INTO
PARASITOLOGY
PARASITOLOGY
is a science that studies a phenomenon of parasitism.
 PARASITISM is the association between a host and a
parasite.
 PARASITE is a living organism (may be animals,
plants, bacteria or viruses) which depends on other
organism for food, shelter, protection and
reproduction.
 HOST – an organism which harbours the parasite.
ANIMAL ASSOCIATIONS
in nature
Mutual cooperation
Beneficial
associations
● Mutualism
● Symbiosis
Neutral
associations
● Commensalism
● Synoikia
Mutual antagonism
Harmful
associations
● Parasitism
Beneficial associations
 When two different species of organisms live together
and lead a mutually beneficial life, it is called
mutualism or symbiosis.
It is ‘an intimate association’ between two different
organisms, in which each one derives benefit from the
other. These animal associations are defined as
synonymous.
 However, in symbiosis the relationship between the
two partners is more intimate than in mutualism.
When the symbionts are separated from each other,
they cannot lead an independent life.
 On the other hand, the partners of mutualism can
lead an independent life easily.
Beneficial associations
symbiosis
Lichens = green alga + colourless fungus
The alga supplies carbohydrates formed during
photosynthesis to the fungus. In turn the fungus
gives water, mineral salts and protection to the alga.
mutualism
Hermit crab and Sea anemone:
A coelenterate called Sea anemone lives on the external
surface of a gastropod shell occupied by an arthropod called
Hermit crab. The crab carries Sea anemone to different places
where food is available. In return, the Sea anemone gives
protection to hermit crab. As Sea anemones are attached to
the shell, the crabs are not detected easily by their enemies.
further, due to the presence of cnidoblasts in Sea anemone,
the enemies will not approach the crab.
Neutral associations
 When two organisms of different species live together in an
association which is beneficial to one and neither
beneficial or harmful to the other, it is called
commensalism or synokia.
 In commensalism one organism gives shelter and food to
the other species. For example, Entamoeba gingivales,
protozoan of human mouth lives in oral cavity. Bacteria in
pockets between the teeth and gums are food for amoeba.
 In synokia one organism receives only shelter from the
another. It occurs intermittently between two organisms
(the sucker fish, Echineis, is temporarily attached to the body of
a shark and carried to different places).
CLASSES of HOSTS
DEFINITIVE
or primary host
PARATENIC
or reservoir host
INTERMEDIATE
or secondary host
ADDITIONAL host
Generally, the parasites complete their life cycle in
one or two hosts. In such a case,
 the first host where sexual reproduction or
adult stage of the parasite takes place is known as the
primary (definitive) host,
 the second one where asexual multiplication or
development of larval stages occur –
as the secondary (intermediate) host.
 When reproduction of parasite is absent and parasite
only accumulates in host organism without further
development, it is called as paratenic (reservoir)
host.
 Additional host is the second intermediary host.
The fish tapeworm (Diphyllobothrium latum)
LIFE CYCLE:
 HOSTS :
●
●
● SECOND INTERMEDIATE
(
)
● PARATENIC
(
)
ORGANISMS:
man and ichthyophagous animals
fresh-water crustacean
(a cyclops and a diaptomus)
zooplankton fresh-water fish
predatory fresh-water fish
(perch, pike)
CLASSES of PARASITES
I. Types of Parasites on Localization:
Parasites
Ectoparasites
Coelozoic parasites
Endoporasites
Intracellular parasites
Histozoic parasites
The parasites, which live on the body of the host,
are called ectoparasites. For instance head louse lives as an
ectoparasite in the hair of man.
The parasites, which live inside the body of the
host, are called endoparasites. These are three types as given below.
These parasites live in the cavities of the host
body. For example, Entamoeba and Giardia live in the lumen of the
intestine of man. Similarly, Trichomonas vaginalis lives in the vagina
of women.
These parasites live in the cells of the
host. For example, Plasmodium lives in the red blood corpuscles and
liver cells of man. Similarly Leishmania lives as an intracellular parasite
in the reticulo-endothelial calls of the internal organs of man.
These parasites live in the spaces found
in between the cells of tissues or organs of the host body. They are also
called as histozoic parasites. For instance, Trypanosomia gambiense
resides in the plasma of blood in between blood cells.
II. Types of Parasites on Time of parasitizing
Parasites
 Temporary parasites
The parasites, which spend only a
part of their life cycle on the host,
are called temporary parasites or
partial parasites. For example, the
mosquito leads a free life during
larval stage and parasitic life
during adult stage.
 Permanent parasites
The organisms, which spend
their entire life as parasites
are known as permanent
parasites. e.g. Ascaris and
Taenia solium.
III. Types of Parasites on Character of parasitizing
Parasites
 Facultative parasites
 Obligate parasites
The parasites, which change their
hosts frequently, are known as
facultative parasites. They spend,
part of their life cycle on the host
and part of it independently. For
example,
Mycobacterium
tuberculosis,
whish
causes
tuberculosis in man is a
facultative parasite.
The parasites, which have to depend
on definite hosts throughout their
life, are called obligate parasites. They
cannot live independently. Hence
they will not leave their hosts. For
example Taenia solium, which lives
in the intestine of man, cannot
survive if it resides somewhere else.
Effects of Parasites on Hosts
Parasitic Adaptation and Effects on Parasites
Feral nidal illness – the illness distributed in certain territory among
wild animals.
The doctrine about feral nidal diseases has been developed by Russian
scientist E.N.Pavlovskii in 1938. For feral nidal diseases are characteristic
the following components:
● areal with the certain complex of natural-climatic conditions;
● presence of the agent of disease;
● presence of the hosts among wild animals necessarily;
● presence of the person unessentially;
● presence of a specific carrier, if illness is obligate transmissible
diseases.
Thus, the disease circulating in the nature irrespective of the person on a
certain area, which is determined by presence wild animals – reservoir
hosts of the parasite, is called feral nidal diseases.