hookworm disease

Hookworm Disease

Definition

Hookworm disease is an illness caused by one of two types of S-shaped worms that infect the intestine of humans (the worm's host).

Description

Two types of hookworm are responsible for hookworm disease in humans. Necator americanus and Ancylostoma duodenale have similar life cycles and similar methods of causing illness. The adult worm of both Necator americanus and Ancylostoma duodenale is about 10 mm long, pinkish-white in color, and curved into an S-shape or double hook.Both types of hookworm have similar life cycles. The females produce about 10,000-20,000 eggs per day. These eggs are passed out of the host's body in feces. The eggs enter the soil, where they incubate. After about 48 hours, the immature larval form hatches out of the eggs. These larvae take about six weeks to develop into the mature larval form that is capable of causing human infection. If exposed to human skin at this point (usually bare feet walking in the dirt or bare hands digging in the dirt), the larvae will bore through the skin and ride through the lymph circulation to the right side of the heart. The larvae are then pumped into the lungs. There they bore into the tiny air sacs (alveoli) of the lungs. Their presence within the lungs usually causes enough irritation to produce coughing. The larvae are coughed up into the throat and mouth, and are then swallowed and passed into the small intestine. It is within the intestine that they develop into the adult worm, producing illness in their human host.Ancylostoma duodenale is found primarily in the Mediterranean, the Middle East, and throughout Asia. Necator americanus is common in tropical areas including Asia, parts of the Americas, and throughout Africa. Research suggests that at least 25% of all people in the world have hookworm disease. In the United States, 700,000 people are believed to be infected with hookworms at any given time.

Causes and symptoms

Hookworms cause trouble for their human host when the worms attach their mouths to the lining of the small intestine and suck the person's blood.An itchy, slightly raised rash called "ground itch" may appear around the area where the larvae first bored through the skin. The skin in this area may become red and swollen. This lasts for several days and commonly occurs between the toes.When the larvae are in the lungs, the patient may have a fever, cough, and some wheezing. Some people, however, have none of these symptoms.Once established within the intestine, the adult worms can cause abdominal pain, decreased appetite, diarrhea, and weight loss. Most importantly, the worms suck between 0.03-0.2 ml of blood per day. When a worm moves from one area of the intestine to another, it detaches its mouth from the intestinal lining, leaving an irritated area that may continue to bleed for some time. This results in even further blood loss. A single adult worm can live for up to 14 years in a patient's intestine. Over time, the patient's blood loss may be very significant. Anemia is the most serious complication of hookworm disease, progressing over months or years. Children are particularly harmed by such anemia, and can suffer from heart problems, mental retardation, slowed growth, and delayed sexual development. In infants, hookworm disease can be deadly.

Diagnosis

Diagnosis of hookworm disease involves collecting a stool sample for examination under a microscope. Hookworm eggs have a characteristic appearance. Counting the eggs in a specific amount of feces allows the healthcare provider to estimate the severity of the infection.

Treatment

Minor infections are often left untreated, especially in areas where hookworm is very common. If treatment is required, the doctor will prescribe a three-day dose of medication. One to two weeks later, another stool sample will be taken to see if the infection is still present.

Key terms

Alveoli — The small air sacs clustered at the ends of the bronchioles, in the lungs in which oxygen-carbon dioxide exchange takes place.Anemia — Any condition where the oxygen-carrying capacity of the red blood cells is reduced; symptoms often include fatigue.Host — The organism (like a human) in which another infecting organism (like a worm) is living.Larva — An immature form of an organism, occurring early in that organism's development.Anemia is treated with iron supplements. In severe cases, blood transfusion may be necessary. Two medications, pyrantel pamoate and mebendazole, are frequently used with good results.

Prognosis

The prognosis for patients with hookworm disease is generally good. However, reinfection rates are extremely high in countries with poor sanitation.

Prevention

Prevention of hookworm disease involves improving sanitation and avoiding contact with soil in areas with high rates of hookworm infection. Children should be required to wear shoes when playing outside in such areas, and people who are gardening should wear gloves.

Resources

Organizations

Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. (800) 311-3435, (404) 639-3311. http://www.cdc.gov.

hookworm

[hook´werm] a parasitic roundworm, found mostly in the southeastern United States, that enters the human body through the skin and migrates to the intestines, where it attaches itself to the intestinal wall and sucks blood for nourishment. The hookworm most common in the United States and Central America is Necator americanus, which literally means “American killer.” It is about 1 cm (half an inch) long, with sharp hooklike teeth and a muscular gullet used in sucking blood. The female, slightly larger than the male, can lay more than 10,000 eggs a day, any one of which can hatch into a larva and invade the human body. Another common hookworm is Ancylostoma duodenale.

Life cycle of a hookworm. From Mahon and Manuselis, 2000.hookworm disease necatoriasis, ancylostomiasis, or infection with some other type of hookworm. Once fairly common, it is now largely confined to rural or poor areas where modern sanitation is lacking.
Larval hookworms enter the body by burrowing through the skin, usually that of the sole of the foot. The first sign of the disease may appear on the skin as small eruptions that develop into pus-filled blisters; this condition is sometimes called “ground itch.” The hookworms then enter blood vessels and are carried by the blood into the lungs. After they leave the lungs, they propel themselves up the trachea, are swallowed and washed through the stomach, and end up in the intestines. Here, if left alone, they will establish a parasitic relationship, using their host's body as a source of nourishment.
By the time they reach the intestines, about 6 weeks after they entered the body as larvae, the worms are full-grown adults. Each worm now attaches itself by hooked teeth to the intestinal wall, where it sucks its host's blood by contraction and expansion of its gullet. If large numbers of worms are present, they can cause considerable loss of blood and severe anemia. The symptoms include pallor and loss of energy; the appetite may increase. The thousands of eggs laid every day by each female worm pass out of the body in the stool, in which they can easily be seen. If the stool is not properly disposed of, the larvae that hatch from the eggs may infect other persons.Treatment and Prevention. A nutritious, high-protein diet supplemented by iron is given to relieve anemia and improve health. Drug treatment is with pyrantel pamoate or mebendazole. When left untreated, hookworms can cause not only anemia but also bronchial inflammation and occasionally stunting of growth, mental retardation, and even death. Hookworm infection can be prevented by installation of sanitary toilets or, if that is not possible, by disposal of human feces in deep holes so that the soil with which the human foot comes in contact is not contaminated. Shoes should be worn outdoors to protect the feet from infection.

an·cy·lo·sto·mi·a·sis

(an'si-lō-stō-mī'ă-sis, an'ki-), Hookworm disease caused by Ancylostoma duodenale and characterized by eosinophilia, anemia, emaciation, dyspepsia, and, in children with severe chronic infections, swelling of the abdomen with mental and physical maldevelopment. Synonym(s): ankylostomiasis, intertropical hyphemia, tropic hyphemia, miner's disease, tunnel disease, uncinariasis