General Characteristics and Epidemiology
General features of Taenia
Taenia is a genus of parasitic cestodes (tapeworms).
- Thick, striated wall
- Contains a 6-hooked (hexacanth) embryo
- T. saginata: < 5 m in length
- T. solium: approximately 2–7 m in length
- Ribbon-like, segmented body:
- Rostellum with 2 rings of hooks in T. solium
- 4 muscular suckers
- Strobila with approximately 1000 proglottids:
- Contains sets of reproductive organs
Clinically relevant species
Taenia tapeworms cause the following diseases:
- T. saginata (beef tapeworm)
- T. solium (pork tapeworm)
- T. asiatica (Asian tapeworm)
- Cysticercosis: T. solium
Geographic distribution of species:
- T. solium and T. saginata: worldwide
- T. asiatica: Asia
- 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
- Approximately 1000 cases diagnosed each year in the United States
- More common in immigrants
- 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
- 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
- Pigs or cattle ingest vegetation that is contaminated with eggs or gravid proglottids.
- Eggs hatch in the intestine → oncospheres
- Invasion into the intestinal wall → bloodstream → migration to striated muscle → develop into cysticerci (larvae within a fluid-filled sac)
- 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
- Adults produce proglottids → mature and become gravid → detach from the tapeworm
- Gravid proglottids and eggs are excreted in the feces → cycle continues
- Humans consume food or water contaminated with T. solium eggs or gravid proglottids.
- Eggs hatch in the intestine → oncospheres
- Invasion into the intestinal wall → bloodstream → migration to tissues and organs → develop into cysticerci → cysticercosis
- Cysticerci can migrate to the CNS → neurocysticercosis
Most patients (particularly adults) are asymptomatic.
- Common symptoms include:
- Passing proglottids in the stool (most common)
- Abdominal pain
- Pruritus ani
- Less common:
- Constipation or diarrhea
- Complications due to obstruction from tapeworm segments:
- Biliary obstruction:
- Intestinal obstruction
- Biliary obstruction:
Signs and symptoms depend on the tissues involved.
Muscular and dermatologic cysticercosis:
- Most are asymptomatic
- Cysts may be palpated under the skin
- Foreign body sensation
- Ocular pain
- Impaired vision
- Sensation of movement in the eye
- Focal neurologic deficits
- Intracranial hypertension:
- Psychiatric disturbances:
- Altered mental status
- Changes in personality
- Learning disabilities
Diagnosis and Management
- Nonspecific laboratory findings:
- 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:
- Other potential findings:
- Hydrocephalus with ventricular enlargement
- Leptomeningeal enhancement
Taeniasis can be treated with anthelmintic therapy:
- Praziquantel (preferred)
- General: Asymptomatic disease does not require treatment.
- Ocular cysticercosis: ophthalmologic evaluation
- Anthelmintic therapy
- Praziquantel may be added.
- 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
- Anthelmintic therapy
- Properly cook meat.
- Identify and treat infected patients.
- Perform proper hygiene.
- Avoid potentially contaminated food and water.
Comparison of Tapeworm Species
|Organism||Diphyllobothrium latum||Taenia saginata||Echinococcus granulosus|
|Transmission||Eating raw infected fish||Eating raw infected beef||Fecal–oral (ingestion of contaminated food or water)|
|Clinical||Depends on location and size of hydatid cysts|
|Diagnosis||Eggs or proglottids in stool||Eggs or proglottids in stool|
|Prevention||Beef should be cooked thoroughly.|
- 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.
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