ParasitoloParasitologygy

IntroductionIntroduction

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

2

3

4

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Mutualism:-Mutualism:-

Mutual benefits is derived from

the association of these two

organisms

Benefit Benefit

Symbiosis:Symbiosis:

Mutual benefit , and the two

organisms can not live

independently (physiological

relationship).

Benefit Benefit

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Commensalisms:-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:-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

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HostParasite

ParasitismParasitism

Types of Parasites

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 live

(occur in abnormal

host).

8. Pseudoparasite:-

A certificate mistaken as a parasite.

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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 or

contaminant faeces after

release.

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Types of Hosts

1. Definitive Host (final or

terminal):-

Harbours the adult or mature

parasite.

In which parasite can reproduce

sexually if it applicable.

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Definitive Host

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.

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Factors Affecting

Prevalence &

Geographical

Distribution of the

Parasites

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].

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General Modes of

Parasites Transmission

1. Congenital (through placenta)

e.g. malaria

2. Direct Contact. [e.g. arthropods,

Leshmania, Tichomonas & 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 insects

[e.g. mechanically by housefly].

• Contamination by food handler.

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5. In water: drinking contaminated

water with protozoa cyst or

helminthes egg or using water

containing the intermediate host,

infective stage [e.g. Schistosomiasis].

6. Contaminated soil [e.g.

Ancylostoma].

7. Animals [e.g. dog worm (dog),

Toxoplasmosis (cat)]

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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 fly) & Leishmaniasis

(by sand fly)]

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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.

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