Basics
Description
- Tapeworms cause 2 major types of zoonotic disease syndromes, depending on whether humans are the definitive or intermediate host.
- When humans serve as definitive hosts, adult tapeworms infect the GI tract and interfere with nutrition; patients may be asymptomatic.
- When humans serve as intermediate hosts for the larval cestode, serious pathology results.
- Causative organisms include the following:
- Taenia saginata (beef tapeworm)
- Taenia solium (pork tapeworm)
- Diphyllobothrium latum (fish tapeworm)
- Dipylidium caninum (dog tapeworm)
- Echinococcus granulosus
Epidemiology
- Beef tapeworm
- Estimated 77 million people infested worldwide
- Widespread in cattle-breeding areas of the world, endemic in Asia, Latin America, Eastern Europe
- Pork tapeworm
- Estimated >50 million people infested worldwide
- Taeniasis: typically asymptomatic infection with adult tapeworm (from undercooked pork)
- Cysticercosis: infection with larval parasite (fecal " oral transmission from carriers).
- High prevalence in developing areas of Asia, Central and South America
- 1,000 new cases of neurocysticercosis in United States annually
- Fish tapeworm
- Infection is most prevalent in temperate climates of Europe (Finland, Estonia, Sweden most common), and Canada.
- Persons who prepare or eat raw freshwater fish are most at risk.
- In the United States, infected salmon have been implicated in most cases.
- Dog tapeworm
- Found in dogs and cats worldwide
- Echinococcosis
- Associated with the practice of feeding sheep viscera to dogs
- It is hyperendemic in sheep-raising areas of South America, Australia, areas of Africa, China, Central Asia, and the Western United States.
General Prevention
- Adult tapeworms
- Proper cooking prevents transmission of beef, pork, and fish tapeworms.
- Pork tapeworm
- Refrigeration of pork infested with cysticerci at temperatures >0 °C (32 °F) does not affect parasite survival. However, storage of pork for 4 days at " 5 °C (21.2 °F) or 1 day at " 24 °C ( " 11.2 °F) kills most cysticerci.
- Fish tapeworm
- Brief cooking (at >56 °C [132.8 °F] for 5 minutes) or freezing ( " 18 °C [ " 0.4 °F] for 24 " 48 hours) renders the fish safe to consume.
- Dog tapeworm
- Periodic deworming of pets
- Echinococcosis
- Careful disposal of sheep viscera and mass chemotherapy of dogs can interrupt the life cycle of E. granulosus as the cestode moves between sheep and carnivore hosts.
Pathophysiology
- Beef tapeworm
- Cattle (intermediate host) ingest the eggs of T. saginata in contaminated feeds. The eggs hatch, releasing embryos which penetrate intestinal mucosa, enter the bloodstream, and settle in skeletal muscle, where they develop into larvae. Larvae in undercooked meat are consumed by humans and mature into adult tapeworms within the human (definitive host) GI tract. They grow up to 25-m long.
- Pork tapeworm: Humans are the only definitive host for the adult pork tapeworm. Both humans and pigs are intermediate hosts for its embryonic form, cysticercosis.
- Pigs ingest T. solium eggs. In the intestine, the eggs release embryos that penetrate the mucosa, enter the bloodstream, and settle in various tissues to differentiate into cysticerci (infective larvae). Cysticerci are ingested by humans (definitive host) who consume undercooked pork.
- Humans ingest food contaminated with human feces containing T. solium eggs. The eggs hatch, liberating embryos which penetrate the intestinal mucosa leading to blood-borne distribution to the brain, subcutaneous tissues, muscle, and eye, where they develop into cysticerci.
- Fish tapeworm
- When sewage containing D. latum eggs contaminates freshwater lakes and streams, eggs hatch into the water becoming embryos. Embryos are eaten by crustaceans and then passed on to fresh water fish. Humans are infected when they consume these undercooked fish. The larvae mature into adult tapeworms in the intestines of humans in 3 " 5 weeks ' time and can survive up to 10 years. Rarely, the tapeworm migrates thru intestinal wall to other tissues (sparganosis).
- Dog tapeworm
- Larvae develop in fleas (intermediate host) after ingestion of the eggs; humans are infected through accidental ingestion of infected fleas.
- Echinococcosis (hydatid disease)
- Humans ingest eggs of E. granulosus through contaminated dog feces. After ingestion, the eggs hatch and release embryos (oncospheres) in the small intestine. Penetration through the mucosa leads to blood-borne distribution to the liver, lungs, and other sites, where development of cysts begins. Within the cysts, new larvae (scolices) develop, accumulate fluid, and encroach on surrounding structures.
Diagnosis
History
- Recent travel or immigration
- GI tract
- Nausea, weight loss, diarrhea, abdominal tenderness or distention
- Fish and, rarely, dog tapeworm infections can be complicated by intestinal obstruction.
- May observe proglottids that resemble rice or seeds in stool from dog tapeworm
- Jaundice
- Hepatic cysts from echinococcosis may be palpable in the right upper quadrant.
- Biliary tree extension can lead to obstructive jaundice and cholangitis.
- Respiratory tract
- Pulmonary hydatid cyst due to E. granulosus causes cough, dyspnea, and hemoptysis; rupture of a cyst can cause anaphylaxis.
- Hematologic
- Anemia from vitamin B12 deficiency occurs in 2% of fish tapeworm infections due to competition for absorption in ileum. Other signs of pernicious anemia include glossitis, peripheral neuropathy, decreased vibration sense, and ataxia.
- CNS
- New-onset seizures (partial or generalized) occur with neurocysticercosis and some species of Echinococcus.
- Neurocysticercosis may present with alteration in mental status, signs of elevated intracranial pressure (headache, vomiting, visual changes), or meningitis.
- Neurocysticercosis and vitamin B12 deficiency due to fish tapeworm can mimic psychotic illness with delirium or hallucinations.
- CNS symptoms in neurocysticercosis typically appear 5 " 7 years after initial infection (range: 6 months to 30 years).
- Note: For echinococcosis, a presymptomatic stage may last for years before the enlarging cysts cause symptoms. The variability of signs and symptoms depends on the target organ.
Diagnostic Tests & Interpretation
Lab
- Beef tapeworm
- Ziehl " Neelsen stain of stool identifies eggs.
- Proglottids or eggs in stool with microscopic examination (62% sensitivity)
- ELISA test detects Taenia antigens in stool (85% sensitivity, 95% specificity).
- Pork tapeworm
- Serum electro immunotransfer blot (most sensitive) and ELISA of serum and/or CSF
- Stool samples for intestinal worms
- Fish tapeworm
- Stool samples for eggs and proglottids are diagnostic, collect multiple specimens.
- Mild eosinophilia (5 " 15%)
- Low vitamin B12 levels (50%)
- Megaloblastic anemia 2%
- Dog tapeworm
- Characteristic egg packets (loose membrane containing up to 20 eggs) or proglottids may be identified in stool.
- Echinococcosis
- IgE levels are elevated. Eosinophilia is present in <25% of infected persons.
- Polymerase chain reaction (PCR) of stool
- Mild elevation of hepatic enzymes may be present with hepatic hydatid cysts.
- The Casoni skin test (injection of hydatid fluid into the dermis) yields an erythematous papule in <60 minutes in 50 " 80% of infected patients. False-positive rate is 30% in uninfected patients.
- Serologic testing is falsely negative in 10 " 50% of cases. False-negative results are more likely in patients with pulmonary hydatid cysts and in children. No serologic test excludes the diagnosis of hydatid cysts.
Imaging
- Pork tapeworm
- Contrast-enhanced CT or MRI of the brain may reveal cysticerci; ring-enhancing lesions with surrounding edema represent a dying parasite; calcification represents a resolved infection.
- Imaging is usually diagnostic.
- Echinococcosis
- On x-ray, pulmonary cysts demonstrate a sharply demarcated, smooth-bordered cyst; there is a crescent-shaped air level after cyst rupture. Liver and spleen lesions may calcify over time.
- Hydatid cysts: Internal septa or daughter cysts after cyst rupture are detected by CT, MRI, or ultrasound; present in ’ Ό50% of patients with unilocular liver cysts
Diagnostic Procedures/Other
Echinococcosis: In seronegative persons, a presumptive diagnosis can be confirmed by demonstrating protoscolices or hydatid membranes in liquid obtained by ultrasound-guided percutaneous cyst aspiration. This procedure is controversial because anaphylaxis may occur with cyst rupture.
Differential Diagnosis
- Non " tapeworm gastroenteritis
- Inflammatory bowel disease
- Cholecystitis or biliary obstruction (i.e., gallstones, neoplasms, or liver disease)
- B12 deficiency from dietary deficiency or pancreatic insufficiency
- Idiopathic epilepsy
- Echinococcal cysts must be differentiated from benign cysts, cavitary tuberculosis, abscesses, and neoplasms.
Treatment
Medication
- Beef, pork, fish, and dog tapeworm (and most other intestinal cestodes)
- Praziquantel: 5 " 10 mg/kg as a single dose; no safety profile exists for children <4 years of age.
- Niclosamide (second line for beef tapeworm): children 11 " 34 kg, 1 g as a single dose; children >34 kg, 1.5 g as a single dose (not available in the United States)
- Supplement with vitamin B12 for fish tapeworm.
- Neurocysticercosis
- Treatment should be individualized based on number, location, and viability of cysticerci on MRI or CT scan.
- Treatment may not be indicated for single degenerating cysts, calcifications, or encephalitis. Most experts recommend therapy for patients with nonenhancing or multiple cysticerci.
- Albendazole: 15 mg/kg/24 h (maximum, 800 mg/24 h) in 2 divided doses for 8 " 30 days or praziquantel 50 " 100 mg/kg/24 h in 3 divided doses for 30 days
- Steroids (1 mg/kg/day of prednisone or 0.5 mg/kg/day of dexamethasone), in combination with albendazole, decrease seizure frequency and number of CNS cysts.
- Antiepileptic drugs are recommended and shunt placement, and/or mannitol should be considered for treatment of hydrocephalus.
- Antiparasitic therapy is contraindicated in patients with diffuse cerebral edema ( "cysticercal encephalitis " ) because the inflammatory response that follows treatment may worsen cerebral edema.
- No definite recommendations exist regarding the use of corticosteroids alone.
- Echinococcosis
- Albendazole 15 mg/kg/24 h (max 800 mg/24 h) divided b.i.d. for 1 " 6 months
- May require 3 courses of therapy with drug-free intervals of 14 days between courses
- Note: The benzimidazoles, including albendazole, are contraindicated in patients with blood dyscrasia, leukopenia, and liver disease. Prolonged courses require monitoring of liver function and hematopoiesis.
Surgery/Other Procedures
- Echinococcosis: surgical resection of intact hydatid cysts, especially if >10 cm, secondarily infected, or causing symptoms
- Subcutaneous sparganosis: surgical resection or ethanol injection
Ongoing Care
Follow-up Recommendations
Patient Monitoring
- Beef tapeworm
- Stool should be checked for eggs and proglottids 1 month after therapy.
- Pork tapeworm
- Repeat CNS imaging studies at 2-month intervals (with continued therapy) until successful elimination of parenchymal brain cysticerci.
- Fish tapeworm
- Perform stool examination 12 weeks after therapy to test for cure.
- Dog tapeworm
- No follow-up stool examination required, but the appearance of proglottids >1 week after therapy indicates treatment failure.
- Echinococcosis
- Requires prolonged follow-up with ultrasound or other imaging procedures.
Complications
- Cysticercosis
- Cysticerci can develop in the brain, muscle, eye, or other organs. Ophthalmologic exam is warranted in cases of neurocysticercosis.
- Echinococcosis
- Cysts grow slowly, causing symptoms only when relatively large.
- They frequently develop in the liver (50 " 70%) and lung (20 " 30%); 5 " 10% of cysts involve other organs, including the eye, brain, spleen, heart, bone, and kidneys.
- Rupture of cysts can cause anaphylaxis.
- Bone involvement can cause pathologic fractures, and renal involvement can cause pain or hematuria.
Additional Reading
- Baird RA, Wiebe S, Zunt JR, et al. Evidence-based guideline: treatment of parenchymal neurocysticercosis. Neurology. 2013;80(15):1424 " 1429. [View Abstract]
- Garc a HH, Gonzalez AE, Evans CA, et al. Taenia solium cysticercosis. Lancet. 2003;362(9383):547 " 556. [View Abstract]
- Moon TD, Oberhelman RA. Antiparasitic therapy in children. Pediatr Clin North Am. 2005;52(3):917 " 948. [View Abstract]
- Schantz PM. Tapeworms (cestodiasis). Gastroenterol Clin North Am. 1996;25(3):637 " 653. [View Abstract]
Codes
ICD09
- 123.9 Cestode infection, unspecified
- 123.2 Taenia saginata infection
- 123.0 Taenia solium infection, intestinal form
- 122.4 Echinococcus granulosus infection, unspecified
- 123.4 Diphyllobothriasis, intestinal
- 123.1 Cysticercosis
- 123.8 Other specified cestode infection
ICD10
- B71.9 Cestode infection, unspecified
- B68.1 Taenia saginata taeniasis
- B68.0 Taenia solium taeniasis
- B67.4 Echinococcus granulosus infection, unspecified
- B69.9 Cysticercosis, unspecified
SNOMED
- 86133004 Cestode infection (disorder)
- 69163003 Taenia saginata infection (disorder)
- 240818004 Taenia solium infection (disorder)
- 75006000 Echinococcus granulosus infection (disorder)
- 59051007 Cysticercosis (disorder)
- 9444005 infection by Dipylidium caninum (disorder)
FAQ
- Q: Can vegetarians develop neurocysticercosis?
- A: Yes, because neurocysticercosis results from ingestion of T. solium eggs in products contaminated with infected fecal matter. GI symptoms result from eating infected pork.
- Q: Is treatment for neurocysticercosis always indicated?
- A: The findings are controversial. In many children, the lesion disappears spontaneously within 2 " 3 months. Guidelines for treatment depend on the number and location of lesions, as well as the viability of the parasites within the nervous system. A growing parasite deserves active management, either with antiparasitic drugs or surgical excision.