Description

• Tapeworms (cestodes) are parasitic flatworms that cause parasitic human and animal infections.
• Taeniasis, diphyllobothriasis, hymenolepiasis, dipylidiasis, sparganosis, echinococcosis, and hydatid disease are also tapeworm infestations.
• Tapeworm infections may be confined to the GI tract (e.g., Taenia saginata, Diphyllobothrium sp.), systemic (Echinococcus, Spirometra), or both (Taenia solium).
• Neurocysticercosis (T. solium) is the most common serious parasitic infectious disease; Hymenolepis nana is the most common human cestode in the United States and worldwide.
• Humans can be definitive hosts or accidental hosts.
• The most common human tapeworms and their usual intermediate hosts and type of infection include:Tapeworm Intermediate Host or Reservoir
  
  
  Name	Host
  T. saginata	Cow
  T. solium, asiatica	Pig
  Diphyllobothrium latum and related species	Freshwater fish
  H. nana, Hymenolepis diminuta	Human, rodent, insect
  Dipylidium caninum	Dog, cat, flea
  Echinococcus granulosus	Human, sheep, cow, dog
  Echinococcus multilocularis	Dog, fox, coyote, cat, rodents
  Echinococcus vogeli	Paca, rodents
  Echinococcus oligoarthritis	Puma, jaguar, rodents, rabbits
  Spirometra sp.	Fish, reptiles, or amphibians

  
  
• T. saginata: intestinal worm from beef source; 2 to 4 months from ingestion to adult; can be up to 3- to 10-m long; usually single tapeworm; proglottids are motile, may crawl out of anus; may live 30 years; T. asiatica also intestinal
• T. solium: from pork; intestinal worm or cysticercosis (tissue larvae) 2- to 7-m long; occasionally multiple; proglottids not motile; may live up to 25 years; ingestion of encysted larvae (cysticerci) causes intestinal tapeworm. Ingestion of T. solium eggs (metacestodes) causes cysticercosis. Eggs are identical to T. saginata in appearance.
• D. latum and less common species usually from freshwater fish; intestinal worm; longest adult tapeworm, up to 25 m; matures to adult in 3 to 6 weeks, may live 10 years
• H. nana: rodents, insects, or humans; intestinal worm; matures to adult worm in 10 to 12 days; seldom exceeds 40-mm long; proglottids rarely seen in stool; eggs can autoinfect, perpetuating infection; fecal–oral transmission; life span 4 to 10 weeks; usually self-cleared by adolescence
• H. diminuta: rodents and insects; intestinal worm; 90-cm long; humans are rare accidental hosts, acquired by ingesting mealworms or beetles from grain source.
• D. caninum: dogs, cats, and fleas; intestinal worm; 10- to 70-cm long; motile proglottids; shape of cucumber seeds; can crawl out of anus; rare accidental infection by ingesting infected domestic flea
• E. granulosus and E. multilocularis: Humans, sheep, and cattle are intermediate hosts, dogs and Canidae are definitive hosts for E. granulosus; dogs, foxes, coyotes, or cats are definitive hosts for E. multilocularis; rodents are intermediate hosts.
  • E. granulosus: cystic echinococcosis (hydatid disease)—often single cyst in liver, lung, other organs less common
  • E. multilocularis: alveolar echinococcus; hydatid disease of liver, spleen, and so forth; adult worm lives in dogs (or rodents); human ingests eggs; larvae hatch and are carried through circulation to organs where they develop into hydatid cysts that enlarge and cause symptoms 5 to 20 years later.
  • E. vogeli: polycystic hydatid disease—usually in liver and some in lungs (15%). It occurs in central and northern South America.
  • Echinococcus oligarthrus: polycystic hydatid disease occurring from Mexico to Argentina
• Spirometra sp.: in East Asia and Southeast Asia; causes sparganosis (SC and CNS lesions)

Pediatric Considerations
H. nana, H. diminuta, and D. caninum most common in children

Epidemiology

Incidence

• Cestode infections relatively rare in United States, common in certain countries
• Associated with immigrant populations and specific cultural culinary habits
• Endemic where fecal contamination impacts water or food supplies or close contact with domestic animals
• All ages can be affected; both genders equally infected
• Cysticercosis affects 50 million worldwide, and in endemic areas is the leading cause of adult epilepsy; ~2,000 cases per year diagnosed in United States

Etiology and Pathophysiology

Ingestion of contaminated food (meat, fish), infected insects in cereals or grains, or fecal–oral contamination

• Head (scolex) of adult worms attaches to host GI tract. Segmented body (strobila) and individual segments (proglottid) contain sets of male and female reproductive organs that produce eggs.
• The life cycle of all, but H. nana, requires an intermediate host, where species grow as larval forms in tissue that is then ingested by the final host, where they develop into adult forms.
• H. nana can complete all stages of development in humans and can cause autoinfection.

Risk Factors

• Taenia: consumption of raw beef or pork, particularly in Africa, Central America, and Asia
• Cysticercosis: a tapeworm carrier who is a close contact; water contaminated with sewage
• Diphyllobothrium: eating raw or undercooked fish, particularly in Northern Europe and Japan
• H. nana: more frequent in children, institutionalized, malnourished, or immunodeficient patients
• E. granulosus: sheep dogs highest risk for hydatid cyst disease
• E. multilocularis: contact with foxes, coyotes; mostly found in northern latitudes
• Sparganosis: consumption of raw or undercooked fish, reptiles, or amphibians

General Prevention

• Treat infected animals. Screen household contacts and those at high risk.
• Proper sewage and waste management; hand hygiene, sanitary food preparation in endemic areas
• Proper cooking, freezing, or irradiation of beef, pork, and fish