Worldwide, hookworms are a significant cause of anemia, with children and pregnant women being particularly vulnerable. According to the World Health Organization, approximately 740 million people are infected with hookworms. Most of these people live in impoverished rural areas in sub-Saharan Africa, Latin America, China and Southeast Asia. Until the early 1900s, hookworm infection was also relatively common in the southern United States, but this public health issue was largely mitigated by the advent of modern plumbing and more frequent use of shoes.
Life Cycle
According to Dr. Corry Kucik in his 2004 article for "American Family Physician," two species of hookworms, Necatur americanus and Ancylostoma duodenale, are found exclusively in humans. Eggs from these worms are deposited on soil in the feces of infected individuals. Within a day or two the eggs hatch to form larvae, which adhere to and tunnel through the exposed skin of passersby. The larvae then enter their host's bloodstream and travel through the blood vessels to the lungs where they penetrate the alveoli, or air sacs, ascend the airways to the throat, get swallowed and finally reach the intestine where they use hook-like teeth to attach to the intestinal lining. Once in the gut, the larvae feed on their host's blood, quickly mature to adulthood and, within six weeks, begin laying eggs to renew the cycle.
Effects
Given time and sufficient numbers, hookworms remove enough blood from their hosts to cause anemia, iron deficiency and protein malnutrition. According to WHO, children with chronic hookworm infestation exhibit impaired physical and mental development, poor school performance and decreased lifelong productivity. Hookworm infection in pregnant women increases the risks for low birth weight infants, poor maternal milk production and higher mortality in infants and mothers.
Solution
Hookworm infections are readily cleared with single courses of several available medications, such as mebendazole, albendazole or pyrantel pamoate. However, the likelihood of re-infection is high in many locations because of poor sanitation and unavailability of footwear. Frequent treatment with anti-parasitic drugs to deal with recurrent infections could lead to drug resistance, so WHO experts, in cooperation with the Sabin Vaccine Institute, are working to formulate a hookworm vaccine, with clinical testing set to begin in 2011.
Anemia
Since hookworms gradually deplete their host's body stores of iron, their continued presence in the gut induces an iron-deficiency anemia. The host's red blood cells become small and pale, and symptoms of anemia, such as fatigue, lightheadedness, poor exercise tolerance, difficulty concentrating, muscle cramps, shortness of breath and fast heart rate, usually ensue. When accompanied by other medical conditions, such as coronary heart disease, anemia can be fatal. According to WHO, individuals with severe anemia, or those with health risks such as pregnant women, may require blood transfusion. Transfusion and oral supplementation with iron can be started before the underlying hookworm infection is treated.
Iron Supplements
Ferrous sulfate is the most commonly used oral supplement for treating iron-deficiency anemia, although ferrous gluconate is also employed. Sustained-release preparations are less effective, as they limit the amount of iron that is available for absorption in the gut at a given time. Ferrous sulfate in a dose of 325 mg provides 65 mg of elemental iron, whereas 325 mg of ferrous gluconate provides 38 mg of elemental iron. According to Dr. Shersten Killip of the University of Kentucky, human bone marrow can respond to a maximum of 20 mg of elemental iron daily, but intestinal absorption of iron varies so widely that multiple daily doses of the chosen supplement are typically required to elicit improvement in anemia. Even after laboratory tests show resolution of the blood cell abnormalities in iron-deficiency anemia, it may take an additional four months to replenish iron stores. Supplementation should continue for several months after treatment for hookworm infection or, where re-infection seems likely, should continue indefinitely.
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