Parasitology notes

1. 1

2. Learning Objectives:
 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

3. Morphology
 E. granulosus & E. multilocularis are smallest
cyclophyllidean cestode (~1 cm).
 Body divided into:
 Scolex having 4 suckers, armed with 2 rows of hooked rostellum
 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
 Genital pore is positioned behind the middle line of gravid
segment
 Eggs are rounded and indistinguishable to those of Taenia
spp & appear in the feces of dogs and wild carnivores.
 Larval stage(hydatid cyst) found in varying organs in
herbivores (e.g. sheeps,cattles), adults are found in small
intestines of carnivores(e.g. canines & felines)
3

4.  The body plan of adult
Echinococcus includes
scolex, neck and
strobila that can extend
for only 3 proglottids
 In strobila several
organs like the
excretory system
extend through the
entire worm
 Proglottid: an
individual segment
Morphology…
4

5. Rostellum
Scolex
5

6. Hydatide sand
6

7. 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.
7

8. Epidemiology
 Echinococcosis affects herbivores & humans
(intermediate hosts) and carnivores (definitive hosts).
 Human infections are due to intimate contact with
dogs/cats, ingestion of contaminated vegetation, food
or water.
 Naturally (in wild) the parasite is maintained through
predator-prey relationship, thus called sylvatic
echinococcosis. Dogs are domestic reservoirs.
 Customs which allow intimate contact of dogs & cats
with humans, promote the infection.
 Infections have been shown in Latin America, India,
China and parts of Central Europe.
8

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 is when hydatid
cyst(s) in the intermediate host (e.g. sheep) is
eaten.
9

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.
10

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
compartments 11

13. 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 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.
 Fluid from the cyst may lead to severe allergic reactions.
 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 of
infected organ and is fatal. 13

14. 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 14

15. Treatment
Surgery is the preferred treatment
Chemotherapy
 Albendazole & Mebendazole may kill the
scolices thus preventing growth of the cyst
and facilitating surgical removal
 Percutaneous-Aspiration-Injection-
Reaspiration (PAIR), involves aspiration of
cyst fluid, injection of ethanol and
reaspiration of the ethanol.
15

16. 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.
16

17. 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.
17

18. 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
of gravid segment
Anterior to the middle
of gravid segment
Length of gravid
segment
> ½ of the body
length
< ½ of the body
length
Hydatid cyst Unilocular
Contain scolices
Alveolar
No scolices
Testis 46 – 60 16 – 26
Host Sheep, Cattle, Horses
etc.
Rodents, foxes,
Wolves etc. 18

19.  Laboratory diagnosis:
 Testing serum for antibody produced in responses the infection.
 Examining of hydatid fluid for brood capsules and protoscoleces following the surgical
removed of cysts.

 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 fifteen 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

20.  Key points:
 High infection rates occur in East Africa (Turkana region in
Kenya), North Africa, South Africa, India, Eastern
Mediterranean Middle East and parts of South America
and Australia
 Unlobular cysts – which is found in internal organs e.g.
liver. Osseous cysts found in bones, arms, legs, and ribs
vertebrate. Alveolar cysts – irregular cysts in shape and
sponch like filled with gelatin fluid and sterile.

21.  Evaluation:
 Describe morphology of Echinococcus granulosus.
 Explain the diseases caused by Echinococcus
granulosus.
 Explain the prevention and control of Echinococcus
granulosus

22.  References
 Brown .H.W. (1968). Basic clinical Parasitology (3rd ed). New York: Meredith
 Cook, G. (2000). Manson’s Tropical Diseases (22nd ed.). London: WB Saunders
 Harwood, R.F., James, M.T., (1979). Entomology in Human and Animal Health (7th ed.).
 Mike, S. (2004). Medical Entomology for students. London: Oxford University Press.
 Monica, C. (1987). Medical Laboratory Manual for Tropical Countries. Volume 1
 Monica, C. (1998). District Laboratory Practice in Tropical Countries. Part 1. Tropical
 Health Technology. Noida India: Gapson Papers Ltd.
 Monica, C. (2000). District Laboratory Practice in Tropical Countries. Part 2. Tropical
 Health Technology, UK: Cambridge University Press.