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Microbiology · Nematodes

Necator americanus / Ancylostoma duodenale !

  • Parasite
  • Exam priority: high

Worms that enter through bare feet, latch onto the gut and suck blood: they cause iron-deficiency anaemia, mostly in children.

Updated 2026-11-01

Also called: hookworm, Old World and New World hookworms

At a glance

Shape
Curved front end; buccal capsule with teeth (Ancylostoma) or cutting plates (Necator)
Family
Ancylostomatidae
Type
Blood-feeding intestinal nematode (soil-transmitted helminth)
Size
Adults about 1 cm

Morphology

  • Thin-shelled, colourless egg, 60–75 × 35–40 µm, with visible blastomeres.
  • Necator and Ancylostoma eggs cannot be told apart under the microscope.
  • Rhabditiform larva with a long buccal canal; sheathed filariform larva with a pointed tail.

Transmission

  • Skin penetration by filariform larvae from soil, usually through bare feet.
  • A. duodenale can also infect orally and through breast milk.
  • Warm, moist, shaded soil contaminated with human faeces.

Reservoir: Humans; Contaminated soil

Isolation precautions

What the care team adds to standard precautions.

  • Standard

Life cycle

  1. Eggs leave in stool and, in warm moist soil, hatch in 1–2 days into rhabditiform larvae.
  2. In 5–10 days they moult into infective filariform (L3) larvae that survive weeks in soil.
  3. The L3 penetrates skin, usually of a bare foot, and travels in the blood to the heart and lungs.
  4. It climbs the bronchial tree to the pharynx, is swallowed and reaches the small bowel.
  5. In the jejunum it attaches, sucks blood and matures; the adult can live for years.
  6. A. duodenale also enters by mouth or breast milk, and some larvae stay dormant in tissues.

Virulence factors

  • The buccal capsule anchors to and lacerates the mucosa.
  • Secreted anticoagulants keep the bite bleeding: chronic loss of iron and protein.
  • Itchy rash at the entry site ('ground itch').
  • Mild cough during the lung passage.

Diseases it causes

Clinical picture

  • Itchy dermatitis on the feet after walking barefoot.
  • Pallor, fatigue and delayed development in children; anaemia in pregnancy.
  • Mild epigastric pain; oedema from hypoalbuminaemia in severe cases.
  • Eosinophilia, especially in early phases.

Diagnosis

  • Eggs on stool microscopy after formalin-ethyl acetate concentration; Kato-Katz or FLOTAC to quantify.
  • Blood count with microcytic hypochromic anaemia and low ferritin.
  • An old sample may hatch and show larvae that mimic Strongyloides: fresh stool is preferred.

Treatment

Benzimidazoles (albendazole or mebendazole), plus iron replacement to correct the anaemia.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

Prevention

  • Wearing shoes.
  • Latrines and safe excreta disposal.
  • Periodic deworming of school-age and preschool children and women of reproductive age in at-risk areas.
  • Hygiene education and handwashing.

Test yourself

Think of the answer, then tap the question to see it.

Why does hookworm infection cause iron-deficiency anaemia?

Adults attach to the jejunal mucosa, secrete anticoagulants and cause chronic blood loss.

What is the usual route of hookworm entry?

Skin penetration by filariform larvae from soil, usually when walking barefoot.

Which hookworm species predominates in the Americas?

Necator americanus.

Why is fresh stool preferred when hookworm is suspected?

In old samples the eggs hatch and the larvae can be mistaken for Strongyloides.

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Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: CDC - DPDx - Intestinal Hookworm (CDC, 2019); Soil-transmitted helminth infections (WHO, 2023); Hookworm infection: MedlinePlus Medical Encyclopedia (MedlinePlus (NLM), 2025); Geohelmintiasis (Ministerio de Salud y Protección Social de Colombia, 2014).

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