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Tapeworms Causes and Treatment

Updated on February 14, 2010

Tapeworms are any of a large class of parasitic flat-worms that infest man and other animals. Although they are often large in size, they produce surprisingly little physical disturbance in the infected individual. They may cause anemia, but contrary to popular belief, they do not cause increased appetite or weight loss.

Tapeworms make up the class Cestoda of the phylum Platyhelminthes (flatworms). The most common large worm that infects man is the beef tapeworm (Taenia saginata), which is found in all parts of the world. The two other large species that infect man, the pork tapeworm (T. solium) and the fish tapeworm (Diphyllobothrium latum), are slightly more limited in their geographic distribution. The pork tapeworm is found in Central and South America, Africa, and Asia. The fish tapeworm is found in Europe, central Africa, and parts of North America, Asia, and South America. The dwarf tapeworm (Hymenolepis nana), about 2 inches (50 mm) long, is found in all temperate and tropical regions. Unlike other species it can be transmitted directly from one person to another. Other tapeworms require at least one intermediate host.

Beef Tapeworm

The adult beef tapeworm usually ranges in length from 10 to 15 feet (3 - 4.5 meters). Like all other tapeworms it consists of a head, or scolex, and a chain of segments, or proglottids, each of which is actually a separate individual with both male and female reproductive organs.

The scolex, the smallest part of the tapeworm, is a tubular structure about 1 inch (25 mm) long and .04 to .08 inch (1-2 mm) in diameter. When viewed under a microscope or magnifying lens it is seen to have four muscular suckers by which it holds onto the lining of the host's intestine. The proglottids are produced one after another at the hind end of the scolex. As they move further away from the scolex they grow and mature. By the time the proglottids reach the end of the worm they are about 19 mm long, and inside each one the uterus is full of fertilized eggs. When fully mature, the end proglottids break off and pass out of the host's body. If deposited on the ground they move about and in so doing cause the uterus to rupture. The hundreds of eggs are then squeezed out onto the ground where they may be eaten by cattle.

If an egg is eaten by a cow or steer, the embryo inside the egg is freed when it gets to the host's stomach. It then travels to a muscle where it forms a cyst. Each cyst contains a scolex, and the person who eats uncooked beef containing a cyst then becomes infected. When the scolex reaches the intestine it attaches itself and within two or three months becomes an entire tapeworm that may live for 10 years or more. A diagnosis of beef tapeworm infestation is confirmed by identifying the proglottids in the person's stool.

Pork Tapeworm

The pork tapeworm has a life cycle similar to that of the beef tapeworm except that the intermediate host is a pig. It closely resembles the beef tapeworm except that the scolex has a circle of tiny hooks in addition to the four suckers. An important feature of this tapeworm is that the cyst stage may occur in humans as well as pigs. When cysts form in a person's muscle tissue they cause little trouble but when they form in the eye or brain they may cause serious damage, and the person may die. The diagnosis of pork tapeworm infestation is made by examining the person's stool.

Fish Tapeworm

This species, which may reach a length of 30 feet (9 meters), is acquired by eating raw freshwater fish, such as pike. The scolex is olive-shaped and has no hooks or suckers. The proglottids are very small and do not break off individually. Each one produces scores of eggs every day, and they are discharged into the intestine in large numbers. The life cycle of the fish tapeworm requires two intermediate hosts: a tiny crustacean (copepod) and a fish. A frequent complication of fish tapeworm infestation is pernicious anemia, caused by the worm's absorbing the vitamin B12 eaten by the person.


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