parasite 1
DESCRIPTION
Parasite 1TRANSCRIPT
The biotical interrelation of living organisms
SIMBIOSIS – Any organism that spends at least a portion of its life very closely
associated with another living organism of a different spieces is known as a
symbiont or symbiote, and the relationship is known as symbiosis.
There are four types of symbiosis: commensalism, phoresis, mutualism, parasitism.
Commensalism - A type of symbiosis in which spatial proximity allows the
commensal to feed on substances captured or ingested by the host, but the two
partners can survive independently.
Phoresis - In this type of symbiotic relationship, the phoront, usually smaller than
the host, is mechanically carried by the host, but unlike in commensalism there is no
dependence in procurement of food between the partners.
Mutualism – This category of symbiosis is an association in which the mutualist and
the host depend on each other physiologically – ties of bilateral interdependence.
Parasitism – A parasite is an organism that is physiologically dependent on the
host. Parasites derive the nutrients they need directly from the host, usually from
blood, lymph, cytoplasm and tissue fluids, or host-digested food. For many
parasites, their host is also their home, in some cases temporary, and permanent in
others.
Commensalism - a type of symbiosis in which spatial proximity
allows the commensal to feed on substances captured or ingested by
the host, and it literally means 'eating at the
same table'.
The relationship between hermit
crab and sea-anemone is an
excellent example of
Commensalism. Hermit crab lives
inside empty shell of mollusc. The
sea-anemone inhabits the outer
surface of shell. Sea-anemone is
transported form place to place to
get food by crab. The sea-anemone
also gets food captured by crab. The
stinging cells of sea-anemone
protect the hermit crab from
enemies. Thus, both partners are
benefited.
Hermit crab and sea-anemone
The commensal shrimp Periclimenes imperator on
Chromodoris tinctoria,
Emperor shrimp on a
large sea-slug
A titan triggerfish creates feeding
opportunities for smaller fish by moving
large rocks too big for them to shift
themselves
Moss is considered a type of
commensalism because it benefits
from the trees it grows on but the
tree is not affected by the moss.
Moss growing on trees benefits
from being raised above the forest
floor and can easily grow and
spread on the trees.
An emperor shrimp
(Periclimenes imperator)
hitches a ride on a purple-
edged large seaslug
ceratosoma nudibranch
(Ceratosoma tenue).
Lembeh Strait, Indonesia.
Shark and remora fish
Phoresis - In this type of symbiotic relationship, the phoront,
usually smaller than the host, is mechanically carried by the host, to
the places, where are better conditions to live and to feed but unlike
in commensalism there is no dependence in procurement of food
between the partners. The host is required to serve as ‘transporter’
only . Sometimes the host can accidentally protect phoront from
potential enemies.
The mites on the head and body of
the Nicrophorus beetle
Mutualism – This type of symbiosis is an association in which the
mutualist and the host depend on each other physiologically – and
each individual derives a fitness benefit (nutritional, hygienic
(sanitary), protectional).
Clown anemonefish in sea-
anemone, Pacific Ocean.
Parazitizmas – A symbiotic
relationship in which one
organism (the parasite) benefits
and the other (the host) is
generally harmed. Parasites
derive nutrition from their host
and may also gain other benefits
such as shelter and a habitat in
which to grow and reproduce.
The Forms of Parasitism. Classification of Parasites
Plasmodium malariae Dust mite
According to the parasites’ level of dependence
on the host ---
They can be grouped into obligate and facultative.
• Obligate parasites are physiologically dependent
on their hosts and cannot live and/or breed
independently.
• Facultative parasites are essentially free-living
organisms that are capable of becoming parasitic
if placed in a situation conductive to such a mode.
Entamoeba histolytica
Hartmannella vermiformis
Infection of Acanthamoeba sp.
May cause ocular keratitis
Acanthamoeba sp.
Larvae visible after manual
opening of the eye.
Oral myiasis caused by the invasion of
tissues by maggots. It is attributed to
poor oral hygiene, alcoholism, senility.
The larvae of common
(House) fly may cause
myasis
Furuncular myiasis
Common (house) fly, Green fly,
Sarcophage (flesh) fly Larvae (maggots)
Mosquito female
Trichinella spiralis
According to the duration of time the parasites interact with
the host ---
They are classified into temporary and permanent
• Temporary (or periodic) parasites –
include blood-sucking arthropoda. They
spend only a part of their lifetime interacting
with the host, most commonly when feeding.
•Permanent parasites are closely
connected to the host for all or most
of their life cycle and cannot
develop freely away from the host.
Head lice Pork tapeworm
According to the location of the parasites in the host ---
they may be classified as ectoparasites or endoparasites
• Ectoparasites act on the surface of the host, or superficially
embedded in it. Some actualy reside there, while others only come
thereto feed.
• Endoparasites live inside the host, in its internal cavities, organs,
tissues and cells.
• location well-defined
• location is not well-defined
According to the specificity of their life cycle,
parasites – especially helminths - are classified into three groups:
bioparasites, geoparasites, contact parasites.
• Bioparasites (biohelminths) – change their hosts, with different
developmental stages occuring in different host species.
• Geoparasites (geohelminths) – do not usually change host
species as they develop, but a certain stage of the parasite must
develop in the outside environment (soil).
• Contact parasites (contact helminths) – develop inside a single
host, and are passed from host to host through direct contact
between hosts.
The adult flukes deposit fully developed
eggs that are passed in the feces (1).
After ingestion by a suitable snail (first
intermediate host) (2), the eggs release
miracidia (2a), which undergo in the snail
several developmental stages
(sporocysts (2b), rediae (2c), cercariae
(2d). Cercariae are released from the
snail (3) and penetrate freshwater fish
(second intermediate host) (4), encysting
as metacercariae in the muscles or
under the scales (4a). The mammalian
definitive host (cats, dogs, and various
fish-eating mammals including humans)
become infected by ingesting
undercooked fish containing
metacercariae. After ingestion, the
metacercariae excyst in the duodenum
(5) and ascend through the ampulla of
Vater into the biliary ducts, where they
attach and develop into adults, which lay
eggs after 3 to 4 weeks (6). The adult
flukes (O. felineus: 7 mm to 12 mm by 2
mm to 3 mm) reside in the biliary and
pancreatic ducts of the mammalian host,
where they attach to the mucosa.
4
4a
Life cycle of Biohelminths
Adult worms (1) live in the lumen of the
small intestine. A female may produce
approximately 200,000 eggs per day,
which are passed with the feces
(2). Unfertilized eggs may be ingested
but are not infective.
Fertile eggs embryonate and become
infective after 18 days to several weeks
(3), depending on the environmental
conditions (optimum: moist, warm,
shaded soil).
After infective eggs are swallowed (4),
the larvae hatch (5), invade the
intestinal mucosa, and are carried via
the portal, then systemic circulation to
the lungs (6). The larvae mature further
in the lungs (10 to 14 days), penetrate
the alveolar walls, ascend the bronchial
tree to the throat, and are swallowed
(7). Upon reaching the small intestine,
they develop into adult worms
(1). Between 2 and 3 months are
required from ingestion of the infective
eggs to oviposition by the adult
female. Adult worms can live 1 to 2
years.
Life cycle of Geohelminths
Eggs are deposited on perianal folds (1). Self-
infection occurs by transferring infective eggs to
the mouth with hands that have scratched the
perianal area (2).
Person-to-person transmission can also
occur through handling of contaminated
clothes or bed linens.
Enterobiasis may also be acquired through
surfaces in the environment that are
contaminated with pinworm eggs (e.g., curtains,
carpeting). Some small number of eggs may
become airborne and inhaled. These would be
swallowed and follow the same development as
ingested eggs. Following ingestion of infective
eggs, the larvae hatch in the small intestine (3)
and the adults establish themselves in the colon
(4). The time interval from ingestion of infective
eggs to oviposition by the adult females is about
one month. The life span of the adults is about
two months. Gravid females migrate nocturnally
outside the anus and oviposit while crawling on
the skin of the perianal area (5). The larvae
contained inside the eggs develop (the eggs
become infective) in 4 to 6 hours under optimal
conditions (1).
Retroinfection, or the migration of newly hatched
larvae from the anal skin back into the rectum,
may occur but the frequency with which this
happens is unknown.
Life cycle of Contact helminths
Hosts and Their Classification
A host is an organism in or on which a parasite lives, and at
whose expense the parasite feeds.
Some species of parasites move from one host to another in
the course of their development. This is named as host change.
In terms of host
change, hosts can be
classified into:
• Definitive or main
• Intermediate
• Transfer or paratenic
• Reservoir
• Accidental or unsuitable.
Definitive host(Fish eating animals and birds)
Adult fish tapeworm
Egg
Free-swimming
ciliated
Coracidia
1-st Intermediate
host(Crustacean)
Procercoid
2-nd Intermediate
host(Small fish)
Plerocercoid
Transfer (paratenic) host(Predatory fish)
Plerocercoid
Example of
Parasite life cycle
Definitive host( Dog, cat)
Adult helminth
Egg(in faeces)
Raidos ciklo
pavyzdys
External environment
Mature egg
Accidental
host(Human)
Larval stageLarval stage
Adult lancet fluke
Dicrocoelium dendriticum –
Sexually mature stage – marita
Definitive hosts are those in which the parasite can
attain sexual maturity and/or multiply sexually
Intermediate hosts are essential to the parasites’
development, but in them the parasites do not
become sexually mature, though asexual
reproduction may take place.
miracidium
I-st sporocyst
II-nd sporocyst
cercaria
Cercaria in snail
slime balls
metacercariaI-st intermediate host –
terrestrial snail
(Zebrina, Helicella gen.)
II-nd intermediate host –
ant
(Formica gen.)
egg
Transfer (paratenic) host, is not obligate to
the parasite life cycle, but serves simply as a
convenient vehicle towards the definitive
host under otherwise unfavorable
circumstances.
Larva stage
in fish A
Larva stage
in fish B
Fish B
Larva stage transfer
from fish A into fish B
Reservoir hosts are those in which parasites do not
reproduce, but in which parasites can reside,
survive, and be passed on to other hosts.
Accidental hosts are those in which a parasite
enters by accident rather than by design. There it
can neither normally develop nor complete its life
cycle.