Soil-transmitted helminths

Soil-Transmitted Helminths - Worms in the Dirt

• Fecal-oral transmission; larvae penetrate skin (Hookworm, Strongyloides) or are ingested (Ascaris, Trichuris).
• Ascaris lumbricoides (giant roundworm): Loeffler's syndrome (eosinophilic pneumonitis), malnutrition, intestinal obstruction.
• Trichuris trichiura (whipworm): Often asymptomatic; heavy infection can cause rectal prolapse.
• Hookworms (Necator, Ancylostoma): Attach to intestinal wall, causing chronic blood loss and iron deficiency anemia.
• Strongyloides stercoralis: Autoinfection cycle.

⭐ Strongyloides hyperinfection, often triggered by corticosteroid therapy, leads to disseminated disease (sepsis, meningitis) with high mortality. 📌 Mnemonic: Get these worms out of your system with bendazoles.

The Main Culprits - Round, Whip, & Hook

• Ascaris lumbricoides (Giant Roundworm)
  • Transmission: Fecal-oral (ingestion of eggs).
  • Clinical: Intestinal or biliary obstruction, malnutrition. Can cause Loeffler syndrome (transient eosinophilic pneumonitis).
  • Diagnosis: Knobby-coated, oval eggs in feces.
• Trichuris trichiura (Whipworm)
  • Transmission: Fecal-oral (ingestion of eggs).
  • Clinical: Often asymptomatic. Heavy load can cause loose stools, anemia, and rectal prolapse in children.
  • Diagnosis: Barrel-shaped eggs with polar plugs in feces.
• Hookworms (Necator americanus, Ancylostoma duodenale)
  • Transmission: Filariform larvae penetrate skin (e.g., walking barefoot).
  • Clinical: "Ground itch" at penetration site. Attach to gut mucosa, causing chronic blood loss.
  • Diagnosis: Non-bile-stained, segmented eggs in feces.

⭐ Hookworm infection is a major cause of microcytic, hypochromic anemia (iron deficiency) in developing countries due to chronic intestinal blood loss.

Special Cases - Autoinfection & Anal Itch

• Enterobius vermicularis (Pinworm):

  • Primary cause of nocturnal perianal itching (pruritus ani), especially in children.
  • Autoinfection occurs when eggs, laid on perianal skin, are ingested via contaminated hands.
  • Diagnosis: "Scotch tape test" to collect eggs from perianal skin for microscopy.
  • Treatment: Albendazole or Mebendazole for the patient and household contacts.

• Strongyloides stercoralis:

  • Autoinfection is a key feature; larvae penetrate the gut wall or perianal skin to re-enter circulation.

⭐ In immunocompromised hosts (e.g., on corticosteroids), Strongyloides autoinfection can lead to a disseminated, high-mortality hyperinfection syndrome.

Wandering Worms - Larva Migrans Syndromes

• Cutaneous Larva Migrans (CLM): "Creeping Eruption"

  • Agent: Ancylostoma spp. (dog/cat hookworm).
  • Path: Larvae penetrate skin from contaminated soil/sand.
  • Sx: Intensely pruritic, migratory serpiginous rash.
  • Rx: Ivermectin, albendazole.

• Visceral Larva Migrans (VLM):

  • Agent: Toxocara canis/cati.
  • Path: Ingestion of eggs (pica is a risk factor).
  • Sx: Fever, hepatosplenomegaly, marked eosinophilia.

  ⭐ Toxocara infection (VLM) is a key cause of profound eosinophilia and hepatomegaly in a child with a history of pica (eating soil).

Diagnosis & Treatment - Stools & Superdrugs

• Diagnosis: Stool microscopy for ova & parasites (O&P). Peripheral eosinophilia is a common finding.
• Treatment: Broad-spectrum antihelminthics are the mainstay.
  • Albendazole or Mebendazole are first-line agents.
  • Pyrantel pamoate is an alternative, often used in pregnancy.

⭐ Loeffler's syndrome, a transient eosinophilic pneumonitis, can occur during the pulmonary migration phase of Ascaris and hookworm larvae.

High‑Yield Points - ⚡ Biggest Takeaways

• Transmission is key: ingest eggs (Ascaris, Trichuris) or larvae penetrate skin (Hookworms, Strongyloides).
• Ascaris lumbricoides causes Loeffler's syndrome and can lead to intestinal or biliary obstruction.
• Hookworms (Ancylostoma, Necator) are a major cause of iron deficiency anemia from chronic blood loss.
• Trichuris trichiura (whipworm) is classically associated with rectal prolapse in children.
• Strongyloides stercoralis features a unique autoinfection cycle, risking hyperinfection in immunocompromised hosts.
• Diagnosis is eggs in stool, but Strongyloides is diagnosed by larvae in stool.