eMedicine Specialties > Emergency Medicine > Infectious Diseases

Tapeworm Infestation

Author: Lisandro Irizarry, MD, MPH, FAAEM, Chair, Department of Emergency Medicine, Brooklyn Hospital Center; Assistant Professor, Department of Emergency Medicine, Weill Cornell School of Medicine
Coauthor(s): Patricia Phan, MD, FACEP, FAAEM, Residency Program Director, Department of Emergency Medicine, Brooklyn Hospital Center
Contributor Information and Disclosures

Updated: Nov 10, 2009

Introduction

Background

Tapeworms are long, segmented worms of the class Cestoda, which comprise 1 of 3 classes of parasitic worms (worms that require a host within which to mature). The other classes are Nematoda and Trematoda. These worms lack an intestinal tract and instead can absorb nutrients through their integument. The adult consists of a head (scolex), where the worms attach to the mucosa of the intestine; a neck; and a segmented body that contains both male gonads and female gonads (proglottids).

Cestodes include the following:

• Taenia solium
• Taenia saginata
• Taenia asiatica¹
• Diphyllobothrium
• Hymenolepis
• Dipylidium caninum
• Echinococcus
• Spirometra
• Taenia multiceps

Adult tapeworm of Dipylidium caninum. Image courtesy of the Centers for Disease Control and Prevention (CDC).

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Adult tapeworm of Dipylidium caninum. Image courtesy of the Centers for Disease Control and Prevention (CDC).

Pathophysiology

• The eggs are passed into the environment from the primary host.
• The eggs are ingested by an intermediate host in which they hatch.
• The larvae enter the tissues of the intermediate host and encyst.
• The primary host ingests the cysts in the flesh of the intermediate host.

When humans are the primary hosts, the adult cestode is limited to the intestinal tract. When humans are the intermediate hosts, the larvae are within the tissues, migrating through the different organ systems.

In most cestode infestations (ie, T solium, T saginata, Diphyllobothrium species, Hymenolepis species, and D caninum), humans are the primary hosts. Adult worms survive inside their human hosts, where they are limited to the intestinal tract. Human fecal contamination of the environment is needed to sustain these life cycles.

In the remaining cestodes (ie, Echinococcus species, Spirometra species, and T multiceps), humans function as the intermediate hosts. Larvae exist within the tissues and migrate through different organ systems.

Hymenolepis species and T solium are the only cestodes for which humans can function as both primary hosts and intermediate hosts. Hymenolepis diminuta is primarily a cestode of rodents, although humans can be a rare and accidental hosts in the life cycle. Humans are infected by swallowing insects that contain cysticercoid larvae, most often by ingesting mealworms or grain beetles that infest dried grains, cereals, flour, and dried fruit.

Cestodes and Their Hosts

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Frequency

United States

Although many cestode infestations occur worldwide, only a few are common in the United States.

Diphyllobothriasis is an infection that occurs from eating raw or undercooked fish infected with Diphyllobothrium species. Diphyllobothrium organisms are present in lakes, rivers, and deltas of freshwaters. Eskimos in western Alaska and the West Coast of the United States are frequent hosts.

Echinococcus multilocularis causes alveolar echinococcosis, which occurs only in the northern hemisphere. In the United States, it occurs particularly in Alaska. Echinococcus granulosis causes hydatid disease, which occurs worldwide.

Although infection with T saginata (obtained from raw or undercooked beef) occurs worldwide, the prevalence in the United States is less than 1% because most cattle in the United States are free of the parasite. Infection with T solium is rare, but with the growing number of immigrants from endemic areas, the frequency is changing.

Infection with H nana is the most frequently diagnosed cestode infection in the United States.

Spirometra species cause sparganosis, which occurs accidentally in humans who ingest water containing infected cyclops, eating raw or inadequately cooked flesh of snakes, frogs, or birds. It has been reported mainly in the southeastern region of the United States.

International

T saginata has a high endemicity in Latin America, Africa, Middle East, and central Asia and has a moderate endemicity in Europe, south Asia, Japan, and the Philippines.

T solium is prevalent in Latin America, the Slavic countries, Africa, southeast Asia, India, and China. The prevalence of T solium infection is low in northwestern Europe and is rare or absent in Canada. Cysticercosis, caused by infection with the larvae stage of the tapeworm, is endemic in all Latin American countries (except Chile, Argentina, and Uruguay).

Diphyllobothrium infection is prevalent in northern Europe (Finland, east Prussia, Russian Karelia), Canada, Africa, Japan, Taiwan, Manchuria, Siberia, Papua New Guinea, Australia, and South America.

H nana infection is the most common cestode of humans. It is prevalent in areas of poor hygiene and sanitation, especially in the warm and arid countries of the Mediterranean, Indian subcontinent, and South America. The prevalence in children in these areas may reach 20%. Infection rates are highest among children.

E multilocularis infection occurs only in the northern hemisphere, especially in central Europe, Russia, China, Japan, Canada, and north Africa. Few regions in the world are completely free from E granulosis. Echinococcus vogeli and Echinococcus oligarthrus infections occur in Central America and South America.

Infection with Spirometra species has been reported worldwide but especially in east Asia (China, Japan, and Korea) and southeast Asia (Malaysia, India, and the Philippines).

Mortality/Morbidity

Many cestode infestations are asymptomatic. However, once symptoms occur, they are usually vague GI complaints such as abdominal pain, anorexia, weight loss, or malaise.

Some of the more serious infestations result in symptoms from mass effects on vital organs, inflammatory responses, nutritional deficiencies, and the potential of fatal anaphylaxis.

• Cysticercosis is a clinical syndrome of expanding embryonal cysts that occurs with T solium. The cysticerci that develop with T solium infestations can be found anywhere in the body, but they mainly occur in the central nervous system (neurocysticercosis) and skeletal muscles, causing local inflammatory responses and mass effects from the cystic growth. Cysticercosis is a common parasitic disease of the CNS. One of the most common manifestations is seizure.^2,3 In endemic areas, it is a major cause of epilepsy. Neurocysticercosis may be the cause of death in many of these affected areas and may leave infected persons with irreversible brain damage.
• Diphyllobothrium species absorb a large amount of vitamin B-12 and interfere with vitamin B-12 absorption from the ileum, resulting in vitamin B-12 deficiency (this can also occur with Taenia species). Severity depends on the proximity of the worm to the ileum, where vitamin B-12 is mainly absorbed in humans. Clinically, it resembles pernicious anemia (ie, hyperchromic, macrocytic, megaloblastic anemia) that responds well to vitamin supplementation therapy without long-term sequelae.
• In Echinococcus infestations, humans ingest the eggs and the embryos escape, penetrate intestinal mucosa, and enter the portal circulation to invade other organs, mainly the liver (60%) and lungs (25%). The patient remains asymptomatic until the cysts cause a mass effect on the organ, which can be 5-20 years after the initial infestation.
  • Rupture or leakage of an Echinococcus cyst produces symptoms of fever, pruritus, urticaria, eosinophilia, and potentially fatal anaphylaxis.
  • Pulmonary hydatid cysts may rupture into the bronchial tree produce cough, dyspnea, chest pain, or hemoptysis. Pulmonary cysts rupture into the pleural space can result in abscess formation and pneumothorax, with or without pleural effusion. In addition, fever and acute hypersensitivity reactions ranging from wheezing to anaphylaxis can occur following cyst rupture.
  • If alveolar hydatid disease is left untreated, more than 90% of patients will die within 10 years from the onset of symptoms and almost 100% by 15 years.

Race

No racial risks or protections regarding cestode infestations are known.

Sex

Gender differences neither protect nor increase the risk of cestode infections.

Age

Many cestode infections are common in children as a result of their youthful habits and relatively less adequate hygiene. For instance, D caninum, one of the most common parasites of domestic dogs and cats, is typically obtained from fleas that live in the fur of these animals. Although infection of D caninum is rare, children, especially those who enjoy handling animals, are affected more frequently than adults.

Clinical

History

• Many cestode infestations are asymptomatic. The organisms may be discovered by patients during defecation with the fecal passage of proglottids. Tapeworms may migrate from the rectum (possibly causing itching) and may be seen on toilet paper or undergarments. However, once symptoms occur, they are usually vague GI complaints of abdominal pain, cramps, anorexia, nausea, diarrhea, weight loss, or malaise.
• T solium infections are usually asymptomatic; however, infected patients may have generalized complaints include epigastric or periumbilical discomfort; nausea; hunger; and weight loss, anorexia, or increased appetite. The cysticerci that develop with T solium infestations can be found anywhere in the body, but they mainly occur in the central nervous system and skeletal muscles, causing local inflammatory responses and mass effects from the cystic growth. If neurocysticercosis develops, seizure is the most common form of presentation, occurring in up to 80% of patients with parenchymal brain cysts or calcifications.
• With T saginata infection, usually, the patient becomes aware of infection when worm segments are passed in the stool. Some patients complain of epigastric pain, diarrhea, and weight loss. Similar to T solium infection, the presence of cysticerci in T saginata infection can result in symptoms of obstruction of the appendix, biliary duct, and pancreatic duct.
• Diphyllobothrium infestations may result in intestinal discomfort, diarrhea, vomiting, weakness, and weight loss.
  • The cestode is not invasive, but it does absorb a large amount of vitamin B-12 and interferes with vitamin B-12 absorption from the ileum, producing a megaloblastic anemia that resembles pernicious anemia (clinically and hematologically). The tapeworm must thus be in a proximal portion of the intestine, and probably intrinsic factor secretion is defective in the host (allowing for diminished capacity to absorb vitamin B-12).
  • Patients may complain of neurologic symptoms resembling pernicious anemia (eg, paresthesias, difficulty with balance, dementia or confusional states).
• Hymenolepis typically produces asymptomatic infections; however, in patients who may have a number of parasites present, the patient can have vague symptoms of anorexia, abdominal pain, and diarrhea (the developing cysticercoids destroy their housing villi, thus with a number of parasites, significant enteritis may develop). The number of worms is regulated by the hosts nutritional and immunity states.
• D caninum infections are mostly asymptomatic with some symptoms of abdominal pain, diarrhea, anal pruritus, and urticaria.
• Echinococcosis infections are potentially dangerous because they typically remain asymptomatic until the cysts cause a mass effect on an organ, which can occur 5-20 years after the initial infestation.
  • Cystic echinococcosis
    • The larvae develop into the fluid-filled hydatid cysts that are implanted after being carried in the bloodstream and expand slowly over several years.
    • The liver is the most common site, followed by the lungs (10-30%) (mostly the right lobe (60%) and the lower lobes (60%); however, almost any tissue may be involved. In children, the lungs may be the most common site of cyst formation. Up to 40% of patients with lung cyst will have liver cysts as well.
    • Most patients have single organ involvement (85-90%), and most will have a solitary cyst (>70%).
    • These cysts do not metastasize, but they may be disseminated by accidental spillage.
    • Pulmonary cystic rupture may result in clinically impressive and misleading symptoms of cough, chest pain, and hemoptysis.
  • Alveolar hydatid disease
    • A lesion in the liver does not appear as a cyst but is a firm, solid, cancerlike mass that is primarily in the liver. Approximately 60-80% of the cysts are located in the right lobe of the liver. Single or multiple foci may be present.
    • Hepatic echinococcosis can cause epigastric pain and dyspepsia (up to 35%) and can mimic cholelithiasis or jaundice (up to 45%) from compression in the bile duct. In one third of the cases, the disease is found incidentally during the checkup for nonspecific symptoms (fatigue, weight loss, hepatomegaly).
    • The disease spreads from the liver by direct extension, by lymphatic or hematologic metastasis, or by peritoneal seeding.
    • Compression of the bile duct can occur, resulting in biliary colic or jaundice.

Physical

• T solium infections
  • The cysticerci that develop with T solium infestations can cause mass effects from the cystic growth leaving the physical findings dependent on the location and the size of the growth.
  • Although most patients have normal neurologic examinations, the most common presentation of neurocysticercosis is the neurologic manifestations of seizures and focal neurologic deficits, along with possible hydrocephalus, meningitis, and dementia. Predictably, signs of increased intracranial pressure occur, as well as headaches, visual changes, vomiting, ataxia, and confusion.
  • Clinical manifestations of spinal neurocysticercosis are nonspecific and dependent on the size and the location of the cysts.
  • To homogenize the diagnosis of neurocysticercosis, revised diagnostic criteria were proposed as followed:⁴
    • Absolute criteria
      • Histologic demonstration of the parasite from biopsy
      • Direct visualization of subretinal parasite on funduscopic examination
      • Evidence of cystic lesions showing the scolex on CT scan or MRI
    • Major criteria
      • Lesions highly suggestive of neurocysticercosis on neuroimaging studies (cystic lesions without scolex, ring or nodular enhancing lesion and parenchymal round calcifications)
      • Positive enzyme-linked immunotransfer blot assay (EITB) for the detection of anticysticercal antibodies
      • Spontaneous resolution of small single enhancing lesions
      • Resolution of intracranial cystic lesions after therapy with albendazole or praziquantel
    • Minor criteria
      • Lesions compatible with neurocysticercosis on neuroimaging studies (CT or MRI showing hydrocephalus, abnormal enhancement of the leptomeninges, and myelograms showing multiple filling defects)
      • Clinical manifestations suggestive of neurocysticercosis (seizures, focal neurological deficits, increased intracranial pressure, intellectual deterioration)
      • Positive CSF ELISA for detection of anticysticercal antibodies or antigen
      • Cysticercosis outside the CNS
    • Epidemiologic criteria
      • Individuals coming from or living in an area where cysticercosis is endemic
      • History of frequent travel to cysticercosis endemic areas
      • Evidence of a household contact with T solium infection
  • Diagnosis is definitive in patients with either (1) one absolute criterion or (2) a combination of two major criteria, one minor criterion, and one epidemiologic criterion. Diagnosis is probable in patients who meet these criteria (1) one major criterion plus two minor criteria; or (2) one major criterion plus one minor criterion and one epidemiologic criterion; or (3) three minor criteria plus one epidemiologic criterion.
  • Ocular cysticercosis can be seen on ophthalmologic examination of the eye. Parasites may be seen in the posterior chamber of the eye.
  • Cysticercosis of the muscle and subcutaneous tissues can be palpated or seen on plain radiographs. Almost all patients with symptomatic muscle cysticercosis are reportedly from Asia.
• Diphyllobothrium infestations
  • Megaloblastic anemia that resembles pernicious anemia (hyperchromic, macrocytic, megaloblastic anemia with thrombocytopenia and mild leukopenia) may be present. Additionally, while true pernicious anemia is associated with gastric achlorhydria, tapeworm-induced anemia is not.
  • Only D latum is associated with macrocytic anemia.
  • Of patients who are infected with this tapeworm, 40% have decreased vitamin B-12 levels, but fewer than 2% of those develop anemia, which seems to occur mainly in Scandinavian countries.
• Echinococcosis infections
  • Hepatic echinococcosis can cause signs of abdominal pain and a palpable mass in the right upper quadrant.
  • The physical examination may mimic cholelithiasis or jaundice from compression of the bile duct. Additionally, the patient may have chronic pancreatitis and signs and symptoms therein as related to the location and the size of the cystic infestation.
  • Rupture or leakage of the hydatid cyst produces fever, urticaria, and potentially fatal anaphylaxis.
  • Pulmonary cystic rupture may result in clinically impressive hemoptysis.
• Sparganosis commonly presents as subcutaneous edema and invades not only the subcutaneous tissue but also the muscles, eyes, urogenital system, abdominal viscera, and rarely the central nervous system.
• Coenurosis caused by T multiceps presents as a space-occupying cystic lesion of the central nervous system and subcutaneous tissues, leading to symptoms of mass effects and obstruction.

Causes

See Pathophysiology.

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