Erinococcus Granulosus - Copy

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Echinococcus granulosus

Causal Agent:Human echinococcosis (hydatidosis, or hydatid disease) is caused by the larval stages ofcestodes (tapeworms) of the genus Echinococcus. Echinococcus granulosus causes cysticechinococcosis, the form most frequently encountered; E. multilocularis causes alveolar

echinococcosis; E. vogelicauses polycystic echinococcosis; and E. oligarthrus is anextremely rare cause of human echinococcosis.

Life Cycle:

The adult Echinococcus granulosus (3 to 6 mm long) resides in the small bowel of the

definitive hosts, dogs or other canids. Gravid proglottids release eggs that are passed in

the feces. After ingestion by a suitable intermediate host (under natural conditions: sheep,goat, swine, cattle, horses, camel), the egg hatches in the small bowel and releases an

oncosphere that penetrates the intestinal wall and migrates through the circulatory

system into various organs, especially the liver and lungs. In these organs, the oncosphere

develops into a cyst that enlarges gradually, producing protoscolices and daughter cysts

that fill the cyst interior. The definitive host becomes infected by ingesting the cyst-

containing organs of the infected intermediate host. After ingestion, the protoscolices

evaginate, attach to the intestinal mucosa , and develop into adult stages in 32 to 80

days. The same life cycle occurs with E. multilocularis (1.2 to 3.7 mm), with the following

differences: the definitive hosts are foxes, and to a lesser extent dogs, cats, coyotes and


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wolves; the intermediate host are small rodents; and larval growth (in the liver) remains

indefinitely in the proliferative stage, resulting in invasion of the surrounding tissues. WithE. vogeli(up to 5.6 mm long), the definitive hosts are bush dogs and dogs; theintermediate hosts are rodents; and the larval stage (in the liver, lungs and other organs)

develops both externally and internally, resulting in multiple vesicles. E. oligarthrus (up to2.9 mm long) has a life cycle that involves wild felids as definitive hosts and rodents as

intermediate hosts. Humans become infected by ingesting eggs , with resulting releaseof oncospheres in the intestine and the development of cysts , , , , , invarious organs.

Geographic Distribution:E. granulosus occurs practically worldwide, and more frequently in rural, grazing areaswhere dogs ingest organs from infected animals. E. multilocularis occurs in the northern

hemisphere, including central Europe and the northern parts of Europe, Asia, and North

America. E. vogeliand E. oligarthrus occur in Central and South America.

Clinical Features:Echinococcus granulosus infections remain silent for years before the enlarging cysts cause

symptoms in the affected organs. Hepatic involvement can result in abdominal pain, a

mass in the hepatic area, and biliary duct obstruction. Pulmonary involvement can producechest pain, cough, and hemoptysis. Rupture of the cysts can produce fever, urticaria,

eosinophilia, and anaphylactic shock, as well as cyst dissemination. In addition to the liver

and lungs, other organs (brain, bone, heart) can also be involved, with resultingsymptoms. Echinococcus multilocularis affects the liver as a slow growing, destructivetumor, with abdominal pain, biliary obstruction, and occasionally metastatic lesions into the

lungs and brain. Echinococcus vogeliaffects mainly the liver, where it acts as a slowgrowing tumor; secondary cystic development is common.

Laboratory Diagnosis:

The diagnosis of echinococcosis relies mainly on findings by ultrasonography and/or otherimaging techniques supported by positive serologic tests. In seronegative patients with

hepatic image findings compatible with echinococcosis, ultrasound guided fine needle biopsy

may be useful for confirmation of diagnosis; during such procedures precautions must betaken to control allergic reactions or prevent secondary recurrence in the event of leakageof hydatid fluid or protoscolices.

Diagnostic findings

Microscopy Antibody detection

Treatment:Surgery is the most common form of treatment for echinococcosis, although removal of theparasite mass is not usually 100% effective. After surgery, medication may be necessary to

keep the cyst from recurring. The drug of choice for treatment echinococcosis isalbendazole (Echinococcus granulosus). Some reports have suggested the use ofalbendazole or mebendazole for Echinococcus multilocularis infections.
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Larvae Stage

Hydatid cysts are large, roughly spherical, fluidfilled hollow bladders containing numerous

protoscolices.

They vary in size; those found in the liver areaprox. 20 cm in diameter, but those found in the

peritoneal cavity are usually largerAdult Stage

Slightly smaller than E. granulosus (max. lengthof aprox 4 mm and consisting of 4-5 proglottids).

Definitive Hosts

Dogs Coyotes Wolves

Intermediate Hosts Sheep Horses Camels Pigs Humans

Life Cycle:

The adult is in the small bowel of the definitive host


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Gravid proglottids release eggs that are passed inthe feces

In the intermediate host the egg hatches in the smallbowel and releases an oncosphere

The oncosphere penetrates the intestinal wall andmoves through the circulatory system to variousorgans

In the organs they develop into cysts and enlargegradually

The cysts produce protoscolices and daughter cysts

Definitive host eats the infected organs andbecomes infected After ingestion, the protoscolices evaginate, attach

to the intestinal mucosa and develop into adultstages

In 32-80 days, the cycle starts over


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Allergic reactions and sometimes anaphylactic shock may occur if the cyst ruptures

Surgery is the most common form of treatment for echinococcosis .

The drug of choice for treatment is albendazole.


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Erinococcus Granulosus - Copy