Intestinal Helminths: Nematodes

General Features & Lifecycle - Nematode Know-How

• Morphology: Cylindrical, unsegmented, bilaterally symmetrical, tapered ends. Body cavity: pseudocoelom. Complete digestive tract. Separate sexes (dioecious); males often smaller with curved posterior.
• Basic Lifecycle: Egg → Multiple larval molts (L1-L5, typically 4 molts) → Sexually mature adult.
  • Infective stage: Embryonated egg or larva (e.g., filariform).
  • Diagnostic stage: Usually eggs or larvae in stool/tissue.
• Transmission Routes: 📌 Mnemonic: Ingest (eggs/larvae) or Penetrate (skin)!
  • Ingestion of infective eggs (e.g., Ascaris, Trichuris).
  • Skin penetration by infective larvae (e.g., Hookworm, Strongyloides).
  • Ingestion of infective larvae in tissues (e.g., Trichinella).
  • Autoinfection (e.g., Strongyloides, Enterobius).

⭐ Most intestinal nematodes are diagnosed by finding eggs in stool.

Ascaris & Hookworms - Giant Worm & Bloodsuckers

• Ascaris lumbricoides (Giant Roundworm)

  • Morphology: Largest intestinal nematode (~15-35 cm).
  • Lifecycle: Ingest embryonated egg → Larvae: Intestine → Liver → Lungs (Loeffler's syndrome 📌 'Loeffler's coughs a lot': cough, eosinophilia) → Swallowed → Matures in small intestine.
  • Clinical Features: Often asymptomatic; pneumonitis, abdominal pain, intestinal/biliary obstruction, malnutrition.
  • Diagnosis: Characteristic bile-stained, corticated (mammillated) eggs in stool; occasional adult worm passage.

• Hookworms (Ancylostoma duodenale, Necator americanus)

  • Morphology: A. duodenale (2 pairs of ventral teeth); N. americanus (semilunar cutting plates).
  • Lifecycle: Filariform larvae in soil penetrate intact skin (ground itch) → Blood → Lungs → Trachea → Swallowed → Mature in small intestine, attach to mucosa.
  • Clinical Features: Ground itch (maculopapular rash), pneumonitis, epigastric pain, chronic blood loss → Iron Deficiency Anemia (IDA), hypoalbuminemia.

  ⭐ Hookworm infection is a major cause of iron deficiency anemia in endemic areas.

  • Diagnosis: Non-bile stained, thin-shelled, transparent eggs (segmented ovum) in stool; occult blood.

Trichuris, Enterobius, Strongyloides - Whip, Pin & Thread

• Trichuris trichiura (Whipworm)
  • Morphology: Whip-like anterior, thick posterior.
  • Clinical: Heavy infection: abdominal pain, bloody diarrhea, rectal prolapse (children).
  • Diagnosis: Barrel-shaped, bile-stained eggs with polar plugs in stool.
• Enterobius vermicularis (Pinworm) 📌 'Pin in the bum, scratchy tum!'
  • Lifecycle: Autoinfection (hand-to-mouth), retrofection.
  • Clinical: Intense nocturnal perianal itching (pruritus ani); irritability.
  • Diagnosis: Scotch tape test for D-shaped, flat-sided eggs.
• Strongyloides stercoralis (Threadworm)

  • Lifecycle: Free-living & parasitic cycles; autoinfection (key for persistence/hyperinfection).

  • Clinical: Cutaneous (larva currens), pulmonary (Loeffler's), GI symptoms. Hyperinfection in immunosuppressed.

  • Diagnosis: Rhabditiform larvae in stool/duodenal aspirate; serology.

  ⭐ Strongyloides stercoralis can cause hyperinfection syndrome in immunocompromised individuals, particularly those on corticosteroid therapy.

Diagnosis & Management - Worm Warfare

• Diagnosis:
  • Stool exam (O&P): Microscopy for ova, larvae, adult worms.
  • Concentration techniques (formalin-ether, zinc sulfate flotation).
  • Kato-Katz: Quantitative egg count for infection intensity.
• Management (Key Drugs):
  • Albendazole (400mg single dose)/Mebendazole: Broad-spectrum; inhibit microtubule synthesis.
  • Pyrantel Pamoate: Neuromuscular blockade (Ascaris, hookworm, Enterobius).
  • Ivermectin: GABA agonist, paralysis (Strongyloides, Onchocerca). Risk: Mazzotti reaction.
• Prevention:
  • Hygiene (handwashing, food/water safety), sanitation.
  • Health education; Mass Drug Administration (MDA) in endemic areas.

⭐ Mebendazole and Albendazole are broad-spectrum anthelmintics effective against most intestinal nematodes.

High‑Yield Points - ⚡ Biggest Takeaways

• Enterobius vermicularis: Perianal itching (pruritus ani); diagnosis via Scotch tape test.
• Ascaris lumbricoides: Largest intestinal nematode; Loeffler's syndrome, intestinal obstruction; bile-stained corticated eggs.
• Trichuris trichiura: Rectal prolapse in heavy infections; barrel-shaped eggs with bipolar plugs.
• Hookworms (Ancylostoma, Necator): Iron deficiency anemia (chronic blood loss); skin penetration by filariform larvae.
• Strongyloides stercoralis: Autoinfection leading to hyperinfection, especially in immunocompromised; rhabditiform larvae in stool.
• Trichinella spiralis: Acquired from undercooked pork; triad: fever, myalgia, periorbital edema; marked eosinophilia.