Taeniasis (tapeworm infection)

What is taeniasis?

Taeniasis is a tapeworm infection. Two parasites commonly cause taeniasis are Taenia saginata and Taenia solium. They require more than one vertebrate host species to complete their developmental cycles.

What are the causes?

Tapeworm infection is acquired by eating raw or undercooked meat of infected animals. Beef generally carries Taenia saginata while pork carries Taenia solium. Certain freshwater fish and salmon may also carry a tapeworm called Diphyllobothrium latum. The larvae from the infected meat develop in the human intestine into the adult tapeworm which grows and can attain lengths greater than 12 feet.

Adults and children with tapeworm (T. solium, pork tapeworm only) can, if appropriate hygiene is lacking, become self-infected by ingesting eggs from their tapeworm which were picked up on their hands while wiping or scratching the anus.

Additionally, these individuals can expose other individuals to T. solium eggs, usually via food handling. Ingested eggs hatch in the intestinal tract and the larvae migrate through the tissues, where they encyst. If the larvae migrate to the brain, they can cause convulsions or fits and other neurological problems. This condition is called cysticercosis.

Tapeworms are segmented, and each segment or proglottid is capable of producing eggs. Eggs are dispersed by individual or groups of proglottids detaching and passing out with the stool. The groups of proglottids from the beef tapeworm are capable of movement and actively crawl out through the anus.

What is the life cycle?

Taenia saginata and Taenia solium pass their life cycles in two hosts. In man, the adult lives in the small intestines. Humans are the only definitive hosts for Taenia saginata and Taenia solium. Eggs or gravid proglottids are passed with faeces, 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, they hatch, invade the intestinal wall, and migrate to the 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 the adult worms is usually 5 metres or less for T. saginata (however it may reach up to 25 metres) and 2 to 7 metres 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 faeces. T. saginata may produce up to 100,000 and T. solium may produce 50,000 eggs per proglottid respectively.

The adult stages of T.saginata and T.solium may persist for several years in infected humans. Mixed infections of both the parasites can occur. Although the lifespan of T. solium is not known it is suspected to be some years.

What is the incubation period?

For the adult tapeworm, it is from 8 to 14 weeks.

What are the symptoms?

Tapeworm infestation does not usually cause any symptoms. Infection is generally recognised when the infected person passes segments of proglottids in the stool, especially if the segment is moving. Taenia saginata taeniasis produces only mild abdominal symptoms. 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.

How is the diagnosis made?

Microscopic identification of eggs and proglottids in faeces 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 proglottid allows species determination.

What is the treatment?

Treatment is simple and very effective. Tapeworms are treated with oral medications, usually in a single dose. The drug of choice for tapeworm infections is niclosamide. Praziquantel and albendazole can also be used.

What is the prognosis?

Complete eradication of the tapeworm occurs following treatment.

What are the complications?