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Textbook
Introduction
1. Anatomy
2. Microbiology
2.1 General bacteriology
2.2 Introduction to systemic bacteriology
2.3 Gram positive cocci
2.4 Gram negative cocci
2.5 Gram positive bacilli
2.6 Gram negative bacilli
2.7 Other important bacteria
2.8 Virology
2.9 Parasitology
2.9.1 Entamoeba histolytica
2.9.2 Acanthamoeba
2.9.3 Naegleria fowleri
2.9.4 Giardia lamblia
2.9.5 Cryptosporidium parvum
2.9.6 Trichomonas
2.9.7 Plasmodium spp.
2.9.8 Babesia
2.9.9 Toxoplasma gondii
2.9.10 Taenia
2.9.11 Hymenolepis nana
2.9.12 Enterobius vermicularis
2.9.13 Trichuris
2.9.14 Trichinella
2.9.15 Ascaris
2.9.16 Hookworms
2.9.17 Strongyloides
2.9.18 Additional information
2.10 Mycology
3. Physiology
4. Pathology
5. Pharmacology
6. Immunology
7. Biochemistry
8. Cell and molecular biology
9. Biostatistics and epidemiology
10. Genetics
11. Behavioral science
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2.9.16 Hookworms
Achievable USMLE/1
2. Microbiology
2.9. Parasitology

Hookworms

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Hookworms

Infection is usually acquired when you walk barefoot on contaminated soil. The larvae penetrate the skin. Less commonly, larvae are transmitted by ingestion.

The pathogenic hookworms are Necator americanus and Ancylostoma duodenale. The infective form is the filariform (L3) larva.

After contacting a human host, the larvae:

  • Penetrate the skin
  • Enter the bloodstream and travel to the heart, then the lungs
  • Penetrate the pulmonary alveoli
  • Ascend the bronchial tree to the pharynx and are swallowed
  • Reach the small intestine, where they mature into adults

Adult worms live in the lumen of the small intestine. They attach to the intestinal wall, causing blood loss in the host. In addition, infection with A. duodenale may also occur via oral and transmammary routes.

Hookworm cycle
Hookworm cycle

High-intensity hookworm infections occur in both school-age children and adults. Blood loss at the site where adult worms attach can cause anemia and protein deficiency. [What type of anemia will be caused in hookworm disease?].

In children with continuous heavy infection, ongoing iron and protein loss can retard growth and mental development.

Other clinical features include:

  • Dermatitis and itching at the site of larval entry
  • Bronchitis and pneumonia due to larval migration

Diagnosis is made by demonstrating hookworm eggs in stool samples.

Hookworm eggs
Hookworm eggs

Hookworm egg in an unstained wet mount, taken at 400x magnification.

Larva
Larva

Filariform (L3) hookworm larva in a wet mount.

Transmission and Lifecycle

  • Acquired by walking barefoot on contaminated soil (larval skin penetration)
  • Infective form: filariform (L3) larva
  • Lifecycle: skin → bloodstream → heart/lungs → alveoli → bronchial tree → pharynx (swallowed) → small intestine (mature to adults)
    • Ancylostoma duodenale can also infect via oral and transmammary routes

Pathogenic Species

  • Necator americanus
  • Ancylostoma duodenale

Clinical Features

  • Blood loss at intestinal wall attachment → anemia (iron-deficiency type) and protein deficiency
  • Children: chronic infection can cause growth and mental development retardation
  • Dermatitis/itching at entry site, bronchitis, pneumonia from larval migration

Diagnosis

  • Identification of hookworm eggs in stool samples
  • Visualization of filariform larvae in wet mount preparations

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Hookworms

Hookworms

Infection is usually acquired when you walk barefoot on contaminated soil. The larvae penetrate the skin. Less commonly, larvae are transmitted by ingestion.

The pathogenic hookworms are Necator americanus and Ancylostoma duodenale. The infective form is the filariform (L3) larva.

After contacting a human host, the larvae:

  • Penetrate the skin
  • Enter the bloodstream and travel to the heart, then the lungs
  • Penetrate the pulmonary alveoli
  • Ascend the bronchial tree to the pharynx and are swallowed
  • Reach the small intestine, where they mature into adults

Adult worms live in the lumen of the small intestine. They attach to the intestinal wall, causing blood loss in the host. In addition, infection with A. duodenale may also occur via oral and transmammary routes.

High-intensity hookworm infections occur in both school-age children and adults. Blood loss at the site where adult worms attach can cause anemia and protein deficiency. [What type of anemia will be caused in hookworm disease?].

In children with continuous heavy infection, ongoing iron and protein loss can retard growth and mental development.

Other clinical features include:

  • Dermatitis and itching at the site of larval entry
  • Bronchitis and pneumonia due to larval migration

Diagnosis is made by demonstrating hookworm eggs in stool samples.

Hookworm egg in an unstained wet mount, taken at 400x magnification.

Filariform (L3) hookworm larva in a wet mount.

Key points

Transmission and Lifecycle

  • Acquired by walking barefoot on contaminated soil (larval skin penetration)
  • Infective form: filariform (L3) larva
  • Lifecycle: skin → bloodstream → heart/lungs → alveoli → bronchial tree → pharynx (swallowed) → small intestine (mature to adults)
    • Ancylostoma duodenale can also infect via oral and transmammary routes

Pathogenic Species

  • Necator americanus
  • Ancylostoma duodenale

Clinical Features

  • Blood loss at intestinal wall attachment → anemia (iron-deficiency type) and protein deficiency
  • Children: chronic infection can cause growth and mental development retardation
  • Dermatitis/itching at entry site, bronchitis, pneumonia from larval migration

Diagnosis

  • Identification of hookworm eggs in stool samples
  • Visualization of filariform larvae in wet mount preparations