Causative Factors of Hookworm Infection


Agent Factors Agent Adult worms live in the small intestine, mainly the jejunum where they attach themselves to the villi. Males, measure about eight to 10 mm, and females about 10 to 13 mm in length. The eggs are passed on in the feces in their thousands, one female A duodenale produces about 30,000 eggs and one female N americanus about 9,000 of them per day. High egg production ensures constant infection.

When deposited on warm, moist soil, a larva rapidly develops in the egg and hatches after one or two days. The newly hatched larva (rhabditiform larva) moulds twice in the soil and becomes a skin–penetrating third stage infective larva within five to 10 days. These lie in wait in the soil to pierce the skin of the human host. They move very little horizontally, but migrate upwards on blades of grass. They can survive in shaded, moist soil for up to one month. Infection occurs when the larva enters the body through the skin, most commonly through the feet. Larvae of A duodenale are also infective by mouth. Once inside the body, they migrate via lymphatics and the blood stream to the lungs. They break into the alveoli, ascend the bronchi and trachea and are coughed up and swallowed to reach the small intestine, where they become sexually mature. Adult A duodenale and N americanus are believed to be capable of surviving for an average of about one and four years, respectively.

Reservoir Man is the only important reservoir of human hookworm infection.

Infective Material Feces containing the ova of hookworms. However, the immediate source of infection is the soil contaminated with infective larvae.

Period of Infectivity As long as the person harbors the parasite.

Host Factors Age and Sex All ages and both sexes are susceptible to infection in endemic areas. The highest incidence is found in the age group 15 to 25 years.

Nutrition Studies indicate that malnutrition is a predisposing factor. The chronic disabling disease does not occur in the otherwise healthy individual, who is well nourished and whose body gets enough iron.