Cestoda Lecture Notes

Cestoda (Tapeworms)

Structural Features

  • Dimensions: Approximately 1 mm to 12-20 m.
  • Body: Ribbon-shaped and segmented.
  • Sections:
    • Scolex (Head): Contains fixation organs like botryas, suckers, and chitinized hooks.
    • Neck: Area where segments form.
    • Strobila: Consists of proglottids (segments).

Stages of Development

  • Egg
  • Oncosphere: Larva with 6 hooks, covered with embryophore.
  • Finn:
    • Types: cysticercus, cysticercoid, cenur, echinococcus, alveococcus, plerocercoid

Types of Finns

  • Cysticercus: Vesicle with liquid and a scolex inside.
  • Cysticercoid: Double-walled vesicle with a scolex, neck, and tail rudiment.
  • Cenure: Bubble with multiple heads.
  • Echinococcus: Single-chamber bubble with capsules containing scolexes.
  • Alveococcus: Irregularly shaped blisters connected, with multiple scolexes.
  • Plerocercoid: Primitive ribbon-shaped finn with a single head and bothria.

Taeniasis and Cysticercosis

  • Caused by Taenia species tapeworms.
  • Taenia solium (pork tapeworm) and Taenia saginata (beef tapeworm) are most common.
  • Adult tapeworms cause taeniasis.
  • Larval stage (T. solium) causes cysticercosis.

Taenia saginata (Beef Tapeworm)

  • Distribution: Widespread.
  • Size: 6-8 m (up to 10-18 m).
  • Fixation: 4 suction cups.
  • Localization: Small intestine.
  • Final Host: Humans.
  • Intermediate Host: Cattle, buffaloes, zebu, yaks, antelope.
  • Infection: Alimentary.
  • Invasive Stage: Cysticercus in connective tissue of skeletal muscles, heart, tongue.
  • Development Time: 7 months.
  • Life Expectancy of Finns: 11-12 months.
  • Human Development Time: 3 months to puberty.
  • Life Span: Up to 15 years.
  • Symptoms: Gastrointestinal irritation, nausea, diarrhea, constipation.
  • Diagnosis: Detection of segments in feces.

Taenia solium (Pork Tapeworm)

  • Causes teniosis and cysticercosis.
  • Distribution: Wherever pig farming is developed.
  • Size: 3-4 m (up to 6 m).
  • Fixation: 4 suction cups and 2 rows of hooks.
  • Final Host: Humans.
  • Intermediate Host: Pigs and humans.
  • Infection: Alimentary.
  • Invasive Stage (Teniasis): Cysticercus in pig muscles.
  • Invasive Stage (Cysticercosis): Oncospheres.
  • Development Time: Cysticerci develop in 3-4 months.
  • Location of Cysticerci: Brain, eyes, heart, skeletal muscles.
  • Life Expectancy of Cysticercus: No more than 2 years.
  • Diagnosis: Detection of segments in feces (teniasis); biopsy, X-ray, ophthalmoscopy, immunodiagnostics (cysticercosis).

Hymenolepis nana (Dwarf Tapeworm)

  • Causes hymenolepidosis.
  • Distribution: Everywhere.
  • Size: 10-50 mm (usually 15-20 mm).
  • Fixation: 4 suction cups and a proboscis with hooks.
  • Host: Humans (final and intermediate).
  • Localization: Small intestine.
  • Infection:
    • Per os (alimentary, contact).
    • Autoinvasion.
    • Re-invasion.
    • Accidental ingestion of intermediate hosts.
  • Symptoms: Abdominal pain, decreased appetite, nausea, unstable stools.
  • Diagnosis: Detection of eggs in feces.

Features of Parasitization (H. nana)

  1. Large number of parasites (up to 1,000+).
  2. Frequent change of attachment location.
  3. Severe intestinal injury.
  4. Auto- and re-invasion.
  5. Rapid spread, mass infection of children.