This document defines and describes different types of parasitism. It begins by defining parasitism as a relationship between species where one benefits at the expense of the other. It then describes 8 types of parasitism: obligate, facultative, ectoparasitism, endoparasitism, mesoparasitism, epiparasitism, brood parasitism, and social parasitism. Each type is defined and an example is provided, such as head lice for ectoparasitism and Plasmodium for endoparasitism. The document concludes by thanking the reader.

1. DR. P. SUGANYA
ASSISTANT PROFESSOR
DEPARTMENT OF BIOTECHNOLOGY
SRI KALISWARI COLLEGE (AUTONOMOUS)
PARASITISM

2. DEFINITION
 Parasitism is a type of ecological association
between species where one of the species
benefits from the association at the expense of
the other, usually without killing the organism.
 The organisms that obtain the benefit from the
association is called a parasite, whereas the
organisms that are harmed by the association is
called the host.
 The term parasite is derived from the Greek word
‘parasitos’ meaning ‘one that eats at the table of
another’ to indicate the feeding habit of the organism.
 Even though traditionally, parasitism was considered
a discrete interaction, many researchers believe that
the interaction merges into other interspecific
interactions.

3.  All infectious agents causing illness in different
groups of living beings are included as parasites.
 The parasites exist in this association to use the host
as both habitat and a source of nourishment;
however, the extent and duration of association might
differ.
 Parasitism is a type of consumer-resource interaction
like predation, but unlike predators, parasites do not
kill their host and often live in or on them for a longer
period of time.
 Some of these associations are highly specific, and
thus, a parasite of one species might not be parasitic
to other species.
 These parasites are smaller than their host with a
highly specialized metabolism. These also have a
high reproduction rate to ensure their survival.

4.  These organisms can also shape the behavior
of individuals in the host population, which leads
to the evolution of behavioral syndromes.
 Even though most parasites feed on host
species for nourishment, some parasites might
use some organisms as secondary hosts for the
transmission of one primary host to another. In
secondary hosts, the parasites do not cause as
much harm in primary hosts.
 The pattern and extent of harm caused to the
host are central to the definitions of parasitism
as different parasites can impair the host’s
health through a wide range of mechanisms.

6. TYPES OF PARASITISM
 Parasitism is of different types depending on
the size, characteristics, interaction with the
host, and their life cycles. Some of the
parasites can exist in multiple classifications
depending on the basis of classification.

7. 1. OBLIGATE PARASITISM
 Obligate parasitism is a type of parasitism where the
parasite is dependent on the host for its survival, and thus
the interaction is obligate.
 These parasites cannot complete their lifecycle without
exploiting an appropriate host.
 The parasites adapt and evolve over time so that they can
no longer exist without the association with a host. The
parasites develop different strategies in order to escape
the host defenses and exploit the host.
 The parasites involved in obligate parasitism usually do
not cause the death of the host as they require a host for
their survival. However, some parasites might kill the host
for transmission.
 Most of the obligate parasites include prokaryotes like
bacteria and viruses. Some insects like head lice are also
considered obligate parasites as they die if removed from
the human scalp.

8. EXAMPLE- RICKETTSIA
 Rickettsia species are intracellular bacteria that
reproduce within the vacuoles of host cells.
 These species cannot be grown on artificial media
and require tissue or cell cultures since these are
obligatory species.
 The transmission of Rickettsia from one host to
another occurs through arthropods like lice and fleas.
 These bacteria have evolved mechanisms to evade
the host immune defenses, mostly by surviving within
the cellular components like vacuoles.
 The parasitic interaction of Rickettsia is necessary for
the completion of their lifecycle, including
reproduction.

10. 2. FACULTATIVE PARASITISM
 Facultative parasitism is a type of parasitism where the
parasites do not depend on the host for survival or the
completion of their life cycle.
 These organisms use facultative parasitism as a form of
survival strategy due to the shortage of resources in the
environment.
 Facultative parasitism is common in bacteria and fungi
that can exist in multiple habitats and transmit between
hosts.
 Some of these parasites feed on living organisms, but
when the organism eventually dies, they continue to feed
on the dead organisms without the need for parasitic
activity. This process is common in many fungi infecting
plant species.
 Facultative parasitism, can, however, develop into
obligate parasitism over time or due to changes in its
habitat and composition.

11. EXAMPLE- ARMILLARIA SPECIES
 Armillaria is a parasitic fungal species that
parasitize living plants for nutrients.
 The fungi feed on the roots of trees, but the
interaction is facultative as the fungi can exist
both as parasitic as well as free-living
organisms.
 However, the fungi can survive even after the
trees dies as the fungi can feed on the woods
without the need for any parasitic activity.
 The organisms are also important ecological
agents involved in the recycling of nutrients
through microbial decomposition.

13. 3. ECTOPARASITISM
 Ectoparasitism is a type of parasitism where the
parasite is present outside or on the surface of the
host’s body.
 These parasites are termed ectoparasites, and they
usually inhabit the skin or outgrowth of the skin on the
host.
 The vast majority of ectoparasites are invertebrates
that result in lesions on the surface of the host body.
 Many of the known ectoparasites are known to be
vectors of pathogens that transmit to the host while
feeding or defaecating.
 Some of the ectoparasites can transform into
endoparasites over time as a form of defensive
mechanism and adaptation to a parasitic lifestyle.

14. EXAMPLE- HEAD LICE
 Lice are ectoparasites that colonize different parts of
the host body ranging from head to lower part of the
human body.
 Head lice mostly live on the hair of the head, but
these can wander to other parts of the body.
 These can get transmitted from one host to another
either by direct contact or by the use of personal
belongings like combs and towels.
 The insects feed on the blood from the scalp of the
host, and the scalp also provides a living space to the
parasite.
 Lice lay eggs on the surface of the human head,
which then develop into larvae and adults as a part of
the life cycle.

16. 4. ENDOPARASITISM
 Endoparasitism is a type of parasitism where the
parasites are present within the body of the host.
 Endoparasitism can either be intercellular where the
parasites reside within the spaces in the host body or
intracellular where they exist within the cells of the
host.
 Most of the intercellular endoparasites are
protozoans and invertebrates like worms, whereas
the intracellular endoparasites include bacteria,
viruses, and fungi.
 Endoparasites directly feed on the nutrients present
in the host body and result in different forms of
diseases.
 Intracellular parasites usually depend on a third
organism, known as vector or carrier for transmission

17. EXAMPLE- PLASMODIUM
 Plasmodium is an endoparasite that feeds on
the red blood cells in mammals, birds, and
reptiles.
 Like most endoparasites, Plasmodium depends
on a third organism (female Anopheles
mosquito) for transmission from one host to
another.
 Plasmodium exists in two different hosts, both of
which are essential for the completion of the life
cycle of the protozoan.
 The protozoans complete their sexual lifecycle
in mammals whereas the gametophytic lifecycle
is completed in the female mosquito.
 The interaction between Plasmodium and

19. 5. MESOPARASITISM
 Mesoparasitism is a type of parasitism where
the parasite lives partly within the host’s body.
 These parasites enter the body of the host
through openings like the ear and cloaca and
live within the body for a particular period of
time.
 The parasitism is mostly facultative as the
species do not need to enter the body of the
host to obtain nutrients or to complete their
lifecycle.
 Most of the species existing in a
mesoparasitism interaction

20. EXAMPLE- COPEPODS
 Copepods are crustaceans that exist in
freshwater and saltwater either as free-living or
parasites.
 The organism parasitizes fish, sharks, and
marine mammals that occasionally enter the
body of the host through gills and cloaca.
 Copepods damage the gills by feeding on the
delicate tissues of the gills. These also feed on
the blood circulating through the gill lamellae.
 These species can also exist as ecto or
endoparasites depending on the stage of their
lifecycle.


22. 6. EPIPARASITISM
 Epiparasitism is a type of interaction between two
parasites where one parasite parasitizes the other.
 Epiparasites are often termed as hyperparasites or
secondary parasites that share some characteristics
with the primary parasites like habitat and nutritional
requirements.
 Depending on the extent of parasitism, there are
different degrees of epiparasitism. Some
epiparasitism associations are facultative or
incidental.
 The facultative or incidental epiparasitism
occasionally occur without co-inhabitation, mostly due
to the lack of food resources.
 Epiparasitism also occur between organisms of the
same species as they share common habitats and

23. EXAMPLE- IN PLANTS
 Species of the family Viscaceae often exist in an
epiparasitic association with each other that can either be
facultative or obligate.
 In plants, the bark strands occasionally come in contact
with the vascular cambium of the host and establish a
position within the cambium.
 The continued interaction leads to the formation of sinkers
that extend from the bark across the phloem to the xylem
tissue.
 As a result, the parasitic species gain water and nutrients
produced by the host species for their growth and
survival.
 Some species even grow through the flowers resulting in
persistent seeds and fruits. The parasitic plants thus, find
better reproduction and dispersal through the interaction.


25. 7. BROOD PARASITISM
 Brood parasitism is a type of parasitism where the
parasites depend on the host to raise their young
ones. This is a form of parasitism as the parasites
conserve energy whereas the host has to spend extra
energy.
 This form of parasitism usually exists in birds, insects,
and fishes where the parasites manipulate the host to
raise their young ones on their own.
 In some cases, the parasites even kick off the young
ones of the host species forcing the host to raise the
young ones of the parasite.
 The parasitic parents thus can use the energy
conserved to spend on finding food and producing
other offspring.
 Some of the young ones of parasites might exhibit
mimicry in that they appear similar to that of the host
young ones while others show no evolved trait.

26. EXAMPLE- BIRDS
 Brood parasitism is most common in birds as many
avian brood parasites utilize the interaction to escape
the process of development of their young ones.
 Some of the birds might be specialists that parasitize
a single host species or a small group of species
whereas some can parasitize a wide rade of host
species.
 A common example is a common cuckoo where the
male parasitizes a wide variety of hosts, but the
female specializes in a single species.
 The female has genes that regulate egg coloration
that allow them to lay mimetic eggs in the nest of the
host species.
 The host species for female common cuckoo include
reed warbler that feeds and raises the young ones of
the parasite species.

28. 8. SOCIAL PARASITISM
 Social parasitism is a type of interaction between social
animals like ants and bees where a parasitizing organism
depends on the labor provided by the host species.
 The colony of organisms usually consists of one or more
species of the organism consisting of a parasitic species
and host species.
 The interaction can be obligate, facultative, temporary, or
permanent, and the relationship can take many forms.
 The parasitic species usually gain benefits like food and
transportation, but the species eventually evolve to be
weak as they mostly cannot exist without the interaction
over time.
 The nature of interaction might be different in different
groups where some parasitic ants steal the food and eggs
of host ants. Other species might live in the nests
prepared by the host species.

29. EXAMPLE- ANTS
 The most common form of social parasitism is
observed in ants where the parasites are often slave-
makers.
 The parasitic ants raid the colonies of other ants and
steal their eggs and larvae. The larvae and pupae
that are not consumed by the parasites are converted
into worker slaves through chemical imprinting.
 The slave ants or host ants then collect more eggs,
gather food, and feed the parasitic ants. When the
colony moves to a new home, the slaves even carry
the parasitic ends to the new location.
 The colony continues to grow as the association
continues as long as the host ants are alive. It is quite
easy to differentiate between host ants and parasitic
ants as they are different in structure and are of
different species.

31. REFERENCES
 https://microbenotes.com/parasitism/
 https://biologydictionary.net/parasitism/

32. THANK YOU