Hookworm infections are caused by intestinal nematodes (roundworms), with most human infections being caused by either Necator americanus or Ancylostoma duodenale. Less frequently, human hookworm infections may be caused by A. ceylanicum or A. caninum. Occasionally, animal hookworms such as A. brasiliensis cause disease in humans. Hookworm infection is widely distributed throughout tropical and subtropical regions of the world. Favorable conditions for the spread of infection include warm temperatures, high humidity, shade, and contamination of soil with human feces.
It is estimated that up to one-fifth of the world's population is infected with hookworms. Humans harbor the adult worms in their small intestine. Eggs are passed in stool and will hatch within twenty-four to forty-eight hours if conditions are favorable. After hatching, the larvae molt twice in soil and, in approximately ten days, become infective filariform larvae. When a barefoot human walks in contaminated soil these filariform larvae penetrate the skin, migrate through the blood stream to the lungs, break through pulmonary capillaries into the alveoli, and then travel up the tracheobronchial tree to the epiglottis. The larvae are then swallowed and reach the small intestine where they mature into adult worms. Eggs will appear in the stool within one to three months. Female worms will lay between 5,000 and 10,000 eggs a day for up to ten years; the average adult lifespan is four to six years.
Larval penetration of skin may cause local itching and a papulovesicular rash, sometimes called "ground itch." Nonhuman hookworm infections classically produce a very pruritic migratory linear rash. As human hookworm larvae migrate through the lungs there may be mild pulmonary symptoms, usually a cough or wheezing. There may also be gastrointestinal symptoms such as nausea, abdominal pain (peptic ulcer-like symptoms), or diarrhea during the intestinal phase; however, the infection is usually asymptomatic. The major problems attributable to hookworms are iron deficiency, anemia, and protein deficiency, which are frequently seen in malnourished individuals who are infected with a large number of worms. Each hookworm consumes approximately0.03 to 0.15 milliliters of blood each day. A large number of worms can remove enough blood to cause an anemia severe enough to result in growth retardation in children. Anemia does not usually occur in those with normal iron intake.
Diagnosis is made by finding the characteristic eggs in stool. Treatment involves the elimination of the worms and correction of anemia and protein deficiency, if present. Medications that are effective against hookworm include albendazole, mebendazole, and pyrantel pamoate.
Humans are the only reservoir of infection for N. americanus and A. duodenale. Prevention of hookworm infection involves good sanitation systems and public education regarding the risks of contamination of soil with human feces and the importance of wearing shoes in endemic areas.
Elimination of hookworm infection in a population would reduce levels of anemia and malnutrition and result in improved physical and intellectual development. All members of a community are at risk of infection, but certain groups are more vulnerable to the effects of chronic infection, including preschoolers, school-age children, and women of child-bearing age. Community control programs are often targeted specifically at these groups.
Humans do not develop an immunity to hookworm infection and can be reinfected with subsequent exposures. For this reason, eradication programs such as mass treatments of a population need to be repeated on a regular basis.
Bundy, D. A. P., and de Silva, N. R. (1998). "Can We Deworm This Wormy World?" British Medical Bulletin 54(2):421–432.
Chin, J., ed. (2000). Control of Communicable Diseases, 17th edition. Washington, DC: American Public Health Association.
Grencis, R. K., and Cooper, E. S. (1996). "Enterobius, Trichuris, Capillaria, and Hookworm, Including Ancylostoma Caninum." Gastroenterology Clinics of North America 25(3):579–597.
Hotez, P., and Pritchard, D. (1995). "Hookworm Infection." Scientific American, June.
World Health Organization (1996). Report of the WHO Informal Consultation on Hookworm Infection and Anemia in Girls and Women. Geneva: Author.