The document provides an overview of parasitology, focusing on the study of parasites, their hosts, and the relationships between them. It categorizes parasites based on biological nature, location in the human body, and pathogenicity, while also discussing types of hosts and sources of exposure to parasitic infections. The significance of parasitology is particularly emphasized for developing countries, highlighting the need for improved living conditions to mitigate parasitic diseases.

1. INTRODUCTION TO
PARASITOLOGY
MR. ELUZAI LOU
MSc.HSM [UMU]
MHSI
14th
SEPT.2015

2. Learning objectives
At the end of this session, students are
expected to be able to:
1.Describe the concepts of Parasitology
2.Describe the concept of parasitism
3.Classify parasites of medical importance
4.Describe types of hosts and vectors
5.Explain the sources of exposure to parasitic
infections

3. Concepts of Parasitology
• Parasitology is a science that deals with an organism that lives
in or on another organism in order to have shelter and or
nutrition.
• Is the study of parasites, their hosts, and the relationship
between them.
• It is a science which deals with organisms that take up their
residence, temporarily or permanently, in or on other
organisms for the purpose of procuring nourishment. The host
may also provide shelter and protection.
• Medical Parasitology study parasites that is capable of
causing disease in humans.

4. Concepts of Parasitology cont..
• A parasite is an organism that lives on or in
a host and gets its food from or at the expense of
its host.
• Parasites can cause disease in humans. Some
parasitic diseases are easily treated and some are
not.
• The burden of these diseases often rests on
communities in the tropics and subtropics, but
parasitic infections also affect people in
developed countries.

5. Concept of Parasitism
• A Parasite: Is an organism that lives in or on
another organism called ‘host’, usually larger
than itself, from which it obtains nourishment
and which may or may not harm the host.
• Usually the host also provides shelter and
protection to the parasite.

6. Concept of Parasitism cont..
• Parasitism: Is any life association in which one
species depends on another species. But usually
refers to an association in which one organism, the
‘host’ is injured, to some degree, by the activities
of the other, the ‘parasite’.
• A host: Is an organism that harbours a parasite.
• Infestation: Is the invasion of the epithelial
surfaces of the outer body surfaces and body
cavities by the parasite.
• Infection: Is the invasion of the body tissues and
organs by the parasite.

7. Types of Parasitism
Symbiosis:
The word symbiosis is derived from the greek word ‘symbioum’ meaning
‘living together’
Symbiosis is the relationship in which the two associates cannot exist
independently
They provide protection, nutrition or other advantages to one another
Example normal flora in the GIT produces Vitamin K and Vitamin B-complex,
while the host provides shelter
Mutualism:
The word is derived from the Latin word ‘mutuus’ meaning ‘exchanged’
Is the relationship in which both associates benefit from each other.
Commensalism: Commensalism is the relationship where the parasite derives
benefit without reciprocation but also without injury to the host, e.g.
Entamoeba coli in the intestine and Entamoeba gingivalis in the buccal
cavity.

8. Importance of Parasitology
• The study of Parasitology has more
importance to developing countries where the
social and economic conditions require great
deal of improvement in terms of better
clothing, shelter, food, provisions of wells and
latrines and sewages and other waste disposal
facilities together with the means of
controlling vectors.

9. Classification of Parasites
Parasites of medical importance can
be classified according to three
criteria
a)Biological nature (taxonomic)
b)Location in human body
c)Pathogenicity

10. Classification according to
biological nature
1. Protozoa
2. Helminths
3. Arthropods

11. Protozoa
• Protozoa are microscopic, one-celled
organisms that can be free-living or parasitic
in nature. They are able to multiply in
humans, which contributes to their survival
and also permits serious infections to develop
from just a single organism.

12. Protozoa cont..
The protozoa that are infectious to humans can be classified
into four groups based on their mode of movement:
• Sarcodina – the ameba, e.g., Entamoeba histolytica
• Mastigophora – the flagellates, e.g., Giardia, Leishmania
• Ciliophora – the ciliates, e.g., Balantidium
• Sporozoa – organisms whose adult stage is not motile
e.g., Plasmodium

13. Helminths
• Helminths are large, multicellular organisms
that are generally visible to the naked eye in
their adult stages. Like protozoa, helminths
can be either free-living or parasitic in nature.
In their adult form, helminths cannot multiply
in humans.

14. Helminths cont..
There are three main groups of helminths
(a) Trematodes (flukes)
(b) Cestodes (tapeworms)
(c) Nematodes (roundworms)

15. Arthropods
• Arthropods (ectoparasites)are important in causing
diseases in their own right, or transmitters, of many
different pathogens that cause tremendous morbidity
and mortality from the diseases they cause.
• They are blood-sucking organisms such as mosquitoes
(because they are dependent on a blood meal from
a human host for their survival), however the term
arthropod is generally used more narrowly to refer to
organisms such as ticks, fleas, lice, and mites that attach
or burrow into the skin and remain there for relatively
long periods of time (e.g., weeks to months).

16. Classification according to Location in
the body
–Intestinal (gut) parasites e.g.
Hookworms
–Tissue parasites e.g. Filaria
–Blood parasites e.g. Plasmodium
–Genital urinary parasites e.g.
Trichomonas

17. According to their Pathogenicity:
1. Pathogenic parasites:- It causes disease in the
host. E.g., E. histolytica
2. Non-Pathogenic (commensal) parasite:-The
parasite derives food and protection from the
host without causing harm to the host. E.g.
Entamoeba coli
3. Opportunistic parasites:- Parasites which cause
mild disease in immunologically healthy
individuals, but they cause severe disease in
immuno-deficient hosts.E.g. Pneumocystis carnii.

18. Types of Hosts
1. Definitive host:- Depending on the parasitic
species, it is either a host which harbors the
adult stage of a parasite or most highly
developed form of the parasite occurs; or
sexually mature stages of a parasite and
fertilization takes place in it, e.g., man is the
definitive host of Taenia saginata and
trypanosomes

19. Types of Hosts cont..
2. Intermediate host:- Is a host harboring
sexually immature or larval stage of a parasite
and in which no fertilization takes place in it.
E.g. Cow is the intermediate host for Taenia
saginata.
3. Amplifier host:- Intermediate hosts in which
parasites under go multiplication.

20. Types of Hosts cont..
4. Reservoir host:- A wild or domestic animal which
harbors a parasite and acts as sources of
infection to humans.
5. Carrier host:- A host harboring and disseminating
a parasite but exhibiting no clinical sign.
6. Accidental (Incidental) host:- Infection of a host
other than the normal host species. A parasite
may or may not continue full development in this
host.

21. Sources of Exposure to Parasitic Infections
A. Contaminated soil:-
Soils polluted with human excreta is commonly responsible for
exposure to infection with Ascaris lumbricoides, S.stercolaris,
Trichuris trichuria and hook worms.
B. Contaminated water:- Water may contain
(a) Viable cysts of Amoeba, flagellates and T. solium eggs,
(b) Stages of human blood fluke and cyclops containing larva of
Dracunculus medinesis,

22. Sources of Exposure to Parasitic
Infections cont..
C. Insufficiently cooked meat of pork and beef
which contains infective stage of the parasite.
e.g., Taenia species.
D. Blood sucking arthropods:-These are responsible
for transmission of: e.g.,
1. Malaria parasites by female anopheles mosquito
2. Leishmania by phlebotomus
3. Trypanosoma by tsetse fly
4. Wuchreria by Culicine mosquito

23. Sources of Exposure to Parasitic
Infections cont..
E. Animals (a domestic or wild animals
harboring the parasite),e.g.
1.Dogs.
2.Jackals
3.Etc