(Parasitology),
PhD Molecular Parasitology
Shameeran S. Ismael/ Biology theory.
health Sciences, 2021

Introduction and Classification
of Parasitology
Shameeran S. Ismael/ Biology theory. health Sciences, 2021

• Parasite:- Any living
organisms (Multicellular or
unicellular organisms) that
lives on or inside another
organism and causing a
diseases.
Shameeran S. Ismael/ Biology theory. health Sciences, 2021
Introduction
Parasitology:- Is the study of parasites, their hosts, and
the relationship between them

Types of Parasites

:
1. Ectoparasites Parasites: Parasites
that live on the surface of host (e.g.
lice, mite)
2. Endoparasites Parasites: Parasites
that live inside the body of the host,
in the blood, tissues, body cavities,
digestive tract and other organs. (e.g.
Giardia lamblia, Ascaris lumbricoides
etc.) Shameeran S. Ismael/ Biology theory.
I.Parasite is divided according to
location into:

This can be further subdivided, based on their
life cycles:
Temporary parasite: Visits its host for a short
period.
Permanent parasite: leads a parasitic life
throughout the whole period of its life.
II. Types of parasites

Facultative parasites: parasites able to live both
free living and parasite living e.g.
Strongyloides species
Obligatory parasite: If an organism is
completely dependent on the host during a part
or all of its life (Toxoplasma gondii)

Occasional or Accidental Parasite: Attacks an
unusual host.
Wandering or Aberrant parasite: Happens to
reach a place where it cannot live.
Free living: The term free living describes the
non parasitic stages of existence

Host and its types
Host: it is an organism that harbors a parasite it supplies
the parasite with nourishment and shelter, it is the injured
partner.
Definitive (final) host: harbors adult or sexually
reproductive stage of a parasite.
Intermediate host: harbors larval or asexually
reproductive stage of a parasite.
. Shameeran S. Ismael/ Biology theory.

Reservoir host(carrier): It is a host which harbor
the parasite and serves as an important source
of infection to other susceptible hosts.
Epidemiologically, reservoir hosts are important
in the control of parasitic disease.
Paratenic Host: ( A carrier and transport host)-A
host where the parasite remains viable without
further development

General parasitological Terms
• Vector: A carrier, especially the animal that
transfers an infectious agent from one host to
another, usually an arthropods, also the vectors
can be divided into two different types:
1. Biological vectors: vectors may carry
pathogens that can multiply within their
bodies and be delivered to new hosts usually
by biting, such as ticks and mosquitoes.

2. Mechanical vectors: vectors can pick up
infectious agents on the outside of their bodies
and transmit them through physical contact,
e.g house fly for transport of amoebal cysts

• Disease: a condition characterized by presence
of clinical signs and symptoms.
• Carrier: a host carrying a parasite but not
showing any clinical signs or symptoms.
• Etiology: the cause of a disease.

Pathogenic: can cause disease in host.
Non pathogenic: does not cause disease in host
(commensal organism).A non-pathogen can infect
man but it causes no harm. It inhabits your body and
multiplies.
Pathogenesis: the processes involved in the
development of the disease (immunological,
biochemical, genetic, and morphological events).
Epidemiology: a field of science dealing with the
relationships of various factors which determine the
frequency, distribution and transmission of infection

Infection: multiplication of organisms inhabiting the body.
Infective Stage: Is a stage when a parasite can invade human
body and live in it .
Diagnostic Stage:- A developmental stage of a pathogenic
organism that can be detected in stool, blood, urine,
sputum, CSF or other human body secretions.
Zoonosis: Refers to animal’s diseases which can be
transmitted to man.

Infective Route: is the specific entrance through which
the parasite invades the human body.
Route of infection: It is means how the parasite invades
host body. Mechanisms of infection a parasitic
infection may occur by various routes, depending on
the nature of both parasite and host:
1. Feco-oral transmission(Entamoeba histolytica,
Giardia lamblia)
2. Actively penetrate the skin by infective larvae
(Schistosoma Spp.)

3.Sexual transmission (Trichomonais vaginalis)
4. Transmission by vector (Malaria)
5. Congenital-Infection with T.gondii and Plasmodium
spp. May be transmitted from mother to fetus
transplacentally.
6.Iatrogenic infection-Malaria parasites may be
transmitted by transfusion of blood from the donor
with malaria containing asexual forms of
erythrocytic schizogony

Life cycle: Is the process of a parasite’s growth,
development and reproduction. There are two
types of life cycle:
1. Direct life cycle (not required intermediate host).
2. Indirect life cycle (required intermediate host).
Life cycle and its types:

Classification of parasites:
• There are three Phylum of parasites that are
of Major Medical Importance:-
I.Protozoa
II.Helminths
III.Arthropdes

Classification of parasites:
• General classification: animal parasites are
classified according to international code taxonomy –
Each parasite belong to a:
• Kingdom
Phylum
Class
Order
Family
Genus
Species
• Some have further divisions to:
Sub – order, super family, sub – species

• Each parasite have two names i.e. Genus and
species.
• The former begins with an initial capital and the
latter with an initial small letter
• The Genus and species names are in italic, If
italics are not used, each name must be underlined
separately
Entamoeba histolytica
Genus Specie
s
How to write the scientific name of
the parasite?

• Symbiosis - “living together,” a close association
between two organisms, there are four kinds of
symbiosis:
1.Mutualism - both organisms are benefited
(bacteria in bowel).
Parasites, their hosts, and the relationship
between them”

2.Commensalism - “eating at the same table;” One
organism is benefited, and the other is unaffected.
3.Parasitism - A form of symbiosis in which one
organism (called parasite) benefits at the expense of
another organism usually of different species(called
host).

4.Phoresis (Phoresy):The term phoresis means “to
carry” . It is a type of symbiotic relationship in
which one organism (the smaller phoront) is
mechanically carried on or in another species (host)
In this relationship, there is no physiological or
biochemical dependence on the part of the host or
symbiont.

I. Protozoa

Introduction & classification of
Protozoa
• Protozoa are unicellular organisms, under
the kingdom Protista and sub kingdom:
protozoa
• The basic structure of the protozoan body is
the protoplasm.
• Protoplasm is differentiated into the
cytoplasm & nucleus.

I.Cytoplasm: is divided into two parts:
1. Ectoplasm: Transparent external portion of the
cytoplasm. It function locomotion & sensation.
2. Endoplasm :The inner granular portion of the cell. It
contains food vacuoles (which help in digestion of food).
Contain various granules such as glycogen, fat, proteins,
bacteria & pigments etc. Its function are nutrition,
excretion & reproduction.

II.Nucleus
• Consists of a network of fine reticulum enclosed
by a nuclear membrane. Inside the network are
chromatin.
• A mass of concentrated chromatin is called
karyosome
• No. of nucleus may be one or more
• Type of nucleus, may be vesicular with central
karyosome or granular with chromatin grains
• Shameeran S. Ismael/ Biology theory.

• Nutrition: occurs by osmosis (holophytic) or by
ingestion (holozoic).
• Respiration : By osmosis
• Excretion: Excretion of waste products occurs by
contractile vacuoles or by osmosis

Locomotion organelles
• Protozoa move by basic types of organelles:
1- Flagella
2- Cilia
3-Pseudopodia
4- Undulating ridgs

Organs of Locomotion

1.Class: Nematoda
Common Name: Round worm
II. Helminth

General Features OF Nematodes
• Elongated, cylindrical, smooth, unsegmented, flesh-
colored bodies.
• Sex: is separated; the female is usually larger than the
male
• Body is usually tapered to a pointed posterior end, and
to a rounded anterior end.
• The body is covered by cuticle

Female
Male

•Cuticle is secreted by underlying hypodermis, which project
into the body cavity forming two lateral cord carry the
excretory canals, and a dorsal and ventral cord carrying the
nerves.
Cuticle may be modified to form various structures:
1- Leaf crowns consisting of rows of papillae occurring
as fingers round the rim of the buccal capsule
(internal and external leaf crwon)
2- Cephalic vesicle
3- Cervical vesicle

4-Cervical ala
5- Cervical papillae
6. Cervical notch
7- Copulatory bursa in some species of male of nematodes,
which embrase the female during copulation. Which is
supported by bursal rays

• The muscle cells, arranged longitudinally lie between
hypoderms and the body cavity.
• Locomotion is effected by undulating wave of muscle
contraction and relaxation.
• They absorb oxygen through their skin in a process
known as diffusion.
Cross section of adult nematodes

• They have complete digestive system with mouth,
oesophagus, midgut and end with anus in female,
while in cloaca in male, because the cloaca is the
common opening for both digestive sys. and genital
system.
• Intestine is a tube (enclosed by a single layer of cells)
The type of mouth:
1.The mouth of many nematodes is a simple opening
which may surrounded by two or three lips and leads
directly into the oesophagus.
2- Large and open into a buccal capsule, which may be
contain teeth or cutting plate.

• The nematodes have direct life cycle, Nematodes have
a relatively simple basic life cycle consisting of an egg
stage, four larval or juvenile stages, and an adult stage
• Stages: egg, L1, L2,L3,L4,L5 (adult)
• Female may be oviparous, viviparous or
ovoviviparous

Infections is transmitted by:
1) Ingestion of eggs (Ascaris lumbricoides )
2) Penetration of larvae (L3) through surfaces
(Hookworm)
3) Insect bite (Filaria)
4) Ingestion of encysted larvae (Trichnella spiralis)

2. Class Trematoda

Introduction to Trematoda
• Flattened dorsoventrally, leaf like un-segmented
worms
• Body cavity is absent
• Hermophrodites, except Shistosoma species
(sexes are separated)
• Most flukes have two suckers for attaching to the
host, one close to the mouth (dorsal sucker) and on
the ventral side (ventral sucker).

• Digestive system is simple, the
oral opening leading to a
pharynx, oesophagus & pair of
branched intestinal caeca
which end blindly.
• Excretory system includes:
flame cells, capillaries,
collecting tubules and an
excretory bladder

• The body is covered with tegument, which may
partially or completely covered with spines, tubercles
or smooth
• All member are oviparous.
• Infective stage is usually a encysted metacercria,
except for Schistosoma species is cercaria
• Have indirect life cycle
• Intermediate host is snail

Trematode stages:
• Egg
• Miracidium
• Sporocyst (mother and daughter)
• Redia (redia1 and redia2)
• Cercaria
• Metacercaria and
• Adult

Stages of Trematodes

3. Class: Cestoda

General Features of Cestodes
 Segmented tape-like worms & hermaphrodite
 Each segment containing one & some time two set of male
& female reproductive
•Flattened dorso-ventrally with out body cavity
• Covered with a protective cuticle
• Each cestode consist of three basic structure: scolex, neck &
strobila

 No mouth or gut. (food absorption is through the cuticle)
 Scolex, is the organ of attachment, has either suckers or
bothria (groove)

• The neck region is responsible for the formation of new
segments
 Strobila (chain of segment). it represents the trunk or body
of adult worm. It composed of various No. of segments:
Echinococcus granulosus (have only 3-4 segments)
D. latum (posses 4000 segments)

There are three types of proglottids:
1. Immature segment (male & female organs
are undifferentiated)
2. Mature segment (male & female organs are
identifiable)
3. Gravid segment, gravid uteri filled with
eggs

Body wall is composed of 3 layers:
1. An outer layer (elastic layer)
2. A middle layer which consist of a circular
muscle layer & longitudinal muscle layer
3. Inner layer, which consist of radially
arranged tegumental cells

Reproductive sys.:
• Have double set or single set of reproductive
organs. Thus the genital pore may be located
bilaterally or unilaterally

There are 2 subclasses:
Cyclophyllidae
Pseudophyllidae

I. In members of cyclophyllidae:
•Organ of fixation are sucker
•Eggs, have two layers & contain a mature embryo,
with contains of 6 hooklets & a hexacanth embryo

II.In members of Pseudophyllidae:
•Organs of fixation are grooves (bothria)
•Eggs are operculated & unembryonated
Diphyllobothrium latum

 The life cycle is indirect
 All tapeworms require one or more intermediate
hosts (except H.nana)
• The larval stage( metacestodes or larval stage of
cestode) of Cyclophyllidea: (Cysticercus, Coenurus,
strobilocercus, Hydatid cyst, Cysticercoid)
• The larval stage of Pseudophyllidea (procercoid,
plerocercoid)

• Trauma - damage to tissues, intestine, liver, eye.
• Lytic action - activity of enzymes scereted by organism.
• Tissue response - localized inflammation, eosinophilia.
• Blood loss - heavy infection with hookworm may cause
anemia.
• Secondary infections: weakened host susceptible to
bacterial infection, etc.
Parasitic Damage to Host:

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