lec 3 echinococcus-hymenolepis

8/4/2019 lec 3 echinococcus-hymenolepis

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Belong to family TaeniidaeContains 3 species

E. granulosus

E. multilocularisE. vogeli

humans are host to the larval stageShare the same Life cycle, Diagnosis, Treatment and

Prevention & Control


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Epidemiology:primarily involves parasitized members of the canine

family

most important specie producing human diseaseinfection of this parasite is very rare in the Phil


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(red) E. granulosus - Russia, Siberia, Bavaria, Tyrol- heavy infection occurs in sheep raising areas of theworld, South America, Iceland, Tasmania, Africa, Asia

(black) E. multolocularis: common in the highlands of Europe i.e.Switzerland and Germany, in Canada, Alaska and Northern Russia

(green) E. vogeli: Central and South America

geographicdistribution


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larval stage: Hydatids or Hydatid Cyst

3 forms hydatid cyst :1. Unilocular hydatid cyst

Unilocular hydatid disease ( E. granulosus)

2. Multilocular/alveolar hydatid cyst

Multilocular/alveolar hydatid disease (E. multilocularis)

3. Polycystic hydatid cyst

Polycystic hydatid disease (E. vogeli)


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Larval stage: Hydatid cyst

are large, roughly spherical, fluidfilled bladders

cyst wall consists of:- outer laminate hyaline wall,

supporting the whole cyst- Inner germinal layer studded with

developing brood capsulesthe protoscolices are formed within the brood capsules,

which may rupture to give off free protoscolices in the fluidfilled cyst

thousands of protoscolices can fill the hydatidHydatid cyst usually grow slowly but steadily (1-5 cm/year)

producing protoscolices and daughter cysts that fill the cystinterior, they are usually well tolerated until their sizebecomes a problem or they rupture


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Hydatid sand

a granular material, consisting offree protoscolices, andamorphous materials which isfound in older hydatid cysts due

to rupture of the brood capsule

sometimes aspirated fordiagnostic purposes


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- measures 3 to 6 mm long

- Only 3 proglottods: 1 immature, 1 mature and1 gravid proglottids

Scolex- rostellum - armed with 2 circular rows of28-50 large and small hooklets

Mature proglottids- more elongated, and contains fully developed

reproductive organs w/c consist of pyriformtestes, 45-65 in number, and located

anterior to cirrous sac- Bilobed ovary at the posterior portion

- Clubshaped uterus

Gravid proglottids- longer than wide-Uterus at median, gives rise to 12-15 lateraluterine pouches filled with eggs

Adult


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Egg- spherical shaped, with radially

striated embryophore- Cannot be distinguished from those

of Taenia spp.- This genus compensate their very

minute size by producingthousands of eggs


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larva: hydatid (unilocular) cyst

limiting membrane Thick & laminated

germinal epithelium Grows to the internal cavity of the cyst

appearance Unilocular cyst

Amount of fluid more

- larvae develop into a unilocular cyst which gives rise to unilocular hydatid disease

- characterized as having only one bladder or many completely isolated bladders, eachenclosed in its own well-developed envelope


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MOT:Accidental ingestion of tapeworm eggs excreted in thefeces of infected dogsIntimate association with dogsContaminated fingers and food2 seeding from ruptured cyst

incubation period for all species of Echinococcus can bemonths to years or even decades

The disease will vary in their seriousness depending on:- the location of the cyst in the body and how fast the

cyst is growing, and how large it grows

- where in the body the hydatid develops

- how large it grows

Unilocular Hydatid Disease


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Organaffected

% ofCases

Symptoms

Liver 66% abdominal pain,hepatic mass, bile ductobstruction, jaundice,ascites, liver abscess

Lungs 10% chest pain, cough,hemoptysis pleuraleffusion,

pneumothoraxAbdominalcavity

8%

brain 7% Mass with neurologicsymptoms

kidney 7%Heart,spleen,bones

2% Tumor, PericardialeffusionEmbolism


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Sometimes the infection is asymptomatic- the only evidence of infection being the presence ofcalcified cysts on autopsy after death due to an unrelated

cause

the major pathology is due to the size of the cyst, givingrise to pressure related injury by expanding size of the

hydatid cystcysts can grow to be the size of softball or basketball,

and may contain several smaller "balloons inside themain cyst

Pressure effects can cause local tissue damage andobstruction


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Leakage of hydatid fluid synsitizes the patient and eliciteosinophilia

rupture of cyst: trauma, muscular strain, aspiration,coughing or during operation

the hydatid cyst fluid is highly allergenic and cyst rupturemay result in severe allergic manifestations, anaphylactic

shock and rapid death

deadliest tapeworm parasitizing humans


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Diagnosis:Radiographic findings and/or ultrasonography

(demonstate hydatid cyst) combined with a historyresidence in an endemic area, and close association

with dogs are important in the diagnosis(+) serological tests (Indirect HAI, ELISA, CF) are helpfulStool exam charac. Ova & gravid segmentsX-ray, CT scan, Ultrasound

Liver puncture hydatid sandBlood smear eosinophilia


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Therapeutic Modalities for all types of Hydatid Disease:treatment of choice: Surgical resectionRecent surgical trend:Percutaneous Aspiration, Injection

of hypertonic saline or other scolocidal fluid and

Reaspiration (PAIR)Drug of choice: Albendazole

- dose: 10mg/kg BW or 400mg 2x/day x 4 weeks- given at least 1 day before surgery/aspiration

Praziquantel active protoscolicidal agent with excellent

result when given in conjunction with AlbendazoleIvermectin injected directly into cysts was found to kill

protoscolices in experimental animal


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Prevention & Control:Avoid fondling of infected dogsStrict personal hygieneAvoid eating contaminated foodsDogs should be dewormed periodically with Praziquantel

every 6 wks


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Echinococcus multilocularis

Other name: Dog tapeworm, Hydatid wormDisease: Multilocular Echinococcosis

Multilocular / alveolar hydatid disease

recognized as distinct specie from E. granulosusdefinitive hosts: primarily foxes and to a lesser extent dogs,

cats, coyotes and wolves

intermediate host: small rodents, miceMan is an accidental host by the ingestion of eggsmore adaptations for colder climates


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Multilocular / Alveolar Hydatid Disease

Adults adult tapeworm is usually non-pathogenic to its canine hosts 1.2 to 3.7 mm longvery similar to E. granulosus, with a maximum length of

approximately 4mm, and consisting of 4-5 proglottids

Larvaelarval growth remains indefinitely in the proliferative stagethe 'cyst' grows invasively by external budding, to proliferate

in any direction, forming a diffuse growth through theinfected organ replacing that organ tissues, resulting ininvasion of the surrounding tissues


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limiting membrane thin

germinal epithelium Grows externally, to proliferate in any direction

and act like a neoplasm with local infiltration or

even to metastasize

appearance Alveolar or Multilocular cyst

Amount of fluid less

Larvae: multilocular cyst


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Multilocular / Alveolar Hydatid Disease

MOT- eating foods contaminated with feces of the hosts- hunters can be infected while handling foxes & wolves

common site: liver next lung and other organGrowth in the vena cava or portal vein may lead to

metastases, usually to the lungs or brain and other body

organsPrognosis is poor and depends on extent of organ

involvement

the multilocular cyst is highly pathogenic due to its fastgrowth rate and invasive nature, in extreme cases

completely replacing liver tissue thus simulatinghepatocellular carcinoma with local pressure effects andallergy


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Echinococcus vogeliOther name: Dog tapeworm, Hydatid wormDisease: Polycystic Echinococcosis

(Polycystic hydatid disease)

found in Central and Northern South Americadefinitive hosts: bush dogsIntermediate host: large rodents (pacas and spiny rats)


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Adults - up to 5.6 mm long , similar toE. granulosus, but rather longer;non-pathogenic

LarvaeThe germinal membrane of the hydatids proliferates

both inward, in the original cyst, forming septa thatdivide it in many sections and outwards to form newmulti-chambered cysts resulting in multiple vesicles

(polycystic hydatid cyst)

In humans, hydatids are found in the liver, but also thelungs, pleura, pericardium, heart, intercostal muscles &

diaphragm, stomach, omentum and mesenteries


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Belong to family Hymenolepidae2 species:Hymenolepis nanaGeog. Dist:cosmopolitan with highest infection in tropicscommon in warm than cold regionendemic in Central Europe, India, Latin America and

some Asian countries

Hymenolepis diminutaGeog. Dist:cosmopolitanendemic in Japan, China, Africa, Argentina, Russia,

Latin America, & USA


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Hymenolepis nanaOther name: Dwarf tapewormDisease: Hymenolepiasis, Dwarf Tapeworm Infectioninfection is more common in children than in adultsDefinitive host: house mouse, humanIntermediate host: grain beetle*Does not require an obligatory intermediate host

has the unusual characteristic of being able to complete itslife-cycle without the aid of the intermediate host

this makes H. nanathe only tapeworm in which an adultwill grow after the definitive host ingests the eggs


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Adultmeasures 25-40m length x 1 mm

widthSmallest cestode infecting humansScolexrhomboidal-shaped with 4 cup-shaped

suckersrostellum armed with 1 circle of 20 to

30 hooks

Immature proglottidswider than long and trapezoidal-shaped


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Mature proglottidswider than long1 set of male & 1 set of femalereproductive organs 3 ovoidal testes arranged in straight

line with a bilobed ovary in betweena compact vitelline gland and a large

uterus opening to a lateral genital poreon the side of the segment

Gravid proglottidswider than longsaclike uterus completely filled with80-180 eggsAlso contains cirrous pouch, seminal

receptacle


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Infective stage: cysticercoid larvaA small larva that is characterized bypossession of a single invaginatedscolex but without the bladdercharacteristic cycticercus


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Eggthin and smooth outer shellovoidal, hyaline & colorless, 30-47umUsually liberated from the gravid

segments before they become detached

composed of inner layer (embryophore)& outer layer (thin membranous);the shell is provided with bipolar knobs& filaments (4-8) at each pole

These filaments are visible in the spacebetween the embryo and the outer shell

Polar filaments


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life cycle:

Adult worm develop following ingestion of the egg by

definitive hosts

eggs hatch in the duodenum, releasing oncospheresand lie in the lymph channels of the villi

oncospheres develops into a cysticercoid, whichattaches to

the small intestine and matures into an adult

gravid proglottids then release and pass out through feces

along with eggs


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Modes of Transmission:

(1)an oral-anal cycle in which eggs are passed from onehuman to another or recycle externally in a single host

(2) eggs can hatch and infect original host and start cycle over- internal autoinfection, whereby eggs hatch within

the gut and initiate a 2nd generation infection

without ever exiting the host

(3) eggs can be ingested by insects, where it will developinto cysticercoid

- an indirect 2-host cycle involving rodents as primary

definitive hosts and intermediate host (grain beetles)that feed on contaminated rodent droppings


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Hymenolepiasis / Dwarf Tapeworm InfectionPathogenesis:Light infections are usually asymptomaticWhen large number of worms are present:Clin. Manifestations: abdominal pain, diarrhea, headache,

dizziness, anorexia, and various nonspecific symptoms

Diagnosis: Stool exam characteristic eggTreatment:Drug of choice: Praziquantel 25mg/k single oral dose

alternative: Niclosamide daily for 5 days

Prevention & Control:- Proper personal hygiene- Protect food from being contaminated with mice, and

grain beetles


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Hymenolepis diminutaOther name: Rat tapewormDisease: Hymenolepiasis, Rat tapeworm infectionLarger than H. nanaprimary zoonoticDefinitive host: ratsintermediate hosts flour beetle, flour mothshuman is an incidental host, occasionally infected thru

accidental ingestion of infected intermediate host that carrythe parasite in their body cavities

Infective stage: cysticercoid larva


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Morphology:

AdultH. diminutais slightly larger, measures

20-50 cm long x 4mm wideGreatest length reported: 1meter

Scolexsmall, knob-shaped with 4 cup-shaped

suckers and small rudimentary apicalunarmed rostellum

Mature proglottids - same with H. nanaGravid proglottidssacculate-like uterus filled with eggs


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EggRound or slightly oval, yellow-

brown color the shell is relatively thick,

60-80m in diameterfine concentric striations in the

outer shell

space between the membranesis smooth or faintly granular,inside is the oncosphereenclosed in 2 membrane with 2polar thickening but no polar

filaments


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Life cycle:

The adult tapeworm is found in the hosts small intestine

Eggs are passed in the hosts feces

Eggs are eaten by intermediate host(flour beetle, flour moth)

Oncosphere hatch and penetrate the intestinal wall ofintermediate host

larva develops into cysticercoid larva in the body cavityof insects ingested by rodents or accidentally by humans


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Hymenolepiasis / Rat tapeworm infectionmost asymptomatic but occasional patients may have mild

GI complaints: nausea, anorexia, diarrhea and abdominal

discomfortno autoinfectionEosinophilia, anemia may also be presentDiagnosis: Stool exam characteristic eggTreatment: drug of choice: Niclosamide

Praziquantel equally effective

Prevention & Control:Proper rodent control measures

Destruction of intermediate hostsProper disposal of stools of infected person


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lec 3 echinococcus-hymenolepis

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