2. Learning Objectives
By the end of this session, students are expected to be able
to:
Explain the geographical distribution Echinococcus
granulosus
Explain the habitat of Echinococcus granulosus
Describe morphology of Echinococcus granulosus.
Describe the mode of transmission & life cycle of
Echinococcus granulosus
Explain the diseases caused by Echinococcus
granulosus.
Explain the prevention and control of Echinococcus
granulosus
Explain the laboratory diagnosis of Echinococcus
granulosus
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3. Geographical Distribution
The parasite has a worldwide distribution
especially where sheep has close association
with dogs and wild carnivores.
High rates of infection occurs in East Africa
(Turkana region in Kenya), North Africa, South
Africa,, India, Eastern Mediterranean, Middle
East and parts of Southern America and
Australia.
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4. Habitat
Eggs – May be found in faeces of host (dogs and
herbivores, domestic and wild animals which eat
meat) or passed in gravid segment or may
adhere to the coat of host when gravid segment
disintegrates. It is infective to man.
Larvae stage (hydatid cyst) – found in varying
organs in herbivores (e.g. sheep, goats, cattle
and man).
Adult worm - lies attached to the mucus of
small intestine of carnivores(e.g. canines &
felines)
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5. Morphology
E. granulosus & E. multilocularis are smallest
cyclophyllidean cestode, Measures 3 – 5 mm in length.
Body divided into:
Scolex having 4 suckers, armed with 2 rows of hooked
rostellum bearing about 22-28 hooklets.
Short neck.
Strobila contains 3 proglottids. (One immature, one
mature and one gravid). The size of the gravid segment
is more than a ½ of the body length.
The uterus is unbranched
Genital pore is positioned behind the middle line of gravid
segment
Eggs are rounded and indistinguishable to those of Taenia
spp.
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6. Morphology…
The body plan of adult
Echinococcus
In strobila several
organs like the
excretory system
extend through the
entire worm
Proglottid: an
individual segment
Uterus
Gravid
Proglottid
By Mwamkoa MJ (BScHLS)
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9. Life cycle
Intermediate hosts acquire infection through
ingestion of eggs in contaminated substances
Eggs hatch in small intestine releasing an
oncosphere which penetrate the intestinal wall
& carried along the body by blood circulation
to be trapped in organs like liver, lungs etc.
These are then transformed into protoscolices
in a (hydatid) cyst
Infection of the definitive host (dog) is when
hydatid cyst(s) in the intermediate host (e.g.
sheep) is eaten.
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10. Life cycle…
The cyst wall is digested, the protoscolices are
liberated, which develop into adults.
The gravid proglottids break away and are
expelled singly (may force their way out
through anal sphincter).
On drying they rupture releasing eggs with fully
developed larvae.
Hydatid cyst is a bladder that contains
inverted scolices, brood sacs with scolices, and
within those brood sacs, daughter cysts with
their own inverted scolices.
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11. Life cycle…
If the scolices separate from the inner lining of
the capsule, they are called hydatid sand.
Hydatid cyst may be unilocular, osseous
(E.granulosus) or alveolar/multilocular (E.
multilocularis)
Unilocular has a single compartment with 2
layers, the inner layer produces protoscolices &
brood capsules, when these detach they are termed
as hydatid sand
Osseous are smaller found in vertebrae & marrow
cavities
Alveolar have multiple divisions of the cyst into
11
compartments
14. Pathogenesis & pathology
The pathology is primarily due to impairment
as a result of pressure from the growing cyst,
symptoms are subject to organs affected, size &
number of the cyst.
Pulmonary infection result into coughing &
allergic responses.
Seizures & comma may be a result of brain
invasion.
Rupture of the cyst release the protoscolices to
the circulation, which may lead to secondary
echinococcosis.
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15. Pathogenesis & pathology…
Fluid from the cyst may lead to severe allergic
reactions (anaphylactic shock).
Like osseous, alveolar cysts are usually difficult
to remove, the former may lead to spontaneous
fracture of bones where the later may lead to
strong impairment & obstruction of infected
organ and is fatal.
May cause calcification of tissue when the cysts
die.
Few patients are reported to have generalized
eosnophilia.
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16. Diagnosis
Laboratory diagnosis - post-surgical
Microscopic demonstration of scolices in hydatic fluid
Immunodiagnosis
Casonis’ test, involves skin/intradermal injection of
irradiated cystic fluid, which on presence of antibodies a
burning swelling will be formed
Serodiagnosis
Detection of antibodies & antigens due to the
parasite by ELISA, etc
Imaging methods
X-rays, ultrasounds, etc show presence of the
hydatid cysts in organs
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17. Casoni Test: Intradermal Test
Antigen is prepared from filtered hydatid fluid or saline
extraction of ground
If 0.2mls of hydatid fluid is sterilized by filtration is
injected intradermal into the patient suffering from
hydatid cysts a wheel is produced in about 15 minutes
surrounded by concentric erythromatous zone, which
later disappear with a wheal.
A second similar reaction (i.e. after 20 minutes)
frequently takes place at the same point a few hours (or
minutes) later.
Between 50% and 100% of infected individual react
positively
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18. Prevention
Regular treatment of dogs with anthelmintics.
Elimination of stray dogs
Preventing dogs from eating infected offal's of
dead animals through disinfecting or disposal
of refuse from slaughterhouses.
Avoiding contact with infected animals (dogs
& cats).
Improving personal hygiene through hand
washing especially after feeding or contacting
dogs.
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19. ECHINOCOCCUS MULTILOCULARIS
Most of the E. multiculoris are said to be sterile
because they don’t have protoscolices in their
parent cyst.
Although there may be few if any protoscolices
produced
In genera the rupture of hydatid cyst release
the hydatid sand.
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20. Differences btn E.granulosus &
E.multilocularis
E. granulosus
E. multilocularis
Strobila
3 segment only
3-5 segment
Size
3 - 9mm long
1.2 – 5.5 mm long
Genital pore
Behind the middle line Anterior to the middle
of gravid segment
of gravid segment
Length of gravid
segment
Hydatid cyst
> ½ of the body
length
Unilocular
Contain scolices
Testis
Host
46 – 60
16 – 26
Sheep, Cattle, Horses Rodents, foxes,
etc.
Wolves etc.
< ½ of the body
length
Alveolar
No scolices
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