This document provides an introduction to parasitology, defining parasites as organisms that infect other living beings by living in or on their bodies and obtaining nourishment. It discusses different types of parasites like micro and macro parasites. It describes the relationships between parasites and hosts, the classes of parasites like ecto and endoparasites, types of hosts, life cycles of parasites like Ascaris, modes of infection, symptoms, immunity, and methods for laboratory diagnosis of parasitic infections. The main groups of parasites are identified as protozoa, platyhelminthes, and nemathelminthes.

1. Introduction to parasitology

2. DefinitionDefinition
 Parasites are organisms that infect otherParasites are organisms that infect other
living beings.living beings.
 They live in or on the body of another livingThey live in or on the body of another living
being (HOST) and obtain nourishment from it.being (HOST) and obtain nourishment from it.
 Medical parasitology deals with parasites whichMedical parasitology deals with parasites which
causes human infections and diseases theycauses human infections and diseases they
produceproduce

3.  Micro parasite: small, unicellular Eg.,
viruses, bacteria and protozoa
 Macro parasite: large, multicellular Eg.,
helminths

4. Host parasite relation
commensalism
symbiosis
parasitism
Parasite
Host

5. Classes of parasite
 Ectoparasite
 Endoparasite

6. ECTOPARASITE
 Ecto parasite: living on
the surface of the skin.
 It will not penetrate into the
tissues.
 The infection caused by
these are called as
infestation.
eg., head louse, body louse
etc.,

7. ENDOPARASITE
 Endoparasite: living within
the body of the host
(infection)
 Usually these are
responsible to cause human
infections.
eg., protozoa & helminths

8.  This can be further subdivided into …..
Obligate parasite : cannot exist without
host eg., Toxoplasma gondii
Facultative parasite: capable of living
either as parasite and as free living state
eg., pathogenic free living amoeba

9.  Accidental parasite: attack an unusual host
eg., Hydatid disease of man
 Aberrant parasite: cannot live or develop
further. One that can’t be transmitted from
human to human. eg., Toxocara canis

10. HOST
 Defined as an organism which
harbours the parasite and provides the
nourishment.
 Larger, when compared to parasite.

11. HOST - Types
 Definitive host
 Intermediate host
 paratenic host
 Reservoir host

12.  I. Definitive host: harbors adult parasite or
where parasite replicates sexually
 II.Intermediate host: harbors larval form or
parasite replicates asexually
 III.Paratenic host: larval stage survives but
does not develop further
 IV.Reservoir host: source of infection to

13. SOURCES OF INFECTION
 Contaminated soil
and water
(Embryonated eggs
of parasite)
 Fresh water fishes
(Infecting larvae/
Intermediate host)
 Crab and cray fishes
 Raw or
undercooked

14. Mode of Infection
 Blood –sucking insects
(Tick , Reduviid bugs,
Mosquito etc.,)
 Housefly
 Dog
 Cat
 Cow
 Pig
 Human
 Autoinfection (Finger to
mouth – pinworm)
Tick
Chagas
Flea
Bug
Cat & Dog
Human

15. PORTAL OF ENTRY INTO THE BODY
 Mouth
 Skin
 Sexual contact
 Kissing
 Congenital
 Inhalation
 Iatrogenic

16. Life
cycle
 SIMPLE: life cycle completed in a single host,
eg., Entamoeba histolytica
 Some may require two different host to complete their life
cycle.
eg., Leishmania donavani (man and sandfly)
 COMPLEX: parasite requiring two different host, one
definitive and one or more intermediate host
eg., Schistosoma

17. Life cycle of human parasites-Ascaris

18. COMPLICATIONS
 Inflammatory reactions in the cells.
 Inflammation of large intestine.
 Inflammation of tissues, vessels.
 Inflammation of respiratory tract.
 Some may also causes allergic
manifestations.

19. COMPLICATIONS

20. Immunity in parasitic
infections
 Immunity refers to the resistance offered
by the host towards injury caused by
parasite.
 INNATE: inherited eg.,
1. Girls and young women are susceptible to
anaemia by hookworm infection.
2. Gastric acidity cause resistance towards
Giardia cysts

21. ……
 ACQUIRED: both AMI and CMI plays role
in prevention
 CONCOMITANT IMMUNITY: a host
infected with a Schistosome resist
reinfection with fresh cercariae at the same
time maintains adult Schistosome

22. Laboratory diagnosis
 Demonstration of parasite
 Immunodiagnosis
 Molecular biological methods

23. Demonstration of parasites
 Blood
 Stool
 Urine
 Genital specimens
 CSF
 Sputum
 Tissue biopsy and aspiration

24. Demonstration of parasites in blood
Malarial Parasite
Microfilaria
Leishmania
Ring forms of
Plasmodium
falciparum

25. Demonstration of parasites in
Stool
Ankylostoma duodenale
Entameoba histolytica Trichuris trichuria

26. Other Methods
 Culture
 Animal inoculation
 Immunodiagnosis
 Skin tests
 Serological tests
 Molecular methods

27. Classification of parasites
The parasites are divided into three main
groups:
 Phylum Protozoa- single-celled organism,
multiply in human host. Eg., Entameoba,
Giardia, Plasmodium, Leishmania
 Phylum Platyhelminthes (flatworms):
Flukes & tapeworms

28. Contd….
 Phylum Nemathelminthes (round worms):
Ascaries, Filarial worms etc.,- multicellular worms,
do not normally multiply in human host,
 Phylum Arthropoda

29. Taenia solium (Tape worm)
Wuchereria bancrofti(Filarial worm)
Nematode Cestode
Trematode
Paragonimus westermani (Flukes)