Soil-transmitted helminths

Soil-transmitted helminths

Soil-transmitted helminths

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Soil-Transmitted Helminths - Worms in the Dirt

Life Cycles of Soil-Transmitted Helminths

  • 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.

Comparison of soil-transmitted helminth eggs

⭐ 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.

Strongyloides stercoralis life cycle with autoinfection

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. Cutaneous larva migrans on foot
  • 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

Microscopy of soil-transmitted helminth eggs and larva

  • 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.

Practice Questions: Soil-transmitted helminths

Test your understanding with these related questions

A 4-year-old girl presents with recurrent abdominal pain and a low-grade fever for the past 2 months. The patient’s mother says that she has lost her appetite which has caused some recent weight loss. She adds that the patient frequently plays outdoors with their pet dog. The patient is afebrile and vital signs are within normal limits. On physical examination, conjunctival pallor is present. Abdominal examination reveals a diffusely tender abdomen and significant hepatomegaly. There is also a solid mass palpable in the right upper quadrant measuring about 3 x 4 cm. Laboratory findings are significant for the following: Hemoglobin (Hb%) 9.9 g/dL Total count (WBC) 26,300/µL Differential count Neutrophils 36% Lymphocytes 16% Eosinophils 46% Platelets 200,000/mm3 Erythrocyte sedimentation rate 56 mm/h C-reactive protein 2 mg/L Serum globulins 5 g/dL Laparoscopic resection of the mass is performed, and a tissue sample is sent for histopathology. Which of the following is the organism most likely responsible for this patient’s condition?

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Flashcards: Soil-transmitted helminths

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A positive germ tube test is strongly indicative of _____.

TAP TO REVEAL ANSWER

A positive germ tube test is strongly indicative of _____.

Candida albicans (what fungus)

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