Taenia solium

(Pork Tapeworm)

Table of Content

 

 

 

History of Discovery (return to top)

Tapeworm infections have been recorded in history from 1500 B.C. and have been recognized as one of the earliest human parasites. Taenia solium infection has been recognized since biblical times and the parasite life cycle has been identified by the 1850s. Although T. solium and T. saginata are very similar, the extraintestinal T. solium infection is far more dangerous and serious.

 

 

 

Morphology (return to top)

T. solium is a flattened ribbon like tapeworm that is white in color. Although it is very morphologically similar to the T. saginata, T. solium is slightly shorter and have a modified scolex.

The attachment organ, or scolex, has 4 large suckers with a double row of hooks. The adult tape worm grows to be about 6mm in width and 2-7 m in length with about 800 segments called proglottids. As the tapeworm grows in the intestine, mature proglottis called gravid proglottis will be casted off out of the human body. Each gavid proglottids contains both male and female reproductive organs and houses 30-40 thousand eggs. The eggs are indistinguishable between T.solium and T. saginata as they both measure 31-43 micrometers and contain an embryo (an oncosphere).

(compare T. solium with T. saginata)

 

 

 

 

Incubation Period (return to top)

It takes about 5 to 12 weeks for the worm to mature into adulthood in the human intestine. Usually only a single worm is present at at time. However, multiple worms have been known to inhabit the human body. T. solium may survive up to 25 years or more.

 

 

 

Transmission/Reservoir (return to top)

T. solium has a very similar transmission pattern to T. saginata. Humans are the only known definitive hosts for the T. solium. Human infection begins with the ingestion of infected raw or undercooked pork. The T. solium larvae gets digested out of the meat and attaches itself to the upper small intestine region. There it will mature and increase its number of proglottids. Terminal gravid proglottids will break off from the main body and will either pass out with the stool or worm its way out of the anus. In certain cases, 3 or 4 attached proglottids will pass out together. The eggs housed in the proglottids will be released and remain viable in the soil, sewage, and land for weeks.

However, unlike T. saginata, both pigs and humans can become intermediate hosts to the T. solium. When pigs and humans ingest the eggs, the oncospheres will pierce through the intestinal walls, travel through the circulatory system, and plant itself in the subcutaneous and intramuscular tissues such as the brain and eyes. Cysticercosis will develop in these areas and will become invective in 9-10 weeks. Pigs will die in several months. In humans, cysticercosis has a variety of damaging effects on the central nervous system, vision, and brain functions.

In humans, autoinfection of T. solium eggs can occur by reverse peristalsis of the intesine.

Click here for more information in cysticercosis.

 

Symptoms (return to top)

The presence of T. solium worms in the human intestines usually does not cause major problems. Diarrhea, constipation,, indigestion, and other mild stomach symptoms are common. Proglottids may also also crawl out of the anus and cause some discomfort or embarrassment. Also, patients may have higher IgE level in their serum and a low-grade eosinophilia (mostly under 15%).

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For patients with cysticercosis, devastating effects may occur as the larvae develops in the skeletal/cardiac muscles and the brain. The presence of cysticerci (neurocysticercosis) is the most common parasitic infection of the human brain. It is known to cause adult-set epilepsy, siezures, abnormal behavior changes, and lesions in the brain. Cysticerci in the eye can cause permanent blindness. Also, the racemose or proliferating form of cysticercus can cause tumor like growths. For more information concerning symptoms, click cysticercosis.

 

 

 

 

 

 

Diagnostic Tests (return to top)

Taeniasis is diagnosed by recovering eggs or gravid proglottids from the feces of the infected human host. T. saginata and T. solium are virtually identical in morphology. However, identification at the species level can be made by the number of lateral uterine branches in the gravid proglottids and differing scolexes. T. solium has 7to 13 branches and 4 hooks in the scolex. (compare with T. saginata)

Diagnosis of cysticercosis depend primarily on confirming the presence hooks of the scolex of T. solium under the microscope. Calcified larvae in the subcutaneous and muscle tissues can be identified by an X-ray examination. CT scans and MRI can detect lesions in the brain. However, making a neurocysticercosis diagnosis is difficult. Often times, doctors rely on the presence of brain tumors or ocular cysticercosis to make a diagnosis. For more information concerning diagnosis, click cysticercosis.

 

 

 

 

Management and Therapy (return to top)

An oral drug niclosamide is highly effective in getting rid of the T. solium tapeworm. Since there is a high probablity of autoinfection, patients are treated immediately.

Human tissue infected with T. solium.

 

Cysticercosis outside the central nervous system is treated surgically. For patients with ocular cysticercosis, the cysts are removed. Excisonal biopsies are performed on subcutaneous cysticercosis. For patients with brain cysticercosis, two drugs praziwuantel and albendazole are relatively successful as treatments. The prognosis for a patient with adult tapeworms that can be removed surgically or medically treated is good. The prognosis for patients with racemose form of the parasite is bad.

 

 

 

 

Epidemiology (return to top)

T. solium is found everywhere in the world. However, prevalance of T. solium are high in Mexico, Central and South America, Africa, Asia, Spain, and Portugal. Areas of poor sanitation, large fecal human contamination, and areas where pigs or swines graze have high rates of T.solium infection. Countries where people like to eat their meat undercooked (like some parts of Europe and Asia) also have high infection rates. Taeniasis and cysticercosis are very rare in Muslim countries.

 

 

 

Public Health and Prevention Strategies (return to top)

For a number of reasons, T. solium is a matter of great public health concern. Neurocysticercosis has a large impact on human health. T. solium is the only source of infection in humans and pigs (epidemiologically controllable), and T. solium can be contained with few, simple steps.

 

 

 

 

Clinical Presentation in Humans (return to top)

Case #1: A single case of cysticerosis involving the scrotum has been reported. It involved a 9 year old Hispanic boy who was born and raised in the United States. He did not travel outside of the US. Histrologic testing confirmed his condition.

 

 

 

Useful web links (return to top)

http://www.biosci.ohio-state.edu/~parasite/taenia.html

http://www.dpd.cdc.gov/dpdx/HTML/ImageLibrary/Taeniasis_il.htm

http://www.geocities.com/Area51/Keep/8895/taeniasis1.html

http://www.nlm.nih.gov/medlineplus/ency/article/001391.htm#prognosis

http://www.dpd.cdc.gov/dpdx/HTML/Taeniasis.htm

http://martin.parasitology.mcgill.ca/JIMSPAGE/TAENIA.HTM

 

 

 

References (return to top)

Garcia, Lynne S. Diagnostic Medical Parasitology. Washington DC: ASM Press, 2001.

Markell, Edward, David John, Wojciech Krotoski. Medical Parasitology. Philadelphia: W.B Saunders, 1999.

Warren, Kenneth. Immunology and Molecular Biology of Parasitic Infections. Boston: Blackwell Scientific, 1993.

www. biosci.ohio-state.edu

www.dpd.cdc.gov

www.nlm.nih.gov