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