Tapeworms and their effect on humans

Tapeworms and their effect on humans

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I've read that some people in some countries actually use tapeworms as a form of losing weight. What are the dangers to these people?

I haven't really found much on this topic (besides popular sites) but I can summarize it here: There are quite some tapeworms (or cestoda), I found numbers of up to 3500 species. They attach to the intestinal wall of the humans and then start to take up predigested food through their skin. With that, they reduce food from their host and start to grow, some get as long as 15 meters!

Some of the worms seem to be relatively harmless (besides stealing food), but this is more true for the first world. In poor countries, where there is not enough food, tapeworms can cause severe malnutrition.

Some tapeworms can migrate into the blood stream and from there into other tissues or organs like muscles, eye and brain. There they can cause cysts which can lead to organ failure and death.

For more information see this CDC webpage and this article: "Biochemistry and physiology of tapeworms.". This popular article is probably also interesting.

An addition to the answer by Chris.

Probably the most dangerous tapeworms for humans are Echinococcus. In humans they form cysts (in a variety of organs including brain) [it's because humans are "interpreted" as intermediate hosts], which can become very large and can cause death when untreated or disrupted.

24.4: Fungal Parasites and Pathogens

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Parasitism describes a symbiotic relationship in which one member of the association benefits at the expense of the other. Both parasites and pathogens harm the host however, the pathogen causes a disease, whereas the parasite usually does not. Commensalism occurs when one member benefits without affecting the other.

Tapeworms and their effect on humans - Biology

Adult specimen of the pork tapeworm,
Taenia solium, from the intestine
of a human.

Specimens and information databases of
the U.S. National Parasite Collection
are a unique and irreplaceable resource
for parasite biodiversity research.
Zoologist Eric Hoberg examines a specimen.

Hoberg examines a specimen of a Taenia
tapeworm from a North American lynx.

Hoberg reviews phylogenetic trees with
information about carnivorous final hosts,
herbivorous intermediate hosts, and
geographic distribution.

The disease caused by tapeworms is known as cestodiasis. As a systematist, Hoberg carefully examines living species of tapeworms and other parasites and describes them by meticulously detailing their distinguishing characteristics—morphological, biochemical, and molecular. (See "Searching for Parasitic ‘Roots,’"Agricultural Research, December 1996, pp. 4-7.) "Systematists deal with taxonomy, phylogeny—that is, recognizing evolutionary relationships among species—and ultimately, classification, in which organisms are grouped hierarchically based on their evolutionary relationships," says Hoberg. "These classifications represent everything we know about the relationships among these organisms. "More importantly," he says, "these classifications help predict species behavior. If we know which order, family, or genus a parasite is in, we can predict—with some certainty—patterns of life history and what effect it will have on hosts within the same or related families. "Parasites have characteristic host and geographic distribution, as well as predictable life cycles and transmission patterns," says Hoberg. He's one of just a few U.S. systematic parasitologists who also examine where parasites are distributed geographically and how they co-evolve with their hosts.Looking at Clues From the Past Hoberg uses the vast U.S. National Parasite Collection and his expertise in parasite systematics to examine evolutionary relationships between hosts and parasites. This research, called cospeciation analysis, includes studies of where hosts and parasites occur now and where they originated. "The past is the key to the present," Hoberg says. "Historical studies involving tapeworms contribute to a predictive foundation for understanding today's environments and communities of living things. Besides telling us something about their hosts, parasites can tell us about their geographical links to long ago. They're both the products of a current environment and, at the same time, of a long ancestry reflecting millions of years of association with their hosts." Hoberg's past research includes studies of the systematics and evolution of tapeworms of seabirds, seals, and sea lions. This expertise has helped him to examine tapeworm cospeciation and to perform biogeographic analysis—the study of their geographic distribution. Based on their analysis, Hoberg's team showed that 12 named genera of taeniid tapeworms belong to 1 genus,Taenia. Recently, they completed the first phylogenetic study ofTaenia species based on analyses of morphological characteristics of adult and larval parasites. Their study "provides information that will enhance our ability to predict and understand the life history and geographic distribution for this large genus," Hoberg says.Basic Life Cycle of the Parasite "Taenia tapeworms can range in size from about 0.04 inch to over 50 feet," says Hoberg. "They're internal parasites, infecting all types of mammals—including humans and domestic animals. Their life cycles are very complex. They require one intermediate host—always an herbivore—and a final or definitive host—always a carnivore—in which to reproduce." The final host is the host in which the adult tapeworm lives.Taeniid tapeworms have a global economic impact because of the sickness and death they can cause in humans and the production losses in domestic stock, including cattle and swine. Hoberg says, "Three species of these taeniid worms—T. solium, T. saginata, andT. asiatica—infect only humans. Their life cycles depend on domesticated cattle and swine as intermediate hosts." The pork tapeworm,T. solium—often found wherever raw or undercooked pork is eaten—lives in the human intestine in its adult stage. Each segment, or proglottid, may contain as many as 40,000 eggs. "Like most tapeworms,T. solium are hermaphroditic. That means that functional reproductive organs of both sexes occur in the same individual," Hoberg says, "and they're often self-fertilizing." If the embryos, which pass out with the host's feces, are then eaten by a pig, the larvae emerge in the pig's digestive tract. They bore through the intestinal wall into a blood vessel and are carried to muscle tissue where they encyst, or form a protective capsule. The larval parasite that develops is then called a cysticercus, or bladder worm. "If the cysticercus is eaten alive in raw or undercooked meat or a visceral organ like the liver, it attaches itself to the final host's intestine and develops directly into a mature adult," Hoberg says. This completes theT. solium life cycle. "T. solium is unique in having a broad range of intermediate hosts such as domestic and wild swine, dogs, and primates including humans. But only humans serve as final hosts," Hoberg says. The life cycle of the beef tapeworm,T. saginata, which occurs worldwide where beef is eaten raw or improperly cooked, resembles that of the pork tapeworm. With this species, cattle serve as the intermediate host, while humans are the final host.Humans Got Tapeworms First! Hoberg and his colleagues have evidence—phylogenetic, geographic, ecological, and molecular—indicating that, well over 10,000 years ago, ancestors of modern humans, living on the savannas of Africa, became hosts forTaenia. "This occurred before the origin of modern humans and substantially earlier than the domestication of swine and cattle and the development of agriculture," he says. This conclusion was inferred from an examination of evolutionary histories for hosts and parasites and from evidence for the rate of molecular evolution betweenT. saginata andT. asiatica.

About 2 million years ago, Hoberg believes, African hominids (our early ancestors), who scavenged for food or preyed on antelope and other bovids, were exposed to colonization by these tapeworms. "The worms were using hyena and large cats as definitive hosts and bovids as intermediate hosts."

Hoberg says that species ofTaenia tapeworms are historical ecological indicators of the foraging behavior and food habits of our early ancestors during the diversification ofHomo sapiens, or humans. "These tapeworms tell a story about the ecological linkage between hominids and large carnivores that shared prey on the savannas of Africa." Hoberg says, "Surprisingly, rather than humans' acquiringTaenia from cattle and pigs, we believe man gave tapeworms to these domestic animals, because the association betweenTaenia and hominids was established before the domestication of these food animals." In fact, transmission from humans, he says, has occurred at least three times, represented byT. saginata in cattle andT. asiatica andT. solium in swine. "This means that the spread ofT. solium among humans may have been enhanced by cannibalism or by humans eating dogs." Hoberg's team did DNA studies that gave more evidence for the idea that prehumans acquired these tapeworms before cattle and swine were domesticated about 10,000 years ago. When the team studied the DNA of these worms, they estimated—based on a molecular clock—that divergence between the human-parasitic sister speciesT. saginata andT. asiatica occurred at least 160,000 years ago. "These sister species may have diverged coincidental with the migration of early humans from Africa to Asia," says Hoberg. "There, the worms continued to parasitize their hosts, and an isolated group evolved to becomeT. asiatica."

"Out of Africa: The Origins of the Tapeworms" was published in the May 2001 issue of Agricultural Research magazine.

What are the Different Types of Flatworms

Flatworms are soft-bodied invertebrates. This article provides an insight about the various types of flatworms and their life cycles.

Flatworms are soft-bodied invertebrates. This article provides an insight about the various types of flatworms and their life cycles.

Flatworms are members of the phylum Platyhelminthes. There are more than 20,000 known species of flatworms. They can be found in freshwater, marine, or damp terrestrial environment. Most flatworms are free-living, however, some are parasites. Parasites live in the host body and can be harmful to the host. Flatworms have bilaterally-symmetrical flat bodies. They are ribbon-shaped and are flattened dorsoventrally. There are four major classes of flatworms such as Cestoda (tapeworms), Turbellaria (planarians), Trematoda (flukes), and Monogenea. The class Turbellaria (planarians) is free-living. Cestoda (tapeworms) and Trematoda (flukes) are parasitic.

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Planarian is also known as Dugesia and lives in freshwater. It is hermaphroditic (having both male and female sex organs). It has a simple brain (ganglia) and nervous system, arrow-like head, and two eyespots. It has an ability of regeneration. It is a scavenger or a carnivore. Planaria are harmless flatworms.

Tapeworms are the intestinal worms. They live in the intestinal tract of many species, including dogs, cats, and even human beings. Tapeworms have segmented bodies and each segment is known as proglottid. Each proglottid is a reproductive organ. Tapeworms do not have a well-developed digestive system. They can grow very long. They remain attached to the intestine of the host using the hooks and suckers present on the head.

Flukes have complex life cycles and they live within one or more hosts. They are characterized by a well-developed digestive system with mouth at the anterior end and one or more suckers surrounding the mouth. Suckers are used to remain attached to the internal body surface of the host. Schistosoma (blood flukes) spends some part of its life in snails. When humans wade in the water containing snails, they get infected. A larva of a Schistosoma invades the blood vessels of humans. Its eggs are passed through human feces into water and the snail is infected.

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Nematode and Human Diseases | Helminths

The following points highlight the nine major human diseases caused due to infestation with the nematodes . The human diseases are: 1. Ascariasis 2. Ancylostomiasis 3. Enterobiasis 4. Trichuriasis 5. Trichinosis 6. Strongyloidiasis 7. Filariasis or Elephantiasis 8. Loiasis 9. Onchocerciasis.

Human Disease # 1. Ascariasis:

Ascariasis is a highly prevalent disease caused by the largest nematode (roundworm) Ascaris lumbricoides. It resembles an ordinary earthworm.

When fresh from the intestine, it is light brown or pink in colour but it gradually changes to white. It is most frequently seen in the stool of children. The male of A. lumbricoides measures about 15 to 25 cm in length, while the female is longer and stouter measuring 25 to 40 cm in length.

The egg-laying capacity of mature female Ascaris has been found to be enormous, liberating about 200,000 eggs daily.

The eggs liberated by a fertilised female pass Out of the human host with the faeces and may remain alive for several days. Infection is effected by swallowing ripe eggs (embryonated eggs) with raw vegetables cultivated on a soil fertilised by infected human excreta. Infection also occurs by drinking contaminated water.

Among children playing in the contaminated soil, there is also hand to mouth transfer of eggs by dirty fingers. Infection may also occur by inhalation of desiccated eggs in the dust reaching the pharynx and swallowed. A rhabditiform larva is developed from un-segmented ovum within the egg-shell in 10 to 40 days in the soil.

The ripe egg containing the coiled-up embryo is infective to man.

When ingested with food, drink or raw vegetables, the embryonated eggs pass down to the duodenum where the digestive juices weaken the egg-shell. Splitting of the egg-shell occurs and the rhabditiform larvae are liberated in the upper part of the small intestine. The newly hatched larvae burrow their way through the mucous membrane of the small intestine and are carried by the portal circulation to the liver.

Finally they pass out of the liver and via right heart enter the pulmonary circulation. Breaking through the capillary wall they reach the lung alveoli. From the lung alveoli the larvae crawl up the bronchi and trachea, they are propelled into larynx and pharynx and are once more swallowed.

The larvae pass down the oesophagus to the stomach and localize in the upper part of the intestine, their normal abode. The larvae on reaching habitat grow into adult worms and become sexually mature in about 6 to 10 weeks’ time. Four moultings of the larva occur-one outside while within the egg-shell, two in the lungs and one in the intestine.

The symptoms attributed to Ascaris infection may be divided into two groups:

(i) Those produced by migrating larvae, and

(ii) Those produced by the adult worms.

(i) Symptoms due to the migrating larvae:

In heavy infections typical symptoms of pneumonia such as fever, cough and dyspnoea may appear. Urticarial rash and eosinophilia are seen in such cases. Disturbances have been reported due to their presence in the brain, spinal cord, heart and kidneys.

(ii) Symptoms due to the adult worms:

With the adult worms inhabiting the intestine the patient complains of abdominal pains, vomiting, headache, irritability, dizziness and night terrors. Sometimes there is a diarrhoea and salivation. Often the patient grits his teeth in the sleep. When the adult worms migrate through the intestinal wall they cause severe peritonitis.

Wandering Ascaris may enter the lumen of the appendix, causing appendicitis. Obstructive jaundice and acute haemorrhagic pancreatitis have been known to occur when the worm has entered into the biliary passage. At times it penetrates high up in the liver causing one or more abscesses.

The treatment of human ascariasis has been fairly successful through the oral administration of piperazine citrate syrup (two spoonful twice a day for one week, followed by another course after a gap of one week) and hexyl-resorcinol tablets (10 mg taken at bed time with water).

Other drugs which are known to have specific action on Ascaris include the following tetramisole, pyrantel pamoate, bephanium hydroxynaphthoate, diethylcarbamazine (Hetrazan), thiobendazole and mebendazole.

Human Disease # 2. Ancylostomiasis:

Ancylostomiasis is caused by two hookworms Ancylostoma duodenale and Necator americanus. Both the hookworms are parasites within the intestine. The adult worms live in the small intestine of man particularly in jejunum, less often in duodenum and rarely in ileum.

They are most frequent in rural areas. Female hookworms produce 5000 to 10,000 eggs per day which pass out in the stools. Man acquires infection when the eggs hatch and the larvae penetrate through the skin of the hands and feet. Infection occurs when man walks bare-foot on the faecally contaminated soil. The filariform larvae penetrate directly through the skin with which they come in contact.

The most common sites of the entry are:

(i) The thin skin between the toes

(ii) The dorsum of the feet, and

(iii) The inner side of the soles.

Infection may also occur by accidental drinking of water contaminated with filariform larvae.

The filariform larvae enter the blood vessels and are carried to the lungs. Now they make their way to one of the bronchi, trachea and larynx, crawl over the epiglottis to the back of the pharynx and are ultimately swallowed. The growing larvae settle down in the small intestine, undergo moulting and develop into adult worms.

The characteristic symptoms of ancylostomiasis are ancylostome dermatitis or ground itch, and creeping eruption by ancylostome larvae, and gastro-intestinal disorders, and severe anaemia by adult worms. Gastro-intestinal manifestations produce dyspeptic troubles associated with epigastric tenderness stimulating duodenal ulcer.

Due to severe anaemia the skin becomes pale yellow in colour and the mucous membrane of the eyes, lips and tongue becomes extremely pale. The face appears puffy with swelling of lower eyelids and there is oedema of the feet and ankle. The general appearance of the patient is a pale plumpy individual with protruded abdomen and dry lustreless hair.

For the treatment of hookworm infection the following steps are to be taken:

(i) Expulsion of worms by antihelminthic drugs and

Human Disease # 3. Enterobiasis:

Enterobiasis is caused by Enterobius vermicularis commonly called pinworm, threadworm or seatworm.

These worms are small and white in colour. Male worm measures 2 to 4 mm and female worm measures 8 to 12 mm in length. Adult worms (gravid females) live in the caecum, colon and vermiform appendix of man. The females migrate out through the colon and rectum and enormous number of eggs in the skin folds about the anus, where they cause intense itching.

Each of the egg, newly laid in perianal skin, containing a tadpole-like larva completes its development in 24 to 36 hours time, in the presence of oxygen.

Infection occurs by the ingestion of these eggs. When the skin about the anus is scratched, eggs are easily picked upon the fingers and under the nails from where they find their way to food and are swallowed. The egg-shells are dissolved by digestive juices and the larvae escape in the small intestine where they develop into adult worms.

The pinworm infection is more frequent in children than in adults. The symptoms of enterobiasis include severe itching around the anus, loss of appetite, sleeplessness and sometimes inflammation of the vermiform appendix. Enterobiasis is treated with antihelminthics such as piperazine citrate, pyrevinium pamoate (Povan), pyrental pamoate, stibazium iodide, thiobendazole and mebendazole.

Human Disease # 4. Trichuriasis:

Trichuriasis is caused by Trichuris trichura, commonly known as whipworm. The adult worms live in the large intestine of man, particularly in the caecum also in vermiform appendix.

The worm resembles a whip in shape and general appearance. Male measures 3 to 4 cm and female measures 4 to 5 cm in length. The females lay enormous number of eggs daily that pass in the stool. Development proceeds slowly in water and damp soil.

A rhabditiform larva develops within the egg in the course of 3 to 4 weeks in tropical countries. The embryonated eggs are infective to man. Man is infected when the embryonated eggs are swallowed with food or water. The egg-shell is dissolved by the digestive juices and the larva emerges.

The liberated larvae pass down into the caecum, their site of localisation. They grow directly into adult worms and embed their anterior parts in the mucosa of the intestine. The worms become sexually mature within a month from the time of ingestion of the eggs and gravid females begin to lay eggs. The cycle is then repeated.

The patient suffering from trichuriasis (whipworm disease) shows the symptoms of acute appendicitis. In heavy infections the patient often complains of abdominal pain, mucous diarrhoea often with blood streaked stool and loss of weight. Prolapse of rectum has occasionally been observed in massive trichuriasis.

The drugs at present most commonly used for the treatment of trichuriasis are stibazium iodide, deftarsone, thiobendazole and mebendazole.

Human Disease # 5. Trichinosis:

Trichinosis is caused by Trichinella spiralis, the trichinia worm. It is one of the smallest nematodes infecting man. The male measures 1.4 to 1.6 mm and female measures 3.0 to 4.0 mm in length. This disease is common and widespread in Europe and America. Although it prevails in areas where pork is eaten. Humans become infected by eating undercooked or raw meat containing encysted larvae mainly pork.

The cysts, located in striated muscles, are digested liberating larvae that mature to adult worms that attach to the wall of small intestine. Female worms there liberate larvae that invade the intestinal wall, enter the circulation and penetrate the striated muscles, where they encyst and remain viable for years. Usually one larva is present in a single cyst.

The early symptoms of trichinosis is eosinophilia. The invasion of muscle by larvae is associated with muscle pain, swelling of the eyelids and facial oedema, eosinophilia and pronounced fever. Respiratory and neurologic manifestations may appear. On invasion of the muscle layer the larvae cause inflammation and destruction of muscle fibres.

The most frequently involved muscles are those of limbs, diaphragm, tongue, jaw, larynx, ribs and eyes. Larvae in other organs, including the heart and brain cause oedema and necrosis.

The diagnosis is made by identifying larvae in muscle biopsies or by serological tests. Antihelminthic drugs remove adult worms from the intestine. Promising results have been obtained in the treatment of trichinosis by thiobendazole (Botero, 1965). Corticosteroids have been found to be useful in alleviating clinical symptoms.

Human Disease # 6. Strongyloidiasis:

Strongyloidiasis is an infection caused by the nematode Strongyloides stercoralis, commonly called threadworm.

It is found worldwide but is most common in tropical countries. S. stercoralis is a complex organism that has three life cycles which are as follows:

(i) Parasitic pathogenic females live in the human small intestine and lay eggs that hatch in the mucosal epithelium, releasing rhabditiform larvae. These larvae become infective filariform larvae in the intestine or on the perianal skin and invade human host directly (the autoinfection cycle).

(ii) The rhabditiform larvae pass in the faeces, become infective filariform larvae in the soil and later penetrate human skin (direct development cycle).

(iii) The rhabditiform larvae passed in the faeces become free-living adults in the soil and eventually produce infective filariform larvae. These infective larvae penetrate the skin, enter blood vessels and pass to the lungs, where they invade alveoli. They ascend the trachea, descend the oesophagus and mature to become parthenogenic females in the small intestine.

Invading larvae cause dermatitis. Larvae migrating through lungs may provoke cough, haemoptysis and dyspnoea, severe infection of the intestine causes vomiting, diarrhoea, and constipation. Female worms and rhabditiform larvae living in jejunum crypts cause mild eosinophilia and chronic inflammation.

By contrast patients with hyperinfection may have ulceration, oedema, congestion fibrosis and severe inflammation of the intestine. The diagnosis is made by identifying larvae in the stool.

The most specific antihelminthic drug for treatment of strongyloidiasis is thiobendazole.

Human Disease # 7. Filariasis or Elephantiasis:

Filariasis is caused by Wuchereria bancrofti commonly called the filaria worm. The adult worms inhabit lymphatic vessels, most frequently those in the lymph nodes, testes and epididymis. The female worm discharges microfilariae that circulate in the blood. Humans are the only definitive host of these worms.

Insect vectors which serve also as intermediate hosts, include 80 species of mosquitoes of the genera Culex, Aedes, Anopheles and Mansonia. Filariasis is endemic in large regions of Africa, coastal areas of Asia, Western Pacific islands and coastal areas and islands of the Caribbean basis.

In India, it is distributed chiefly along the sea coast and along the banks of big rivers (except Indus) it has also been reported from Rajasthan, Punjab, Uttar Pradesh and Delhi. Following copulation the female worm delivers larvae called microfilariae. These, at night, get in the blood capillaries of the skin to be sucked up by the mosquito with blood meal.

When the infected mosquito bites a human being, the microfilariae are not directly injected into the blood but are deposited on the skin near the site of puncture. Later, attracted by the warmth of the skin, the microfilariae either enter through the puncture wound or penetrate through the skin on their own.

After penetrating the skin, microfilariae reach the lymphatic channels, settle down at some spot (inguinal, scrotal, or abdominal lymphatics) and begin to grow into adult forms.

Features of acute infection include fever, lymphangitis, lymphadenitis, orchitis, epididymitis, urticaria, eosinophilia and microfilaremia. Chronic infection is characterised by enlarged lymph nodes, lymphoedema, hydrocele and elephantiasis. Filariasis also causes tropical eosinophilia which is characterised by cough, wheezing, eosinophilia and diffuse pulmonary infiltrates.

The infection of the filaria worms also causes enlargement of the limbs, scrotum and mammae. The swelling takes place due to blockage of the lymph circulation by the parasitic worms resulting into the inflammation of lymph vessels and lymph glands. The diagnosis is usually made by identifying the microfilariae in the blood.

There is no effective drug for the eradication of the filaria worm. The drug of choice is diethylcarbamazine (Hetrazan) which kills microfilariae and possibly adult worms.

Human Disease # 8. Loiasis:

Loiasis is an infection caused by the filarial nematode Loa loa, the African eyeworm or loa- worm. It inhabits the rain forests of Central and West Africa. Humans and baboons are definitive hosts and infection is transmitted by mango flies (Chrysops species).

The adult L.loa migrates in the skin and occasionally crosses the eye beneath the conjunctiva, making the patient actually aware of his infection. Gravid worms discharge microfilariae that circulate in the blood stream during the day but reside in capillaries of the skin, lungs and other sense organs at night.

Most infections are symptomless but persist for years. Ocular symptoms include swelling of lids, congestion, itching and pain. Female worms, and rarely male worms may be extracted during their migration beneath the conjunctiva. Systemic reactions include fever, pain, itching, urticaria and eosinophilia.

The diagnosis is made by identifying microfilariae in the blood films taken during the day, by removal of adult worm from conjunctiva, or by identifying microfilariae or adult worms in biopsy specimen. Diethylcarbamazine (Hetrazan) is an effective remedy for loiasis, causing a quick disappearance of microfilariae from the peripheral blood and even death of adult worms in some cases.

Human Disease # 9. Onchocerciasis:

Onchocerciasis is the infection caused by the filarial nematode Onchocerca volvulus. It is one of the world’s major endemic diseases, afflicting an estimated 40 million people, of whom about 2 million are blind. Man is the only known definitive host. Onchocerciasis is transmitted by several species of black flies of the genus Simulium, which breeds in fast flowing streams.

There are endemic regions throughout the tropical Africa and in focal areas of Central and South America.

The adult worms live singly and as coiled entangled masses in the subcutaneous tissues of man. The gravid female worms produce millions of microfilariae which migrate from the nodule into the skin, eyes, lymph nodes and deep organs causing the onchocercal lesions. The diagnosis is made by identifying the microfilariae in tissue sections of skin and the adult worms in the subcutaneous nodules.

The cardinal manifestations are subcutaneous nodules, dermatitis and eye disease. Nodulectomy removes adult worms in palpable nodules. Suramin kills adult worms but has dangerous side effects. Oral diethylcarbamazine (Hetrazan) kills microfilariae. A new drug, ivermectin, kills microfilariae but with a lesser allergic reaction than diethylcarbamazine.

Tapeworm Symptoms

Sometimes tapeworms cause symptoms such as:

However, often tapeworms don't cause symptoms. The only sign of tapeworm infection may be segments of the worms, possibly moving, in a bowel movement.

In rare cases, tapeworms can lead to serious complications, including blocking the intestine, or smaller ducts in the intestine (like the bile duct or pancreatic duct).

If pork tapeworm larvae move out of the intestine, they can migrate to other parts of the body and cause damage to the liver, eyes, heart, and brain. These infections can be life-threatening. Seizures are the most common symptom of cystocercosis, the infection caused by the larvae of the pork tapeworm.

Tachyzoites Breaking Out of a Fibroblast Cell

  • Eventually, the tachyzoites produce another form of the parasite known as a bradyzoite.
  • Bradyzoites multiply slowly, unlike tachyzoites. They are located inside a cyst, which is sometimes known as a tissue cyst to distinguish it from an oocyst. Tissue cysts tend to form in particular areas of the body, including the brain, the eyes, the heart, and the skeletal muscles.
  • The tissue cysts become dormant and may stay where they are formed for many years—perhaps even for the life of their host. However, the cysts may sometimes come out of their dormancy and release the cells inside them. These may become tachyzoites, which infect new cells.
  • If a cat eats an animal part containing tissue cysts, the cysts become active in the cat&aposs intestine. The parasites invade the intestinal lining, producing male and female reproductive cells. These cells join to make a zygote, which becomes an oocyst. The cycle then begins again. A summary of the parasite&aposs somewhat complex life cycle is shown below.

Published by the Royal Society under the terms of the Creative Commons Attribution License, which permits unrestricted use, provided the original author and source are credited.


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Characteristics of Cestodes

All tapeworms share a body plan. At the front end is a head region called the scolex. The scolex maintains a hold on the host's digestive tract and has many suckers and hooks for this purpose. The scolex also contains the tape-worm's sense organs, which consist primarily of cells sensitive to touch and chemical stimuli, as well as the modest concentration of nervous tissue that makes up the tapeworm brain.

The scolex is followed by a short neck region and a trunk, which is divided into a series of segments known as proglottids. New proglottids are produced in the neck region. As these form, older proglottids are pushed back toward the rear of the animal. The proglottids house the reproductive organs, which mature gradually as proglottids move to the back. Tapeworms are hermaphroditic , so that each proglottid includes both male and female gonads and generates both sperm and eggs. A tapeworm can reproduce sexually, either through self-fertilization or cross-fertilization with another tapeworm, or asexually, by breaking off proglottid segments at the end of the trunk. These reproductive traits are admirably adapted to reproduction in an environment (in the body of a host) in which worms are not guaranteed to encounter individuals of the same species.

Proglottids and fertilized eggs exit the host's digestive tract along with the host's excrement. In most tapeworm species, eggs or proglottids are first ingested, or taken in, by an intermediate host, often an arthropod or a different vertebrate species. The cestode may develop into a larval form or may become temporarily dormant within the intermediate host. The ultimate host becomes infested with the cestode when it consumes an infested intermediate host.

Because of the cestodes' parasitic lifestyle, certain organ systems are unnecessary. The most obvious of these is the digestive tract, which is absent from the group. Because cestodes live in an environment that is not only rich in nutrients, but one in which the nutrients are already well processed, further digestion is unnecessary. Instead, food absorption occurs over the entire surface of the cestode body, in an ectodermal, or skin, layer known as the integument. The integument is covered with tiny projections called mitotrichia, which increase the surface area available for absorption.

Subclasses of Cestodes

Cestodes are divided into two subclasses, Cestodaria and Eucestoda. Cestodaria is a small subclass of relatively small tapeworms that are parasites to elasmobranch fishes (sharks, rays, and chimeras). The trunks of cestodarians are not segmented into proglottids. The rear of the body includes a small sucker. Eucestoda is a much more diverse group, and includes all other cestodes. Eucestodes are characterized by the presence of proglottids.

see also Phylogenetic Relationships of Major Groups.


Brusca, Richard C., and Gary J. Brusca. Invertebrates. Sunderland, MA: Sinauer Associates, 1990.

Gould, James L., and William T. Keeton. Biological Science, 6th ed. New York: W. W. Norton and Co., 1996.

Hickman, Cleveland P., Larry S. Roberts, and Allan Larson. Animal Diversity. Dubuque, IA: Wm. C. Brown, 1994.


We are indebted to numerous persons who kindly provided valuable information as well as those who sent clinical samples of tapeworms for molecular evaluation. Special thanks are due to Manuel Tantaleán, Universidad Peruana de Cayetano Heredia, Lima, Peru, for providing valuable information on D. pacificum and Andrea Gustinelli, University of Bologna, Bologna, Italy, for material. Helpful suggestions and critical remarks of anonymous reviewers are also greatly appreciated.

This study was partly supported by the Grant Agency of the Czech Republic (project no. 524/04/0342 and 524/08/0885) and the Institute of Parasitology (project no. Z60220518 and LC 522).


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