Echinococcus granulosus

1. ECHINOCOCCUS
Santosh Kumar Yadav
M.Sc. Clinical
Microbiology
IOM, TUTH

2. Introduction to cestodes
 Adult worm is usually found in the
intestine of men and animals and
are long, segmented, flattened
dorsoventrally, tape like worms
hence also called as tapeworms.
 Size : vary from few mm to several
meter. Hymenolepis nana is the
smallest tapeworm (1–4 cm) where
as Diphyllobothrium is the longest
Cestode measuring 10 meters or
more.
 Adult worm consists of three parts:
1. Head or scolex
2. Neck
3. Strobila (body or trunk) : immature,
mature and gravid.

3.  No body cavity
 Body Wall (or Tegument) : It is made up of three
layers—outer microvillus like structure called as
microthrix, middle basal plasma membrane and
inner muscular layer (outer circular and inner
longitudinal muscle coats).
 Female Reproductive Organs : Present on the
ventral side and consists of: A bilobed ovary,
Oviduct, Ootype, Vagina, Uterus, Vitelline gland and
Mehlis’ gland.
 Male Genital Organs : testes, vas deferens,
seminal vesicle and cirrus (equivalent of penis).
 Nervous System : It is rudimentary, consists of
brain like structure (central ganglion, lateral and
rostellar ganglia connected by central nerve ring)

4.  No circulatory system
 Excretory System : It is also rudimentary and present in
each segment. It consists of two lateral canals (dorsal and
ventral) connected by transverse canals in each segment.
The excretory canals are built up of flame cells (terminal
cells) and canal cells.
 Eggs : Eggs are released into the uterus of parasites
following fertilization and fill the gravid proglottids.

5. Larva : Embryonated eggs undergo further development to
form larva
Pseudophyllidean cestodes: Larva is solid without
any sac. They are:
Coracidium: First stage larva of Diphyllobothrium
Procercoid: Second stage larva of Diphyllobothrium
Plerocercoid: Third stage larva of Diphyllobothrium
Sparganum: Larval stage of Spirometra
Cyclophyllidean Cestodes: Larvae contain bladder like
sacs. They are:
• Cysticercus: Larval stage of Taenia
• Hydatid cyst: larval stage of Echinococcus
• Coenurus: Larval stage of Multiceps
• Cysticercoid: Larval stage of Hymenolepis.

6.  Life cycle : Cestodes complete their life cycle in two hosts
(definitive host and intermediate host) except:
1. Hymenolepis (requires only one host—man)
2. Diphyllobothrium requires three hosts (one definitive
host—man and two intermediate hosts–cyclops and fish).

7. Echinococcus spp
Echinococcus causes hydatid disease.
There are four species of Echinococcus
known to infect humans.
1. E. granulosus: Causes cystic hydatid
disease
2. E. multilocularis: Causes alveolar
hydatid disease
3. E. vogeli and E. oligarthrus : Cause
polycystic hydatid disease.

8. Echinococcus granulossus
 Echinococcus granulosus, also called dog tape
worm or hydatid worm belongs to class
Cestoda.
 E. granulosus causes cystic echinococcosis or
hydatid disease in livestock and humans
beings which acts as intermediate hosts and
parasitize the small intestines of adult canids i.e.
definitive hosts.
 It is a zoonotic disease.

9. Geographical Distribution
• The disease is prevalent in most parts of
the world, though it is most extensive in
the sheep and cattle raising areas of
Australia, Africa, and South America.
• It is also common in Europe, China, the
Middle East and India.
• It is seen more often in temperate than in
tropical regions.

10. Habitat
• The adult worm lives in the jejunum and
duodenum of dogs and other canine
carnivora (wolf and fox).
• The larval stage (hydatid cyst) is found in
liver and other visceral organs of humans
and herbivorous animals (sheep, goat, cattle
and horse)

11. Morphology
Adult worm :
 The adult tapeworm ranges in
length from 3 mm to 6 mm.
 It comprises of a scolex (head) ,
neck and strobilla or
proglottids consisting of 3 or 4
segments.
 The 1st segment is immature ,
2nd is mature and the last one or
two is gravid.
 The terminal segment is by far
the biggest (2-3mm x 0.6mm)
 The scolex bears four suckers
and also has a rostellum with
two rows of hooks.

12.  Echinococcus is triploblastic,
anus is absent and it has no
digestive system.
 Its body is covered by tegument
and the worm is divided into a
scolex, a short neck, and three to
six proglottids.
 The adult worm lives for 6–30
months
Egg :
 ovoid in shape and resembles
other taenia. Measures 32-36 μm
x 25-32 μm and contains a
hexacanth embryo with 3 pairs of

13. Larval Form
• Found within the hydatid cyst developing inside various
organs of the intermediate host.
• Represents the structure of the scolex of adult worm
and remains invaginated within a vesicular body.
• After entering the definitive host, the scolex with
suckers and rostellar hooklets, becomes exvaginated
and develops into adult worm.

15. Life Cycle
 Host: E. granulosus life cycle passes
through two hosts:
1. Definitive host: Dogs and other canine
animals
2. Intermediate host: Sheep and other
herbivores. Man acts as an accidental
intermediate host (dead end).
 Mode of transmission: Men (and other
intermediate hosts) acquire the infection by
ingestion of food contaminated with dog’s
feces containing E. granulosus eggs. Rarely
flies serve as a mechanical vector of the
eggs.

16. Development in man
Eggs transform to larva (hydatid cyst):
 In duodenum of man or sheep and cattle , the
oncosphere is released by the rupture of ova.
Onchosphere hatches and penetrates into the
intestinal wall, enters the portal circulation and
carries to the liver (60–70% of cases) or lungs or
rarely to other organs.
 Host immune response may destroy many
oncospheres, but few may escape destruction and
develop into hydatid cyst.
 The oncospheres are encysted by the fibrous tissue
(produced by fibroblasts) and transform into fluid
filled bladder like cyst called as hydatid cysts
 The hydatid cyst undergoes maturation increases in

17.  Full development takes 10–18 months in
sheep.
 This stage is infective to dog and other
definitive hosts
 Man is a dead end (as dogs don’t feed on
human viscera)
Development in Dog
 Dog and other canine animals acquire infection by
consumption of the contaminated viscera of
intermediate hosts (sheep and cattles) containing
mature hydatid cysts.
 The hydatid cyst (larva) transforms into adult
worm in dog’s intestine.
 The adult worm becomes sexually mature, self

19. Life Cycle

21. Pathogenicity
 Pathogenicity is related to the deposition of the
hydatid cysts (larval form of the parasite) in
various organs.
Hydatid cyst : Fully developed hydatid cyst of E.
granu losus is unilocular, subspherical in shape
and size varies from few milimeters to more than
30 cm (usual size 5–8 cm).
 It appears as fluid filled bladder like cyst.

22.  Cyst wall consists of three layers:
a. Pericyst (outer layer, host
derived): Consists of fibrous
tissue and blood vessels
produced by the host cellular
reaction
b. Ectocyst (middle layer, parasite
derived): It is a tough elastic,
glycan rich acellular hyaline layer
of variable thickness (1 mm). It
resembles the white of a
hardboiled egg
c. Endocyst ( inner layer, parasite
derived): Germinal layer, 22–25
μm thickness. It consists of
number of nuclei embedded in
protoplasmic mass. Its function is

23. Hydatid fluid:
 It is clear, colorless to pale yellow
 It has a pH of 6.7 and specific
gravity of 1.005 to 1.010
 Chemical composition : sodium
chloride, sodium sulfate, sodium
phosphate and succinates
 It is antigenic, toxic and
anaphylactic
Brood capsules : arise from
the inner side of the endocyst and
contains number of protoscolices
(future head)
Hydatid sand: Some of the
brood capsules and protoscolices
break off and gets deposited at the

24. Variety of hydatid cyst:
 Primary cyst: Formed directly from the oncosphere
released from the eggs ingested
 Secondary cysts: Formed due to the breakage of the
primary cyst by trauma. The secondary cysts are carried
in the circulations to various organs
 Acephalocyst: Cysts without brood capsules and
protoscolices
 Endogenous daughter cysts: Formed by the breakage of
the brood capsule into the hydatid fluid; surrounded by
ectocyst and endocyst
Fate of the hydatid cyst:
 Spontaneous resolution may happen to few cysts
 Rupture of the cyst may either lead to:
− Formation of secondary cysts

25. Clinical Features
Infection usually occurs in childhood but gets
manifested in adult life.
Site: Most common site of location of the cyst
is liver (60–70%, right lobe) or lung (20–30%)
but may be found in any organs like spleen
and kidney (3–5%), brain and heart (1–1.5%)
and rarely bones
 They grow upto 5–10 cm in size within the
first year and can survive for years or even
decades
Asymptomatic: Many cases are asymptomatic
and infection is detected only incidentally by
imaging studies

26. Symptoms occur due to:
a. Pressure effect of the enlarging cyst: Leads to palpable
abdominal mass, hepatomegaly, abdominal tenderness,
portal hypertension and ascites
b. Obstruction: Daughter cyst may erode into the biliary
tree or a bronchus and enter into the lumen to cause
cholestasis and dyspnea
c. Secondary bacterial infection can cause pyogenic
abscess formation in the hydatid cysts
d. Anaphylactic reactions: Cyst leakage or rupture may be
associated with a severe allergic reaction to hydatid
fluid antigens; leading to hypotension, syncope and
fever
Outcome of the disease: It depends on the cyst size and
location
a. Younger children are more associated with extrahepatic
cysts in lungs, brain and orbital sites

28. Skin test (Casoni test) : It is an immediate
hypersensitivity reaction to hydatid fluid antigens.
Developed by Casoni in 1911
Antigen used: Sterile hydatid fluid derived from
unilocular cysts from dog or man (sterilized by filtration)
Procedure: 0.2 mL of the antigen is injected in one arm;
sterile saline is injected to the other arm as control
Interpretation: Sensitive patients develop large wheal
measuring 5 cm or more with formation of pseudopodia
within 30 minutes with no reaction in the control arm
Disadvantage:
 It has low sensitivity (60-80%) and gives false positive
results in cross reactive cestode infections
 It is obsolete now days and replaced largely by the
serological tests.
Laboratory Diagnosis

29. Antibody detection
 Screening tests: Various antibody detection methods
are evaluated using crude E. granulosus cyst fluid
antigen. They show variable results (60–90%
sensitivity) .These tests are:
a. Indirect hemagglutination (IHA)
b. Latex agglutination test (LAT)
c. Indirect fluorescent antibody tests (IFA)
d. ELISA
 Confirmatory tests:
a. Immunodiffusion and electro immunodiffusion
b. Western blot: Detecting antibody against antigen B
fragment. This test is 92% sensitive and 100% specific.
Antigen B fragment binds specifically to IgG4

30. Antigen detection : ELISA, CIEP (countercurrent
immunoelectrophoresis) and LAT are available to detect
specific antigens in serum and urine.
Imaging methods : Imaging methods play an
important role as they are noninvasive methods, which
can detect the cysts incidentally in asymptomatic
individuals and in seronegative cases.
a. Xrays: to detect hepatomegaly and
calcified cysts and cysts in lungs.
b. Ultrasound (USG): detects both single and multiple
cystic lesions
c. Computed tomography (CT scan): It can
detect 90–100% of cases. It detects more accurately the
number,

31. Hydatid fluid microscopy : exploratory cyst
puncture ( not advised)
 Aspirated hydatid fluid is examined for brood capsules
and protoscolices by direct microscopy or staining with
acid fast stain.
 Drop of centrifuged fluid is placed between two slides
and the slides are rubbed over the fl uid. Hydatid sand
is felt as grating of the sand grains in between the
slides.
 Purulent material can be examined after treating with
hydrochloric acid.
Histological examination : Surgically removed cysts
can be subjected to histopathological stains like
Giemsa, hematoxylin and eosin (H & E) and Periodic
acid Schiff (PAS) stain to demonstrate the three layers

33. Molecular Methods : PCR targeting mitochondrial DNA
has been developed. PCRRFLP can be used to detect
genotypes of E. granulosus.10 genotypes have been
identifi ed from G1 to G10; each has a particular host
specificity and geographical distribution. G1 is the most
common genotype in India.
Other tests
 Eosinophilia is present in 20–25% cases
 Hypergammaglobulinemia.

34. Echinococcus eggs in feaces of
dog

35. Treatment
 Surgical Removal of Hydatid Cyst : 90% effective but can be
risky depending on location, size, and advancement of cyst
 It may need chemotherapy to prevent recurrance
 Chemotherapy: Albendazole is preferred treatment because it
penetrates into hyatid cysts. Dosage: 10mg/kg body weight or
400mg 2x daily for 4 weeks
 Mebendazole Dosage: 40mg/kg body weight 3x daily for 3-6
months
 Dogs are effectively treated with Praziquental
PAIR Treatment : Puncture, aspiration, injection and re-
aspiration: It is an alternate method recommended instead of
surgery. It involves four basic steps:
 Percutaneous puncture of the cyst
 Aspiration of 10–15 mL of cyst fl uid
 Infusion of scolicidal agents like hypertonic saline, cetrimide, or

36. Prevention
 In order to prevent transmission to dogs from
intermediate hosts, dogs can be given
anthelminthic vaccinations
 Clean slaughter and high surveillance of
potential intermediate host during slaughter is key
in preventing the spread this cestode to its
definitive host
 Proper disposal of carcass and offal after
slaughter to prevent dogs access to offal from
livestock
 Boiling livers and lungs which contain hydatid
cysts for 30 minutes has been proposed as a
simple, efficient and saving way to kill the

37. Echinococcus multilocularis
 Most of the E. multiculoris are said to be
sterile because they don’t have protoscolices
in their parent cyst.
 In general the rupture of hydatid cyst release
the hydatid sand.
Life Cycle : Life cycle is similar to that of E.
granulosus. Only the hosts are different.
1. Definitive host: Foxes and wolves (and also
dogs and cats)
2. Intermediate hosts: Small wild rodents like
squirrels, voles, mice, etc.
 Man is an accidental intermediate host.

38. Clinical Features
 E. multilocularis is the
causative agent of alveolar
(or multilocular) hydatid
disease. So named
because the cysts have
multiple locules or cavities
with no fluid or no free
brood capsule/scolices .
 Liver is the most common
organ aff ected (98% of
cases)

39. (Intermediate)