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Taenia solium

Microbiology > Parasitology > Cestodes
Taenia solium (Pork Tapeworm)

Structure: Helminth, Cestode, Pork Tapeworm

Pathobiology:
• Pigs acquire infection upon ingesting vegetation and/or water contaminated with infected human feces. In the animal’s intestine, the eggs hatch, penetrate the intestinal wall and migrate to the striated muscles, brain, liver and other tissues where they develop cysticerci (larval cysts).  
• Humans become infected by ingesting larval cysticerci in undercooked pork muscle. The larvae develop in the small intestine by attaching to the intestinal mucosa via its scolex (head) containing suckers and a crown of hooks. The tapeworm can grow to several meters (2-7 m) as it absorbs nutrients digested by the human host. As a hermaphroditic tapeworm matures, it releases proglottid segments containing fertilized eggs which migrate to the anus or are passed in feces.  
• Humans develop cysticercosis by ingesting eggs, not undercooked pork (larval cysts), via a fecal-oral transmission route.

Epidemiology:
• Worldwide, particularly in Eastern Europe, Central and South America and parts of Africa, India and Asia.  The incidence is higher in areas where pigs are raised and sanitary conditions are suboptimal.  Infections in the USA are rare.

Disease Manifestations:
• Taeniasis:  Adult T. solium in the intestine seldom causes appreciable symptoms.  If symptoms do occur, they may include abdominal discomfort, diarrhea or weight loss.
• Cysticercosis:  Larval cysts present in tissues, often asymptomatic.
• Neurocysticercosis: Larval cysts present in CNS, which can result in seizures and/or headaches and occasionally confusion, brain swelling, stroke or death.

Laboratory Diagnosis:
• Intestinal Infection (Taeniasis):  
o Microscopic stool exam (O&P) for eggs and/or proglottids.  Several samples may be required as these are shed intermittently.
o Eggs are indistinguishable from Taenia saginata (beef tapeworm).  Taenia eggs are round, 30-40 microns in diameter surrounded by a double-walled radially striated membrane.  
o The proglottids are distinguishable; T. solium: <12 uterine branches,  T. saginata: 15-20 uterine branches.
o If a scolex (head) is found (rarely, unless treated), T. solium: a crown of hooks and four suckers, T. saginata:  4 lateral suckers, no hooks.
• Tissue Infection (Cysticercosis): cysticerci consistent lesions by CT or MRI, direct visualization of cysticerci in the anterior chamber of the eye.
• Serology (strong cross reaction with Echinococcus antibody) may be helpful
• Peripheral eosinophilia Is usually absent.
• Stool O&P exam for cysticercosis is insensitive as at the time of diagnosis it is rare for viable intestinal tapeworms to be present.
Differential Diagnosis:  Other intestinal parasites, brain tumor, brain abscess, mycotic granuloma, tuberculoma, toxoplasma, nocardia, epilepsy, stroke, hematoma.

Therapy:
• Taeniasis: Praziquantel, single dose
• Neurocysticercosis:  Albendazole plus a corticosteroid.  The increased inflammation surrounding treated, degenerating cysts may exacerbate neurological symptoms.
• Antiepileptics to control seizures

 
Key Words:
Cysticercosis,
Neurocysticercosis,
Taeniasis,
Pork tapeworm,
Brain lesions

 
 
Web links:
www.cdc.gov/parasites
Life Cycle:
The cestodes (tapeworms) Taenia saginata (beef tapeworm) and T. solium (pork tapeworm). Taenia solium eggs can also cause cysticercosis.


Taeniasis is the infection of humans with the adult tapeworm of Taenia saginata or Taenia solium. Humans are the only definitive hosts for T. saginata and T. 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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