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Humans are the only
definitive hosts for Taenia saginata and Taenia solium. Eggs
or gravid proglottids are passed with feces
;
the eggs can survive for days to months in the environment. Cattle (T.
saginata) and pigs (T. solium) become infected by ingesting
vegetation contaminated with eggs or gravid proglottids
. In the
animal's intestine, the oncospheres hatch
, invade
the intestinal wall, and migrate to the striated muscles, where they develop
into cysticerci. A cysticercus can survive for several years in the
animal. Humans become infected by ingesting raw or undercooked infected
meat .
In the human intestine, the cysticercus develops over 2 months into an adult
tapeworm, which can survive for years. The adult tapeworms attach to the
small intestine by their scolex
and reside in the small intestine
.
Length of adult worms is usually 5 m or less for T. saginata (however
it may reach up to 25 m) and 2 to 7 m for T. solium. The adults
produce proglottids which mature, become gravid, detach from the tapeworm,
and migrate to the anus or are passed in the stool (approximately 6 per
day). T. saginata adults usually have 1,000 to 2,000 proglottids,
while T. solium adults have an average of 1,000 proglottids. The
eggs contained in the gravid proglottids are released after the proglottids
are passed with the feces. T. saginata may produce up to 100,000 and
T. solium may produce 50,000 eggs per proglottid respectively.
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