PARASITOLOGY LECTURE 7 – Taenia + Echinococcus - Dr. NgNotes from LectureUSTMED ’07 Sec C – AsM

TAENIA SOLIUM (pork tapeworm)

the pork tapeworm producing taeniasis solium or pork tapeworm infection

DISTRIBUTION

Cosmopolitan distributiono Countries:

Mexico Pakistan Latin America India North China USA (rare) Manchuria

o Associated with eating raw or insufficient cooked pork

DISEASES

Taeniasis solium - refers to infection of humans with adult pork tapeworm

Human cysticercosis - refers to infection of humans with larval stage of parasites

Diseases produced by infection with larval taenia solium is not uncommon in regions where Taenia solium adult infection exist

In human cysticercosis: Man becomes the intermediate host.

MORPHOLOGY

1. Adult worm

Measurement – 2-3 meters (exceptionally 8 meters in length)

Compositiono Head

Head or scolex

globular in shaped with 4 cup-shaped suckers

provided with conspicuous, rounded rostellum armed with double rows of large and small hooks numbering 22 to 36 and measuring 140 to 200 um and 100 to 150 um in length.

o Neck (cervical region) short measuring 5 to 10 mm in

length (only about one-half as thick as scolex)

o Proglottids Numbers : 800 to 1,000

proglottids Composed

i. Immature proglottid - broader than long

ii. Mature proglottid - nearly square- containing full set of

functioning male and female reproductive organs

- 150 to 200 follicles distributed throughout the dorsal plane

- uterus – rises from the anterior face of ootype

- trilobed ovary – situated in the posterior of the proglottid with the presence of accessory ovarian lobe

- half as many testes as T.saginata

- Genital pores on consecutive segments

iii. Gravid proglottid - longer than broader- consists:

o common genital pore with muscular sphincter

o gravid uterus with 5 to 13 lateral uterine branches arranged in a Dendritic or finger like fashion

2. Egg Shape – spherical Color – pale buff to walnut

brown Measurement – 5 to 10 um in

diameter 2 radially-striated shells

a. Outer shell – thin and rarely seen

b. Inner shell – brown, thick and striated– embryo or oncosphere with six hooklets

Eggs escape from the uterus through the ruptured wall at the anterior end after the ripe proglottids become free

3. Larval stage or bladder worm also called Cysticercus

cellulosae measurement – 5 to 10 mm

in length and 5 mm in diameter

Consists – dense milky white spot at one where the invaginated scolex with hooks and suckers are located

LIFE CYCLE: TAENIA SOLIUM

Life Cycle of Human Cysticercosis

Human Being Harbor Cysticercus Cellulosae:

1. Hetero Infection – eggs liberated from disintegrating gravid proglottides passed by one individual get into the mouth of another and are swallowed

2. External autoinfection – eggs maybe transferred from anus to mouth or unclean fingertips of an individual who has an intestinal infection with Taeniasis solium

3. Internal autoinfections – gravid proglottids in an individual harboring the adult Taenia solium may become detached from the main strobila or regurgitated into the stomach and then return to duodenal canal where they disintegrate and liberate ripened eggs

PATHOLOGY AND CLINICAL MANIFESTATIONS

1. Pathology brought about by adult taenia solium in lumen of the small intestines maybe negligible

a. Mild transitory intestinal obstructionb. Vague abdominal pain similar to hunger

pain which is due to heavy cysticercosis resulting to regurgitation of gravid segments in to the stomach of patients suffering from taeniasis solium

2. pathology brought about by larval stage (cysticercus cellulosae)- serious, because it may lodge in vital organs

like brain, spinal cord, heart, liver and the eyes

- Symptoms:a. cellular reactionsb. blood cell infiltration c. fibrosisd. necrosis

- cysticercosis in the brain may cause:a. epilepsyb. behavioral changesc. intermittent obstructive hydrocephalusd. disequilibriume. meningoencephalitis

f.f.f.f.f.f.f.f.f.f.f.f. failing vision

Cross section of Cysticercosis Single cysticercus of T. soliumCysticercus cyst in of Brain (left cerebral cortex)Human muscle

Section of eye with a single Cysticercus of Taenia solium

DIAGNOSIS

1. Demonstration of eggs in stool a. Direct fecal smearb. Scotch tape swab

Taenia spp. Differentiation is not possible through eggs examination

2. Demonstration of gravid proglottids in the stool

3. Recovery of scolex after antihelminthic therapy

SPECIES DIFFERENTIATION

T. solium and T. saginata can be made possible thru:

1. scolex:

T. solium – has rostellum armed with spines or hooklets

T. saginata – no well defined rostellum nor spine

2. Segment differentiationa. Segments:

o T. solium – 800-1000 segmentso T. saginata – 1000-2000 segments

b. Lateral branches:o T. solium have less than 13 lateral

uterine brancheso T. saginata have more than 15 lateral

uterine branches

EPIDEMIOLOGY

1. T. solium infection- prevalence of infection is directly related to

eating habit of people (raw or insufficient cooked pork)

- Man is the only known definitive host and the pig appears to be the only intermediate host

a. Man become the intermediate hostb. Can be caused by:

o ingestion of eggs from contaminated food or water

o contamination from dirty fingerso by internal autoinfection when the eggs

are carried by reverse peristalsis back to the duodenum or stomach

TREATMENT, PREVENTION AND CONTROL

1. Treatmenta. Praziquantel

- Dosage: 10 to 20 mg per kg single dose- Effect: expel worm in toto

b. Niclosamidec. Paramomycin

2. Prevention and controlo Taeniasis solium

- avoid eating raw or insufficiently cooked pork

- proper excreta disposalo Human cysticercosis

- good personal hygiene- avoidance of drugs which

causes disintegration of gravid segments

TAENIA SAGINATA (Adult Beef Tapeworm)

infection of man with the adult beef tapeworm Mode of transmission: eating raw or insufficiently

cooked beef containing the cysticercus] Longest human parasite capable of growing to 7.5

m therefore most individuals harbor only one adult worm

cosmopolitan in distributiono Africao Mexicoo Argentinao Middle Europeo USAo Asian-Pacific region

Korea Indonesia Philippines Thailand

man serve only as definitive host and never as intermediate host therefore cysticercosis due to Taenia saginata does not occur

It thrives in the upper half of the small intestine

MORPHOLOGY

1. Adult worm

Color: Whitish opaque in color Measurement: 5 to 10 meters but may extend up

to 25 meters or more Composition

o Scolex Similar to T. solium except that

the rostellum is not well defined and has no spines or hooklets

Serve as an organ of attachment in the mucosa of small intestines

Head or Scolex

o Neck o Proglottids

Usual numbers between 1,000 to 2,000 proglottids

Extending the small intestine, sometimes reaching the jejunum

Composed:

i. Immature proglottids

ii. Mature proglottids- broader than longer- contain both male and female

reproductive organ- genital organs same with T.

solium- contains twice as many testes

as T. solium- Bilobed ovary with absence of

an accessory ovarian lobe

iii. Gravid or Ripe proglottids- narrower and longer- uterus containing more than

15 to 20 mm arranged in lateral uterine branches arranged in a tree-like or dichotomose pattern

2. Eggs are indistinguishable between species of T. solium

and T. saginata Shape: rount to slightly oval Measurement: 31 to 43 um Have thick, striated shell and contain the six-

hooked embryo (oncosphere) Can remain viable in soil for days to weeks Eggs of T. saginata by man do not result in

infection

3. Larva (cysticercus bovis) Hexacant (six-hooked) larva hatched from egg,

actively penetrates the small intestine and migrates by hematogenous route to all organ

Disadvantage – causes the proglottids to rupture and releases innumerable eggs into the bowel lumen and increase risk of cysticercosis

system Mostly they lodge in the skeletal muscles, where

they encyst in the fascial tissues and develop into cysticercus, the stage infective to man

LIFE CYCLE: TAENIA SAGINATA

SPECIES DIFFERENTIATION

Each proglottid may contain about 80,000 eggs More segments in T. saginata than T. solium (1000

to 2000 segments in T. saginata) More lateral uterine branches (15 or more) in T.

saginata

DIAGNOSIS

1. demonstration or identification of the proglottids passed by patients

a. Method: fixing in 10% formaldehyde solution and the uterine branches injected with India ink

b. Twelve or more uterine branches are characteristic of gravid proglottid of Taenia saginata

2. Demonstration of Eggs in the Perianal skino Scotch tape swab

eggs in the stool can be identified only as Taenia species because the eggs of all tapeworms look alike

PATHOGENESIS

It would appear that it is more dangerous to be infected with Taenia solium than Taenia saginata because there seems to be no cysticercosis in man due to T. Saginata

Is mainly due to its large size which is frequently responsible for the disturbances in the normal function of digestive tract

Absorbed by-product of the worm may also cause systemic intoxication

Does not cause obstruction although the large tapeworm occupies a substantial proportion of the lumen of the small intestine flexibility and relatively fragile

There are no host responses against the worm and therefore no tissue reaction

Proglottids usually pass from the patient during the period of sleep and are found in the bedding or clothing, the following morning

Patient may pass a large segment of the worm either during defecation or spontaneously

TREATMENT, PREVENTION AND CONTROL

A. Treatment Drug of Choice – Niclosamide action: damage to the point of dissolution

B. Prevention and Control1. protection of cattle from coming in contact

with human excreta2. Thorough cooking of beef

SUMMARY: COMPARATIVE ANALYSIS OF T. SOLIUM AND T. SAGINATA

ECHINOCOCCUS GRANULOSUS

Parasite of dog Smallest tapeworm (5 mm in length) Only the larval form of infection is found in the

human host and causes space occupying lesions known as hydatid cysts

Infection is considered serious and might result to fatalities

World wide distribution Man becomes an accidental intermediate host

DISEASE

Hydatid disease Unilocular echinococcosis Echinococcus disease

MORPHOLOGY

1. Adult Tapeworm smallest tapeworm parasitizing man measurement: 2.5 mm to 9 mm in length consisting:

o scolex has prominent rostellum with a

double row of 20 to 40 large and small hooklets and “cup-like” suckers

o necko 3 segments

i. one immature proglottidii. one elongated mature proglottid

narrowest consists

genital pore ootype ovary uterus seminal receptacle testes vagina vas deferens vitellaria vitelline duct

iii. one long gravid proglottid (terminal) broades and longest consists of hundreds of infective

eggs breaks off and disintegrates in

the large bowel releasing hundreds of infective eggs that pass out with the feces

2. Eggs has brown radially striated

oncosphere or embryosphere cannot be differentiated from

Taenia spp.

3. Larval Stage (oncoshpere) Measurement: 20 cm in

diameter Consisting of an enveloping

membrane with 2 layersa. Outer laminated milky

opaque non-nucleated layer

b. Inner nucleated germinal layer which will give rise to protoscolex or protoscoleces

from this inner membrane arises buds or broad capsule which

i. may remain attached to the inner membrane by stalks

ii. may be set free into the fluid of the cystic cavity

the free broad capsules or free scolices are referred to as “hydatid sand”

LIFE CYCLE: ECHINOCOCCUS GRANULOSUS

PATHOGENESIS AND CLINCIAL MANIFESTATIONS

The pathology produced by the hydatid cyst in the human body is both mechanical and toxic

A. Mechanical1. Growing hydatid cyst lodged in the vital

organs like liver, lungs, brain, heart interferes with the functions of the organs

2. Infection may become fatal due to growing cyst which can cause obstruction to the organo A unilocular cyst located in the bone cells

is called osseous hydatid cystB. Toxic

1. Rupture of the cyst may produce allergic or anaphylactic shock

DIAGNOSIS

Unilocular cysts are diagnosed only after they grown to a tremendous size

Hydatid disease can be diagnosed by:o X-rayo Exploratory cyst punctureo Immunologic tests

1. intradermal test2. Precipitin test

3. Complement fixation test4. Hemagglutination test5. Bentonite latex slide agglutination

test6. Fluorescent antibody test

EPIDEMIOLOGY

Echinococcus infection is very rare in the Philippines

2 cases reportedo Hydatid cyst in the kidneyo Hydatid cyst in the lung

Prevalence in countries (sheep and cattle raising regions)

o Europeo Chinao Japano Vietnamo Canadao Alaskao USA

TREATMENT, PREVENTION AND CONTROL

A. Treatment1. Surgery

o Precaustion – prevent the spilage of the cyst fluid or hydatid sand into the operative cavity lead to the development of secondary cyst

2. Albendazoleo Dosage – 400 mg twice daily for 4 weeks

B. Prevention and Control1. Personal hygiene2. Prevent dogs from eating carcasses of sheep,

cattle and hogs

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