Hookworm in Emergency Medicine
- Author: Anika Baxter Tam, MD; Chief Editor: Rick Kulkarni, MD more...
Background
Two species of hookworms commonly infect humans, Ancylostoma duodenale and Necator americanus. These species are found throughout the tropics and subtropics. The distribution of each species significantly overlaps that of the other.
Hookworms are estimated to infect more than 740 million people around the world, but most people who are infected are asymptomatic.[1] These worms are much smaller than the large roundworm, Ascaris lumbricoides, and the complications of tissue migration and mechanical obstruction so frequently observed with roundworm infestation are less frequent in hookworm infestation. The most significant risk of hookworm infection is anemia secondary to loss of iron (and protein) into the gut.
Pathophysiology
A duodenale and N americanus are small, off-white worms. Males are 8-11 mm in length, and females are 10-13 mm. The sexes cannot be distinguished by the naked eye. Hookworm larvae emerge from passed eggs within 24 hours and molt once to an infective filariform larval stage in another 24 hours. After molting, larvae are able to penetrate intact skin. This rapid external portion of the hookworm life cycle is different from that of the roundworm, Ascaris, whose eggs require 3 weeks in the soil before becoming infective.
Walking barefoot in soil contaminated with feces (the source of hookworm eggs and larvae) is the most common method of exposure. After skin penetration, the venous circulation carries larvae to the pulmonary bed, where they lodge in pulmonary capillaries. Within 3-5 days, the larvae break through into alveoli and travel up the ciliary escalator from the lungs into the bronchi, the trachea, and the pharynx. Upon reaching the pharynx, larvae are swallowed and gain access to the GI tract. Once in the GI tract, worms attach to the wall of the intestine and begin to feed on the blood of the host. A N americanus adult worm consumes approximately 0.3 mL of blood per day, while the A duodenale consumes approximately 0.5 mL of blood each day. Chronic loss of blood and serum proteins leads to hookworm anemia and impaired nutrition.
Eggs begin to appear in the stool approximately 6-8 weeks after initial infection with N americanus and as long as 38 weeks after initial infection with A duodenale. The lifespan of the worm is up to one year for A duodenale and up to 5 years for N americanus.
Epidemiology
Frequency
United States
Hookworm infection is rare in the United States.
International
The prevalence of infection is as high as 80% in lesser-developed countries with moist tropical climates but is only 10-20% in areas with drier climates.
Mortality/Morbidity
Hookworm infection is rarely fatal, but anemia can be significant in heavily infected individuals. Children and pregnant women with physiologically low iron reserves may suffer greater complications from hookworm anemia. Pulmonary complaints such as cough or wheezing are generally less common than in A lumbricoides infection.
Age
Children are infected more commonly and more heavily than adults. This is because children are more likely than adults to come in direct contact with fecally contaminated soil that contains infective larva.
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