Hookworm disease, also called ancylostomiasis or “miners’ anemia” is a disease of warm climates where human feces contaminate the soil. Two nematode (round worm) species are involved: Ancylostoma duodenale and Necator americanus.
Hookworm Life Cycle
Adult hookworms reside in the human small intestine, where they attach themselves by gripping intestinal lining with their mouths. They ingest blood and cause bleeding at the attachment site:
- Female worms produce eggs, which are delivered to the outside world in the feces. If feces are deposited on the ground, and the weather is warm, larvae develop and emerge in about two days.
- In warm soil with sufficient moisture, larvae mature in about a week, and can survive for long periods if conditions are right.
- Larvae that come in contact with bare human skin burrow in and travel to the lungs in the blood or lymph.
- Traveling up the air passages to the throat, the larvae are swallowed. They pass through the stomach into the small intestine.
- Larvae attach to the intestinal lining and mature to adult worms.
- At about five months of age, worms begin producing eggs.
Facts About Hookworms and Hookworm Disease
Hookworm disease is rare outside the tropics because the larvae can’t survive in colder climates:
- Cold, acid or alkaline conditions, flooding, exposure to direct sunlight, dry conditions and salt all kill hookworm larvae.
- The relatively stable warmth and humidity in mines allow hookworm larvae to survive there even outside the tropics, which explains the name “miners’ anemia.”
- Ancylostoma duodenale causes more severe illness with lower numbers of worms than N. americanus.
- Exposure to hookworms may have a moderating effect on the human immune system, reducing the risk of allergies and some diseases involving immune malfunctions.
- Ancylostoma duodenale can also be acquired by eating the raw or undercooked flesh of infected animals: larvae can penetrate the skin of various animals and survive in their muscle tissue.
- Larvae of Ancylostoma duodenale can remain dormant in human tissue too, delaying development until seasonal conditions are right for survival of offspring in soil.
Symptoms of Hookworm Disease
Hookworm disease can be so mild – when there are only a few worms present – that there are no symptoms at all. People with long-term infections with higher numbers of worms tend to be thin, tired, and weak, and the associated anemia tends to cause a pale yellowish skin colour. Specific symptoms range from abdominal pain and malnutrition through bloody diarrhea, vomiting, and heart failure. The range of symptoms varies widely and depends on the nutritional status and overall health to begin with, as well as the species of worm and the number of individual worms involved.
Related Content
The History of Hookworms and Hookworm Disease
Sources:
Diagnostic Medical Parasitology 3rd ed. Garcia, Lynn S. and David A. Bruckner. Washington: ASM Press, 1997.
Foundations of Parasitology 6th ed. Roberts, Larry S. and John Janovy Jr. Boston: McGraw Hill, 2000.
"Review Series on Helminths, Immune Modulation and the Hygiene Hypothesis: the Broader Implications of the Hygiene Hypothesis." Rook, Graham A. Immunology 126 (2008), 3-11.
 |
 |
 |
