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[Microbiology](https://durgical.com/en/microbiology/) · [Nematodes](https://durgical.com/en/microbiology/groups/nematodes/)

# Necator americanus / Ancylostoma duodenale

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- 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

## Key points

- Entry through the skin of bare feet; lung passage.
- Classic cause of iron-deficiency anaemia in tropical children.
- Necator americanus predominates in the Americas.
- A. duodenale is also transmitted orally and through breast milk.
- The eggs of both species are identical.

## 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

- Eggs leave in stool and, in warm moist soil, hatch in 1–2 days into rhabditiform larvae.
- In 5–10 days they moult into infective filariform (L3) larvae that survive weeks in soil.
- The L3 penetrates skin, usually of a bare foot, and travels in the blood to the heart and lungs.
- It climbs the bronchial tree to the pharynx, is swallowed and reaches the small bowel.
- In the jejunum it attaches, sucks blood and matures; the adult can live for years.
- 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

- Intestinal hookworm infection [Soil-transmitted helminthiasis (ascariasis, hookworm, trichuriasis) →](https://durgical.com/en/conditions/soil-transmitted-helminthiasis/)
- Microcytic iron-deficiency anaemia and hypoalbuminaemia with heavy loads [Iron deficiency anaemia →](https://durgical.com/en/conditions/iron-deficiency-anaemia/)

## 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:

- [Albendazole](https://durgical.com/en/pharmacology/albendazole/)
- [Mebendazole](https://durgical.com/en/pharmacology/mebendazole/)

## 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.

## In Colombia

The national school survey (2012–2014) found hookworms in 6.4% of children, more in warm rural areas. They are included in the Ministry of Health's mass school deworming.

## Memory aid

Bare foot in, iron out: the hookworm walks in through the sole and sips the blood away.

## 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.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/necator-americanus-ancylostoma-duodenale/)

## Related

- [Ancylostoma braziliense / Ancylostoma caninum](https://durgical.com/en/microbiology/ancylostoma-braziliense-ancylostoma-caninum/)
- [Strongyloides stercoralis](https://durgical.com/en/microbiology/strongyloides-stercoralis/)
- [Ascaris lumbricoides](https://durgical.com/en/microbiology/ascaris-lumbricoides/)

## Related conditions

- [Soil-transmitted helminthiasis (ascariasis, hookworm, trichuriasis)](https://durgical.com/en/conditions/soil-transmitted-helminthiasis/)
- [Iron deficiency anaemia](https://durgical.com/en/conditions/iron-deficiency-anaemia/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

[← Back to the group: Nematodes](https://durgical.com/en/microbiology/groups/nematodes/)

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](https://www.cdc.gov/dpdx/hookworm/index.html) (CDC, 2019); [Soil-transmitted helminth infections](https://www.who.int/news-room/fact-sheets/detail/soil-transmitted-helminth-infections) (WHO, 2023); [Hookworm infection: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000629.htm) (MedlinePlus (NLM), 2025); [Geohelmintiasis](https://minsalud.gov.co/salud/publica/PET/Paginas/geohelmintiasis.aspx) (Ministerio de Salud y Protección Social de Colombia, 2014).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/necator-americanus-ancylostoma-duodenale/