CESTODES – TAENIA SAGINATA AND TAENIA SOLIUM

CESTODES – TAENIA SAGINATA AND TAENIA SOLIUM

1. Definition – Taenia saginata (beef tapeworm) and Taenia solium (pork tapeworm) are flat, segmented cestodes that live in the human intestine and cause taeniasis.

2. Cause – ingestion of raw/undercooked infected beef (T. saginata) or pork (T. solium) or accidental ingestion of eggs (T. solium).

3. Types – two human‑infecting species:
   a. T. saginata – cattle as intermediate host.
   b. T. solium – pig as intermediate host; also causes cysticercosis when eggs are ingested.

4. Morphological differences –
   • Scolex: T. saginata → four large suckers, no rostellum or hooks; T. solium → four suckers + rostellum with a double row of small hooks.
   • Length: T. saginata 4–10 m (longer); T. solium 2–4 m (shorter).
   • Gravid proglottids: T. saginata → >15 cm, many uterine branches (15–30); T. solium → 5–10 cm, 7–13 uterine branches.
   • Eggs: both spherical, 30–35 µm, but T. solium eggs have thick radially striated embryophore, T. saginata eggs are thinner, smoother.

5. Life cycle of T. saginata –

   1. Adult tapeworm lives in human small intestine →
   2. Gravid proglottids detach and release eggs in feces →
   3. Cattle ingest eggs while grazing →
   4. Egg → oncosphere hatches in cattle gut →
   5. Oncosphere penetrates intestinal wall → enters bloodstream →
   6. Lodges in skeletal muscle → develops into cysticercus (fluid‑filled bladder) →
   7. Human eats undercooked infected beef → cysticercus evaginates → adult tapeworm matures in intestine.

6. Life cycle of T. solium –

   1. Adult tapeworm in human intestine →
   2. Eggs shed in feces →
   3. Pig ingests eggs (normal cycle) → oncosphere → muscle → cysticercus → human eats undercooked pork → adult tapeworm.
   4. Autoinfection/accidental ingestion of eggs by human → oncosphere → bloodstream → tissue (brain, eye, muscle) → cysticercosis (extra‑intestinal disease).

7. Pathogenesis of taeniasis –
   • Ingestion of cysticercus → evagination of scolex → attachment by suckers (and hooks in T. solium) → nutrient absorption from host gut.
   • Tapeworm grows by adding proglottids → massive length may cause mild irritation.
   • Nutrient loss and vitamin B12 deficiency may occur in heavy infections.

8. Clinical features –
   • Most infections are asymptomatic (carrier state).
   • Mild abdominal discomfort, dyspepsia, nausea, occasional diarrhea or constipation.
   • Weight loss or increased appetite (parasite “steals” nutrients).
   • Passage of whole proglottids in stool (often noticed by patients).
   • Rare intestinal obstruction with very long worms.

9. Complications –
   • Nutritional deficiencies (especially B12) in heavy load.
   • Cysticercosis (only with T. solium egg ingestion) → neurocysticercosis, ocular cysticercosis, subcutaneous nodules.

10. Laboratory diagnosis –
    • Stool microscopy – identification of characteristic eggs (spherical, 30 µm) in fresh smear.
    • Examination of expelled proglottids – size, number of uterine branches, presence/absence of rostellar hooks distinguishes species.
    • Concentration techniques (formalin‑ether) increase yield.
    • Serology (ELISA, immunoblot) – mainly for cysticercosis, not routine taeniasis.
    • Molecular PCR – species‑specific confirmation (research/epidemiology).

11. Management –
    • Single dose praziquantel 5–10 mg/kg OR niclosamide 2 g single dose (effective for both species).
    • Albendazole 400 mg single dose also works (especially for cysticercosis).
    • Re‑treatment after 2 weeks if proglottids still seen.
    • Health education – cook meat thoroughly, wash hands, improve sanitation.

12. Prevention –
    • Proper cooking of beef/pork (≥ 63 °C).
    • Meat inspection and condemnation of cysticercus‑infested carcasses.
    • Safe disposal of human feces, latrine use.

13. Memory trick –
    • “Cattle chew, humans chew‑beef; Pigs chew, humans chew‑pork; Hooked worm (solium) can also hide in your brain.”
    • Rhyming flow for T. saginata: “Egg → Cow → Muscle → Beef → Worm.”
    • Rhyming flow for T. solium: “Egg → Pig → Pork → Worm; Egg → Human → Brain → Pain.”