Taenia/Taeniasis

Taenia belong to the Cestoda class of helminths. Humans are infected with these tapeworms by eating undercooked beef (T. saginata) or pork (T. solium and T. asiatica). Taeniasis is often asymptomatic, but the ingestion of larvae can cause abdominal discomfort, nausea, and constipation or diarrhea. Passing proglottids in the stool is the most common sign of taeniasis. A patient who ingests T. solium eggs can develop cysticercosis, which may present with muscular and dermatologic cysts, ocular involvement, or neurologic manifestations (neurocysticercosis). The diagnosis is made by identifying proglottids or eggs in the stool. Characteristic findings on CT or MRI will help diagnose neurocysticercosis. Management generally includes anthelmintic therapy.

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General Characteristics and Epidemiology

General features of Taenia

Taenia is a genus of parasitic cestodes (tapeworms). 

Eggs: 

  • Spherical
  • Thick, striated wall
  • Contains a 6-hooked (hexacanth) embryo

Adults:

  • Size:
    • T. saginata: < 5 m in length
    • T. solium: approximately  2–7 m in length
  • Ribbon-like, segmented body:
    • Scolex: 
      • Rostellum with 2 rings of hooks in T. solium
      • 4 muscular suckers
    • Strobila with approximately 1000 proglottids:
      • Segmented
      • Contains sets of reproductive organs

Clinically relevant species

Taenia tapeworms cause the following diseases:

  • Taeniasis:
    • T. saginata (beef tapeworm)
    • T. solium (pork tapeworm)
    • T. asiatica (Asian tapeworm)
  • Cysticercosis: T. solium

Epidemiology

Geographic distribution of species:

  • T. solium and T. saginata: worldwide
  • T. asiatica: Asia

Taeniasis:

  • Affects approximately 50 million people worldwide
  • Rare in the United States
  • Highest incidence occurs in areas where:
    • There is poor access to clean water
    • Ingestion of raw or undercooked meat is common 

Cysticercosis:

  • Approximately 1000 cases diagnosed each year in the United States
  • More common in immigrants

Pathogenesis

Hosts

  • Definitive host: humans
  • Intermediate hosts:
    • T. saginata: cattle
    • T. solium and T. asiatica: pigs

Risk factors for hosts

  • Eating raw or undercooked beef or pork
  • Those living in:
    • Rural areas
    • Developing countries 
  • Poor sanitation
  • Close contact with infected animals

Transmission

  • Taeniasis: ingestion of larval stages in meat
  • Cysticercosis: ingestion of T. solium eggs through:
    • Contaminated food or water
    • Fecal–oral transmission

Life cycle and pathophysiology

Taeniasis:

  1. Pigs or cattle ingest vegetation that is contaminated with eggs or gravid proglottids.
  2. Eggs hatch in the intestine → oncospheres
  3. Invasion into the intestinal wall → bloodstream → migration to striated muscle → develop into cysticerci (larvae within a fluid-filled sac)
  4. Humans ingest raw or undercooked beef or pork → develop into an adult tapeworm in the intestine and attach to the intestinal wall with the scolex
  5. Adults produce proglottids → mature and become gravid → detach from the tapeworm
  6. Gravid proglottids and eggs are excreted in the feces → cycle continues

Cysticercosis:

  1. Humans consume food or water contaminated with T. solium eggs or gravid proglottids.
  2. Eggs hatch in the intestine → oncospheres
  3. Invasion into the intestinal wall → bloodstream → migration to tissues and organs → develop into cysticerci → cysticercosis
  4. Cysticerci can migrate to the CNS → neurocysticercosis
life cycle T. solium and the development of cysticercosis versus taeniasis

Life cycle of Taenia solium and the development of cysticercosis versus taeniasis.

Image: “Cysticercosis” by CDC. License: Public Domain

Clinical Presentation

Taeniasis

Most patients (particularly adults) are asymptomatic. 

  • Common symptoms include:
    • Passing proglottids in the stool (most common)
    • Nausea
    • Anorexia 
    • Abdominal pain
    • Pruritus ani
  • Less common:
    • Constipation or diarrhea
    • Headache
    • Dizziness
    • Anxiety
  • Complications due to obstruction from tapeworm segments:
    • Biliary obstruction: 
      • Cholecystitis
      • Pancreatitis
    • Intestinal obstruction
    • Appendicitis

Cysticercosis

Signs and symptoms depend on the tissues involved.

Muscular and dermatologic cysticercosis:

  • Most are asymptomatic
  • Cysts may be palpated under the skin
  • Myalgia
  • Myositis

Ocular cysticercosis:

  • Foreign body sensation
  • Ocular pain
  • Floaters
  • Impaired vision
  • Sensation of movement in the eye
  • Redness
  • Photophobia

Neurocysticercosis:

  • Seizures
  • Focal neurologic deficits
  • Intracranial hypertension:
    • Headache
    • Nausea
    • Vertigo
    • Papilledema
  • Psychiatric disturbances:
    • Altered mental status
    • Changes in personality
    • Learning disabilities
Cysticercosis eye

A cysticercus of the Taenia solium pork tapeworm in the pupil of a patient’s eye:
Although rare, cysticerci may float in the eye, causing vision changes.

Image: “14629” by CDC/Dr. H. Zaiman, Dr. Myron G. Schultz. License: Public Domain

Diagnosis and Management

Diagnosis

  • Nonspecific laboratory findings:
    • Anemia
    • Eosinophilia
  • Stool studies:
    • Identifying eggs or proglottids will establish the diagnosis of taeniasis.
    • ELISA for Taenia antigens
    • PCR to identify DNA
  • Serology for cysticercosis: enzyme-linked immunoelectrotransfer blot
  • CT or MRI may be used in patients with suspected neurocysticercosis.
    • “Swiss cheese” appearance
    • Lesions can be:
      • Cystic
      • Calcified
      • Ring-enhancing
    • Other potential findings:
      • Hydrocephalus with ventricular enlargement
      • Leptomeningeal enhancement
Neurocysticercosis

MRI from a patient with neurocysticercosis:
Note the “Swiss cheese” cystic lesions present throughout the brain.

Image: “ Neurocysticercosis” by Shushruth. License: Public Domain

Taeniasis management

Taeniasis can be treated with anthelmintic therapy:

  • Praziquantel (preferred)
  • Niclosamide

Cysticercosis management

  • General: Asymptomatic disease does not require treatment.
  • Ocular cysticercosis: ophthalmologic evaluation
  • Neurocysticercosis:
    • Anthelmintic therapy
      • Albendazole
      • Praziquantel may be added.
    • Corticosteroids
      • Prednisone or dexamethasone
      • Given prior to and during anthelmintic therapy
      • Reduce inflammation caused by dying cysts
    • Antiepileptic medications
    • Neurosurgical consultation for: 
      • ↑ Intracranial pressure 
      • Intraventricular cysticerci

Prevention

  • Properly cook meat.
  • Identify and treat infected patients.
  • Perform proper hygiene.
  • Avoid potentially contaminated food and water.

Comparison of Tapeworm Species

Table: Characteristics and diseases of different tapeworm species
OrganismDiphyllobothrium latumTaenia saginataEchinococcus granulosus
Characteristics
  • Approximately 10 m long
  • No hooks
  • Bothria present
  • > 3000 proglottids
  • < 5 m long
  • No hooks
  • No neck
  • Approximately 1000 proglottids
  • 2–7 mm long
  • Hooks present
  • 3–6 proglottids
TransmissionEating raw infected fishEating raw infected beefFecal–oral (ingestion of contaminated food or water)
DiseaseDiphyllobothriasisTaeniasisCystic echinococcosis
Clinical
  • Abdominal discomfort
  • Weight loss
  • Vitamin B12 deficiency
  • Bowel obstruction
  • Usually asymptomatic
  • Mild GI symptoms
Depends on location and size of hydatid cysts
DiagnosisEggs or proglottids in stoolEggs or proglottids in stool
  • Imaging
  • Serology
Management
  • Praziquantel
  • Niclosamide
  • Praziquantel
  • Niclosamide
  • Albendazole
  • Percutaneous drainage
  • Surgical excision
Prevention
  • Freeze fish.
  • Thoroughly cook fish.
  • Water sanitation measures
Beef should be cooked thoroughly.
  • Personal hygiene
  • Avoid contact with stray dogs.
  • Avoid potentially contaminated food.
  • Improve water sanitation.

Differential Diagnosis

  • Ascariasis: infection caused by the parasitic roundworm, Ascaris lumbricoides: Transmission of the worm occurs from ingestion of water or food that is contaminated with Ascaris eggs. Patients may be asymptomatic or experience cough and hemoptysis. A large worm burden can cause intestinal obstruction and impair growth in children. Examination of the stool may show the presence of worms or eggs. Management is with anthelmintic therapy.
  • Gastroenteritis: inflammation of the stomach and intestines, commonly caused by infections from bacteria, viruses, or parasites: Common clinical features include abdominal pain, diarrhea, vomiting, fever, and dehydration. Diagnostic testing with stool analysis or culture is not always required but can help determine the etiology in certain circumstances. Most cases are self-limited; therefore, the only required treatment is supportive therapy (fluids). 
  • Inflammatory bowel disease (IBD): includes Crohn’s disease and ulcerative colitis and is characterized by chronic inflammation of the GI tract owing to a cell-mediated immune response to the GI mucosa. Symptoms include diarrhea, abdominal pain, weight loss, and extraintestinal manifestations. Diagnosis includes imaging, endoscopy, and biopsy. Management involves steroids, aminosalicylates, immunomodulators, and biologic agents.
  • Pernicious anemia: causes vitamin B12 deficiency and megaloblastic anemia due to a deficiency of intrinsic factor, which is required for vitamin B12 absorption: Patients may have fatigue, cognitive decline, neuropathy, ataxia, and glossitis. Low vitamin B12 levels, anti-intrinsic factor antibodies, and the Schilling test can be used for diagnosis. Management includes vitamin B12 replacement.
  • Bacterial meningitis: life-threatening bacterial infection of the meninges: Bacterial meningitis can present with fever, headache, meningeal signs, and seizures.  The diagnosis is made by clinical examination and confirmed by finding bacteria in the CSF, which is obtained by lumbar puncture. Management involves corticosteroids and IV antibiotics directed against the identified bacteria.
  • Intracranial tumors: benign or malignant growth of cells in the brain: Intracranial tumors present as headache, unexplained nausea or vomiting, blurred vision, and difficulty in speech or hearing. The diagnosis is made with a neurologic examination, imaging (MRI or CT), and sometimes biopsy. Management includes radiation, chemotherapy, and/or surgery.
  • Brain abscess: a collection of pus in the brain parenchyma due to an infection: Brain abscess presents with fever, headache, seizures, nausea, and vomiting. The diagnosis is based mainly on imaging, as it is difficult to arrive at a definitive diagnosis on the basis of clinical presentation alone. Management includes antibiotic therapy and surgery to drain the abscess. 

References

  1. Craig P, Ito A. (2007). Intestinal cestodes. Curr Opin Infect Dis 20:524–532. http://reference.medscape.com/medline/abstract/17762788
  2. O’Neal S, Noh J, Wilkins P, Keene W, Lambert W, Anderson J. (2011). Taenia solium tapeworm infection, Oregon, 2006-2009. Emerg Infect Dis 17:1030–1036. http://reference.medscape.com/medline/abstract/21749764
  3. O’Keefe KA, Eberhard ML, Shafir SC, Wilkins P, Ash LR, Sorvillo FJ. (2015). Cysticercosis-related hospitalizations in the United States, 1998-2011. Am J Trop Med Hyg 92:354–359. http://reference.medscape.com/medline/abstract/25385857
  4. Garcia HH, Del Brutto OH. (2005). Neurocysticercosis: updated concepts about an old disease. Lancet Neurol 4:653–661. http://reference.medscape.com/medline/abstract/16168934
  5. CDC Centers for Disease Control and Prevention. (2020). Parasites—taeniasis. Retrieved April 20, 2021, https://www.cdc.gov/parasites/taeniasis/
  6. Leder K, Weller PF. (2019). Tapeworm infections. In Baron EL (Ed.), UpToDate. Retrieved April 20, 2021, from https://www.uptodate.com/contents/tapeworm-infections
  7. Pearson RD. (2020). Taenia solium (pork tapeworm) infection and cysticercosis. MSD Manual Professional Version. Retrieved April 20, 2021, from https://www.msdmanuals.com/professional/infectious-diseases/cestodes-tapeworms/taenia-solium-pork-tapeworm-infection-and-cysticercosis
  8. Pearson RD. (2020). Taenia saginata (beef tapeworm) infection. MSD Manual Professional Version. Retrieved April 20, 2021, from https://www.msdmanuals.com/professional/infectious-diseases/cestodes-tapeworms/taenia-saginata-beef-tapeworm-infection
  9. Pearson RD. (2020). Taenia asiatica (Asian tapeworm) infection. MSD Manual Profession Version. Retrieved April 20, 2021, from https://www.msdmanuals.com/professional/infectious-diseases/cestodes-tapeworms/taenia-asiatica-asian-tapeworm-infection
  10. Lesh EJ, Brady MF. (2021). Tapeworm. StatPearls. Retrieved April 20, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK537154/
  11. The Australian Society for Parasitology Inc. (n.d.). Taenia. Retrieved April 20, 2021, from https://parasite.org.au/para-site/text/taenia-text.html
  12. Tengsupakul S. (2018). Taenia infection. In Steele RW (Ed.), Medscape. Retrieved April 20, 2021, from https://emedicine.medscape.com/article/999727-overview

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