Sponges, Cnidarians, Flatworms, and Roundworms
Posted February 1, 1998
One billion people, about one-fifth of Earth's inhabitants, are estimated to be infected with hookworms. These worms are parasites that attach to the intestinal wall
and extract blood. One hookworm feeds on less than a teaspoonful of blood each day. However, people often are infected by 20, 100, or even 1,000 worms, which could result in a loss of
almost a cup of blood each day. When this amount of blood is removed, the result may be iron deficiency, anemia, and protein malnutrition. In children, infection by hookworms can lead
to severely slowed growth and development. In infants, hookworms can be fatal. Because of the serious nature of this disease, scientists agree that a vaccine to prevent hookworm infection
is needed. This is especially true in developing countries where medication to kill worms may not be readily available.
The route to hookworm infection is complex. Each day adult female worms release thousands of fertilized eggs that pass out of the host's body with feces. The larvae
hatch if the soil is warm. When the worms grow to the infective stage, they move from the soil to plants where they come in contact with the skin on the legs or feet of a human host.
From the skin, the larvae move to the circulatory system and then the lungs where they are coughed up and swallowed. Maturation is completed in the intestine.
The best way to prevent hookworm infection is to improve sanitation. Improved sanitation has eradicated human hookworm disease from the southeastern U.S. In other
parts of the world, however, a vaccine is needed. Because the hookworm is able to evade the immune system of the human body, a vaccine would have to use proteins from the worm to cause
an immune response. These might be proteins that make up the body of the worm, proteins the worm produces, or proteins such as the anticoagulants that are secreted by the worm to prevent
the clotting of the blood it feeds upon.
References
Hotez, Peter J. and David Pritchard. "Hookworm Infection," Scientific American, June 1995, pp. 67-74.
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