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INTRODUCTION TO PARASITOLOGY

ISNA INDRAWATIDEPARTMENT OF PARASITOLOGY

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Medical Parasitology

• science that deals with the study of the dependence of organism (parasite) on another (host) without making any useful return.

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Parasite • organism that lives on or within

another organism for survival• usually cannot exist as free –

living, except Strongyloides stercoralis

• dependent on the host for existence.

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• An endoparasite: a parasite that lives within

another living organism; invade deep and internal organs of the body e.g. : Ascaris lumbricoides, Giardia lamblia

• An ectoparasite: a parasite that lives on the

external surface of another living organism, e.g. : lice (Pediculus), ticks

05/03/2023 Even semester 2012/2013

05/03/2023 Even semester 2012/2013

• Obligate organism which are completely

dependent on the host for existence.e.g. : Nematodes

• Facultative when a parasite is capable of living

even without a host can exist as free – living or as parasite, e.g. Strongyloides stercoralis

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Life cycle of Strongyloides stercoralis

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• Permanent parasite that remains on or in the

body of the host from early life until maturity or for its entire life , e.g. Ascaris , Pediculus humanus capitis

• Temporary visit their host only for a short period of time, e.g : bugs, ticks

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HOST• Definitive

where the parasite lives & complete their life cycle /completion of sexual reproduction

• Intermediate completion of larval stage , asexual

reproduction, and for transmission to the definitive host, e.g: Snail for Schistosoma

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• Reservoir host other animal that harbors the

same parasite & act as additional source of human infection, e.g : rat fro Schistosoma

• Paratenic host one which incidentally carries

the infective stage of parasite in an arrested state ( no continuity of life cycle )

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Vectors:• Intermediate host playing an

active role in the transmission of the parasite.

• Usually arthropodes that harbors infective stage of parasite

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Helminthes

Protozoa

Arthropodes

• Class Nematoda• Class Trematoda• Class Cestoda

• Class Rhizopoda• Class Mastigophora• Class Sporozoa• Class Ciliophora

• Class Insecta • Class Arachnida• Class Crustacea• Class Chilopoda• Class Diplopoda

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INFECTION• Autoinfection

infection acquired by an individual resulting from their own direct source of exposure.

• Reinfection when a person is infected with a parasite after months of cure gets reinfected with the same specie of parasite.

• Superinfectionwhen a host is harboring more than one parasite at a time.

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Source of exposure to parasitic infection

1. Contaminated water and soil2. Food containing immature

infective stage of parasite3. Blood – sucking insects as

vectors.

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Source of exposure (cont’d)

5. Domestic Animals harboring the parasite, e.g : dog flea contained infective stage of D. caninum

6. Another person, his clothing or bedding

7. One’s self

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Portal of Entry:1.Mouth/oral : most common2.Skin : penetration of infective

stage larva3.Airborne : parasite inhaled

nose nasopharynx intestine, e.g : E. vermicularis

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4.Transplacental : parasite from mother transmitted to the fetus in utero, e.g. : T. gondii

5. Sexual : acquired through sexual contact

e.g : T. vaginalis

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05/03/2023 Even semester 2012/2013

Nomenclature of animal parasite

• binomial scientific names are assigned to each parasite which are LatinA. Genus name : begin with capital letterB. Species : small letter

e.g: Ascaris lumbricoides A. lumbricoides

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Diagnosis of parasitic infection:• Clinical diagnosis– easy when the doctor familiar

with the symptom/ in endemic area/ specific manifestation of infection.– problem if disease is uncommon

in the community or with migrants in the community.

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• Laboratory–purpose is to make specific

diagnosis– collect proper specimen like stool, urine, blood, sputum, aspirate from body orifices, tissue scrapings

–know how & when specimen is to be obtained

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• Other laboratory method used:

• 1) X – ray/ USG•2) Serology•3) Biopsy