Cystic Echinococcosis (Ehinoccoccus
granulosus sensu lato)
Predilection
site:
Anterior small intestine (final host); mainly liver and lungs (intermediate
host)
Final hosts: E. granulosus
granulosus: dog and many wild canids; E. granulosus equinus: dog and red fox
Intermediate
hosts:
man and hervorous ruminants.
The adult Echinococcus granulosus (sensu
lato) (2—7 mm long)
resides
in the small intestine of the definitive host. Gravid proglottids release
eggs
that
are passed in the feces, and are immediately infectious. After ingestion by a
suitable intermediate host, eggs hatch in the small intestine and release
six-hooked oncospheres
that
penetrate the intestinal wall and migrate through the circulatory system into
various organs, especially the liver and lungs. In these organs, the oncosphere
develops into a thick-walled hydatid 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.
(Humans are aberrant intermediate hosts, and become
infected by ingesting eggs
.
Oncospheres are released in the intestine
,
and hydatid cysts develop in a variety of organs
.
If cysts rupture, the liberated protoscolices may create secondary cysts in
other sites within the body (secondary echinococcosis).)
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