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CESTODES
Dr. R. Tan
Parasites
Protozoa Metazoa
Sarcodina(Amoebas)
Sporozoa(Sporozoans)
Mastigophora
(Flagellates)
Ciliata(Ciliate
s)
Platyhelminthes(Flatworms)
Nemathelmithes(Roundworms)
Trematoda
(Flukes)
Cestoda(Tapeworms
)
Classification of Parasites
PHYLUM PLATYHELMINTHES
CESTODES TREMATODES(Tapeworms) (Flukes)
Pseudophyllidea Cyclophyllidea
Genus Diphyllobothrium Genera: Taenia, Hymenolopis, Dipylidium, Echinococcus
Cyclophyllidean Tapeworms
Family Genus Species
Taeniidae Taenia
Multiceps
Echinococcus
solium
saginata
multiceps
granulosus
multilocularis
vogeli
Hymenolepidae Hymenolepis nana
diminuta
Dipylidiae Dipylidium caninum
Pseudophyllidean Tapeworms
Diphyllobothriiidae Diphyllobothrium latum
pacificum
Spirometra houghtonimansoni mansonoides
CESTODES(TAPEWORMS)
exclusively parasitic Adult worms are flattened, segmented with ribbon-like body
that inhabit the small intestine, where they live attached to the mucosa
do not have digestive system obtain their nutrition by direct absorption across their
teguments The tegument is the body surface of the adult tapeworm (the
surface structure layer of cell) from the host`s intestine Sexual organs are highly elaborated and complicated sexes combined in a single parasite --- hermaphroditic
(both sex in one organ)
Sexual reproduction occurs by either self-fertilization or by cross-fertilization between proglottids
Wide range of pH (4-11) portal of entry: mouth The disease produced is due to the fact that tapeworms
absorb significant quantities of nutrients and vitamins, excrete toxic wastes and interfere with the normal passage of food through the intestine
Body parts: (1) Scolex / Head
the anterior portion that contains the cephalic ganglion, or “brain”
has hooks and suckers that permit anchoring in the host`s intestinal wall
strictly an attachment organ The main nerve center of a cestode is in its scolex
Motor and sensory innervation depends on the number and complexity of the scolex
cyclophyllideans rostellum is a retractable, conelike structure that is located
on the anterior end of the scolex, and in some species is armed with hooks
Acetabula (sucker-like organ, normally 4) pseudophyllideans
bothria are long, narrow, weakly muscular grooves, called "sucking grooves," and function like suction cups
(2) Neck Constricted area is the organ for growth from which proglottids proliferate
(3) Proglottids / Strobila Strobila : Chain of segments Proglottids: segments ( immature/mature/gravid) the strobila grows throughout the life of the tapeworm by
continuous proliferation of new proglottids in the neck region sexually complete unit is thin, resembling a strip of tape (tapeworm)
Number of strobila varies with: size of worm age of host host-parasite compatibility harmful effects on the host
Conditions that cause avulsion of the strobila: Increased peristalsis Starvation Intoxication
(a.) immature proglottids immature proglottids continue to grow from the neck area and
push older maturing proglottids downwards Do not contain fully developed internal structures
(b.) mature proglottids Are larger and found near the middle of the chain each may contain one or two sets of both male & female
reproductive organs
(c.) gravid proglottids terminal portion of the strobila that is usually filled with eggs eggs are enclosed in the uterus gravid proglottid of some specie may become detached in the
intestine and pass out in the feces; but some maybe too small to be seen in gross examination
After leaving the host, the proglottids rupture and eggs are released
Precise identification of the tapeworm is usually made on the basis of eggs or proglottids, the scolex of each specie is quite characteristic and is sufficient for specific diagnosis
Pathogenicity is attributed to: Mechanical obstruction Tissue margination pyogenic actions/inflammatory reaction toxic action
Cyclophyllidean Tapeworms
Scolex transversely quadrate/globular 4 cup-like muscular suckers w/ rostellum
(spine/hooks)
Female reproductive SystemOv - Ovary
Oo - Ootype (where the egg is formed) Ut - Uterus
Ut p. - Uterine pore - absent in cyclophilledeans, Uterus ends blindly
V - Vagina (a long straight tube) Vt - Vitelline glands Vt d. - Vitelline duct (connecting the vitelline gland)
Male Reproductive SystemT - Testes Few and large (Hymenolepis) * Numerous (500 or more) large and small (Taenia)
V - Vas deferens C - Cirrus (a protrusible muscular organ, opening anterior to the vagina in a common genital atrium) Other Features LG A - Lateral Genital Atrium/ Pore
- Margins of each proglottid may be located: * both sides in an irregular pattern (Taenia spp.) * same lateral side (Hymenolepis spp) * one on each side (D. caninum)L E C - The Lateral Excretory Canal
Eggs- have a very thick, resistant egg shell, with no operculum- spherical, mature, embryonated when laid- the cyclophyllidean eggs are released only when the tapeworms shed gravid proglottids into the intestine - Some proglottids disintegrate, releasing eggs that are voided in the feces, whereas other proglottids are passed intact
embryo of Cyclophyllidean- Hexacanth embryo / Oncosphere / 6-hooked embryo
(3 pairs of hooklets, - non-ciliated)
Larva
Host - one intermediate host; one definitive host
T. SoliumT. Saginata H. nana/diminuta D. Caninum E. granulosus
Cysticercus cellulosaCysticercus bovisCysticercoid larvaCysticercoid larvaHydatid cyst
Pseudophyllidean Tapeworms Scolex
narrow, spoon-shaped, elongated 2 sucking grooves (bothria)
Female Reproductive System Ov - Ovary (central, bilobed in D. latum.)
Oo - Ootype
Ut - Uterus - mature uterus - Coiled tube opening on surface via the uterine pore - gravid uterus – filled with eggsUt p. - Uterine pore - located at center of proglottids on ventral surface
V - Vagina (a long straight tube)
Vt - Vitelline glands/ vitellaria
- secreting substances that will make up the egg yolk and shell
- numerous, small scattered laterally (D. latum)
Vt d. - Vitelline duct (connecting the vitelline gland)
M - The Mehlis gland (A cluster of unicellular shell glands, absent in some species)
Male Reproductive System T - Testes (dorso-lateral, numerous (500 or more) and small, arranged on the lateral margins ) V - Vas deferens C - Cirrus (a protrusible muscular organ, opening anterior to the
vagina in a common genital atrium)
Other Features G A - Genital Atrium/ Pore (a cup shaped sinus, where the cirrus
and vagina have common openings) - located at the center of segmentL E C - The Lateral Excretory Canal
Eggs- ovoidal, immature, non-embryonated with a thin shell wall, and an operculum, which on hatching opens to release the free swimming larvae-Eggs exit through a uterine pore in the center of the ventral surface rather than through a genital atrium
embryo of Pseudophyllidean: Coracidium (ciliated) Larva: Procercoid , Plerocercoid
Host: 2 intermediate hosts and 1 definitive host
Pseudophyllidean Tapeworms
Diphyllobothrium latum
Broad or fish tapeworm, or broad fish tapeworm Disease: Diphyllobothriosis longest tapeworm in humans, averaging 10 meters long Adults can shed up to a million eggs a day Geog. Dist:
worldwide Occurring in northern temperate areas of the world where
pickled or insufficiently cooked fresh-water fish are prominent in the diet
High prevalence in Scandinavia, Finland, Alaska and Canada
Many recent cases in South-East Asia and South America
The life cycle requires 2 intermediate host 1st intermediate host: copepods (fresh-water crustaceans) 2nd intermediate host: fish, snakes, toads
Definitive host: In addition to humans, canids, felines, bears, and many other mammals can also serve as definitive hosts for D. latum
Morphology: Adult worm
measures 3-10 meters or more (ave. 10meters) Longest human tapeworm May have as many as 4,000 proglottids
Scolex Elongate, spoon-shaped the anterior organ of attachment is a bothria, a pair of shallow, elongated muscular grooves
Proglottids Immature segments
Mature segments Wider than long numerous testes and vitellaria arranged on
the lateral margins with a central bilobed ovary
Gravid segments wider than long Uterus is a coiled tube confined to a
relatively small area in the center of the segment likened to a “rosette formation”
An important difference between this parasite and the other tapeworms of man is that the uterus open to the exterior via the uterine pore
(cyclophyllidean tapeworms have closed uterus)
Eggs are therefore actively deposited by the parasite, in contrast to the disintegration of the proglottids seen in the other human tapeworms
Egg 58 to 76 µm L x 40 to 51 µm W Shell is ovoid or ellipsoidal, smooth, and of
moderate thickness possess an operculum at one end for the
escape of the larva At the opposite (abopercular) end is a small
knob that can be barely discernible Immature, unembryonated, operculated
eggs are discharged from the proglottids
(up to 1,000,000 eggs per day per worm) and are passed in the feces
Eggs appear in the feces 5 to 6 weeks after infection
Life cycle of D. latum
Coracidium emerging from the eggs, is internally similar to the
hexacanth larvae of the Cyclophyllideans, being equipped with 6 hooks, but this hexacanth larvae is covered in a ciliated embryophore
is a free swimming stage, but cannot survive long, so for further development it must be ingested by 1st IH
Procercoid larva 1st larval stage developing from the hexacanth larva
appearing as solid bodies with the remains of the embryonic hooks from the onchosphere larvae at the posterior of the parasite
found in the first intermediate host
Plerocercoid larva (sparganum) 2nd larval stage developing from the procercoid larva
which has lost the hooks, the body is elongated, wormlike with an anterior invagination
found in the second intermediate host Infective stage for humans
Diphyllobothriasis Infection is relatively harmless and asymptomatic Symptoms: non-specific abdominal signs, including abdominal
pain and loss of weight D. latum absorbs much more vitamin B12, (10-50x more) from the
host’s intestinal tract than other tapeworms and interferes with the patient's ability to absorb vitamin B12
(vit B12 having an important role in formation of RBC) Infection may therefore result in pernicius anemia
(a macrocytic, hypochromic anemia) Treatment
Drugs of choice: Praziquantel 10mg/kg single dose (95% cure rate) Niclosamide
Control Proper disposal of human feces Fish should be thoroughly cooked or frozen at -10°C for 24-48hrs
RELATED SPECIES
Diphyllobothrium pacificum Found in the costal areas of Peru is the most common tapeworm
infecting humans It is a natural parasite of seals which acquire infection by eating fish Ceviche – a delicacy in Peru and other Latin American countries
using fish marinated in lime juice but not cooked
Diplogonoporus Related genus of tapeworms common in Japan, where it is probably
acquired by consumption of raw anchovies or sardines
Spirometra Family: Diphyllobothriidae
Genus: Spirometra
Species: S. erinacei (cats, dogs)
S. felis (big zoo cats)
S. mansoni (cats, dogs)
S. mansonoides (cats, dogs, raccoons)
S. houghtoni
S. proliferum
pseudophyllidean tapeworm similar to Diphyllobothrium spp. that occurs in the intestines of wild carnivores and domestic cats and dogs
the plerocercoid larvae infest amphibians but humans can also be infected, the resulting disease being known as sparganosis
Sparganum plerocercoid larval form wrinkled, whitish, ribbon-shaped organism,
3 mm in width and up to 30 cms long The sparganum is a solid-bodied larva that lacks
a bladder, and has bothria at the anterior end The larva has an unsegmented strobila
20 to 30 cm in length, bundles of longitudinal muscle fibers scattered throughout the mesenchyme, and a thick tegument
Life cycle:
1st intermediate host is the copepod
(planktonic crustacean of the genus Cyclops)
ingests coracidia that develop from Spirometra eggs when they reach the water with the feces of dogs or cats
In the tissues of the copepod, the coracidium turns into the
first larval form (procercoid larvae)
2nd intermediate host (a wide spectrum of vertebrates including amphibians, reptiles, birds and small mammals) ingests an
infected copepod, the procercoid develops into a
second larval form (plerocercoid larvae or sparganum)
the sparganum develops into the adult Spirometra in the intestines of dogs and cats, which are the definitive hosts
Sparganosis Humans can acquire mainly by:
ingesting larvae contained in raw or undercooked meat of animals (the 2nd intermediate hosts) infected with sparganum
Drinking water containing copepods infected with the procercoid larval stage larva penetrates the gut wall/ and works its
ways to the muscles or subcutaneous tissues where it grows into the sparganum larva
Eating raw snakes or tadpoles for medicinal reasons Placing poultices of frog or snake flesh on open wounds or other
lesions, especially the eyes
Clinical Presentation: manifestations depend on which organs or tissues are involved Subcutaneous tissues are most likely to be infected by the parasite, but
visceral organs and the orbit of the eye, and rarely, the brain the early migratory stages is asymptomatic, but when it has reached its
final site and begins to grow, its presence elicits a painful inflammatory reaction in the surrounding tissues
ocular sparganosis- Produces intense reaction, with periorbital edema, intense pain,
irritation, excessive lacrimation, and marked swelling of the eyelids- If retrobulbar in position, the orbit maybe forced out, the lids do not
close and corneal ulcers develop- Ocular sparganosis may result in blindness, as the parasite migrates
to the conjunctiva and enters the orbit
cerebral sparganosis - characterized by seizures, fatigue, confusion,
headaches, memory loss, coma, fever, paresthesias, hemiparesis, motor weakness and other CNS symptoms
- Cerebral sparganosis most likely involves the cerebral hemispheres, especially the frontoparietal lobes, in some cases
extends to the cerebellum - The disease may appear as
a massive cerebral hemorrhage
Proliferative sparganosis Caused by a peculiar budding type of
larva known as Sparganum proliferum
branched, proliferating larvae may break up into segments capable of further independent development
begins with a subcutaneous tumor in the thigh, shoulder, or neck, and eventually spreads to other parts of the skin, the muscles, and the internal organs, such as the lungs, abdomen, and brain
Nodules may open because of ulceration or scarification
Infection progresses over 5 to 25 years fatal in all reported cases
Diagnosis: Made following surgical removal of the worm Presumptive preoperative diagnosis: painful migratory
subcutaneous nodule
Management and Therapy: Surgical removal of sparganum larvae is usually curative Praziquantel 120-150 mg/kg body weight, over a 2-day period
However, praziquantel has no effect on adult worms in the CNS
There is no available treatment for proliferative sparganosis
Prevention: people should be advised of the dangers of drinking water from
ponds and ditches, which may contain infected copepods Basic public health infrastructure should be strengthened so that all
people have access to clean drinking water the use of potentially infected animals for medicinal purposes must
be discouraged
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