General Introduction in Medical Parasitology
1st lecture
for
First year medical students,
Faculty of Medicine
Presented
By
Dr. Nawras Mowafy
Prof. of Parasitology
&
Dr. Manal Zaki
Prof. of Parasitology
Lectures (6): Introduction to parasitology I
(Definitions and Terminology)
By the end of the lecture the student will be able to :
1. Define the different terms of medical parasitology.
2. State parasitism and host-parasite relationship.
3. List the different types of hosts.
4. List the different types of parasites.
5. Explain host-parasite relationship.
Study Resources
Garcia, Lynne Shore, and David A. Bruckner. Diagnostic Medical Parasitology.
New York: Elsevier, 2016.
Websites : for Microbiology, immunology and parasitology
Medical Parasitology
❑
Medical Parasitology: A science which deals with the
study of parasites that produce harm or disease in
humans.
❑
Parasite: A living organism that lives in or upon another
organism (host) driving its nutrient directly from this
host and causes a certain amount of harm to it.
❑
Host: is an organism that harbours the parasite, provides
the nourishment and shelter.
Parasite-Host Relationship
❑
Symbiosis: Permanent association of two organisms that cannot
exist independently. Both organisms living together get benefit
from each other, harm or even death happen to both if they are
separated. (e.g.: Flagellates live in the gut of termites. Termites
feed on the woods and Flagellates digest cellulose).
❑Mutualism:
(Both organisms are benefited ). Both organisms get
benefit from each other. Nothing happen to them if they are
separated (e.g.: Bacteria flora that form vitamin B complex in
human).
Parasite-Host Relationship (Cont.)
❑ Commensalism: (Eating at the same table). One
organism gets benefit while the other organism is not
affected (e.g.: Entamoeba coli in human intestine).
❑ Parasitism: One organism (Parasite) gets benefit and
always causes injury to the other (Host) which usually
suffers from the association (e.g.: Plasmodium species
causing malaria).
Types of Parasites
1- Ectoparasite: A type of parasite that lives on outer surface or
in the superficial tissues of the host e.g. arthropods
(infestation).
2- Endoparasite: This lives within the body of the host e.g.
Schistosoma sp. (infection).
3- Obligate parasite: This completely dependent upon its host
and can’t live far from this host (e.g.Toxoplasma gondii).
4- Facultative parasite: This can lives both free and parasitic life
(e.g. Strongyloides species).
Types of Parasites
5- Temporary parasite: This visits the host only at intervals for
food (e.g. mosquitoes).
6- Permanent parasite: This lives in or on its host without
leaving it (e.g. lice).
7- Erratic parasite (ectopic parasite): This lives in normal host
but in abnormal habitat (e.g. Oxyuris in vagina &
Ascaris in bile duct).
Types of Parasites
8- Incidental parasite: This can establish itself in a host in
which it doesn't ordinarily live (e.g. D. caninum & H.
diminuta in man).
9- Accidental parasite: This inhabits an unusual host and its
life cycle is expected to be incomplete within that
host [e.g.Toxocara canis (a dog parasite) in man].
10- Opportunistic parasite: This produces disease in Immunodeficient or immunocompromised patients (like AIDS
and cancer patients) (e.g. Toxoplasma gondii ,
Strongyloides stercoralis).
Types of Parasites
11- Pseudo parasite: An artifact mistaken for a parasite.
12- Coprozoic (spurious) parasite: A free-living or non-human
parasite passing through the alimentary tract without
infecting man, or contaminating his stool after being
passed.
13- Zoonotic parasite: It is an animal parasite that is transmitted
to man & producing infection.
Type of Hosts
1- Definitive or Final host {D.H.}: A host
that harbours the adult stages in
case of helminth parasites (e.g.
man in Schistosoma) or the
sexual stages in case of protozoal
parasites (e.g. mosquitoes
in
Plasmodium ).
2- Intermediate host {I.H.}: A host that
harbours the larval stage of
helminthes (e.g. snails in case of
Schistosoma) or the asexual stage
of protozoan parasite (e.g. man
in Plasmodium).
Type of Hosts
3- Reservoir host {R.H.}:
An animal that
harbours the adult parasite and acts
as an important source of infection
to man (e.g. cats and dogs in
Heterophyes heterophyes).
4- Transport host (Paratenic host): A host that
acts as a transport vehicle only (no
development
place
to
domestica).
the
or
multiplication
parasite)
(e.g.
takes
Musca
Type of Hosts (Cont.)
5- Vector: Is usually an arthropod that
transmits the parasite to its
host.
•It can be a definitive host e.g. Female
Anopheles
in
case
of
Plasmodium
Or
* Intermediate host (Female Culex in
case of Wuchereria bancrofti.
Habitat
The habitat is where the parasite lives and multiplies in
the body of the definitive or intermediate host, like:
▪ Small intestine
▪ Large intestine
▪ Blood vessels
▪ Organs; liver, lung, heart, brain, …..
▪ Muscles
▪ Lymphatics
▪ Reticuloendothelial system
▪ Cells as red blood cells
Nomenclature of parasites
BINOMINAL SYSTEM OF NOMENCLATURE
Genus + species
e.g.: Ascaris lumbricoides (italics)
Ascaris lumbricoides (underlined)
- Genus scientific name starts with a capital letter and
species name with small letter.
-Binominal scientific names are written in
italics or underlined.
Medical Parasitology includes the study
of 3 major groups of parasites.
These groups are
Protozoa
☺
One-celled
organisms
Helminths
➢
➢
Worms:
Trematodes
➢
Cestodes
➢
Nematodes
Arthropods
☺
☺
insects