Introduction To Parasitology

INTRODUCTION TO PARASITOLOGY Dr. Mejbah Uddin Ahmed

History of Parasitic Disease  Parasitic

diseases were known from ancient

times. Egyptians, Chinese, Indians & Greeks knew about parasitic diseases during the period from 3000-300 BC.  Antonie

Von

Leeuwenhook

discovered

microscope at the end of the 17th century which followed the recognition and discovery of protozoa.

TERMS AND DEFINITIONS  Parasitology:

The branch of medical science which deals with the study of parasites of medical importance.

 Parasite:

A living organism which depends on another living organism for food and accommodation and do herm to the host.

Types of parasite  Ectoparasite:

Some arthropods cause some human diseases but they remain outside the body are consider as ectoparasite, e.g. Reduvid bug, body louse etc.

 Endoparasite:

Lives inside the body of the host: blood, tissue, body cavity, digestive tract and other organs of the body.

Types of parasite  Permanent

parasite: Leads a parasitic life through out the whole period of its life.

 Opportunistic

parasite: Leads a parasitic life when opportunity arises.



Obligatory parasite: Can not exist without a parasitic life.

Types of host  Host:

Are the organisms which give shelter and nourishment to the parasites.

 Types

of host:

 Definitive

host

 Intermediate  Accidental

host

host

 Paratenic

host

 Reservoir

host.

 Definitive

host: harbor the adult stage of the

parasite, e.g. - Mosquito is the definitive host for the malarial parasite. 

Intermediate host: harbor larval stage of the parasite, e.g. - human are the intermediate host for malarial parasite.

 Accidental

host: where parasites do not

develop normally but when infection occur accidentally, the parasite either able to complete it’s life cycle or eventually die. e.g. - Man is the accidental host for Ancylostoma canium.

 Paratenic

host:

are

the

hosts

where

parasites undergo an arrested development on infection, larval forms accumulates in these host until they have chance of infecting the

definitive

granulosus.

host.

e.g.-

Echinococcus

 Reservoir

host:

harbor

a

particular

pathogen and acts as long term source of infection and are essential for maintenance of the infection during times when active transmission do not occur. e.g. - Dog is the reservoir host for Leishmania donovania.

Association between host and parasite  Symbiosis:

When two species of organisms

live together, with no implication regarding the length or outcome of the association is known as symbiosis. These include mutualism, commensalisms and parasitism.

 Mutualism:

Is the relationship, which advantageous or necessary for one or both and none of them cause harm to another.

 Commensalism:

Is the relationship, where one is benefited and the other is neither benefited or harmed.

 Parasitism:

Is the relationship, where one

member depends on another for its nutrients, accommodation or other life function. It is harmful to one of the partner.  Parasitoidism:

A relationship in which the

host is killed by the parasite. It occurs in ants, bees, flies etc.

 Zoonosis:

Evolution of a human disease

naturally acquired from an infection primarily confined

to

vertebrate

animals.

Leishmaniasis, Trypanosomiasis.

E.g: