Hookworm

Aka: Hookworm, Necator americanus, Ancylostoma duodenale, N. americanus, New World Hookworm, A. duodenale, Old World Hookworm

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II. Epidemiology

  1. Second to Pinworm as most common US Helminth infection
  2. Found in areas of poor sanitation and severe poverty
  3. Widespread endemic areas
    1. Asia (China, India, Japan)
    2. Mideast
    3. Africa
    4. Southern Europe
    5. Caribbean
    6. Central America
    7. South America

III. Pathophysiology

  1. Human Hookworm: Blood sucking Nematode
  2. Similar life cycle to Ascaris Lumbricoides (except Ascaris infection is via ingestion, not bare skin)
  3. Size of both species
    1. Length: 10-12 mm females, 6-8 mm males
    2. Eggs: 60-70 um
  4. Infection
    1. Skin contacts larvae, typically in contaminated soil
    2. Bare feet are a common entry point (may also enter via hands, buttocks, legs)
    3. Skin penetration may be associated with intense localized itch ("ground itch)
  5. Life cycle
    1. Eggs hatch into rhabditform larvae
    2. Larvae ingest soil Bacteria
    3. Rhabditform larvae molt into filariform larvae over a 1 week period
    4. Filariform larvae infect humans via pores, Hair Follicles, on bare skin
    5. Larvae mature in blood
    6. Invade via alveolar capillaries into lung
    7. Ascend Bronchial tree via cough to be swallowed
    8. Mature worm attaches to Small Intestine wall via mouth and feeds off intestinal wall blood
    9. Worms sexually reproduce with other worms, laying eggs that are fertilized in the Small Intestine
    10. Eggs are then passed in stool to return to the soil and infect another person
  6. Species
    1. Necator americanus (New World Hookworm)
      1. Predominates in Americas and Carribean
      2. Mouth with both dorsal and ventral cutting plates
    2. Ancylostoma duodenale (Old World Hookworm)
      1. Predominates in Asia, Africa and Europe
      2. Mouth with 2 pairs of cutting teeth

IV. Symptoms

  1. Initial (often asymptomatic)
    1. Intensely pruritic erythematous dermatitis
      1. Develops at site of infection (e.g. between toes)
    2. Mild respiratory symptoms (cough)
  2. Later: Gastrointestinal (onset 6 weeks after infection)
    1. Diarrhea
    2. Abdominal Pain
    3. Weight loss
    4. Anemia-Related symptoms secondary to blood-sucking worm (see below)

V. Complications

  1. Anemia due to blood loss
    1. Hookworm ingests 0.25 ml of blood per day
  2. Results of Anemia in Children
    1. Malnutrition
    2. Failure to Thrive
    3. Mental Retardation

VI. Labs

  1. Microscopy for Ova and Parasites exam
    1. Examine fresh stool sample at room Temperature
    2. Rhabditiform Larvae hatch
      1. Contrast with Strongyloides
  2. Complete Blood Count
    1. Hypochromic Microcytic Anemia (Iron Deficiency Anemia)
    2. Eosinophilia

VII. Imaging

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

VIII. Management

  1. Treat concurrent Iron Deficiency Anemia
  2. Eradication of Helminth infection
    1. Mebendazole 100 mg PO bid for 3 days
    2. Albendazole 400 mg PO for one dose
    3. Pyrantel Pamoate 11 mg/kg up to 1 gram for one dose

IX. Prevention

  1. Always wear shoes in endemic areas
  2. Ensure adequate sanitation system

X. References

  1. Gladwin, Trattler and Mahan (2014) Clinical Microbiology, Medmaster, Fl, p. 362-81
  2. Kucik (2004) Am Fam Physician 69(5):1161-8 [PubMed]
  3. Schonau (2024) Am Fam Physician 109(6): 569-70 [PubMed]

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