5. Parasitism
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Jt is a type of symbiotic relationship wherein one
organism thrives at the cost of other. The
organism which benefits is known as the
'parasite', while the one which has to bear the
brunt of the relationship is known as the 'host'.
The parasites are typically characterized by their
relatively small size and tendency to reproduce
faster as compared to the host organism
6. Parasitism
Parasitism is a non-mutual relationship between
organisms of different species where one
organism, the parasite, benefits at the expense
of the other the host.
Traditionally parasite referred to organisms with
lifestages that needed more than one host.
Parasites reduce host biological fitness by
general or specialized pathology, such as
parasitic castration and impairment of secondary
sex characteristics, to the modification of host
behaviour. Parasites increase their fitness by
exploiting hosts for resources necessary for their
survival, e.g. food, water, heat, habitat, and
transmission. 10/5/2022
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7. Types of parasites
Parasites are classified based on their interactions with their
hosts and on their life cycles.
Human head lice (Pediculus humanus capitis) are ectoparasites.
Parasites that live on the surface of the host are called
ectoparasites (e.g. some mites).
Those that live inside the host are called endoparasites
(including all parasitic worms). Endoparasites can exist in one of
two forms: intercellular parasites (inhabiting spaces in the
host’s body) or intracellular parasites (inhabiting cells in the
host’s body).
Intracellular parasites, such as protozoa tend to rely on a third
organism, which is generally known as the carrier or vector. The
vector does the job of transmitting them to the host. An example
of this interaction is the transmission of malaria, caused by a
protozoan of the genus Plasmodium, to humans by the bite of an
anopheline mosquito.
Those parasites living in an intermediate position, being half-
ectoparasites and half-endoparasites, are sometimes called
mesoparasite. 10/5/2022
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8. Transmission
Some endoparasites infect their host by penetrating its
external surface, while others must be ingested. Once inside
the host, adult endoparasites need to shed offspring into the
external environment to infect other hosts. Many adult
endoparasites reside in the host’s gastrointestinal tract, where
offspring can be shed along with host excreta. Adult stages of
tapeworms, thorny-headed worms and most flukes use this
method. Among protozoan endoparasites, such as the malarial
parasites and trypanosomes, infective stages in the host’s
blood are transported to new hosts by biting-insects, or
vectors.
Larval stages of endoparasites often infect sites in the host
other than the blood or gastrointestinal tract. In many such
cases, larval endoparasites require their host to be consumed
by the next host in the parasite’s life cycle in order to survive
and reproduce. Alternatively, larval endoparasites may shed
free-living transmission stages that migrate through the host’s
tissue into the external environment, where they actively
search for or await ingestion by other hosts. The foregoing
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9. Hosts response
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Hosts respond to parasitisms in many ways ranging
from the morphological to the behavioural. In some
cases, plants produce toxins to deter parasitic fungi
and bacteria.[14] Vertebrate animals have developed
complex immune systems, which can target parasites
through contact with bodily fluids.[citation needed] Animals
are also known to resort to behavioral defenses,
examples of which are the avoidance by sheep of
open pastures during spring, when roundworm eggs
accumulated over the previous year hatch en masse;
and the ingestion of alcohol by infected fruit flies as
self-medication against blood-borne parasites.[15] In
humans, parasite immunity is developed prominently
by Immunoglobulin E antibodies.
