Hydatid Disease

ECHINOCOCCOSIS
HUMAN ECHINOCOCCOSIS
• Echinococcosis is a parasitic/zoonotic disease caused by infection with

tiny tapeworms of the genus Echinocococcus.
• Echinococcosis is classified as either cystic echinococcosis (also known

as hydatid disease or hydatidosis) or alveolar echinococcosis.
Cystic Echinococcosis
• It is caused by Echinococcus granulosus; also called as dog tapeworm.
General Morphological characteristics
It is a tissue cestode, exits in three morphological forms— adult, larva
(called hydatid cyst), and egg.
• Adult worm resides in dog’s intestine. It measures 3–6 mm long, consists
of head, neck and a strobila or body made up of three proglottids/
segments.
• The larval form is called as hydatid cyst. It is the pathogenic form, forms
cystic lesions in liver and other viscera of man and other herbivores.
• Eggs: E. granulosus eggs are morphologically similar to Taenia eggs,
consists of an embryo with six hooklets.
Epidemiology & Risk Factors
1. Host: E. granulosus passes its life cycle through two hosts:
Definitive host: Dogs and other canine animals

Intermediate hosts: Sheep and other herbivores are the usual intermediate
host. Man acts as an accidental intermediate host (dead end)
The disease is most commonly found in people involved in raising sheep and
the presence of working dogs that are allowed to eat the offal of infected
sheep.
For Echinococcus multilocularis:-
• Definitive host: Foxes and wolves (and also dogs and cats)
• Intermediate hosts: Small wild rodents like squirrels, mice, etc. Man is
an accidental intermediate host.
2. Infective form: Eggs are the infective form.
3. Mode of transmission: Man (and other intermediate hosts) acquires the
infection by ingestion of soil, water or food contaminated with tapeworm eggs.
4. Incubation period: 32-80 days
5. Distribution: Echinococcus granulosus is found in Africa, Europe, Asia, the
Middle East, Central and South America, and in rare cases, North America. It is
more frequently found in rural, grazing areas where dogs ingest organs from
infected animals.
Echinococcus multilocularis is found across the globe and is especially
prevalent in the northern latitudes of Europe, Asia, and North America.
Life cycle
Hydatid cyst
• Majority of embryo or oncosphere are destroyed by host immune response, few
escape and develop into fluid filled bladder-like cyst called as hydatid cysts.
Average size measures 5–8 cm (from few mm to >30 cm).
• It consists of:
Cyst wall
Brood capsule: which secretes the hydatid fluid. The brood capsule contains
number of protoscolices (future head)
Hydatid fluid: It is clear, pale yellow colored fluid, which is antigenic, toxic and
anaphylactic.
Hydatid sand: Some of the brood capsules and protoscolices break off and get
deposited at the bottom as hydatid sand
• The hydatid cyst may undergo—(i) spontaneous resolution, or (ii)
rupture of the cyst, which may lead to either formation of secondary
cysts (carried to other organs) or anaphylactic reaction to the hydatid
fluid antigens.
Hydatid cyst from liver
Clinical features (Cystic echinococcosis)
• Infection usually occurs in childhood but gets manifested
in adult life.
• Site: Most common site of the cyst is liver (60–70%, right lobe) or lung
(20%), followed by kidney, muscle, spleen, soft tissue, brain, bone and
others.
• Asymptomatic: The cysts grow up to 5–10 cm in size within the first
year and can survive for years or even decades, without any
symptoms
• Symptoms: Few patients develop symptoms which may
be due to:
• Pressure effect of the enlarging cyst: Leads to palpable abdominal
mass, hepatomegaly, abdominal tenderness, portal hypertension and
ascites
• Obstruction: Daughter cysts may erode into the biliary tree or a
bronchus and enter into the lumen to cause cholestasis, cholangitis,
and dyspnea.
• Secondary bacterial infection, causing pyogenic abscess in liver
• Anaphylactic reactions: Cyst leakage or rupture may be associated
with a severe allergic reaction to hydatid fluid antigens; leading to
hypotension, syncope and fever.
Clinical features (Alveolar echinococcosis)
• It produces alveolar (or multilocular) hydatid disease. So named because the
cysts have multiple locules resembling lung alveoli. The cysts are usually sterile,
do not produce brood capsule and protoscolices.
• Liver is the most common organ affected (98% of cases)
• Signs and Symptoms developed are similar to that of E. granulosus such as due
to hepatomegaly and portal hypertension. Cyst has an ability to migrate rapidly
to other organs mimicking a malignant tumor. However, there is no malignant
potential.
Alveolar echinococcosis
Diagnosis
• Hydatid fluid microscopy: direct mount or staining with
acid-fast stain)—detects brood capsules and protoscolices.
Diagnostic aspiration is not usually recommended because of the risk of
fluid leakage which may lead to anaphylaxis or dissemination of infection.
• Antibody Detection: ELISA and Western blot technique. Antigen B is the

antigen of choice used for sero-epidemiological study for the detection of
antibody.
Diagnosis
• Imaging:
1. X- rays: detect hepatomegaly and calcified cysts and cysts in lungs
2. Ultrasound (USG): It is the imaging method of choice because of its
low cost and high diagnostic accuracy of 90%.
Diagnosis
• WHO classification of USG imaging: WHO has classified the USG
images of cysts into six types according to its activity (CL and CE1 to
CE5). This is useful in determining whether the cyst is active or not. It
is also used for epidemiological studies to detect the prevalence of
hydatid cyst in population.
WHO classification of USG imaging
Diagnosis
3. CT and MRI scan: to detect smaller cysts, extrahepatic cysts and to
differentiate hydatid cyst from other cystic lesions.
Diagnosis
• Molecular methods: PCR
• Skin test (Casoni test): Now this test is obsolete.
Treatment
• PAIR (puncture, aspiration, injection and re-aspiration):
Percutaneous puncture of the cyst Aspiration of 10–15 mL of cyst
fluid Infusion of scolicidal agents like hypertonic saline, cetrimide,
or ethanol Re-aspiration of the fluid after 5 minutes
• Surgery
• Anti-parasitic agents
Albendazole is the drug of choice, given to prevent recurrence
and to reduce the size of the cyst before surgery or PAIR and is
given at 15 mg/kg daily in two divided doses; 1 week before to 4
weeks after the procedure.
• Percutaneous thermal ablation

It is a noninvasive method, involves percutaneous radiofrequency
ablation of the germinal layer of the cysts
Prevention and control
Cystic echinococcosis is controlled by preventing transmission of the parasite.
Prevention measures include limiting the areas where dogs are allowed and
preventing animals from consuming meat infected with cysts.
• Prevent dogs from feeding on the carcasses of infected sheep.
• Control stray dog populations.
• Restrict home slaughter of sheep and other livestock.
• Do not consume any food or water that may have been contaminated by fecal
matter from dogs.
• Wash your hands with soap and warm water after handling dogs, and before
handling food.
• Teach children the importance of washing hands to prevent infection.
Prevention and control
Alveolar echinococcosis can be prevented by avoiding contact with wild
animals such as foxes, coyotes, and dogs and their fecal matter and by
limiting the interactions between dogs and rodent populations.
• Do not allow dogs to feed on rodents and other wild animals.
• Avoid contact with wild animals such as foxes, coyotes and stray dogs.
• Do not encourage wild animals to come close to your home or keep them
as pets.
• Wash your hands with soap and warm water after handling dogs or cats,
and before handling food.
• Teach children the importance of washing hands to prevent infection.
Thank you

Hydatid Disease

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ECHINOCOCCOSIS

• Echinococcosis is a parasitic/zoonotic disease caused by infection with

• Echinococcosis is classified as either cystic echinococcosis (also known

1. Host: E. granulosus passes its life cycle through two hosts:

Definitive host: Dogs and other canine animals

• Antibody Detection: ELISA and Western blot technique. Antigen B is the

• Percutaneous thermal ablation

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