*All tapeworms that parasitize humans belong to orders Pseudophyllidea and Cyclophyllidea* Intestinal Cestodes- Taenia saginata, Taenia solium, Hymenolepis nana, Hymenolepis diminuta, Dipylidium caninum, Raillietina garrisoni, Diphyllobothrium latum*Extraintestinal Cestodes- Echinococcus sp., Sparganosis

ORDER PSEDUDOPHYLLIDEA General life cycle involve crustacean 1st

intermediate hosts and fish 2nd intermediate hosts

Family Diphyllobothriidae Diphyllobothrium latum Broad fish tapeworm Infects canines, felines, mustelids, pinnipeds,

bears and humans Epidemiology: 9 million affected worldwide,

persons become infected after eating raw/undercooked fish

Morphology Adult may attain length of 10 m and shed up

to a million eggs/day Scolex is finger-shaped Has dorsal and ventral bothria Proglottids have greater width than length May have 4000 proglottids Numerous testes and vitelline follicles

scattered throughout each proglottid Male and female genital pores open

midventrally Eggs

Ovoid, 60 μm by 40 μm Has a lidlike operculum at one end and a

small knob at the other end

Biology Eggs

Released at the uterine pore Must reach water for embryogenesis

Infection of copepods (Diaptomus and Cyclops)impairs their motility rendering them more liable to predation

2nd IH-freshwater fishes (pike or any of the salmon family)

2nd IH fish can be eaten by bigger fishes, plerocercoids can migrate into the new hosts; larger fish being a paratenic host

Plerocercoids are unencysted and coiled up in the fish musculature, may also be encysted in the viscera (seen as white masses in uncooked fish)

Life Cycle1. Definitive hosts are any number of fish-

eating mammals2. Adult worms reside in mammalian small

intestine3. Shelled embryo is passed out in feces at

the early stage of development4. Embryogenesis continues in water, and

free-swimming coracidium hatches5. Coracidium eaten by copepod (1st IH)

and oncosphere penetrates intestines into hemocoel

6. Procercoid develops into hemocoel7. Copepod eaten by fish (2nd IH), where

procercoid penetrates into muscle and develops into plerocercoid

Pathogenesis Many are asymptomatic Non-specific symptoms

Vague abdominal discomfort Diarrhea Nausea Weakness

can cause megaloblastic anemia in few cases (vitamin B12 absorbed by the worm)

Diagnosis and Treatment demonstration of eggs and proglottids in the

stool DOC: niclosamide (Yomesan) and praziquantel

Other Pseudophyllideans Found in Humans D. cordatum, D. pacificum, D. cameroni, D.

hians, D. lanceolatum (pinnipeds), D. ursi (bears), D. dentriticum, D. nihonkaeiense (predominant in Japan), Diagramma brauni, Ligula intestinalis, Diplogonoporusgrandis (whales)

Sparganosis Accidental ingestion of procercoids when a

person ingests infected copepods through drinking water

References:Robert’s Foundations of Parasitology-7th edPhilippine Textbook of Medical

CESTODES (TAPEWORM)

Also through ingestion of insufficiently cooked amphibians, reptiles, birds or mammals

Also through treatment of skin ulcers, inflamed vagina or inflamed eye by poulticing the area with split frog or flesh of a vertebrate infected with spargana

\ORDER CYCLOPHYLLIDEA

Have scolices with 4 acetabula Has a single, compact postovarian vitelline

gland Rostellum is typically present Genital pores are lateral May grow up to 10 m

Family Taeniidae Most medically important tapeworms of human With nonrectractable rostellum

With numerous testes, ovary-bilobed mass near the posterior margin of the proglottid

Taenia solium most dangerous adult tapeworm of humans humans serve as IH (contamination of food

with eggs passed by infected person) and definitive host

infection with eggs results in development of cysticerci (cysticercosis)

Morphology scolex of an adult bears nonretractable

rostellum with two circles of 22-32 hooks, spheroid about 1mm in diameter

2-3 m but may grow to 10 m Mature segments wider than long Gravid segments longer than wide with 7-13

lateral uterine branches Gravid proglottids contain 30-50k ova

Biology Blowlies can carry eggs from infected feces to

uninfected meat readily eaten by pigs Dogs and cats can also serve as IH Worms can live up to 25 years

Life Cycle1. Adult tapeworm resides in the small

intestines of humans.2. Gravid proglottids detach from the strobila

and migrate out of the anus or passed with feces.

3. If eaten by humans, the oncosphere hatches, migrates to some site in the body, and develops into a cysticercus.

OR3. If eaten by pig, oncosphere in intestine

migrates to muscle of the pig and develops into cysticercus in pig muscle.

4. The cycle is completed when a person eats raw/undercooked pork.

Cysticercosis Develop readily in humans Occurs when shelled larvae pass through the

stomach and hatch in the intestine Acquired from infected persons who

contaminate their households Cysticerci can be found in subcutaneous

tissue, eye, brain, muscle, heart, liver, lungs and coelum

Symptoms corresponds to the area of cysticerci

Severe inflammatory response develops after a cysticercus dies

Has three types Cellulose-with an invaginated scolex and a

fluid-filled bladder about 0.5-1.5cm in diameter

Intermediate-with a scolex Racemose-with no evident scolex, much

larger and more dangerous

Taenia saginata Most common in humans Acquired from eating infected beef Lacks rostellum or scolex armature Commonly 3-5 m but may reach up to 20 m Consists of around 2000 segments Killed at 56⁰C Humans serve as definitive host, never as an

IH Cosmopolitan in distribution A gravid proglottid may contain 97-124K ova DOC: Praziquantel, 5-10mg/kg as single dose Criteria for treatment: recovery of the scolex,

negative stool examination 3 months after treatment

Morphology Scolex with 4 suckers, cuboidal up to 2 mm in

diameter Segments slightly wider than long Eggs

Spherical or subspherical Brownish in color Embryophore is thick riddled with

numerous tiny pores (giving a striated appearance)

Difficult to distinguish from other species

Biology When gravid segments detach, they behave

like individual worms. As a segment dries up, a rupture occurs at the midventral body wall allowing eggs to escape

Tangled proglottids may result to intestinal obstruction

Motile proglottids were documented to cause obstruction in bile and pancreatic ducts and the appendix

IH-primarily cattle. Also reported in llamas, goats, sheep, giraffes and reindeer

Eggs hatch in the duodenum under influence of gastric and intestinal secretions

Hexacanth penetrate mucosa and enter intestinal venules to be carried throughout the body

Nonspecific symptoms- epigastric pain, vague discomfort, hunger pangs, weakness, weight loss, loss of appetite

Life Cycle*same with Taenia solium, with cattle being the IH

Taenia asiatica Similar in morphology to Taenia saginata Cysticerci develop in pigs primarily in the liver

and other viscera not in the muscle Cysticerci have small hooklets on their scolex

Other Taeniids of Medical Importance Taenia multiceps (sheep), T. glomeratus, T.

brauni, T. serialis

Echinococcus granulosus Smallest tapeworms in Taeniidae Form huge cysts that are capable of infecting

humans Cause cystic echinococcosis Definitive hosts- carnivores particularly dogs

and other canines Adults live in the small intestine Measure 3-6mm long when mature, consist of

a typical taeniid scolex, short neck and 3 proglottids

Nonretractable rostellum bears a double crown of 28-50 (usually 30-36) hooks

SegmentsAnteriormost-immatureMiddle- usually matureTerminal-gravid

Eggs cannot be differentiated from other Taeniids

Same hatching and migration as Taenia saginata except liver and lungs are usually the sites of development

Genital pore is equatorial Has 45-65 testes with a few located anterior to

the cirrus pouch Symptoms correspond to the location where

hydatid cysts are found Up to 20 years may elapse between infection

and overt pathogenesis Host are sensitized to Echinococcus antigens

and sudden release of massive amounts of hydatid fluid results to anaphylactic shock

Life Cycle1. Shelled oncosphere is passed in the feces

and eaten by hooved animals or humans2. Oncosphere penetrates gut wall and is

carried to the liver and other sites by circulation

3. Hydatid cysts form in the organs of intermediate hosts (example sheep)

4. After ingestion of a canid, hydatid cyst is digested and scolex evaginates

5. Scolex attachés to the intestinal wall and develops into strobila

Epidemiology Humans-accidental intermediate hosts Dogs are usually infected by feeding on offal

of butchered animals Different cultural practices that promote

infection Tanning of leather with dog feces in Lebanon Eating of dog intestine in Kenya Lack of appropriate burial practice in Kenya

result to corpse being eaten by carnivores. In this case, humans become true intermediate host

Diagnosis and Treatment X-ray, ultrasonography, CAT scan,

immunodiagnostic techniques Surgery-routine treatment Albendazole-inoperable cyst

Echinococcus multilocularis Causes alveolar echinococcosis Boreal in distribution, widespread in Eurasia Parasites of foxes but dogs, cats and coyotes

are definitive hosts Small rodents- voles, lemmings and mice are

IH Is 1.2-3.7 mm long Genital pore is preequatorial Has 15-30 testes located posterior to the cirrus

pouch Metacestode form is called alveolar or

multilocular hydatid Has a thin outer wall that grows and infiltrates

processes into the surrounding host tissue Protoscolices may not develp in humans Praziquantel enhance growth of alveolar

hydatids Albendazole may be effective for treatment Prevention: avoiding dogs and their feces in

endemic areas; washing of strawberries, cranberries and the like that may be contaminated by dung

Echinococcus vogeli Cause polycystic echinococcosis Definitive host-bush dogs, Speothus venaticus

Cyst are relatively large, fluid filled vesicles with numerous protoscolices

IH- pacas and agoutis (rodents)

Echinococcus oligarthrus Infections are rare Definitive host-several species of wild cats Cyst are relatively large, fluid filled vesicles

with numerous protoscolices IH- pacas and agoutis (rodents)

Family Hymenolepididae Most characteristic morphological feature of

the group is the small number of testes: usually 1 to 4

The combination of few testes, usually unilateral genita pores, and a large external seminal vesicle permits easy recognition of the family.

All except H. Nana require arthropod intermediate hosts.

Hymenolepis nana Commonly called the dwarf tapeworm

because it is the smallest tapeworm infecting humans.

It is found worldwide, mainly among children. The only human tapeworm, which can

complete its entire life cycle in a single host, indicating that it does not require an obligatory intermediate host.

Man can harbour both the adult and the larval stages of the parasite.

Morphology Adults are found in the Ileum Has strobila measuring from 25-45 mm in

length and 1 mm in with. Scolex

o subglobular with 4 cup-shaped suckerso bears a retractable rostellum, armed

with a single circle of 20-30 Y-shaped hooklets.

Neck is long and slender, and the segments are wider than long.

Genital pores are unilateral Mature proglottids contains 3 ovoid testes and

one ovary in a more or less straight pattern across the segment

When segments become gravid, the testes and the ovary disappear while the uterus hollows out and becomes filled with eggs.

Gravid segments are separated from the strobila and disintegrate as they pass out of the intestines, releasing eggs in the stool.

Eggso 30-47 um in diametero Oncosphere is covered with a thin,

hyaline, outer membrane and an inner, thick membrane with bipolar thickenings that bear several polar filaments embedded in the inner membrane.

Life Cycle- has dual pathwayDIRECT

1. The host ingests eggs which hatch in the duodenum.

2. The liberated embryos penetrate the mucosal villi and develop into the infective cysticercoids larvae.

3. After 4-5 days, the larvae break out of the villi and attaches to the intestinal mucosa to develop into adults.

INDIRECT1. It is usually via the accidental ingestion of

infected arthropod intermediate hosts like the rice and flour beetles.

2. The cysticercoids larvae are released and will eventually develop into the adult tapeworms in the intestine of the host.

It takes 20-30 days from the time of ingestion, for the eggs to appear in the feces.

Eggs are optimally viable immediately after discharge from the bowel.

Autoinfection can occur through the fecal-oral route or within the small bowel.

Oncospheres from the eggs are released and they invade the host villi to start a new generation.

Pathogenesis and Clinical Manifestations: Hymenolepiasis Symptoms are generally produced because of

the patient’s immunological response to the presence of the parasite.

Light infection: generally asymptomatic o Headache, dizziness, anorexia, pruritus

of nose and anus, diarrhea, abdominal pain, and pallor.

Some infected children are restless, irritable and are observed to exhibit sleep disturbances.

Rarely, convulsions occur. Heavy infection

o enteritis due to necrosis and desquamation of the intestinal epithelial cells.

With time, regulatory immunity may limit or eventually clear the H. Nana population spontaneously

Diagnosis Demonstration of the characteristic eggs in

the patient’s stools. In light infections: concentration of stool

specimens on alternate days is useful. Generally, proglottids are not recovered

because they undergo degeneration prior to passage with stools.

Treatment DOC: Praziquantel (25 mg/kg single dose) –

causes vacuolization and disruption of the tegument in the neck region

Drug dosage for hymenolepiasis is higher than that for taeniasis because of the relatively resistant cysticercoids in the intestinal tissue.

Epidemiology found in countries with warm climate:

Southern USA, Latin America, the Mediterranean, East Asia, and the Philippines.

Transmission generally occurs where there is poor sanitation, overcrowding, and poor personal hygienic practices.

Direct contact plays an important role because the eggs cannot survive long outside the host.

It is also found among mice and less frequently among the rats.

Prevention and Control Environmental sanitation, good personal

hygiene Rodent control Treatment of human cases Food must be properly stored and protected

from possible infestation with grain beetle.

Hymenolepis diminuta Common name: rat tapeworm Accidental human infections do occur

resulting in hymenolepiasis. Requires an intermediate host unlike H.

Nana

Biology Adult

o larger than H. Nanao 60 cm in lengtho Scolex :has rudimentary unarmed

rostellumo Proglottids: like H. nana are broader

than they are long but larger and may reach 0.75 mm in length and 3.5 mm width)

o Arrangement and number of sexual organs are similar with H. nana (3 testes and 1 ovary in straight pattern across the segment).

o Genital pores are unilateralo Each gravid proglottid contains a sac-

like uterus filled with eggs. Eggs

o Circular, 60-80 um in diameter; bile-stained

o Oncosphere is enclosed in an inner membrane, which has bipolar thickening but lacks the bipolar filaments.

The hooklets usually have a fan-like arrangement.

Gravid proglottids separate from the main body of the worm, disintegrate, and release eggs into the feces.

Eggs when ingested by a wide range of adult and larval insects like fleas, beetles, mealworms, earwigs and cockroaches develop into the infective cysticercoids larvae.

When infected insects are ingested by the rat or accidentally ingested by man, the larva is released and develops into the adult worm in about 3 weeks.

Pathogenesis and Clinical Manifestation Worm burden in rodents is relatively low Clinical manifestations are minimal and non-

specific.

Diagnosis ID of eggs from the stool

o H. diminuta eggs are distinguished from H. nana eggs by their more circular shape, larger size, and lack of bipolar filaments.

At times, the whole worm is expelled and the morphology of the scolex may be used as an aid in diagnosis

Treatment DOC: Praziquantel given as a 25 mg/kg

single dose

Epidemiology More common among children than adults

in poor communities with rat infestation.

Prevention and Control Rodent control Elimination of the insect intermediate hosts,

protection of food, especially the precooked cereals

Sanitary disposal of human wastes Treatment of human cases

Dipylidium caninum Very common intestinal parasite of dogs

and cats worldwide. Dipylidiasis in human is accidental.

MorphologyAdult

o Pale reddish, 10-70 cm in lengtho Scolex: small and globular with 4 deeply

cupped suckers and a protrusible rostellum, which is armed with 1-7 rows of rose-thorn shaped hooklets.

o Proglottids: narrow with 2 sets of male and female reproductive organs and bilateral genital pores (double-pored tapeworm)

o Gravid proglottid: have the size and shape of the pumpkin seed; filled with capsules or packets of about 8-15 eggs enclosed in an embryonic membrane.

o When the gravid segments are detached, they either migrate out of the anus or are passed out with the feces.

o They may also crawl out of the anus, and may be passed out involuntarily.

o Ova are released by contraction of the proglottid or by its disintegration outside the host.

Eggso Spherical, thin-shelled with hexacanth

embyo.

Life Cycle1. Some of the egg capsules may remain in the

fur of the host in the host’s resting place.2. Larval fleas ingest the ova as they feed on

epidermal debris.3. In the body cavity of the arthropod, the

hexacanth embryo develops into the cysticercoids larvae, which is able to survive the flea’s development.

4. When the insect is ingested by mammalian hosts (dog, cats, humans), the cysticercoids is liberated and becomes an adult in 3-4 weeks.

Pathogenesis and Clinical ManifestationDipylidiasis

infection is rarely multiple Symptoms are minimal

o Slight intestinal discomfort, epigastric pain, diarrhea, anal pruritus, and allergic reactions

Some patients are asymptomatic

Diagnosisrecovery of the characteristic gravid

proglottids passed out singly or in chain.Stool examination for the presence of egg

capsules is not recommended, since the gravid proglottids do not disintegrate in the intestines but in the environment. Thus, egg capsules are rarely recovered from the stool.

TreatmentDOC: Praziquantel 5-10 mg/kg given as a

single dose

Epidemiologyhuman infection is rare but has been

reported in European countries, USA, Argentina, Rhodesia, China, and the Philippines.

Infants and the very young children are usually infected because of their close contact with their pets.

Prevention and ControlPeriodic deworming of pet cats and dogsInsecticide dusting of pets are effective

against fleas *****end*****