CESTODES
Dr.jagadeesh(P.G)
31-12-14
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INTRODUCTION TO CESTODES
CLASIIFICATION
MORPHOLOGY
DIFFERENCE BETWEEN PSEUDOPHYLLEAN
AND CYCLOPHYLLEADIAN CESTODE
• DIPHYLLOBOTRIUM SPECIES
Classification
• Cestodes belong to Phylum –Platyhelminthis
Class—Cestoidea
Subclass—Eucestoda
Order—Pseudophyllidea
Cyclophyllidea
Order
Family
Genus
Pseudophyllidea Diphyllobothriidae Diphyllobdthrium
Spirometra
Cyclophyllidea Taeniidae
Taenia
Echinococcus
Hymenolepididae Hymenolepis
Dipylidiidae
Dipyllidium
Classification based on Habitat
• Intestinal Cestodes—Diphyllobotrium ,
Taenia,Hymenolepis,Dipylidium spicies
• Somatic or Tissue Cestodes(Larvae in
Human Muscle or Organ)—
T.solium,T.multiceps,Echinococcus,Spiro
metra species
Morphology of Cestodes
• They exist in three morphology—Adult
worm , Egg and, Larva .
• Adult worm---intestine of human and
animals . They are usually long,
segmented, Flattened and tape like.
• Few mm to meters—1 to 4cm to 10
mts.
Body structure
• Adult worm consists of—Head or scolex , Neck ,
Strobila (trunk)
• Head—Organ of attachment
In Cyclophyllidean- scolex has four cup like
muscular suckers (acetabula).In some scolex has
beak like apical protrusion –rostellum and may
be armed with hookelets
In pseudophyllidean –no suckers but a pair of
longitudinal grooves -bothria
Cestode
• Neck-next to head from which the
segments arise.
• Strobila-Has body wall called tegument
It consist of number of segments or
proglottids
It bear both reproductive organs ---Three
types Immature , Mature and Gravid
Mature proglottid of Cestodes
Female reproductive organs
• Present on ventral side consists of a bilobed ovary.
• Oviduct- join spermatic duct & open into ootype.
• Ootype -is the chamber of fertilization may be self or
cross fertilization
• Vagina- a tube connecting genital pore to ootype
through which sperm enter . At its inner end is
seminal recepticals and spermatic duct .
• Uterus-straight tube arising from ootype , where
fertile eggs are stored in gravid female , It may be
closed or open .
• Vitelline gland and Mehlis gland-present near ootype
may occur singly or in mass
Male genital organ
• Present in dorsal aspect and consists of
• Testes-multiple follicles and release sperm to
vasa efferentia which join to form vas
deference .
• Vas deference is a convoluted tube open in
common genital pore
• It bears a seminal vesicle and ends in the
common genital pore as a swollen muscular
protrusion called cirrus .
• Nervous system is rudimentary consisting of
brain like structure in scolex
• Longitudinal nerve trunk arise from that and
pass through all the segments and joined by
transverse nerves in each segments
• Rudimentary excretory system consists two
lateral canal connected by transverse canal
• Excretory canal are built of flame cells and canal
cells
• No circulatory system or body cavity.
• Tegument is of three layers microthrix, basal
plasma membrane and muscular layer.
Eggs
• Pseudophyllidean cestode- eggs are ovoid ,
operculated surrounded by a single layer called
egg shell.
• Embryo inside contains three pairs of hooklets.
• Membrane lining embryo is ciliated
• The eggs when laid first in the feces are not
embryonated.
• Maturation takes place in water
• Cyclophillidean cestodes-eggs are round to
oval covered by two layers –outer egg shell
filled with yolk material and inner thick
radially striated embryophore .
• Eggs are embryonated from the begining .
• It contains six hoocklets but lining membrane
is not ciliated
Larva
• Embryonated egg undergo further development to
form larva
• Pseudophyllidean cestode- larva is soiled without
any sack .They are Coracidium , Procercoid ,
Plerocercoid stages of Diphyllobothrium ‘
• Cyclophyllidean cestode - Larvae contains bladder
likes sacs They are Cystecircus , Hydatid cyst ,
Coenurus , Cystecercoid .
Life cycle of cestodes
• Cestodes complete their life cycle in two hosts
Definitive
Intermediate
Diphyllobothrium Species
• Largest cestode in human , also known as fish
tape worm or broad tape worm
• Species includes D.latum ,D.dendricum ,
D.facificum D.mehonkaiense .
• D.latum belong to order-Pseudophyllidea and
Family-Diphyllobothriidae
Epidemology
• Mainly endemic in temperate climates Baltic
countries of Europe ,Japan ,S .America .
• Very rare in India
Habitat- live in small intestine of human
(jejunum and ileum
Morphology
• Adult worm-longest tapeworm affecting
human upto 10 mts with over 3000
proglottids .
• Head or scolex-spoon shaped ,two
longitudinal grooves-bothria for attachment to
small intestine ,No suckers and rostellum .
• Neck-next to scolex and represent growing
end from which proglottide arises , it is
unsegmented and longer than head
• Strobila—more than 3000 segments divided into
immature ,mature and gravide segments.
• Mature segment broader than length 10-20mm
x2-4mm and contain male and female organs
consists of bilobed ovary ,coiled and rosette
shaped uterus , vitelline gland scattered and a
vagina .Mid ventral genital pore .Male organs
consists of testes , v.diference and cirrus.
• Gravid segment filled with eggs .
• Some gravid segments become shrunken and
empty due to constant discharge of eggs ,break of
and passed in stool (pseudoapolysis )
Egg-oval 70um x50um ,operculated at one end and
bears a knob at other end When freshly passed are
unembryonated,surrounded by an egg shell
.Embryonated egg contains a hexacanth oospore
lined by a ciliated membrane
Larva- three stages corcidium
,procercoid,plerocercoid
Life cycle
• Host-human are definitive host
• Two intermediate host-First is fresh water copepods
mainly Cyclops and Diaptomus .Second is fresh
water fish
• Infective form-plerocercoid larva
• Mode of transmission-ingestion of undecoocked
fresh water fish containing third stage plerocercoid
larva
• Development in definitive host—plerocercoid
larvae undergo further development to form
adult worm which attach to small intestine by
bothria
• They become sexually mature in four weeks ,
fertilization takes place and they began to lay
eggs.
• Millions of eggs are released every day.
• Development in fresh water---Embryonation and formation of LI larver
(coracidium) ---Eggs unembryonated when
freshly passed in feces become
embryonated after 8-12 days in fresh
water.
The ciliated embryo is released through the
operculum of the egg into fresh water
which is known as the first stage larva
• Development in first intermediate
host (LI toL2 transformation )Coracidium is taken up by copepods
• It looses its cilia and penetrates the
intestine inter body cavity of
copepods transform within 2-3 wks
into 0.5mm second stage procercoid
larva (infective to fish)
• Development in 2nd intermediate host (L2
to L3)—Fresh water fish get infected after
eating copepods containing procercoid
larva.
• The procercoid penetrate fish intestine
,migrate to muscles ,liver and fat where
get transformed into an elongated 1020mm x2-3mm L3 stage –Plerocercoid
larva in 1-2wks
• This stage is infective to man and cycle
repeats
• Paratenic host—IF small fish is eaten up by a
big suitable fish ,then the plerocercoid
penetrate the intestine of big fish and survive
with out further development –this type of
host is called paratenic host
Pathogenesis and Clinical
• Most of infection is asymptomatis .
• Minor manifestation—abd. Discomfort ,diarrhea
vomiting ,weakness and weight loss,rarely abd.
Pain and intestinal obstruction ,cholangitis and
cholecystitis .
• Vitamin B12 deficiency-adult worm absorb large
quantities of B12 and interfere with ileal B12
absorption lead to megaloblastic anemia and
lead toneurological sequelae like parasthesia
Lab diagnosis
• Stool examination—Characteristic eggs
surrounded by egg shell and operculum at one
end and knob at other end .Proglottides in stool.
• Blood examination—Eosinophilia , Incresed MCV
, MCH and MCHC
• Macrocytes may be present
• Treatment--Praziquintal-5 to 10 mg/Kg once
Niclosamide
Parenteral B12
Prevention—Proper coocking(10 minutes at 50*)
and deep freezing (-10* for 24 hrs )
QUESTIONS
• Write note on
Diphyllobothriasis
Difference between -pseudo and cyclophyllidean cestode