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Diseases & Conditions
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Parasitic Roundworm Diseases
(Also Called 'Enterobiasis')

Overview
A parasite is an organism that exists by depending on another organism. Parasites that infect humans are much more widespread than many of us realize. These diseases affect not only poverty-stricken peoples in remote areas of the world, but they also can be important health problems for people throughout the world, including the United States. As with other parasitic diseases, roundworm infections are more common in warm climates than in cooler, temperate areas. Many roundworm parasitic diseases result from human carelessness and a lack of appropriate personal hygiene and sanitation measures. Thus, the best solution to the problem rests in preventing these infections rather than in curing them. Roundworms, or nematodes, are a group of invertebrates (animals having no backbone) with long, round bodies. They range in size from those plainly visible to the naked eye to those several hundredths-of-an-inch long and visible only under a microscope. Most roundworm eggs or larvae are found in the soil and can be picked up on the hands and transferred to the mouth or can enter through the skin. With the exception of the roundworm that causes trichinosis, mature adult roundworms eventually end up or live in human intestines and cause a variety of health problems. Some of the most common parasitic roundworms in humans are
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Enterobius vermicularis, the pinworm that causes enterobiasis

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Ascaris lumbricoides, the large intestinal roundworm that causes ascariasis Necator and Ancylostoma, two types of hookworms that cause ancylostomiasis Trichuris trichiura, the whipworm that causes trichuriasis Strongyloides stercoralis that causes strongyloidiasis Trichinella spiralis that causes trichinosis

Pinworm infection (Enterobiasis)
A pinworm is the most common roundworm parasite in temperate climates-even in areas with high levels of sanitation. In the United States, it is the most common of all parasitic roundworm infections, affecting up to one-third of children in some areas. Because pinworm infection is spread mainly by children, it is found most often in family groups, day-care centers, schools, and camps. Pinworms are small, threadlike roundworms found primarily in the colon and rectum. The life cycle of the pinworm-egg, larva, and mature worm-takes place inside the human body and requires from 3 to 6 weeks to complete.

How do pinworms get into the body?
Pinworms enter your body when eggs are swallowed. The female pinworm expels thousands of eggs into the environment. Because the eggs are moist and a bit resistant to drying, they may be able to infect someone for several days after being distributed in dust. They can cling to the fingers of children. Exposure to infective eggs may occur if you are infected and then scratch the contaminated area (the area around the anus where the female worm deposits her eggs), transferring the eggs to your fingertips and from there to your mouth. The eggs may be scattered into the air from bed linen and clothing, and can cling to doorknobs, furniture, tubs and faucets, and even food. Although you may have no symptoms over a long period, episodes of infection may return repeatedly. Folklore is filled with fantastic descriptions of symptoms and abnormal behavior blamed on pinworm infection. Actually, the symptoms are usually mild and vague. Movement of egg-laden female worms from the anus will often produce itching of the anus or vagina that, in some cases, may become very intense and even interfere with sleep.
Diagnosis

Your health care provider can diagnose pinworm infection by finding the eggs. The most common way to collect the eggs is a rather simple one involving swabbing the anal area with the sticky side of a piece of transparent cellophane tape. The tape is then transferred to a slide where it can be looked at under a microscope.
Prevention

You can prevent becoming infected or reinfected with pinworms by:
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Bathing frequently Using clean underclothing, night clothes, and bed sheets Washing your hands routinely, particularly after using the bathroom

Treatment

Some health care providers believe that treatment is not necessary for pinworm infections that have no symptoms. This is because children usually outgrow the infection. Because of the strong probability that small children will get infected again outside the home, strenuous efforts to eliminate the eggs from the household are of little help. If your health care provider does prescribe medicine, all members of your household should take it, regardless of whether they have symptoms. Medicines such as mebendazole and pyrantel pamoate (Povan) are the most useful in treating pinworm infections. To relieve intense itching that often accompanies pinworm infection, your health care provider may prescribe a soothing ointment or cream.

Roundworm infection (Ascariasis)
The name Ascaris lumbricoides reflects the resemblance of this intestinal roundworm to the common earthworm known as Lumbricus. Ranging in length from 6 to 13 inches, the female worm may grow to be as thick as a pencil. Ascaris infections are common throughout the world in both temperate and tropical areas. In areas of poor sanitation, everyone may be harboring the parasite. Amazingly, up to a hundred worms can infect one person.

How is ascariasis spread?
Almost more than any other parasitic disease, human carelessness causes ascaris. Human feces in streets, fields, and yards are a major source of infective eggs in heavily populated areas. The eggs of ascarids do not infect humans when first excreted by the worm. The eggs are very resistant to extremes of temperature and humidity. They usually are transmitted by hand to mouth, although the use of human feces as fertilizer may also permit transmission of infective eggs by food that is grown in the soil and eaten without being thoroughly washed. The eggs require several weeks to develop and become infective. If you swallow the infective eggs, they pass into your intestine where they hatch into larvae. The larvae then begin their journey through your body. Once through the intestinal wall, they reach your lungs by means of the blood or lymphatic system. In the lungs, they pass through the air sacs, are carried up the bronchial tree with respiratory secretions, and are re-swallowed to be returned to the small intestine where they grow, mature, and mate. The worms become mature in about 2 months.
Pets can transmit these worms to humans

Other species of ascarids such as Toxocara, which infect dogs and cats, can, under certain circumstances, be picked up by humans. In dogs and cats, these ascarids have a migratory cycle similar to A. lumbricoides. In humans, however, they fail to reach the intestine. Instead they remain active in other body tissue for some time. This state of larval migration is known as visceral larva migrans. Young puppies and kittens that defecate outdoors contribute most to contamination of soil by eggs that must incubate for some time in the soil. Almost all dogs are infected at birth. Older dogs, however, have usually become immune to the parasite.
Symptoms

A few worms in your intestine may cause no symptoms or may give rise only to vague or intermittent abdominal pain. Heavy infection may cause partial or complete blockage of your intestine resulting in severe abdominal pain, vomiting, restlessness, and disturbed sleep. The heavier or greater the worm infection, the more severe your symptoms are likely to be. Occasionally, the first sign of infection may be the presence of a worm in vomit or in the stool.
Diagnosis

If a large number of larvae invade your lungs at one time, they may cause an illness resembling pneumonia. This stage of the disease precedes the intestinal phase by weeks, and the symptoms are difficult to diagnose. Once mature female worms are present in your intestine, however, a health care provider can diagnose the infection by finding characteristic eggs in the stool.
Treatment

Your health care provider can treat ascariasis successfully with mebendazole, albendazole, or pyrantel pamoate.

Hookworm disease (Ancylostomiasis)
One of the most common roundworm infections is hookworm. You can pick up hookworms as a result of unsanitary conditions. Hookworm eggs are passed in human feces onto the ground where they develop into infective larvae. When the soil is cool, the larval worms crawl to the nearest moist area and extend their bodies into the air. They remain there-waving their bodies to and fro-until they come into contact with the skin, usually when stepped on by a bare foot, or until they are driven back down by the heat. Hookworm is widespread in those tropical and subtropical countries in which people defecate on the ground and soil moisture is most favorable. Necator americanus is the prevailing species in the southeastern United States.

How hookworms get into your body
You can get hookworms by walking barefoot over contaminated soil. In penetrating the skin, the larvae may cause an allergic reaction. It is from the itchy patch at the place where the larvae

entered that the early infection gets its nickname "ground itch." Once larvae have broken through the skin, they enter the bloodstream and are carried to the lungs. (Unlike ascarids, however, hookworms do not usually cause pneumonia.) The larvae migrate from the lungs up the windpipe to be swallowed and carried back down to the intestine.
Pets can transmit these parasites to humans

Some animal hookworms can become accidental parasites of humans in a manner similar to the ascarids. If you are exposed to these animal hookworm larvae, they can penetrate your skin but, like the ascarids, cannot complete their life cycle. This results in these larvae wandering around in the subcutaneous tissue beneath the exposed skin, a condition called cutaneous larva migrans.
Symptoms

Diarrhea, particularly if you have never been infected, sometimes starts as the worms mature in your intestines and before eggs appear in the stool. Other signs and symptoms at this stage include vague abdominal pain, intestinal cramps, colic, and nausea. Scientists have learned that people in good health and on a diet containing adequate iron can tolerate the presence of these worms in small or moderate numbers without having problems. In chronic infections, if the number of parasites becomes great enough, you can develop serious anemia because of blood loss from the worms attaching themselves to the intestine and sucking the blood and tissue juices. When this situation is combined with poor nutritional intake, pregnancy, and/or malaria, the resulting anemia can be severe. Ancyclostoma canium, an illness caused by a particular species of dog hookworm, has been described in Australia. This worm may almost complete its development in the lower small intestine, but produces a severe inflammatory reaction in the bowel, causing abdominal pain, diarrhea, and an increase in certain white blood cells called eosinophils.
Diagnosis

A laboratory worker will examine your stool specimens to look for and count the number of eggs. If the egg output is large enough-more than 2,000 eggs per gram of stool-your health care provider will assume that the infection may cause anemia and start treating you.
Treatment

Once you have been diagnosed with hookworm disease, your health care provider can prescribe medicines such as mebendazole or albendazole. You might also be given an iron supplement with this treatment.

Whipworm disease (Trichuriasis)
The name whipworm comes from this parasite's long, very thin, whiplike shape. This parasitic roundworm infection of the large intestine often has no symptoms, but a health care provider usually can diagnose it by examining your stool and finding whipworm eggs. Heavy infections

may cause intermittent stomach pain, bloody stools, diarrhea, and weight loss. Fertilized eggs develop outside the body, and an embryonated egg is produced in 3 weeks in a favorable environment; that is, warm, moist, shaded soil. Although the incidence of whipworm infection is high, its intensity is usually light. In the United States, the infection occurs principally in warm, moist climates, most frequently among children. You can get infected by accidentally eating whipworm eggs on your hands or in food or drink. Severe infections in young children can result in serious disease with bloody diarrhea and a condition called rectal prolapse.
Treatment

Health care providers treat whipworm disease most often with mebendazole or albendazole.

Strongyloidiasis
The parasitic roundworm called Strongyloides stercoralis mainly infects humans. This parasite has different types of life cycles. One is direct, similar to that of the hookworm. After a short feeding period and development in the soil, the larvae penetrate human skin, enter the blood stream, and pass through the right side of the heart to the lungs. From the lungs, the adolescent parasites go up the windpipe into the mouth, are swallowed, and reach the upper part of the small intestine where they develop into mature worms. Under certain conditions, parasites may undergo an indirect life cycle in which free-living mature male and female worms develop in the soil and produce a new generation of large numbers of larvae. At times, the larvae may develop rapidly into the infective state in the intestine where they penetrate the intestinal lining instead of passing out of the body in the feces, as occurs normally. This modification of the life cycle, called internal autoinfection, explains persistent strongyloidiasis, as long as 40 years in people who have moved to areas where the disease is not generally found. Autoinfection may produce heavy infections and severe disease (also known as disseminated strongyloidiasis), especially in people with reduced immunity such as those receiving corticosteroids or other immunosuppressive drug treatment, or those with acquired immunodeficiency due to human retroviruses (HIV or HTLV-1).
Symptoms

Many Strongyloides infections are mild and go unnoticed. Moderate infections may cause a burning pain in your abdomen. You may have nausea and vomiting and alternating diarrhea and constipation. Severe infections result in anemia, weight loss, and chronic diarrhea. Disseminated strongyloidiasis in severely immunocompromised people can cause a variety of symptoms, including an ARDS-like pneumonia (Acute Respiratory Distress Syndrome).
Diagnosis

Your health care provider can use blood tests to help establish the diagnosis, but those tests are prone to error. You may have to have repeated stool examinations.
Treatment

Thiabendazole (Mintezol) given twice daily for 2 or 3 days is the one of the treatments health experts recommend. Ivermectin given in a single dose for 1 or 2 days has become the medicine of choice. Albendazole given in two courses 10 days apart is also effective. Disseminated disease requires longer treatment.

Trichinosis
Trichinosis is an infection caused by the larvae of a most versatile roundworm, Trichinella spiralis. This parasite can infect virtually every meat-eating mammal. Unlike the other parasitic roundworm diseases that we have discussed, trichinosis is not an intestinal infection in the usual sense. It is the migration of T. spiralis larvae through the body and their encystment (becoming enclosed in a capsule) in muscle tissue that creates serious problems. The parasite is especially common in rats and in swine that feed on uncooked garbage. The disease occurs in humans when they eat undercooked infected pork. Although trichinosis is sometimes found in cities, it is much more common in rural areas, particularly in the hog-raising areas of the United States. Because many states have adopted laws requiring that all garbage fed to hogs be sterilized, fewer people get trichinosis. Human cases have also been associated with eating undercooked home-made sausage that contains pork or horse meat, as well as eating walrus or bear meat. Typically, the life cycle of the parasite begins when a person or an animal eats contaminated meat containing larvae. Digestive juices from the stomach dissolve the capsule-like cyst and release the parasites. The larvae then penetrate into the intestine where they mature and mate. Female worms then pass larvae into the blood stream where they make their way through the capillaries (tiny blood vessels) into the muscle fibers. Once in the muscle fibers, they encyst again and begin a sometimes long life.
Symptoms

The average case of trichinosis is not severe and produces no noticeable discomfort. It can produce symptoms that are frequently overlooked or ignored-a slight stomachache and achy muscles and joints. Invasion by a large number of parasites, however, produces symptoms that mimic food poisoning followed by severe "muscular rheumatism."
Diagnosis

Although your health care provider may suspect that you have trichinosis on the basis of clinical signs, it is usually diagnosed one or two ways.
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A blood test that shows an increase in the number of eosinophils, a type of white blood cell

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Microscopic examination of muscle tissue to look for the larvae

Treatment

Your health care provider can prescribe medicine only to relieve your symptoms. There is no treatment for the infection. If your health care provider diagnoses infection while you are still having digestive symptoms, standard antiparasite medicines can be used to dislodge some of the worms. Once encystment of the parasite has begun, treatment is for any symptoms. Your chances of recovery are good. Albendazole may help you if treatment is begun very early, during the incubation state. Corticosteroids can relieve the inflammatory reaction during the larval migration state, and you should take them with albendazole. Steroids could, however, prolong the intestinal phase of the infection.
Prevention

Health experts have known all the basic facts necessary for preventing trichinosis in humans for years. You can kill the parasites by cooking (allowing all parts of the meat to reach at least 150 degrees Fahrenheit) or freezing (16 degrees Fahrenheit for 36 hours). Irradiation can also kill them. Smoking, pickling, and other methods of processing or preserving meats do not kill the parasites.
Research

Researchers at the National Institute of Allergy and Infectious (NIAID) diseases are conducting basic and clinical research on the prevention, control, and treatment of a variety of parasitic diseases, including some caused by parasitic roundworms. NIAID scientists are trying to determine the factors that allow Strongyloides stercoralis roundworms to infect humans and cause disease. The findings from this research may help scientists develop a skin test to diagnose stronglyloidiasis. Tapeworm Diseases

Definition
Tapeworms are a group of parasitic worms that live in the intestinal tracts of some animals. Several different species of tapeworms can infect humans. Tapeworm disease or cestodiasis occurs most commonly after eating raw or undercooked meat or fish that contains the immature form of the tapeworm.

Description
Tapeworm infections pose a serious public health problem in many less developed countries due to poor sanitation conditions. The disease is most common where livestock, such as cattle and pigs, are raised in areas where human feces are not disposed of in a sanitary manner. Another common source of human tapeworms are certain species of freshwater fish. Tapeworm infections

tend to occur more frequently in areas of the world where the people regularly eat raw or undercooked beef, pork, or fish. Persons of all ages and both sexes are susceptible to tapeworm infection, but children are generally not exposed until they are old enough to begin eating meat or fish. Tapeworm infections in humans are less common in industrialized regions of the world, although German public health experts reported in 2003 that the rate of these infections is higher in Europe than the official statistics indicate. Travel to areas where tapeworm infections are more common and immigration of people from these areas serve as new sources of the parasite. Infected persons are often unaware of the presence of adult tapeworms in their intestinal tract, as they may have no obvious symptoms of infection. Some tapeworms can live in an infected person for over 10 years if diagnosis is not made and treatment is not administered. In addition to the typical infection caused by eating undercooked meat or fish, people may also be directly infected by ingesting tapeworm eggs shed by the adult worm. This type of tapeworm infection can lead to a condition referred to as cysticercosis, in which the larvae continue to develop within tissues other than the intestinal tract. One of the most serious forms of this disease occurs when the tapeworm larvae infect the central nervous system, a disease referred to as neurocysticercosis. In contrast to a typical tapeworm infection, which may not be associated with symptoms, neurocysticercosis is a serious condition that may cause seizures and is potentially life-threatening.

Causes and symptoms
Several species of tapeworm can infect people. The two most common species are the pork tapeworm (Taenia solium) and the beef tapeworm (Taenia saginata). Improperly treated human sewage may be used to fertilize pastures or crops. Pigs or cattle become infected by grazing in contaminated pastures or drinking water contaminated with tapeworm eggs from human feces. The pea-sized larvae of these tapeworms are deposited in certain tissues of the body of infected pigs and cattle, including the muscles. The infection is then transmitted to people when raw or undercooked meat containing tapeworm larvae is consumed. The immature tapeworm develops into the adult form in the human intestine and may remain there for many years if not identified and treated. The Taenia tapeworms attach to the intestinal walls but cause only mild inflammation at the site of attachment. As a result, most tapeworm carriers show no symptoms (asymptomatic) and usually become aware of the infection only after noticing tapeworm segments in their feces. Segments of the beef tapeworm may spontaneously pass through the anus causing a noticeable sensation. Mild gastrointestinal symptoms, such as nausea or abdominal pain, can occur in infected individuals. In rare cases where the tapeworm segments migrate into the appendix, pancreas, or bile duct, there may be a sudden onset of severe abdominal discomfort. Cysticercosis is a potentially serious complication of Taenia solium infection in which the larvae develop outside the intestinal tract. This type of infection is less common and occurs following accidental consumption of tapeworm eggs released from the adult worm. These eggs initially are localized in the anal area, but they may also contaminate the fingers or other parts of the body. Infection can occur in the person harboring the adult tapeworm or in other people with whom that individual comes in contact. The tapeworm larvae may develop in various tissues throughout the body. The most serious clinical problems occur when the larvae develop in the central nervous system (neurocysticercosis), potentially causing seizures and other neurological

problems. An important aspect of this type of infection is that poor hygiene on the part of the individuals harboring an adult tapeworm can lead to an infection in an individual who may never consume meat. This is a particular problem if infected individuals are employed as food handlers. Another important tapeworm that may infect people is the fish tapeworm (Diphyllobothrium latum). This is a frequent human intestinal parasite in many areas where raw freshwater fish is consumed. Human infection with the fish tapeworm is referred to as diphyllobothriasis. Feces from infected hosts or raw sewage contaminates a fresh water source. Tapeworm larvae are initially ingested by freshwater crustaceans and then are eaten by fish. Human infection occurs when a person consumes raw fish contaminated with the tapeworm larvae. Adult tapeworms then develop in the human intestinal tract. Most infections with the fish tapeworm are not associated with symptoms. The tapeworm causes little damage to the lining of the intestine. Infected individuals may report diarrhea, fatigue, weakness, or sensation of hunger more commonly than uninfected individuals. One problem unique to this tapeworm is that it may compete with the host for absorption of vitamin B12 from the small intestine, causing the person to become deficient in this vitamin and leading to a condition called pernicious anemia. Two smaller species of tapeworms may also infect people. The dwarf tapeworm (Hymenolepis nana) is a common infection throughout the world that can be passed from one person to another. Transmission is usually the result of inadvertent ingestion of tapeworm eggs from feces eliminated by infected individuals. As a result, infection with this tapeworm is encountered most frequently in children, the developmentally disabled, and psychiatric patient populations. Abdominal pain that is not localized to any particular area is the most common complaint. Patients may experience loose bowel movements or diarrhea with mucus, but bloody diarrhea is rare. Another small tapeworm capable of infecting people is the rodent tapeworm (Hymenolepis diminuta). Rats, mice, and other rodents are the usual hosts for the adult tapeworm (definitive host), but humans can become infected following accidental consumption of insects containing tapeworm larvae. Meal worms or grain beetles that infest cereal, flour, or dried fruit are the most likely source of infection. Most human infections are not associated with symptoms, although some individuals report headaches, anorexia, nausea, and diarrhea.

Diagnosis
Identification of tapeworm segments or eggs in a stool sample is necessary for diagnosis of an adult tapeworm infection. In many cases, a tentative diagnosis may be made on the basis of a patient's description of short chains of tapeworm segments in their stool. Further evaluation is recommended to determine the actual species involved since infection with Taenia solium is potentially more serious due to the added risk of cysticercosis. Whenever possible, tapeworm segments should be carefully collected in water or salt solutions, using strict precautions to avoid contamination. Stool examination should be performed in a laboratory having experience in the diagnosis of intestinal parasites. It is recommended that at least three stool samples be collected on alternate days to increase the likelihood of being able to make an accurate diagnosis. Although the general appearance of tapeworm segments from the two Taenia species is quite similar, trained laboratory personnel can detect distinct differences between the beef and pork tapeworms when samples are examined under a microscope. Tapeworm segments and eggs from

the fish tapeworm and the dwarf tapeworm have characteristic appearances that allow accurate differentiation from the Taenia species of worms. Other diagnostic procedures may be necessary when cysticercosis is suspected. Blood samples from an infected individual are collected to look for the presence of antibodies against the tapeworm larvae. In 2004, researchers isolated an antigen diagnostic for cysticercosis alled GP50. In cases in which infection of the central nervous system is present, advanced imaging tests, such as computed tomography scans and magnetic resonance imaging (MRI), may be necessary to determine the exact location of the tape-worm larvae within the body. Ultrasound imaging is also being used as of 2003 to diagnose tapeworm infections. Because of the recent rise in immigration and travel, clinicians in developed countries are seeing more patients with tapeworms. The World Health Organization (WHO) has developed standardized sets of ultrasound images to help doctors recognize the signs of a parasitic infection. In some cases, ultrasound allows the doctor to see the tapeworm directly.

Treatment
Effective treatment of tapeworm infections involves administering compounds that are toxic to the adult worm. Many of the early treatments were also somewhat toxic to the patient, so treatment was often quite an ordeal. Newer medications are much more easily tolerated and are highly effective in eliminating the parasite from the body. It is important, however, to completely eliminate the head and neck regions of the tapeworm, as the entire worm can regenerate from these parts. One treatment that has been in use since the early 1960s is niclosamide (Niclocide). This drug is poorly absorbed from the digestive tract and rapidly kills tapeworms upon exposure. It has been shown to be effective against Taenia species and the fish tapeworm, but treatment of the dwarf tapeworm (Hymenolepis nana) may require a more prolonged treatment schedule. Side effects reported with niclosamide are infrequent and typically mild. When present, side effects may include nausea, abdominal discomfort, vomiting, diarrhea, light-headedness, and skin rash. This medication should be taken in the morning on an empty stomach. The tablets are chewed thoroughly and swallowed with water. For young children, the tablets may be pulverized and mixed with water. Patients are allowed to eat two hours after treatment. Recommended dosage is 2 grams for adults and about half this for children. Another oral medication that has been shown to be 95% effective in the treatment of tapeworm infections associated with both Taenia and Diphyllobothrium latum species is praziquantel (Biltricide). Side effects reported for praziquantel are mild and appear to be short-lived. They include nausea, abdominal pain, itching, sore joints, and muscle pain. It is recommended that follow-up stool samples be examined at one month and three months after treatment has been completed. Treatment can be considered successful if no eggs are present in several stool samples. It should be noted that the tapeworm medications do not kill the tapeworm eggs when they kill the adult worm, so the potential for infection with eggs still exists as the dead worm segments are passed. Proper personal hygiene in individuals receiving treatment will greatly reduce this potential. Cases of neurocysticercosis, where larvae have developed in the central nervous system, may also be treated with praziquantel or albendazole. If the patient is treated promptly, damage to the central nervous system will be minimized.

As of late 2003, researchers in developing countries are working on a vaccine for pigs to help control neurocysticercosis; however, the vaccine is not likely to be available for several years.

Prognosis
When confined to the intestinal tract, tapeworms cause minimal damage to their human host. Once the diagnosis of an intestinal tapeworm infection has been made, prognosis following treatment with niclosamide or praziquantel is good. The worms can be eliminated from the intestines with oral treatment, and there are usually no residual side effects. Serious problems from tapeworm infections occur when tapeworm eggs are consumed and the larvae localize in tissues outside the digestive tract (cysticercosis). Prompt diagnosis and treatment of this condition is necessary to prevent permanent damage to the central nervous system and other internal organs. In fact, cysticercosis is becoming increasingly recognized as an important cause of severe neurologic disease in the United States. Untreated cases of cysticercosis have the rare potential to be life-threatening; in some cases, liver transplantation has been necessary to save the patient's life.

Key terms
Cestodiasis ² Parasitic infection caused by the presence of adult tapeworms of the class Cestoda within the intestinal tract. Infection is caused by accidental consumption of tapeworm larvae. Cysticercosis ² Parasitic infection caused by the presence of immature tapeworm larvae (cysticerci) that have developed outside the intestinal tract. Infection is caused by accidental consumption of tapeworm eggs. Diphyllobothriasis ² Parasitic infection caused by the presence of tapeworms from the Diphyllobothrium genus, such as the fish tapeworm (Diphyllobothrium latum). Hymenolepiasis ² Parasitic infection caused by the presence of tapeworms from the Hymenolepis genus, such as the dwarf tapeworm (Hymenolepis nana) or the rodent tapeworm (Hymenolepis diminuta). Neurocysticercosis ² Parasitic infection caused by the presence of immature tapeworm larvae within the central nervous system. Pernicious anemia ² Type of anemia caused by a deficiency in vitamin B12. Taeniasis ² Parasitic infection caused by the presence of tapeworms from the Taenia genus, such as the pork tapeworm (Taenia solium) or the beef tapeworm (Taenia saginata).

Prevention
The best way to prevent infection with tapeworms is to eliminate the exposure of livestock to the tapeworm eggs by properly disposing of human feces. The next best strategy is to thoroughly cook or freeze all meat and fish before it is eaten to prevent consumption of live tapeworm larvae in infected samples. Larval cysts in pork and beef are killed by moderate temperatures of 150°F (65°C) or if frozen for at least 12 hours. Proper cooking of freshwater fish could also eliminate the possibility of human infection with the fish tapeworm. Freezing fresh fish for 24 hours will also kill the larval form.

People who raise sheep or horses should have these animals checked regularly by a veterinarian and dewormed if necessary. The Centers for Disease Control and Prevention (CDC) recommends that people traveling abroad should wash their hands with soap and water before handling food; should wash and peel all raw vegetables and fruits before eating; and should drink only bottled or boiled water, or carbonated drinks in cans or bottles.

Resources
Books Beers, Mark H., MD, and Robert Berkow, MD., editors. "Cestodes (Tapeworms)." In The Merck Manual of Diagnosis and Therapy. Whitehouse Station, NJ: Merck Research Laboratories, 2004.

Tapeworm Diseases (Taeniasis and Cysticercosis) Clinical Manifestations Etiology Epidemiology Diagnosis Treatment Isolation of the Hospitalized Patient Control Measures

CLINICAL MANIFESTATIONS: TAENIASIS. Infection often is asymptomatic; however, mild gastrointestinal tract symptoms, such as nausea, diarrhea, and pain, can occur. Tapeworm segments can be seen migrating from the anus or feces.

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CYSTICERCOSIS. Manifestations depend on the location and numbers of pork tapeworm cysts (cysticerci) and the host response. Cysts may be found anywhere in the body. The most common and serious manifestations are caused by cysts in the central nervous system. Cysts of Taenia solium in the brain (neurocysticercosis) can cause seizures, behavioral disturbances, obstructive hydrocephalus, and other neurologic signs and symptoms. In some countries, neurocysticercosis is a leading cause of epilepsy. The host reaction to degenerating cysts can produce signs and

symptoms of meningitis. Cysts in the spinal column can cause gait disturbance, pain, or transverse myelitis. Subcutaneous cysts produce palpable nodules, and ocular involvement can cause visual impairment.

ETIOLOGY: Taeniasis is caused by intestinal infection by the adult tapeworm, Taenia saginata (beef tapeworm) or T solium (pork tapeworm). Taenia asiatica causes taeniasis in Asia. Human cysticercosis is caused only by the larvae of T solium (Cysticercus cellulosae).

Top Previous Next

EPIDEMIOLOGY: These tapeworm diseases have worldwide distribution. Top Prevalence is high in areas with poor sanitation and human fecal contamination in Previous areas where cattle graze or swine are fed. Most cases of T solium infection in the Next United States are imported from Latin America or Asia. High rates of T saginata infection occur in Mexico, parts of South America, East Africa, and central Europe. Taenia asiatica is common in China, Taiwan, and Southeast Asia. Taeniasis is acquired by eating undercooked beef (T saginata) or pork

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