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[NOTES] CESTODES (2nd Year BS Medical Technology)
Clinical Parasitology (Centro Escolar University)
Studocu is not sponsored or endorsed by any college or university
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lOMoARcPSD|19987950
CLINICAL PARASITOLOGY
Module 4 – Cestodes
Transcribed by PORPION
References: PowerPoint presentation, Canvas introduction,
and video discussion
TABLE OF CONTENTS
Taxonomy
Introduction
General Characteristics
✓ General Structures
Comparison of Pseudophyllidean and Cyclophyllidean
Parasites
Order Pseudophyllidea
✓ Diphyllobothrium latum
Order Cyclophyllidea
✓ Taenia spp.
✓ Hymenolepis spp.
✓ Dipyllidium caninum
✓ Echinococcus spp.
✓ Raillientina garrisoni
TAXONOMY
Kingdom Animalia -> Subkingdom Metazoa -> Phylum
Platyhelminthes -> Class Cestoida -> Subclass Cestoda ->
Order Pseudophyllidea and Order Cyclophyllidea
✓
✓
✓
✓
✓
✓
✓
✓
✓
✓
✓
✓
✓
✓
✓
✓
✓
✓
INTRODUCTION
Known as ‘tapeworms’
They have an extensive size variation: 3mm – 10m
They generally require intermediate hosts
Their method of growth involves addition of segments
(proglottids)
•
Each proglottid, when mature, produces infective
eggs for the intermediate host
The anterior headlike segment are known as scolex
•
The scolex has suckers
•
Some species have hooklets on their scolex as a
means of attachment to intestinal mucosa
•
Their necks are directly behind the scolex
Treatment is targeted at detaching the scolex from the
mucosa because the neck area is where proglottid
production occurs
Gravid proglottids at the distal end of the organism
discharge eggs into the feces
Most tapeworm eggs contain hexacanth embryo or
oncospheres
Transmission to humans is through ingestion of their
larval stage, known as cysticercus, cysticercoid, or
plerocercoid larva
•
These are found in raw or undercooked meat/fish or
in insects that harbor the larval stage
•
This larval stage contains an invaginated scolex
inside a protective membrane
Diagnosis is done by finding the eggs in feces
•
Proglottids can be used if intact when passed
through feces
GENERAL CHARACTERISTICS
Flat and ribbon-like
White yellow-ish in color
Segmented
Monoecious (hermaphroditic and partially parthenogenic)
•
They can self-fertilize but they usually need the
opposite sex
No gastrointestinal tract
No circulatory system
Has well-developed reproductive organs
•
Have testes, ovaries, and uterus
Has tegument
•
Outer-covering
•
For entry of nutrients and exit of wastes
Habitat
Mode of transmission
Eggs
Life cycle
Small intestine
Oral route
Generally non-operculated
and mature/embryonated
NOTE: Except for D. latum
Egg -> larva -> adult
GENERAL STRUCTURES
Scolex
✓ Attachment organ (to the lining of the small intestine)
✓ SHAPE – globular, pyriform,
spoon-like
(spatulate-shaped
only in D. latum)
✓ MAJORITY – with 4 cup-like
suckers/grooves/acetabulum
✓ Recovery of the scolex indicates
success of treatment
✓ Rostellum
•
Fleshy extension of scolex
(crown area)
•
May be armed or unarmed
o Armed rostellum have hooklets
Neck
✓ Region of growth
•
Location
of
germination
process
✓ Point of proliferation for the next
set of segments
✓ The segments nearer to the neck
are the younger segments, the
ones farther are the older
segments
Proglottids
✓ Each segment
✓ STROBILA – chain of proglottids/segments
✓ Types
•
IMMATURE – nearest to the neck
•
MATURE – middle portion; this is where the
reproductive structures are formed and found
•
GRAVID/RIPE – farthest from the neck
o Filled with eggs (in the uterus)
o Can be detached through apolysis
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COMPARISON OF PSEUDOPHYLLIDEAN AND
CYCLOPHYLLIDEAN PARASITES
Species
PSEUDOPHYLLIDEAN
CYCLOPHYLLIDEAN
Diphyllobothrium
latum
Spriometra
T. solium
T. saginata
Dipylidium caninum
Hymenolepis nana
E. granulosus
NOTE: They are
known as false
tapeworms
✓ Spoon,
spatula,
or
almond
shaped
✓ With
bothria
(sucking
grooves
✓ No hooklets
✓ Anapolytic
(doesn’t shed
segments)
✓ Segments
have uterine
pore
and
genital
pore
(both
are
centrally
located)
✓ All
reproductive
structures
are seen
✓ Their uterus
has
a
rosette-like
appearance
NOTE: They are
known
as
true
tapeworms
✓ Globular
or
pyriform shaped
✓ Quadrate (four
cup-like suckers)
✓ With/without
rostellum
(with/without
hooklets)
✓ Apolytic (sheds
segments)
✓ Only genital pore
is present
Ova
Oval,
operculated, and
immature
Larval stage/s
1st – Coracidium
2nd – Procercoid
3rd
–
Plerocercoid/spar
ganum
Intermediate
host
1st – Crustaceans
(copepods,
cyclops)
2nd – Freshwater
fishes
Hexacanth
embryo/oncosphere
(spherical,
nonoperculated,
embryonated, with
hooklets)
Cysticercus
(specific for Taenia
spp.), cysticercoid
(for
Hymenolepis
spp.), hydatid (for E.
granulosus)
Zero
to
one
intermediate host
Scolex
Strobila
Gravid
proglottid
NOTE: They have
three hosts (2 IH
and 1 DH)
Only uterus can be
seen (in different
shapes/patterns)
Habitat
Diagnostic stage
Infective stage
1st Intermediate host
2nd Intermediate host
Paratenic host
Larval stages
Mode of transmission
Treatment
Prevention
✓ Fish tapeworm
Small intestine
Egg/scolex (because only
this parasite has a spatulate
scolex)
Plerocercoid larva
Copepods
(cyclops,
diaptomus)
Freshwater
fish
(small
fishes)
Carnivorous fishes
NOTE: These larger fishes
eat small fishes, the larger
fishes are ultimately eaten
by man
Coracidium -> Procercid ->
Plerocercoid
Ingestion
Praziquantel
✓ Freezing of fishes (18°C for 24-48 hours)
✓ Proper
cooking
of
fishes (50°C for 10
minutes)
Eggs
✓ 1 million eggs/ova per day
✓ Non-embryonated
•
They embryonate in water
✓ Operculum on one end with terminal
knob (abopercular knob) on the
other end
✓ With underdeveloped coracidium
✓ Mistaken with P. westermani eggs
Adults
✓ Their lifespan is 25 years
✓ Length
•
3-5 meters to 10 meters
✓ Mistaken for Spriometra
•
Species
found
in
canines/felines that can
infect man which leads to
hearing loss
✓ Scolex
•
Spatulate/spoon/almond
shaped
•
With 2 bothrium (slit-like sucking organ)
✓ Uterus
•
Rosette-like appearance
✓ Strobila
•
Up to 4000 proglottids
•
Have uterine pore aside from the genital pore
NOTE: They have
one to two hosts (1
IH and 1 DH)
ORDER PSEUDOPHYLLIDEA
✓
✓
Diphyllobothrium latum
New name is Dibothriocephalus latus
It is the largest tapeworm of man
NOTE: Refer to the PowerPoint presentation for the life cycle
Common name
✓
✓
Broad fish tapeworm
Broad
tapeworm
(Belizario de Leon)
Pathology
✓ Tapeworm/bothriocephalus anemia
•
Adults may take up large amounts of vitamin B12
o Vitamin B12 is important for the production of
RBCs
•
Macrocytic, megaloblastic anemia
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Increase in cell size of RBCs and increase in
size of immature RBC cells
Presence of megaloblastic cells in the circulation
Sometimes demonstrates Pernicious anemia
o This is also a macrocytic, megaloblastic anemia
o Impaired uptake of vitamin B12 from the
intestine due to the lack of cells that produce
intrinsic factors (these factors facilitate the
uptake of vitamin B12 in the intestine)
These cells also produce gastric acids (HCl)
which leads to achlorhydria (absence of
gastric HCl)
o
•
•
Strobila
Gravid
proglottid
s
NOTE:
This is the
uterus
1000-2000
segments/proglottids
15-20 to 30 lateral
branches
(dichotomous/treelike) with 97-104
thousand ova
<1000
segments/proglottids
7-13 to 15 lateral
branches
(dendritic/finger-like)
with 30-50 thousand
ova
4-10 meters (upto 25
meters)
7
meters
meters)
Laboratory Diagnosis
✓ Stool exam
•
DFS, Kato-katz
•
Look for eggs or scolex
✓ Examination for gastric juice
•
Free hydrochloric acid
•
To differentiate Diphyllobotriasis from Pernicious
anemia
o Presence of HCl indicates diphyllobotriasis
ORDER CYCLOPHYLLIDEA
Taenia spp.
NOTE: Refer to the PowerPoint presentation for the life cycle
T. saginata
✓ Beef tapeworm
✓ Unhooked
tapeworm
T. solium
✓ Pork
tapeworm
✓ Hooked
tapeworm
Small intestine
Cattle, cows, camels Pigs, man
Common
name
Habitat
Intermediate
host
Larval stage
Cysticercus bovis
Infective
stage
Mode
of
transmission
Pathology
Treatment
Cysticercus
cellulosae
Cysticercus bovis
Cysticercus
cellulosae
and
embryonated egg
Ingestion of measly Ingestion
of
beef with infective measly pork with
larva
embryonated egg
Taeniasis saginata
✓ Taeniasis
solium (due
to adult)
✓ Cysticercosis
(due to larva)
Praziquantel, Niclosamide
Structural Differences
Scolex
✓
✓
ADULT
T. saginata
With 4 cup-like ✓
suckers
No rostellum nor ✓
hooklets
T. solium
With 4 cup-like
suckers
With
armed
rostellum (two
rows of large
and
small
hooklets)
Length
(2-4
NOTE: This makes it
the longest cestode
NOTE: Drinking alcohol can irritate adult Taenia spp., which
causes the adult Taenia spp. to shed proglottids
Eggs
✓ Spherical and striated
✓ Embryonated when laid/deposited
✓ Has 6 hooklet paris
✓ Motile (the eggs are called 1st stage
larva due to their motility/movement)
✓ Their eggs are indistinguishable
from each other
✓ Adults may lay 594,000 ova per year
Pathology
✓ T. saginata
•
Causes Taeniasis saginata
o Non-specific symptoms – epigastric pain,
hunger pangs, weakness, weight loss, loss of
appetite, pruritus ani
o Intestinal obstruction due to tangled proglottids
✓ T. solium
•
Due to adult – Taeniasis solium
o Abdominal discomfort, hunger, malabsorption
•
Due to larva – Cysticercosis
o Accidental ingestion of egg
o More dangerous than Taeniasis solium
o Can spread to other organs (if it migrates to the
brain, it is neurocysticercosis, the most
common parasitic CNS disease and the most
serious manifestation; it may lead to death)
Laboratory Diagnosis
✓ Stool exam
•
Direct fecal smear, concentration techniques
(sedimentation)
•
Look for eggs, proglottids, scolex
o Presence of eggs in stool is intermittent
o Eggs are just recorded as Taenia spp. because
they’re indistinguishable
✓ Double slide compression method
•
Sample: Gravid proglottids
•
Demonstration of lateral branches in the proglottids
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•
✓
✓
Gravid proglottid is placed between two glass slides
and the lateral branches are observed
India ink stain
•
Black stain
•
Used to visualize the lateral branches in the
proglottids of Taenia spp.
•
Observes the genital pore (lateral) which are
connected to the uterus, once stained, the branches
are easier to view
Perianal swab
•
Eggs may be left in the perianal region as stool is
passed
NOTE: A patient positive for Taenia spp. must practice proper
hygiene because of the possible medical complications that
may arise from the infection
MoT
Structural Differences
Scolex
✓
✓
Other Taenia spp.
T.
T.
T.
T.
multiceps serialis brauni glomerata
Other
Multiceps
N/A
N/A
N/A
name
multiceps
Common
Bladder worm
name
Habitat
Eyes,
Subcut. N/A
N/A
brain
tissue
Larval
Coenurus larva (a unilocular encysted larva)
stage
Infective
Eggs
stage
IH
Sheep
Rabbits
Herbivores
Final Host Canids
Dogs,
N/A
N/A
foxes
A. Host
Man
MoT
Ingestion of eggs in food, water, or fomites
Pathology Human coenurosis (most commonly caused
by T. multiceps)
NOTES: Fomites are non-living materials that are infected
Final
host
Larval
stage
Infective
stage
H. nana
Dwarf tapeworm
H. diminuta
Rat tapeworm
Small intestine
Direct – N/A
Arthopods (Grain
Indirect – Rice/flour beetle,
flea,
beetles (Tribolium & cockroach,
Teneborio spp.); Dog mealworms,
flea (Ctenophalides earwigs,
canis); Human flea myriapods,
(Pulex irritans); Rat lepidopterans)
flea
(Xenopsylla
cheopsis)
Man
Rat,
man
(accidental host)
Cysticercoid larva
Cysticercoid
larva
Direct – Embryonated Cysticercoid
ova (in man)
larva
✓
✓
Strobila
Gravid
proglottids
Length
ADULT
H. nana
Subglobular in
✓
shape
With 4 cup-like
✓
suckers
With retractable
armed
rostellum
(single row of
20-30 Y-shaped
hooklets)
H. diminuta
With 4 cup-like
suckers
With unarmed
rostellum
175-220 segments/
800-1000 segments/
proglottids
proglottids
Sac-like uterus filled with eggs
2-4cm
20-60cm
NOTE: They are the
smallest cestode
NOTE: Their proglottids are in craspedote form (over-lapping)
Eggs
Hymenolepis spp.
Common
name
Habitat
IH
✓
Asian Taenia spp.
Taenia saginata asiatica
Pigs, cattle, goats, wild
boar, monkeys
Cysticercus viscerotropica
Larval stage
Ingestion
of
cysticercoid larva
NOTE: H. nana normally has no intermediate hosts. It is the
true human tapeworm since its final host is man. It is also the
most common cestode of man.
Taenia asiatica
✓ Old name is Taiwan Taenia spp.
✓ Third specie of Taenia
✓ Closely resembles T. saginata
Common name
Other name
Intermediate host
Indirect – Cysticercoid
larva (in the case that it
has an intermediate host)
Ingestion of embryonated
ova/cysticercoid larva
Hooklets
Polar
thickening
Polar
filaments
Embryophore
H. nana
Three
pairs
(hexacanth embryo)
Present (two polars)
H. diminuta
Three
pairs
(hexacanth
embryo)
Present
4-8 polar filaments
Absent
Present (colorless)
Present
(colorless)
Picture
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NOTE: The egg of the H. diminuta is said to have the
appearance of a sunny-side up fried egg
Common
name
Dipyllidium caninum
NOTE: Refer to the PowerPoint presentation for the life cycle
Habitat
Common name
Habitat
Intermediate hosts
Final host
Accidental host
Larval stage
Infective stage
✓ Dog tapeworm
✓ Double-pored tapeworm
✓ Flea tapeworm
✓ Cucumber tapeworm
✓ Pumpkin seed tapeworm
Small intestine
✓ Dog louse (Trichodectes canis)
✓ Dog flea (Ctenophalides canis)
✓ Cat flea (Ctenophalides felis)
✓ Human flea (Pulex irritans)
Dog
Man
Cysticercoid
Cysticercoid
Adult
✓ Length
•
10-70cm
✓ Scolex
•
Globular
•
With four suckers
•
With armed rostellum (club-shaped)
o 1-7 rows of rose-thorn shaped hooklets
✓ Proglottids
•
Double set of reproductive organs
✓ Gravid proglottids
•
Melon/pumpkin shaped
•
With bilateral genital pore
Eggs
✓ Spherical
✓ Thin-shelled
✓ With 6 hooklets (hexacanth
embryo)
✓ Similar with Taenia egg
✓ Enclosed in egg capsule/packet
•
5-30 or 8-15 embryonated
•
egg per packet
✓ Largest ova of cestodes due to
being enclosed in a packet
Laboratory Diagnosis
✓ Stool examination
•
Observe for eggs enclosed in packets, scolex,
proglottids
IH
Final host
A. Host
Larval
stage
Infective
stage
MoT
Pathology
Treatment
Hydatid worm, dog
tapeworm,
unilocular
hydatid cyst
Small
intestine,
connective tissue
Sheep, ox, goat, horse,
camel
Dog
Man
Hydatid cyst
Final host – Hydatid
cyst
IH – Embryonated ova
Ingestion of egg
Hydatid
disease,
hydatidosis,
cystic
echinococcosis
✓ Surgical removal of
cyst
✓ Albendazole,
Mebendazole,
Praziquantel
Alveolar hydatid
worm/cyst
Liver, lungs, brain
Rodents
Fox, wolf
Man
Alveolar hydatid
cyst
Embryonated ova
Ingestion of egg
Alveolar hydatid
disease
Albendazole,
Mebendazole
NOTE: The alveolar hydatid disease is the most fatal form of
echinococcosis. It is also the most lethal of all helminthic
diseases because the cysts are formed in the liver, lungs, or
brain. They are indistinguishable at all stages with E.
granulosus.
Adult E. granulosus
✓ Length
•
3-6mm or 4.5mm
•
They are the shortest
tapeworm of man
✓ Scolex
•
Pyriform
•
With prominent armed
rostellum
o 30-36 hooklets
✓ Proglottids
•
Only
3
segments
(immature, mature, gravid)
✓ Gravid proglottids
•
Widest and longest proglottid
•
With midline uterus
Eggs of E. granulosus
Similar to Taenia spp. eggs
Echinococcus spp.
NOTE: Refer to the PowerPoint presentation for the life cycle
Old name
New name
E. granulosus
Taenia granulosus
Echinococcus
granulosus sensu lato
NOTE: This is a
collective term because
there
are
several
genotypes
E. multilocularis
N/A
N/A
Larva of E. granulosus
✓ Hydatid cyst
✓ Found in human tissue
✓ Slow-growing, fluid-filled, tumor-like,
and space-occupying structure
✓ Attached to laminated germinative
membrane
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✓
✓
✓
Brood capsules
•
Enclosed with laminated germinal membrane
•
Found in the membrane where prostoscolices
develop
o Prostoscolices are developing scolex
Contains daughter cysts
•
Miniaturized hydatid cysts inside the membrane
•
Brood capsules that have separated from the
germinative membrane
Hydatid sand
•
Component of old E. granulosa larva
•
From the disintegration of the brood capsule and
hydatid cysts in the main hydatid cysts when there
are too many daughter cysts causing liberation of the
prostoscolices and the toxic fluid
•
Potentially toxic to man and may cause anaphylactic
shock and death
•
With prominent armed rostellum (Two alternating
rows of 90 to 140 hammer-shaped hooks)
✓ Gravid proglottids
•
Said to have a rice-gran appearance
•
Contains 200-400 egg capsules with one to four
spindle-shaped eggs
Eggs
Egg packets with 1-4 spindle-shaped ova
Laboratory Diagnosis of E. granulosus
✓ Roentgenogram (x-ray)
•
Observed for bunch-of-grapes lesions
✓ Ultrasonography
✓ Immunologic tests
•
Bentonite flocculation test
•
Casoni intradermal test
o Injects hydatid cyst into patient and observes if
there is a reaction
✓ Exploratory cyst puncture
1. Puncture
2. Aspirate
o Removes content of the cyst
3. Inject
o Injects prostoscolicidal (a hypertonic solution)
which ruptures the brood capsules and
daughter cysts
4. Reaspirate
o Obtains what was ruptured
o Repeated until nothing else can be reaspirated
✓
✓
Raillientina garrisoni
Most common intestinal cestode of rodents in the
Philippines
Infected patients appear asymptomatic
Intermediate host
Final host
Accidental host
Larval stage
Infective stage
Flour beetle (Tribolium
confusum)
Rat
Man
Cysticercoid larva
Final host – Cysticercoid
larva
IH – Gravid proglottid
Adult
✓ Length
•
60cm
✓ Scolex
•
Subglobular
•
With 4 suckers
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