life cycle
The life cycle of Echinococcus is illustrated below (courtesy of DPDx)5:
The life cycle of this organism outside of a human can be summed up in six stages:
The adult Echinococcus
granulosus, which is about 3-6 mm in length, resides in the bowel of its
definite host.
Gravid proglottids
release eggs that are passed in the feces.
These eggs are then
ingested by a suitable intermediate host, including sheep, goat, swine, cattle,
horses and camels. The eggs then hatch in the bowels and release oncospheres that
penetrate the intestinal wall. These oncospheres then migrate through the
circulatory system to various organs of the host.
At the organ site,
the oncosphere develops into a hydatid cyst. This cyst enlarges
gradually, producing protoscolices and daughter cysts that fill
the cyst interior.
These
cyst-containing organs are then ingested by the definite host, causing
infection. After ingestion, the protoscolices evaginate, producing protoscolexes.
The scolexes
of the organisms attach to the intestine of the definite host and develop into
adults in 32-80 days.
The life cycle then continues in humans:
Humans can become
infected if they ingest substances infected with Echinococcus eggs.
The eggs
then release oncospheres in the small intestine.
At these places, oncospheres migrate through the circulatory system and produce hydatid
cysts.
Note: The same life cycle occurs with E. multilocularis (1.2 to 3.7 mm) except for these differences:
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Definite hosts = usually foxes and canines |
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Intermediate hosts = small rodents |
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Larval growth remains indefinitely in the proliferative stage, resulting in invasion of the surrounding tissues |
Note: With E. oligarthrus (up to 2.9 mm):
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Definite hosts = wild felids |
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Intermediate hosts = rodents |
Note: With E. vogeli (up to 5.6 mm):
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Definite hosts = bush dogs and dogs |
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Intermediate hosts = rodents |
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Larval stage develops both externally and internally, resulting in multiple vesicles. |