Taenia (genus) - Life Cycle

Life Cycle

The life cycle begins with either the gravid proglottids or free eggs (embryophores) with oncospheres (also knowed as hexacanth embryos) being passed in the feces, which can last for days to months in the environment. Sometimes these segments will still be motile upon excretion— they will either empty themselves of their eggs within a matter of minutes or, in some species, will retain them as a cluster and await the arrival of a suitable intermediate vertebrate host. The intermediate host (cattle, pigs, rodents, etc., depending on the tapeworm species) must then ingest the egg or proglottids. If the host is a correct one for the particular species of tapeworm, the embriophore then hatch, and the hexacanth embryos invade the wall of the small intestine of the intermediate host to travel to the striated muscles to develop into cysticerci larvae. Here they will grow, cavitate, and differentiate into this second larval form shaped like a bladder (and erroneously believed until the middle of the 19th century to be a separate parasite, the bladderworm) which is infectious to the definitive host when a invaginated scolex (protoscolex) is completely developed. To continue the process, the definitive host must eat the uncooked meat of the intermediate host. Once in the small intestine of the definitive host, the bladder is digested away, the scolex embeds itself into the intestinal wall, and the neck begins to bud off segments to form the strobila. New eggs will usually appear in the feces of the definitive host within six to nine weeks, and the cycle repeats itself.

Taenia saginata are about 1,000-2,000 proglottids long with each gravid proglottid containing 100,000 eggs, while Taenia solium contain about 1,000 proglottids with each gravid proglottid containing 60,000 eggs.