Parasitology

Parasitology

Introduction

Parasitology: It is the science that deals with organisms that live on or within

other organisms (Hosts).  Mainly in this course branch we

study the parasites which live on the expense of man.

The

relationship between two living organisms may be one of the following:1

Mutualism

2

Symbiosis

3

Commensalisms

4

Parasitism

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 Mutualism:Mutual benefits is derived from the

association

of

these

organisms Benefit

Benefit

two

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Symbiosis: Mutual benefit , and the two organisms can not live independently (physiological relationship). Benefit

Benefit

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Commensalisms:One

partner

benefits

(commensal)

while the other (host) is unaffected. It may be called a non-pathogenic parasite.

Benefit

No harm ,No benefit

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Parasitism:One organism (parasite) lives at the expense of the other (host) which usually suffer from the association. It is called a pathogenic parasite. Benefit

Harm

Parasitism Parasite

Host

Types of Parasites

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1. Ectoparasite:-

Live outside the body of the host (infestation). e.g. Lice 2. Endoparasite:Live inside the host (infection). e.g. most of human parasite

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3. Facultative Parasite:-

Capable of leading both a free-living and a parasitic existence (live parasitically or none parasitically). 4. Obligate Parasite:-

Completely dependent upon its host and can not lead a free life.

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5. Temporary Parasite:-

Parasitic only during part of its life

cycle. 6. Permanent Parasite:Live parasitically during the whole life

cycle.

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7. Incidental Parasite:-

Can establish itself in a host in which it

does

not

ordinary

(occur in abnormal host). 8. Pseudoparasite:-

A certificate mistaken as a parasite.

live

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9. Specific Parasite:-

Occurs in one particular host.

10.Pathogenic Parasite:-

Causing injury to the host.

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11. Coprozoic Parasite:- [copro= faeces]

Parasite passes the alimentary canal without

infection

faeces after release.

or

contaminant

Types of Hosts

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1. Definitive Host (final or terminal):-

Harbours the adult

or

mature

parasite. In

which

parasite

sexually if it applicable.

can

reproduce

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Definitive Host І

Main Host

ІІ

Secondary Host

ІІІ

Accidental Host

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I.

Main Host:In which the parasite occur more frequently and reach maturity.

II.

Secondary Host:In which the parasite occur less frequently and growth is retarded.

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III.

Accidental Host:In which its occurrence and development is

very difficult.

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2. Intermediate Host:-

Harbours the immature stage of the parasite (larval stage) that reproduce asexually into

infective stage. 3. Reservoir Host:-

Animal that harbours the same species of parasites as man and constitute a source of

infection to him.

Factors Affecting Prevalence & Geographical Distribution of the

Parasites

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1.

Availability of suitable hosts and their habits.

2. Immune status of the hosts. 3. Easy entry & exit of the parasite

to and from the host. 4. Regional habits. 5. Socio-economical status.

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6. Education

[knowledge about parasites reduce the infections rates] 7. Environmental sanitation

[water, food, waste disposal,…..] 8. Suitability of the environmental and

climatic conditions.

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9. Control

of

intermediate

hosts,

treatment of infected cases….ect. 10. Nature of life cycle [e.g. parasites

with simple life cycles have more distribution than with complicated

cycles].

General Modes of Parasites Transmission

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1.

Congenital

(through

placenta)

e.g. malaria 2. Direct Leshmania,

Contact.

[e.g.

Tichomonas

&

arthropods,

Entamoeba

gingivalis ]. 3. Indirect

contact (in contaminated

objects). [e.g. amoebic cyst, helminthes egg as of H. nana , Taenia , Entrobius].

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4. In

food

as

most

parasites

are

intestinal and their infective stage reach food either: • In flesh: [e.g. T. saginata & T. solium]. • In contaminated water [e.g. vegetable

with protozoa cyst & helminthes egg]. •

Contamination

by

[e.g. mechanically by housefly]. •

Contamination by food handler.

insects

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5. In

water:

water

drinking

with

helminthes

containing

contaminated

protozoa egg

the

or

cyst

using

intermediate

or

water

host,

infective stage [e.g. Schistosomiasis]. 6. Contaminated soil [e.g. Ancylostoma]. 7.

Animals

[e.g.

Toxoplasmosis (cat)]

dog

worm

(dog),

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8. Arthropods:

- Transmission occurs either:• Mechanically [e.g. faecal cyst & eggs to

food by house fly]. • Biologically

[e.g.

malaria

&

filariasis

( by mosquitoes), sleeping sickness (by

Tsetse (by sand fly)]

fly)

&

Leishmaniasis

Continue  Praziquantel

is very safe, taken as a single or

divided dose according to the worm type.  Dose

is calculated according to the patient weight.

 Praziquantel

is swallowed, not chewed; as it is very

bitter in taste.