Causal Agents:  
The cestodes (tapeworms) Taenia saginata (beef tapeworm) and T. solium (pork tapeworm).  Taenia solium can also cause cysticercosis.

Life Cycle:

Life cycle of Taenia saginata and Taenia solium          
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.

Geographic Distribution:     
Both species are worldwide in distribution.  Taenia solium is more prevalent in poorer communities where humans live in close contact with pigs and eat undercooked pork, and is very rare in Muslim countries.

Clinical Features:        
Taenia saginata taeniasis produces only mild abdominal symptoms.  The most striking feature consists of the passage (active and passive) of proglottids.  Occasionally, appendicitis or cholangitis can result from migrating proglottids.   Taenia solium taeniasis is less frequently symptomatic than Taenia saginata taeniasis.  The main symptom is often the passage (passive) of proglottids.  The most important feature of  Taenia solium taeniasis is the risk of development of cysticercosis.

Laboratory Diagnosis:         
Microscopic identification of eggs and proglottids in feces is diagnostic for taeniasis, but is not possible during the first 3 months following infection, prior to development of adult tapeworms.  Repeated examination and concentration techniques will increase the likelihood of detecting light infections.  Nevertheless, speciation of Taenia is impossible if solely based on microscopic examination of eggs, because all Taenia species produce eggs that are morphologically identical.  Eggs of Taenia sp. are also indistinguishable from those produced by cestodes of the genus Echinococcus (tapeworms of dogs and other canid hosts).  Microscopic identification of gravid proglottids (or, more rarely, examination of the scolex) allows species determination.

TAKE EXTREME CARE IN PROCESSING THE SAMPLES!  INGESTION OF EGGS CAN RESULT IN CYSTICERCOSIS!

Diagnostic findings

  • Microscopy
  • Antibody detection may prove useful especially in the early invasive stages, when the eggs and proglottids are not yet apparent in the stools.
  • Morphologic comparison with other intestinal parasites

Treatment:
Treatment is simple and very effective.  Praziquantel* is the drug of choice. 

* This drug is approved by the FDA, but considered investigational for this purpose.