- Also called:
- cestode
- Key People:
- Pierre-Joseph van Beneden
- Related Topics:
- Eucestoda
- Cestodaria
- Trypanorhyncha
- dwarf tapeworm
- Amphilinidea
tapeworm
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What is a tapeworm?
A tapeworm is an invertebrate flatworm belonging to the class Cestoda, with around 5,000 species. These parasitic worms range from 1 mm to over 15 m in size and can be found worldwide.
Tapeworms lack a mouth and digestive tract, and instead absorb food through a tough cuticle. They attach to the intestinal tract of their hosts using suckers and hooks on their head (scolex).
Tapeworms can infect invertebrates and the liver or digestive tracts of vertebrates, including humans and domestic animals. The disease caused by tapeworms is known as cestodiasis. Humans can contract intestinal cestodiasis by consuming undercooked beef, pork, or fish that contain tapeworm larvae.
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What kind of animal is a flatworm?
Flatworms belong to the phylum Platyhelminthes, a group of soft-bodied, usually flattened invertebrates. About 80% of flatworm species are parasitic, living on or in another organism to get nourishment. Tapeworms are members of the invertebrate class Cestoda, a group of parasitic flatworms within the phylum Platyhelminthes.
Flatworms are bilaterally symmetrical and lack specialized respiratory, skeletal, and circulatory systems, as well as a body cavity. Tapeworms attach to the intestinal tract using a sucker or sucking groove on their head and, unlike other worms, do not enter the host's tissues.
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How does a tapeworm live inside its host?
Tapeworms are internal parasites that live inside the liver or digestive tracts of vertebrates, including humans and other animals. They attach to the host using suckers and hooks located on their head. Lacking a mouth and digestive tract, tapeworms absorb food through a tough cuticle covering their body.
Tapeworms may also digest materials in contact with their tegument, the flatworm's body covering, through membrane digestion. The microtriches, spinelike structures on the surface of tapeworms, help them attach to the host's gut and absorb nutrients.
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How do tapeworms get the nutrients they need?
Tapeworms are parasitic flatworms that lack a mouth and digestive tract. Instead, they absorb all the nutrients they need through their tough body covering, called the tegument. Amino acids and small carbohydrate molecules cross the tegument via active transport, a process that requires energy. The tapeworm's surface is drawn out into microtriches, which likely aid in nutrient absorption and attachment to the host's gut.
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What are the main parts of a tapeworm’s body?
A tapeworm's body consists of a few main parts. The scolex, or head, is equipped with suckers and hooks that it uses to attach to the host. The strobila (body) consists of numerous segments called proglottids, which vary in number from three to hundreds. Each proglottid is a self-sufficient reproductive unit, containing both male and female sex organs. The body is covered by a tough cuticle that absorbs food.
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How can humans and animals become infected with tapeworms?
Humans and animals can become infected with tapeworms through various means. Eating raw or undercooked meat, especially beef or pork, is a common source of infection. Tapeworm eggs are passed in feces and ingested by intermediate hosts like cows or pigs. The larvae then migrate to the animal's muscle tissue.
Another source of tapeworm infection is through the consumption of fish, particularly in the Northern Hemisphere. The fish tapeworm larvae encyst in the muscle tissue of fish such as trout, salmon, pike, and perch. When these fish are eaten raw or improperly cooked by humans or other mammals, the larvae attach to the intestine and develop into adult tapeworms.
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tapeworm, any member of the invertebrate class Cestoda (phylum Platyhelminthes), a group of parasitic flatworms containing about 5,000 species. Tapeworms, which occur worldwide and range in size from about 1 mm (0.04 inch) to more than 15 m (50 feet), are internal parasites, affecting certain invertebrates and the liver or digestive tracts of all types of vertebrates—including humans, domestic animals, and other food animals, such as fish. Some attack a single host, others require one or two intermediate hosts as well as a final, or definitive, host during their life cycle. The disease caused by tapeworms is known as cestodiasis (q.v.).
Tapeworms are bilaterally symmetrical (i.e., the right and left sides are similar). Some consist of one long segment; others have a definite head, followed by a series of identical segments called proglottids. The head, or scolex, bears suckers and often hooks, which are used for attachment to the host. The body covering is a tough cuticle, through which food is absorbed. There is neither a mouth nor a digestive tract. Tapeworms also lack a circulatory system and an organ specialized for gas exchange.
Most tapeworms are hermaphroditic (i.e., functional reproductive organs of both sexes occur in the same individual). They are usually self-fertilizing, and gonads of both sexes also occur within a single proglottid. The life cycle is complex. The pork tapeworm (Taenia solium, or Taeniarhynchus solium), found wherever raw pork is eaten, lives in the human intestine in its adult stage. Each proglottid, following fertilization, may contain as many as 40,000 embryos encased in separate capsules. If the embryos, which pass out with the host’s feces, are eaten by a mammal such as a dog, camel, pig, monkey, or human being, the larva emerges in the digestive tract. It bores through the intestinal wall into a blood vessel and is carried to muscle tissue in which it forms a protective capsule (encysts) and is called a cysticercus, or bladder worm. If the cysticercus is eaten alive in raw meat, it attaches itself to the host’s intestine and develops directly into a mature adult.
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The life cycle of the beef tapeworm (Taenia saginata, or Taeniarhynchus saginatis), which occurs worldwide where beef is eaten raw or improperly cooked, is much like that of the pork tapeworm. Man is the definitive host; cattle serve as the intermediate host.
The fish tapeworm (Dibothriocephalus latus, or Diphyllobothrium latum), most common in waters of the Northern Hemisphere, infests humans and other mammals that eat fish, particularly bears and dogs. Fertilized eggs pass from the host’s body in the feces. In a water medium they develop into a hairlike larva and are eaten by tiny crustaceans, which, in turn, are eaten by a fish. In the fish, the tapeworm larva encysts in muscle tissue. When the fish is eaten by a mammal, the larva attaches to the mammalian intestine and develops into a mature adult. Fish hosts of this tapeworm include trout, salmon, pike, and perch.