Ascaris

Aka: Ascaris, Ascariasis, Ascaris Lumbricoides

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II. Epidemiology

  1. Prevalence (esp. tropics): >800 Million cases estimated worldwide
    1. Asia (75%)
    2. Africa (10%)
    3. Latin America (10%)
    4. United States (7%)
      1. More common among international travelers and recent Immigrants
      2. Mountainous, rural areas of southeastern U.S. (historically)
        1. Decreasing with modern sanitation and waste management
  2. Transmission
    1. Human feces contaminated fruits and vegetables
    2. Fomites
      1. Flies can deposit eggs on food

III. Pathophysiology

  1. Nematode: Roundworm
  2. Similar life cycle to Hookworm (except Hookworm infection is via bare skin, not ingestion)
  3. Infected patient with Ascariasis secretes eggs in stool
    1. Stool contaminates soil with Ascariasis eggs (and eggs may persist for up to 10 years in soil)
    2. Ascariasis eggs hatch into worms within 2-4 weeks at which point they are infective
  4. Ascariasis eggs are ingested by exposed persons (Foodborne Illness)
    1. Especially communities with open Defecation in fields or where animal feces are used to fertilize crops
    2. Ascariasis eggs that hatch after ingestion (typically by day 4) pass through the cecal mucosa
    3. Ascariasis worms enter lungs via circulatory system or Lymphatic System
  5. Ascariasis matures in lungs for 10-14 days
    1. Once mature, Ascariasis induces cough, and patient swallows coughed secretions, re-entering intestinal tract
  6. Ascariasis worms mature further in intestinal tract
    1. After 9-11 weeks from time of initial ingestion, Ascariasis starts to lay eggs
    2. Infected patients shed up to 200,000 Ascariasis eggs per day
    3. Worms live for 10 months to 2 years and do not reproduce within host patient

IV. Symptoms

  1. Often asymptomatic
  2. Intense lower Abdominal Pain and cramping for days (associated with large infestations)

V. Signs

  1. Distinctive Ascariasis eggs in stool
  2. Roundworm passed in stool
    1. Length: 15-30 cm (6 to 12 inches)
    2. Color: creamy white

VI. Labs

  1. Stool Ova and Parasites
  2. Stool microscopy for eggs or larvae
  3. Worm if available
  4. Eosinophilia (CBC, stool)

VII. Imaging

  1. Chest XRay
    1. Larval migration to lung may result in cough with Pulmonary Infiltrates

VIII. Complications

  1. Bowel Obstruction
  2. Invasion of gastrointestinal organs
    1. Gallbladder and bile duct
    2. Appendix
    3. Liver
  3. Allergic
    1. Urticaria
    2. Asthma
  4. Children
    1. Malnutrition

IX. Management

  1. May start empiric treatment with anti-Helminth agent if classic Roundworm identified
    1. However, still send stool samples as above
    2. Concurrent infection with other Helminth (e.g. Strongyloides) requires additional management
  2. Anti-Helminth agents
    1. Albendazole 400 mg orally for one dose (pregnancy category C)
    2. Mebendazole 500 mg daily for one dose (or up to three days)
    3. Pyrantel Pamoate
      1. Indicated in pregnancy
  3. Patient Education
    1. Medication will result in passing very large numbers of worms in stool
    2. Close contacts are not empirically treated in most cases (unless unreliable for follow-up)
      1. Test suspected cases

X. References

  1. Gladwin, Trattler and Mahan (2014) Clinical Microbiology, Medmaster, Fl, p. 362-81
  2. Mason, Grock and Tenner in Herbert (2017) EM:Rap 17(11): 6

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