Tapeworm is any of a group of tapelike flatworms that live as parasites. Adult tapeworms inhabit the intestines of human beings or other animals. They have a headlike organ called a scolex and a series of blocklike segments in a flat body. A tapeworm has no mouth or intestine. It absorbs food through its body wall. Some tapeworms measure less than 1 inch (2.5 centimeters) long and have only a few segments. Others grow as long as 60 feet (18 meters) and have thousands of segments.
A tapeworm’s scolex has suckers or hooks or both. The worm uses the scolex to attach itself to the intestine of the host—that is, the animal in which the worm lives. The rest of the worm’s body grows from a necklike region behind the scolex. Segments develop as the worm grows. Each segment contains male and female reproductive organs and produces many eggs. Segments filled with eggs may drop off the end of the body. The segments then may pass out of the host with body wastes and release the eggs outside the host.
Almost all tapeworms have one or more larval (immature) stages and develop in two or three hosts. A newly hatched tapeworm is called an oncosphere. It is round and has small hooks. An oncosphere develops in a host that eats it or the egg from which it hatches. The oncosphere burrows through its host’s intestine and travels to other organs or to muscles. If another animal eats this host, the oncosphere may develop into another larval stage or into an adult tapeworm. A person may become infected by a tapeworm after eating improperly cooked fish, pork, or beef that contains tapeworm larvae.
Most adult tapeworms produce no bad effects in people. Sometimes they cause loss of appetite, abdominal discomfort, diarrhea, nausea, weakness, or anemia. Tapeworm larvae are much more dangerous to people. A person who accidentally eats eggs of the pork tapeworm may have young worms develop in almost every organ of the body, including the eyes, brain, and heart.
See also Flatworm.
