2. Learning objectives
By the end of this lecture each student should:
Understand what are parasites and medical
Parasitology.
Know the types of hosts and parasites.
Understand the relationships between hosts and
parasites.
Know the source of parasitic infection and how
parasite enter the human body.
Know the general life cycles of parasites.
Understand the classification of protozoan parasites.
3. What is parasite & Medical
Parasitology??
A living organism that dependent on another
organism (host), for all or part of its life cycle and
takes nourishment requirements from host for
survival.
Parasites may be simple unicellular (protozoa) or
complex multi-cellular (Helminths or
Arthropods).
Medical Parasitology is the science dealing with
parasites that infect man and causing disease,
host response, diagnosis, prevention and control.
4. Types of hosts
Host is an organism which the parasite lives and causes
harm.
Definitive host: is the host where the sexual
reproduction (or adult stages) takes place or present.
Intermediate host: is the host which alternates with
the definitive host and in which the asexual stages of a
parasite are found.
Reservoir host: this is an animal host serving as a
source of infection from which other animals can
become infected.
Carrier host: that is not exhibiting any clinical
symptoms but can infect others.
5. Types of parasites
According to location parasites may be:
Ectoparasites: Organisms live in the external surface of the
body of the host, e.g Pediculus humanus.
Endoparasites: Organisms live within the host. Helminths
and protozoa.
Medicalparasitology
Protozoa (Unicellular)
Helminths(Multicellula
r )
Arthropoda
(Endoparasit
es)
(Ectoparasite
s)
6. Types of parasites
According to parasite – host interaction and environmental
factors they may be one of the following:
Obligatory parasite that is completely dependent on
its host and can’t survive without it e.g. hookworms.
Facultative parasite that can change its life style
between free-living in the environment and parasitic
according to the surrounding conditions. e.g.
Strongyloides stercoralis.
Permanent parasite that lives in its host without
leaving it e.g. Lice.
7. Types of parasites
Temporary parasite that visits the host only for
feeding and then leaves it. e.g. Bed bug visiting
man for a blood meal.
Opportunistic parasite that is capable of
producing disease in an immunedeficient host
(like AIDS and cancer patients) e.g. Toxoplasma
gondii.
Zoonotic parasite that primarily infects animals
and is transmittable to humans e.g. Fasciola
species.
8. Host - parasite relationships
Parasitism: is a relationship in which a
parasite benefits and the host provides the
benefit, which causing harm to the host.
Symbiosis: which both host and parasite
dependent upon each other.
Commensalism: which only parasite derives
benefit without causing any harm to the host.
9. Source of parasitic infections
Contaminated food, water and soil.
Vectors.
Dogs and cats.
Raw or undercooked pork or beef meat.
Raw or undercooked fish & crab meat.
Autoinfection.
Human.
10. Parasites port of entry to humans
Mouth: e.g Entamoeba histolytica and
Giardia lamblia.
Skin: e.g schistosomiasis.
Sexual contact: e.g Trichomonas vaginalis.
Congenital: e.g Toxoplasma gondii.
Inhalation: e.g Entrobius vermicularis.
Kissing: e.g Entamoeba gingivalis.
Blood transfusion: e.g malaria parasite.
11. Life cycle of parasites
Direct life cycle: parasite does not involve
any intermediate host between parasite and its
host.
Indirect life cycle: parasite involves
necessarily one or more intermediate hosts to
complete its life cycle.
12. Protozoa and their classification
Protozoa are unicellular eukaryotic cells,
single cell which performs all necessary
function of metabolism and reproduction.
Belong to Kingdom Protista, Phylum
Protozoa.
Morphologically consists of cytoplasm and
one ore more nucleus.
13. Protozoa and their classification
Protozoa classified into four subdivisions
according to the methods of locomotion:
The amoebae (Sarcodina): move by means of
pseudopodia.
The flagellates (Mastigophora): typically move
by long, whip like structure called flagella.
The ciliates (Ciliata): are propelled by rows of
cilia that beat with a synchronized wavelike
motion.
The Apicomplexa or Coccidian: lack
specialized organelles of motility.
14. The amoebae (Sarcodina)
Consist of a shapeless mass of
moving cytoplasm which is
divided into granular endoplasm
and clear ectoplasm.
They move by pseudopodia
(false feet).
Reproduce asexually by simply
dividing into two (binary
fission).
Have a trophozoite (stage of
protozoa showing motility and
the ability to grow, feed, and
reproduce) and resistant cyst
stage by which it is transmitted.
15. The flagellates (Mastigophora)
Flagellates possess one or
more long hair-like flagella
for locomotion.
They reproduce asexually
by binary fission.
G. lamblia, Trypanosoma
and Leishmania are
examples.
16. The ciliates (Ciliata)
Ciliate trophozoites are
covered with short hairs
(cilia) by which they
move.
They reproduce asexually
by binary fission and
sexually by conjugation.
They have cyst and
trophozoit.
The only ciliate known to
infect human is Blantidium
coli.
17. The Apicomplexa or Coccidian
Coccidia are intracellular
parasites that reproduce
asexually by a process
called schizgony or
merogony and sexually by
sporogony.
Plasmodium species,
Toxoplasma gondii and
intestinal coccidia
Cryptosporiduim parvum
are examples.
