Aetiology and pathogenesis

The adult worm lives in the upper jejunum.

Features include:

• it is about 3m in length and may live for decades.
• the adult worm has usually less than 1000 proglottides.
• eggs are infective for pig and man.
• mode of infection - generally the faecal-oral route; although humans may become auto-infected when gravid proglottide segments (containing the worm eggs) are returned to the stomach (by reverse peristalsis).
• after ingestion, or auto-infection, the embryo is released form the egg and penetrates the intestinal wall. The embryo is then carried by vascular channels to all parts of the body. Over the next 60-90 days the encysted larval stage (so called "bladder worm") occurs in the striated muscle of neck, tongue and trunk. This larval form (cysticerci) can survive for 5 years.
• infection occurs if patients eat undercooked pork containing cystercerci. If the larval stage occurs in humans then this is cysticercosis.