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:

Definite hosts = usually foxes and canines

Intermediate hosts = small rodents

Larval growth remains indefinitely in the proliferative stage, resulting in invasion of the surrounding tissues

Note: With E. oligarthrus (up to 2.9 mm):

Definite hosts = wild felids

Intermediate hosts = rodents

Note: With E. vogeli (up to 5.6 mm):

Definite hosts = bush dogs and dogs

Intermediate hosts = rodents

Larval stage develops both externally and internally, resulting in multiple vesicles.