| Share   Humans as Tapeworm Hosts  Human tapeworm infestations
are most common in regions where there is fecal contamination of
soil and water and where meat and fish are eaten raw or lightly
cooked. In the case of the human tapeworm most common in the
United States (the beef tapeworm, Taenia saginata ) the usual
intermediate host is a cow, which ingests the proglottid while
drinking or grazing. The round-bodied embryos, equipped with
sharp hooks, hatch and bore through the cow's intestinal wall
into the bloodstream, where they are carried to the muscles.
Here each embryo encloses itself in a cyst, or bladder; at this
stage it is called a bladder worm. During the bladder worm stage
the embryo develops into a miniature scolex; it remains encysted
until the muscle is eaten by a primary host, in this case a
human. If the scolex has not been killed by sufficient cooking
of the meat, it sheds its covering and attaches to the
intestinal wall, where it begins producing proglottids.  A human
tapeworm common in Mexic