Platyhelminthes (flat worms)

Platyhelminthes
(flat worms)
…as parasites of medical
interest
Type of parasites
Protozoa
Helminths
Nematodes
Trematodes
Cestodes
Arthropods
Platyhelminthes
Platyhelminthes
Trematoda
Planaria
Monogenea
Digenea
Cestoda
CESTODES
(tape-worms)
General Characteristics
General Characteristics:
Majority are long, segmented and tape-like are called
tapeworms.
Dorso-ventrally flattened.
Size varies from a few mm to several meters.
The life cycle of tapeworms is simple in the sense that
there are few larval stages, but complicated in that at
least one intermediate host is required as well as the
definitive host.
Adult worms are found in the intestinal canal of man and
animals.
General Characteristics:
There are 3 regions in an adult worm:
– Scolex (head)
– Neck
– Strobila (body or trunk)
Consist of a series of segment called proglottids.
Scolex has suckers and sometimes hooks that serve as
organs of attachment.
Once anchored to the host's intestinal wall, the
tapeworm absorbs nutrients through its skin as the food
being digested by the host flows past it, and it begins to
grow a long tail.
General Characteristics:
Sexes are not separate.
– Reproductive system is present and complete in each
segment!!!
– Because each proglottid contains the male and female
reproductive structures, they can reproduce
independently.
Body cavity is absent.
Alimentary canal is entirely absent.
Nervous system is present.
Excretory system is present
– like some other flatworms, cestodes use flame cells
(protonephridia), located in the proglottids, for excretion.
Tapeworms are exclusively
hermaphrodites; they have both
male and female reproductive
systems in their bodies.
The reproductive system
includes one or many testes,
cirrus, vas deferens and seminal
vesicle as male organs, and a
single lobed or unlobed ovary
with the connecting oviduct and
uterus as female organs.
There is a common external
opening for both male and
female reproductive systems,
known as genital pore, which is
situated at the surface opening
of the cup-shaped atrium.
Even though they are
sexually hermaphroditic,
self-fertilization is a rare
phenomenon.
In order to permit
hybridization, crossfertilization between two
individuals is often
practiced for
reproduction.
During copulation, the
cirrus of one individual
connects with that of the
other through the genital
pore, and then exchange
their spermatozoa.
Uterus
General Characteristics
According to maturity of reproductive organs, three
types of segments of the strobila can be recognized:
 Immature: male and female organs are not
differentiated;
 Mature: male and female organs have become
differentiated (male organs appear first);
 Gravid: uteri are filled with eggs (other organs are
atrophied or have disappeared).
 Gravid proglottids can be released from the tapeworm's
posterior end and leave the host in feces. They drop off,
carrying the tapeworm eggs to the next host.
 Older segments are pushed toward the tip of the tail as
new segments are produced by the neckpiece.
Nervous system
The main nerve centre of a cestode is a cerebral
ganglion in its scolex.
– Motor and sensory innervation depends on the
number and complexity of the scolex.
Smaller nerves emanate from the ganglion to
supply the general body muscular and sensory
ending.
– The cirrus and vagina are innervated, and sensory
endings around the genital pore are more plentiful
than other areas.
Sensory function includes both tactoreception
(touch) and chemoreception (smell or taste).
Classification of Cestodes
Infecting Man
Classification of Cestodes
Infecting Man:
Cyclophyllidean cestodes (a, b)
Pseudophyllidean cestodes (c)
Classification of Cestodes
Infecting Man:
Pseudophyllidean cestodes
Scolex (head) has two slit-like sucking grooves
called bothria (1 on the dorsal surface and 1 on the
ventral surface) instead of suckers.
Classification of Cestodes
Infecting Man:
Cyclophyllidean cestodes
Scolex is quadrate with four cup-like round suckers
called acetabula;
An apical rostellum with hooklets may be present.
Order Pseudophyllidea characteristics:
Large worms consisting of a long chain of
segments.
Vitellaria (vitellin glands) are widely scattered in
the parenchyma and are composed of many
acini.
Genital pore is on the ventral surface of the
segment and is not marginal.
Uterus opens to the exterior through a uterine
pore from which eggs come out.
Order Pseudophyllidea characteristics
Eggs are operculated and can develop only in
water.
Eggs are immature when oviposited and
oncosphere gives rise to ciliated embryo
(coracidium).
Larval development proceeds in two
intermediate hosts:
First larval stage is called procercoid
Second larval stage is called plerocercoid
(or spargano).
Order Cyclophyllidea characteristics
Large or small worms consisting of chains of
segments.
Vitelline glands are concentrated in a single
mass.
Common genital pore is marginal (on lateral
side of segment);
No uterine opening for the exit of eggs from the
gravid uterus.
Eggs only escape from the rupture or
disintegration of ripe segments.
Order Cyclophyllidea characteristics
Eggs are not operculated and can develop only
in the intermediate host, fully embryonated.
Oncosphere is never a ciliated embryo;
Larval development proceeds in one
intermediate host:
– Cysticercus
– Hydatid cyst
(or Coenurus)
– Cysticercoid
Main differences between
Pseudophyllidean and Cyclophyllidean Cestodes
Pseudophyllidean
Cyclophyllidean
Head or scolex
bears 2 slit-like grooves
(bothria)
bears 4 cup-like suckers
(acetabula)
uterus
no branching, convoluted branching may or may
uterine tubes assume the not be present
form of rosettes
Uterine pore
present
absent
Common genital
pore
Ventral; in the midline
lateral
eggs
Operculated; gives rise
to ciliated larvae
Not operculated; do not
give rise to ciliated larvae
Pseudophyllidean cestodes
infecting man:
Adult worms in Intestine
– Diphyllobothrium latum (Fish Tapeworm)
Larval stages in Man
– Spirometra mansoni (spargano)
Cyclophyllidean cestodes
infecting man:
Adult Worms in the Intestine
–
–
–
–
–
Taenia saginata
Taenia solium
Hymenolepis nana
Hymenolepis diminuta
Dipylidium caninum
Larval Stages in Man
– Echinococcus granulosus and E. multilocularis (Hydatid
cyst)
– Taenia solium (Cysticercus)
Pseudophyllidea:
Diphyllobothrium latum
Diphyllobothrium latum
Common Name:
Fish Tapeworm
Broad Tapeworm
Morphology
Adult worm is yellowish
grey in colour.
Dark central markings
in the strobila are due
to the egg-filled uterus.
Measures 3 to 10
meters in length!
Life-span is for a period
of 5 to 15 years.
Diphyllobothrium latum
Diphyllobothrium latum
Scolex is spoon-shaped
or spatulate.
Scolex bears 2 slit-like
grooves called bothria
– (1 on the dorsal surface
and 1 on the ventral
surface).
Scolex has no rostellum
and no hooklets.
Neck is thin and
unsegmented and is
much longer than the
head.
Diphyllobothrium latum
3,000 to 4,000 proglottids;
A mature segment is filled
with male and female
reproductive organs.
In gravid proglottids uterus at
the center of the segment
appears in the form of a
rosette.
Terminal segments shrink
and becomes empty as eggs
are constantly discharged.
Dried up segments break off
from the body in chains and
are passed out in the host’s
feces.
Diphyllobothrium latum
Diphyllobothrium latum
Ova
Passed out in the host’s feces in
large numbers.
Contains abundant granules and
unsegmented ovum.
Inconspicuous operculum at one end
and a small knob at the other end.
Does not float in saturated solutions
of common salt.
A single egg gives rise to a single
larva.
Not infective to man.
Egg
Diphyllobothrium latum
larva
Passed first in water and then in the respective intermediate
hosts.
3 stages:
– First larval stage
 Coracidium
Ciliated oncosphere that develops from egg in water
– Second larval stage
 Procercoid
Spindle-like solid body with cephalic invagination
Found inside the cyclops (the first intermediate host)
– Third larval stage
 Plerocercoid
Head is invaginated in the neck
Found in the fresh water fish (the second intermediate
host)
Diphyllobothrium latum
Final Host
Man, dog, cat (small intestine)
1st I.H.
Cyclops or Diaptomus
2nd I.H.
Fresh water fish, pike, trout, salmon, perch
Mode of Infection for humans
Ingestion of imperfectly cooked infected fish or roe containing
plerocercoid larvae
Infection
Diphyllobothriasis
G.I. disturbances and anemia
Diagnosis
Microscopic examination of feces for the characteristic
operculated eggs
Spirometra spp.
Sparganosis
Cyclophyllidea:
Taenia spp.
Taenia spp. life cycle
Taenia saginata
Taenia saginata
Beef Tapeworm;
Unarmed Tapeworm of
Man;
Scolex is globular in
outline with 4 circular
suckers;
Adult worms are white
and semi-transparent;
Measures about 5-10
meters or sometimes up
to 24 meters!!!
1000 to 2000 proglottids;
Live up to 10 years or
more.
Taenia saginata
Common genital pore is
marginally situated;
Vagina is provided with a
sphincter muscle;
Gravid proglottid consists of a
uterus and a central
longitudinal stem with 15-30
branches on each side;
Gravid proglottid contains
97000 to 124000 ova;
Gravid segments are expelled
singly and force their way
through the anal sphincter;
Free gravid proglottid crawls
out of the anal orifice and
oviposits on the perianal skin.
Taenia saginata
Ova
Liberated by rupture of
ripe proglottids;
– No uterine opening;
Spherical, thin, outer
transparent shell;
Inner embryophore is
brown, thick walled and
radially striated;
Has an oncosphere with
3 pairs of hooklets;
Eggs are resistant and
remain viable for 8
weeks;
Infective only to cattle.
Taenia saginata
Final Host: Man
Intermediate Host: cattle, cow buffalo
Mode of Infection: eating beef containing cysticercus
Pathogenesis (Taeniasis):
‾
‾
‾
‾
‾
‾
‾
‾
‾
Passage of proglottids in stool
Mild irritation at site of attachment
Epigastric pain
Hunger fangs
Weakness
Weight loss
Loss of appetite
Pruritis
Obstruction in intestine but also in bile and pancreatic ducts and
appendix because proglottids are actively motile!
Taenia saginata
Diagnosis
Identifying characteristic eggs, proglottids or scolex
Usual specimen is gravid proglottids (lateral
branches 15-20)
Concentration techniques for eggs (eggs rarely
passed out in stool)
Perianal swabs
Treatment
Praziquantel
– 5-10mg/kg single dose
Criteria for cure
Recovery of the scolex
Negative stool examination 3 months after
treatment
Taenia solium
Taenia solium
Pork tapeworm;
Armed tapeworm of man;
Scolex is globular in outline with
4 circular suckers;
Scolex has a rostellum armed
with a double row of alternating
large and small hooklets;
Rostellar hooklets are shaped
like daggers or Arabian poniards.
800-900 proglottids;
Adult worms measure 2-5 meters
and live up to 25 years!
Taenia solium
Common genital pore is
marginal and thick lipped;
Vaginal opening is not
guarded by a muscular
sphincter;
Gravid segments are
expelled passively in
chains of 5-6 at a time
and not singly;
Gravid proglottids
contains approx. 30.000
to 50.000 eggs.
Taenia solium
Ova
– Same as those of T.
saginata;
– Infective to man as
well as pigs;
– Thick brown striated
embryophore
surrounding a
hexacanth embryo.
oncosphere
hooks
Taenia solium
Final Host: Man
Intermediate Host: Pig (accidentally Man,
cysticercosis)
Mode of infection: eating measly pork
containing cysticercus
Diagnosis: stool examination for
proglottids/eggs
Taenia solium
Pathogenesis
Mild, non-specific abdominal complaints
Proglottids are not as motile as T. saginata so organ
obstruction is less likely.
Cysticercosis
Multiple
Develop in any organ or tissue
Neurocysticercosis (most serious zoonotic disease)
Chorioretinitis
vasculitis
Cysticercosis
Taenia solium
Diagnosis:
 Intestinal
Identifying the characteristic proglottids, eggs or scolex
 Cysticercosis
Computed Axial Tomography
Magnetic Resonance Imaging
Treatment
Praziquantel: 5-10 mg/kg single dose for children and adults
Niclosamide not available locally
Criteria for cure:
Recovery of scolex
Negative stool exam 3 months after treatment
Comparison between
T. saginata and T. solium
Taenia saginata Taenia solium
length
5-10 meters
2-5 meters
Head or scolex
Large, quadrate, no
rostellum and hooks
Armed; with rostellum;
with hooklets
Number of proglottids
1000 to 2000
Below 1000
Expulsion
Expelled singly and may
be forced through the
anal sphincter
Expelled passively in
chains of 5 or 6
uterus
Highly branched with 1530 lateral branches on
each side; thin;
dichotomous
Lateral branches 5-10 on
each side, thin, dendritic
and vaginal sphincter is
absent
testes
300-400 follicles
150-200 follicles
Cyclophyllidea:
Echinococcus granulosus
Echinococcus granulosus
Taenia echinococcus
Dog Tapeworm
Hydatid Worm
Man harbours the larval form
and not the adult worms which
however is found in the intestine
of dogs and canines
Echinococcus granulosus
Adult worms are small
(3-6 mm in length)
It is composed of a
Scolex
Neck
Strobila
3 segments
(occassionally 4)
Immature
Mature
Gravid
Echinococcus granulosus
Scolex bears 4
suckers and a
protrusible rostellum
with 2 circular rows of
hooks.
Echinococcus granulosus
Echinococcus granulosus
Echinococcus granulosus
Ova
Ovoid in shape
Resemble Taenia ova
Hexacanth embryo with
3 pairs of hooks
Infective to:
Man
Cattle
Sheep and other
herbivorous animals
Echinococcus granulosus
Larva
Found within the hydatid cyst developing inside
the intermediate host;
Represents the structure of the scolex of the future
adult worm;
Young larva are transformed into a hollow bladder
(hydatis, drop of water);
Brood capsules develop within the cysts and may
contain thousands of scolices;
On entering the final host, the scolex armed with a
rostellum and 4 suckers become adult worms.
Echinococcus granulosus
Definitive Host
Dog
Wolf
Fox
Jackal
Intermediate Host
Sheep
Pig
Cattle
Horse
Goat
Echinococcus granulosus
Echinococcus granulosus
Pathogenesis
Echinococcosis
Pathology is caused by the developing larval cyst
in the intermediate host;
Most common site of involvement is the liver;
Echinococcus granulosus cyst:
– Unilocular hydatid cyst
Echinococcus multilocularis cyst:
– alveolar cyst
Some may be asymptomatic for years;
Rupture of cyst in the lungs may present coughing
accompanied by allergic reactions.
Echinococcus granulosus
Echinococcus granulosus
Encysted scolices of Echinococcus granulosus in lung
"hydatid sand"
Echinococcus granulosus
Encysted scolices of E. granulosus in lung "hydatid
sand"
Echinococcus granulosus
Encysted scolices of E. granulosus in lung "hydatid
sand"
Echinococcus granulosus
Diagnosis
Radiographic findings
Immunodiagnosis
Antibody detection
IHA
IFA
EIA
Antigen detection
Echinococcus granulosus
Treatment
Surgical resection: not 100% effective
Scolicidal agent
Hibitane
95% ethanol
Hypertonic 30% Normal Saline Solution
PAIR technique for inoperable cyst
Puncture, Aspiration, Injection, Reaspiration
Intervention
Albendazole
Hymenolepis species
Hymenolepis sp.
Genus is derived from the membranous character of the
egg shell “hymen”;
3 testes in each mature segment;
Uterus is sac-like and transverse;
Eggs possess two membranes (outer membrane is thin
and transparent);
Larval stage is called cysticercoid;
– Small bladder containing the invaginated head proximally and a
solid, elongated portion as a caudal appendage;
There are 2 species:
Hymenolepis nana
Hymenolepis diminuta
Cyclophyllidea:
Hymenolepis nana
Hymenolepis nana
Dwarf Tapeworm
Smallest tapeworm infecting man
Found worldwide
Mainly among children
Only human tapeworm that can complete its life
cycle in a single host
Man can harbour both the adult and larval
stages of the parasite
Exception to the general rule that: “Helminthes
do not multiply inside the body of the definitive
host”
Hymenolepis nana
Adult found in the ileum
Delicate strobila
25 mm to 45 mm
Worms may be present in
large numbers from 1,000
to 8,000
Short life span, about 2
weeks
Up to 200 proglottids
Transverse uterus
3 testes
Hymenolepis nana
Scolex
Subglobular
4 suckers
Provided with a short
retractile rostellum armed
with a single row of 20-30
hooklets
Rostellar hooklets are
shaped like tuning forks
Hymenolepis nana
Ova
Spherical or oval
– Floats in saturated solutions
of common salt
2 distinct membranes
– Outer membrane is thin
transparent and colourless
– Inner embryophore that
encloses an oncosphere with
3 pairs of lancet shaped
hooklets
– Intermembranous space is
filled with yolk granules and 48 polar filaments emanating
from little knobs at either end
of the embryophore
Hymenolepis nana
Mode of transmission:
Direct
Host ingests eggs that hatches in the duodenum
Indirect pathway
Accidental ingestion of infected arthropod
intermediate host like rice and flour beetles in
which cysticercoid larvae are released and
develop into adult worms in the small intestine of
the host
Hymenolepis nana
Hymenolepis nana
Pathogenesis
Symptoms are produced due to patient’s immunological
response to the parasite
Asymptomatic for light worm burden
Headache
Dizziness (vertigo)
Anorexia
Pruritus of the anus
Abdominal pain
Pallor
Desquamation of intestinal epithelial cell or as serious as
necrosis may occur
Regulatory immunity will eventually limit the
infection
Hymenolepis nana
Diagnosis
Demonstration of characteristic ova in the stool
Proglottids are not recovered because they
undergo degeneration prior to passage
Treatment
Praziquantel
– 25mg/kg single dose
– Drug dosage is higher than that of taeniasis because
of resistant cysticercoids in intestinal tissue
Hymenolepis nana
Epidemiology
Countries with warm temperature
Southern USA
Latin America
Mediterranean
East Asia
Philippines
Cyclophyllidea:
Hymenolepis diminuta
Hymenolepis diminuta
Rat tapeworm
Common parasite of rats and mice
Accidental human infections
Differs from Hymenolepis nana in morphology
and life cycle because it requires an
intermediate host
2 Hosts
Larval stage: cysticercoid is passed in fleas
Adult stage: in rats and mice and accidentally in humans
especially children who accidentally ingest infected fleas
Hymenolepis diminuta
Hymenolepis diminuta
Adult
Larger than
Hymenolepis nana
Measures 60 cm in
length
Hymenolepis diminuta
Scolex
Unarmed
rostellum
4 suckers
Hymenolepis diminuta
Hymenolepis diminuta
Proglottid
(800 – 1000)
Mature proglottids of H.
diminuta from the laboratory
rat.
The three spherical bodies
are testes which surround the
ovaries, ootype and vitelline
glands.
The genital pores are on the
left margin
Hymenolepis diminuta
Ova
Larger than H.
nana
Outer shell is
yellowish in color
Inner embryohore
has 2 knob-like
thickenings
No polar filaments
Hymenolepis diminuta
Cysticercoid of H. diminuta
The suffix indicates it is like
a cysticercus but this larva
has no bladder but instead
has a tail.
The dark body within the
spherical portion is the
scolex.
The longer the tail, the more
mature the cysticercoid.
This stage is found inside
the intermediate host.
Hymenolepis diminuta
Pathogenesis
Hymenolepiasis
Worm burden in rodents is relatively
low
In man, clinical manifestations are
minimal and non-specific
Hymenolepis diminuta
Treatment
– Praziquantel
– 25 mg/kg body weight single dose
Epidemiology
– World wide
– Common among children due to ingestion of infected
grain beetles, dried fruits, flour and cereals
– Prevalence of H. diminuta in Philippine rats is about
8%.
Cyclophyllidea:
Dipylidium caninum
Dipylidium caninum
Double Pored Dog
Tapeworm
Presence of bilateral
genital pores in each
segment
Common intestinal
parasite of dogs
Dipylidium caninum
Adult
10-70 cm in
length
Pale reddish
Dipylidium caninum
Scolex
Small and globular
4 deeply cupped
elliptical suckers
Protrusible/retractile
rostellum
Rostellum has 1-7
rows of rose thorn
shaped hooklets
Dipylidium caninum
Strobila
200
proglottids
narrow
Dipylidium caninum
Mature proglottids
2 sets of male and
female reproductive
organs
Bilateral genital
pores
Dipylidium caninum
Gravid proglottids
A. Have size and
shape of pumpkin
seeds
A
B. Filled with
capsules or
packets of 8-15
eggs enclosed n
an embryonic
membrane
B
Dipylidium caninum
Proglottids
Dipylidium caninum
Dipylidium caninum
Dipylidium caninum
Ova
Passed out in the feces
along with the proglottids
Released by contraction of
proglottids or disintegration
outside the host
Spherical
Thin shelled
With a hexacanth embryo
These eggs, still wrapped in
fragile egg packets, came from
a single motile and gravid
proglottid
Dipylidium caninum
Intermediate hosts:
Dog flea (Ctenocephalides canis, Trichoedectes
canis)
Cat flea (Ctenocephalides felis)
Human flea (Pulex irritans)
Dipylidium caninum
Pathogenesis
Dipylidiasis
Rarely multiple
Symptoms are minimal
Slight intestinal discomfort
Epigastric pain
Diarrhea
Anal pruritus
Allergic reactions
Dipylidium caninum
Treatment
– Praziquantel
– 5-10 mg/kg body weight single dose
Epidemiology
–
–
–
–
–
USA
Rhodesia
Argentina
China
Philippines