Taenia Dr. Shivani Gupta, - PowerPoint Presentation

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Taenia

Dr.

Shivani

Gupta,

PGGCG-11,

Chandigarh

Classification

Tapeworm infestation

is the infection of the digestive tract by adult

parasitic

flatworms called

cestodes or

tapeworms.

Live tapeworm larvae (coenuri)

are

sometimes

ingested by

consuming

undercooked food. Once inside the

digestive

tract,

a larva can grow into a very large adult

tapeworm.

Additionally, many

tapeworm larvae cause

symptoms

in an

intermediate

host. For

example,

cysticerciosis is a disease of

humans

involving larval

tapeworms

in the

human

body

.

Kingdom: Animalia

Phylu

m

:P

l

a

t

yhe

l

m

in

t

hs

Class:

Cestoda

Sublass:

Eucestoda

Major

Attributes:

Endoparasitic.

Acoelomates

Body

is

covered

by

tegument.

Anterior

end

is

a

scolex.

Body

segments

called

proglottids.

Hermaphroditic.

Adult

tapeworm

in

intestine

Morphology

There are three

main

features to a

tapeworms

external

morphology:

the strobila

(proglottids)

the scolex and the

tegument.

1.Strobila/Proglottids

-unique

among the

metazoa

-a

linear

series of

sets

of reproductive organs

of

both sexs - each

is

referred to as a

genitalium

-the area around the genitalium is a

proglottid

-tapeworms

with

mulitple

proglottids

are

describes as being

polyzoic

-new

proglottids

are continuously

differentiated

near the anterior end in a process

called

strobilation - as each segment moves from the anterior end to the posterior end a new one takes it place-the new proglottids are produced in an undifferentiated zone between the scolex and the strobila, called the neck - this area contains stem cells which give rise to the new proglottids

Morphology

-

while the

segments

travel down

the

length of the worm they sexually

mature,

by the

time

they reach

the

end of the worm the

genitalia

have already copulated and

produced

eggs

-a proglottid can

mate

with

itself,

with others in the

same

worm

or

with another worm entirely (it depends on the species of

tapeworm)

-a

segment containing

eggs is

called

agravid-when the gravid reaches the end of the worm, it detaches and passes out of the host in the host feces-from here the eggs can be ingested by a new host, leading to tapeworm infection

Hooks of

tapeworm

Mature

Proglottids

Morphology

Mature

proglottid

Scolex

and anterior

strobila

Morphology

2.

Scolex:

-The tapeworm body consists of an anterior, head-like scolex and the trunk, or strobila, consisting of a linear series of

segments,

or proglottids. The scolex

is

wider than the

strobila

to which it joined by a narrow

neck

.

-The scolex attaches the worm to the gut wall of

the

host. For this purpose it

has

a

retractable

rostellum

armed with

two

rings of

rostellar

hooks

. Just

posterior to

the rostellum

is

a ring of four

suckers

; two

dorsolateral and

two

ventrolateral.

-

T

wo lateral nephridial canals may be visible on each side of the scolex. They connect with each other near the rostellum via a set of convoluted scoelcial nephridial canals and extend posteriorly through the strobila.

Morphology

3.

Body

Wall

:

-The body wall consists of

a

syncytial,

microvilliated,

absorptive

neodermis

,

a

basal

lamina,

and layers

of

circular and longitudinal

muscles.

The nuclei

of

the

syncytium are

submerged

below the basal lamina and muscle layers into the parenchyma. Inside the body wall is connective tissue consisting of the mesenchymal parenchyma in which the reproductive, excretory, and nervous systems are embedded.

Tegument

of

tapeworm

Excretory

System

-

The

excretory

system

consists of numerous

flame

bulb

protonephridia

scattered

throughout the parenchyma of each proglottid

but

they are

not

evident in

these

preparations. Individual

protonephridia

drain

into

an

elaborate system of nephridial canals which

ultimately

open to the exterior

at the posterior end of the

last

proglottid of

the

strobila. Dorsal

and

ventral

lateral

nephridial canals on each side of each proglottid extend the length

of

the

worm. In addition to the two nephridial canals, each side

possesses

a

longitudinal nerve cord

.

-The larger

ventral nephridial canal

is a pale, wide, longitudinal band

lateral

to the

testes.

The dorsal canal is

much smaller in diameter

and is located

medial to the

ventral canal, between it and

the

testis.

In each

proglottid

the

right and

left

ventral canals are connected by a

transverse nephridial canal

extending across the posterior edge of the proglottid just anterior to the

junction

with the

next

proglottid.

The

canals

may

be

easier

to

see

in

immature

proglottids.

Nervous

System

-The

right

and

left

lateral

longitudinal

nerve

cords

arise

from

nerve

rings

in

the

scolex

and

pass

post

e

riorl

y

in

the

s

i

des

o

f

t

h

e

proglottids

.

They

are

slender

longitudinal

lines lateral

to

ventral

nephridial

canals.

Reproductive

System-Male

-Most structures in the proglottid belong to the

reproductive

system.

The

male

and

female systems

share a

common

genital pore (= gonopore) and

genital atrium

but

are otherwise independent of

each

other.

The

common

genital pore

is a large aperture on

either

the right or

left

side of the

proglottid.

It opens into a shallow, cuplike

genital

atrium

.

The

male

and

female systems

both open into the atrium via

its

own

gonoduct.

-The two ducts join the

medial

border of the genital

atrium.

The anterior duct

is the thicker and is the

male

gonoduct.

The

gonoduct

is

regionally

specialized.

The wide portion of the gonoduct

attached

to the atrium is the

muscular

cirrus

sac

. Inside the sac is the convoluted,

eversible,

tubular

cirrus

,

which is the

intromittent

organ,

or

penis. During

copulation

the

cirrus is extended from the genital pore and inserted into the genital

atrium

and vagina of another

proglottid.

-The next region of the

male

gonoduct is the tubular

sperm duct

,

also

convoluted, which extends to

the

testes

. Its entire length is

not

visible.

The

testes

are numerous

small

spheres

scattered

throughout the

parenchyma. Each

is

drained by a tiny

tributary

of the sperm

duct,

but

these cannot

be

seen.

There is no

seminal

vesicle and autosperm

are

stored

in the coils of the sperm

duct.

Reproductive

System-Female

-The

smaller and more

posterior of the two ducts entering the genital atrium is

the

female

gonoduct, which is

also

regionally

specialized. The

first

region

is

the

vagina

. It receives the partner's cirrus and sperm

during

copulation.

The vagina extends

medially

and

posteriorly

to the

small

seminal receptacle

This is a

clear,

unstained, oval

chamber

where allosperm

received by the vagina

are

stored. It is usually

easily

visible. A

short

duct

exits the posterior end of the

seminal

receptacle and joins the

oviduct.

-The

germarium

(= ovary) is divided into large right and

left

lobes

lying

on

either

side of the

seminal

receptacle. It is the

site

of oogenesis and

produces

large numbers of

small,

yolkless

oocytes.

The two

lobes of

the

germarium

are connected across the

midline

by a short, wide, transverse

isthmus

.

-The

follicles

of the

germarium

open into

small

ducts which drain into the

isthmus. The

narrow oviduct arises from the

isthmus

and

extends

posteriorly

for a short distance before receiving the duct from the

seminal

receptacle .After receiving the duct from the

seminal

receptacle the

oviduct

continues posteriorly to

the

ootype.

Fertilization

occurs in the

oviduct.

Reproductive

System-Female

-Yolk

cells

are produced by the single

vitellarium

at the posterior end

of

the

proglottid.

A short

vitelline

duct exits the

vitellarium

and extends

anteriorly to join the oviduct at the ootype. Mehlis’s gland surrounds

the

ootype.

-A

small

uterine duct, usually

not

discernible,

extends from the ootype to

the

uterus

. Shelled eggs

move

from the ootype through

the

uterine

duct into

the

uterus. Within the

shell meiosis

is

completed,

a

zygote

forms,

and development proceeds to the oncosphere larval

stage.

The

uterus is a blind sac with

lateral

branches in which embryonated

“eggs”

are

stored.

The

size

and

visibility

of the uterus vary with

the

maturity

of the

proglottid.

-

As the proglottid ages the

accumulating

“eggs” cause the uterus to

become

larger, darker, and

more

visible.

They will

eventually fill

it,

distending

it so it occupies the entire

proglottid.

There is no opening of the uterus

to the exterior and eggs are released by rupture of the

proglottid.

Mature

Proglottid

(Showing

male and female reproductive system)

Fertilization

and

Development

-Tapeworms are hermaphroditic and

commonly self-fertilize,

a

convenience

for an

animal

that

lives

in a habitat where it

may

be

the

only

member

of

its

species.

Cross-fertilization

may

occur if

more

than

one

worm is present in

the

host.

-

Fertilization

of oocytes (from the

germarium)

by sperm (from the

seminal

receptacle) occurs in

the

oviduct. The fertilized oocyte (with

meiosis

still

in progress)

moves

posteriorly in the oviduct to the ootype where it

associates with a yolk

cell

from

the

vitellarium. The

role of

Mehlis's

gland

is unclear

but

it

may

secrete a thin,

delicate membrane

around the yolk

cells

but

it does

not

secrete the eggshell as was

formerly

thought.

-The eggshell is the product of a joint effort by the yolk

cell

and the

developing

embryo. Shelled

embryonated “eggs”, with

development

in

progress,

move

anteriorly into the uterus where they

accumulate

and are

stored. In the uterus

meiosis

is

completed,

a zygote is

formed,

cleavage

ens

u

es,

and

de

v

e

l

o

p

m

ent

ad

v

ances

to

the

o

n

cos

p

h

e

re

l

a

r

v

a

st

a

ge.

M

a

t

u

r

e,

infective “eggs” in the gravid uterus contain these

larvae.

Life

Cycle

Gravid

Proglottid

-In the gravid proglottid the uterus is

vastly

expanded and packed with eggs Other parts of the

reproductive

system are

degenerate and

may

no longer be

identifiable

but

the nervous and

excretory

systems

are present and

functional,

although not necessarily visible. The

body

wall

musculature remains

and gravid

proglottids

are

mobile

and very

active.

-The

uterus

,

filled

with

small

spherical

“eggs”,

fills all

available

space.

Its lateral uterine lobes are much larger now and so numerous they crowd against each other, filling most of the interior. They are bounded laterally by the ventral nephridial canals.-The genital pore, genital atrium, sperm duct, and vagina are present but no longer functional. Remnants of other parts of the reproductive system may be visible also.

Gravid

Proglottid

Life

Cycle