Two species of hookworms can infect the human intestine: Ancylostoma duodenale and Necator americanus. Although hookworm infections are rare in the United States, this parasitic disease commonly occurs in impoverished, undeveloped areas of Asia, Africa and Latin America. The World Health Organization estimates that 740 million people worldwide have hookworms. The immature larval form of a hookworm infects humans either through the skin or via inadvertent ingestion.
Skin Contact with Contaminated Soil
An adult female hookworm lays up to 7,000 eggs each day in the small intestine, reports the medical reference text "Principles and Practice of Infectious Diseases." The eggs pass in the stool. In the presence of warm temperatures and moist soil, the eggs hatch into immature larvae. The larval forms, not the eggs, of the hookworm prove infectious to humans.
Hookworm larvae most commonly enter the human body by burrowing into the skin. This typically occurs when walking barefoot in fecal-contaminated soil infested with hookworm larvae. The tiny larvae burrow deep into the skin and enter the bloodstream, which carries the worms to the lungs. In the lungs, the larvae enter the airways and crawl to the throat where they are swallowed. The larvae travel with ingested food through the stomach to the small intestine. The immature worms use their sucker-like mouths to attach to the wall of the small intestine. The larvae mature into adult worms and begin laying eggs. Adult worms live in the small intestine for 2 to 5 years, notes "Principles and Practice of Infectious Diseases."
Ingestion of Larvae
Accidental ingestion of hookworm larvae is another route of hookworm infection, reports the Centers for Disease Control and Prevention (CDC). Ingestion gives the parasites direct access to the digestive tract, bypassing the circulation and lungs.
A child playing in soil contaminated with hookworm larvae may put his hands in his mouth and accidentally ingest the tiny worms. Alternatively--in the spirit of curiosity and exploration that children have in such abundance--he may eat a bit of contaminated soil and unwittingly infect himself with the dangerous parasite. Hookworm larvae may also contaminate foodstuffs if human feces are used for crop fertilizer.
Hookworm Signs and Symptoms
Intense itching and a pimple-like red rash, known as "ground itch," develop at the entry site of hookworm larvae, reports "The Merck Manual for Healthcare Professionals." Larval migration through the lungs may provoke wheezing and coughing. Once in the intestine, the worms may cause abdominal cramps, loss of appetite, diarrhea, intestinal gas and weight loss. Anemia commonly develops with chronic hookworm infections because the worms feed on blood from the intestinal wall.
References
- World Health Organization: Hookworm Disease
- "Principles and Practice of Infectious Diseases, Sixth Edition"; Gerald L. Mandell, M.D., et al., Editors; 2004
- Sabin Vaccine Institute: Hookworm
- Centers for Disease Control and Prevention: Hookworm Infection
- The Merck Manual for Healthcare Professionals: Hookworm Infection (Ancylostomiasis)
