A tapeworm is a long, flat, intestinal worm found in humans and many other animals.
Tapeworms are long, flat, intestinal worms called cestodes found in humans and many other animals. Tapeworms do not have an intestinal tract; they absorb nutrients through their body surface. Human tapeworm infestations may be caused by eating meat or fish contaminated with tapeworm larvae * but also by ingesting soil or water contaminated with human fecal matter containing the eggs. Meat contaminated with tapeworm larvae has larvae enclosed in cyst * form within the meat. The larvae are worms at an intermediate stage of the life cycle between eggs and adulthood. They burrow into the animal tissue and form fluid-filled cysts, which are protective capsules. Like other intestinal parasites * , these worms frequently cause infestations in areas with poor sanitation, where livestock animals are exposed to contaminated soil or fish are exposed to contaminated water and have the parasites within their body tissues. Humans are either infested through ingestion of eggs or larvae. The tapeworms mature within the intestinal tract of the human and lay new eggs, which are released into the fecal matter and passed out of the body to begin the cycle again. Tapeworm infection may be prevented by thoroughly cooking meat until juices run clear and the centers are no longer pink or raw. Doing so ensures that any tapeworm cysts in the meat are destroyed.
There are three common species of tapeworms: Taenia saginata (beef tapeworm), Taenia solium (pork tapeworm), and Diphyllobothrium latum (freshwater fish tapeworm). After ingesting contaminated tapewormencysted meat or fish, the larvae travel to the intestines *
Beef and fish tapeworms generally remain limited to the human gastrointestinal tract and usually only migrate to further tissues in animals. The pork tapeworm is unique because it is known for leaving the human gastrointestinal tract in larval form and migrating to other parts of the human body to create cysts of worm larvae in human body tissues. Whereas cysts may form in any body tissue, the most commonly affected part of the body is the central nervous system * , including the brain. The condition of having a tapeworm cyst in body tissues is called cysticercosis. Having one in the brain is known as neurocysticercosis and may cause seizures *
The fish tapeworm is often noted for causing vitamin B12 deficiencies. In the human body, vitamin B12 is absorbed in the end portion of the small intestines known as the ileum. The closer the fish tapeworm is to the ileum, the more severe the vitamin B12 deficiency in the person serving as its host. This vitamin is necessary for red blood cells to function. Vitamin B12 deficiency causes a type of anemia, or red blood cell deficiency, known as pernicious anemia. Because the body tissues are not getting enough oxygen, the individual with pernicious anemia feels tired and weak and may even have nerve damage if the anemia is bad enough. Pernicious anemia responds well to vitamin therapy.
The largest tapeworms can reach an amazing size, measuring more than 45 feet long in some cases. The adult beef tapeworm is usually 15 to 30 feet long (4.5 to 9 meters). An infected person usually has only one or two worms. The tapeworms use their head, called the scolex, to attach themselves to the intestinal wall. They have 1,000 to 2,000 body segments, called proglottids, each containing 80,000 to 100,000 eggs. The eggs can survive for months or years in the environment outside the human body. If humans eat raw or undercooked beef containing cysts, the cysts develop over a two-month period into adult tapeworms. Adult beef tapeworms can live for more than 30 years.
The adult pork tapeworm is about half as long as the beef tapeworm, usually 8 to 11 feet (2.5 to 3.5 meters) long. It also has a scolex for attaching to the intestinal wall and a body of about 1,000 proglottids. Each proglottid contains about 50,000 eggs. Adult pork tapeworms can live up to 25 years.
The adult fish tapeworm is from 3 to 49 feet long (1 to 15 meters) and is the longest human tapeworm. They have 3,000 to 4,000 proglottids that are wider than they are long, giving this tapeworm the name broad tapeworm. The fish tapeworm affects freshwater fish as well as some saltwater fish that have a freshwater component to their life cycle (such as salmon). Fish tapeworm infestations are most common in societies that consume large amounts of raw or pickled fish.
Eggs and proglottids can be seen in stool samples by microscopic examination. In order to differentiate between a beef, pork, or fish tapeworm, a scolex has to be removed and examined. This is seldom done because doctors usually can prescribe the same medication for all types of tapeworm infestation. Stool is checked at three and six months after treatment to ensure that the parasite is gone.
Cysticercosis is diagnosed by examining the muscles or brain with a CT scan *
See also Intestinal Parasites • Parasitic Diseases: Overview • Roundworm Infection
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* larvae (LAR-vee) are the immature forms of an insect or worm that hatches from an egg.
* cysts (SISTS) are shell-like enclosures that contain small organisms in a resting stage.
* parasites (PAIR-uh-sites) are organisms such as a protozoan (one-celled animals), worm, or insect that must live on or inside a human or other organism to survive. An animal or plant harboring a parasite is called its host. A parasite lives at the expense of the host and may cause illness.
* intestines are the muscular tubes that food passes through during digestion after it exits the stomach.
* central nervous system (SEN-trul NER-vus SIS-tem) is the part of the nervous system that includes the brain and spinal cord.
* seizures (SEE-zhurs) are sudden bursts of disorganized electrical activity that interrupt the normal functioning of the brain, often leading to uncontrolled movements in the body and sometimes a temporary change in consciousness.
* CT scans is the shortened name for computed tomography (to-MOG-ra-fee), which uses computers to view structures inside the body. Formerly called computerized axial tomography (CAT).