Hookworm infection is caused by the roundworms (nematodes) Ancylostoma duodenale, Necator americanus, and sometimes Ancylostoma ceylanicum.
People can become infected when walking barefoot on contaminated soil because hookworm larvae live in soil and can penetrate the skin.
At first, people may have an itchy rash where the larvae penetrate the skin, then fever, coughing, and wheezing or abdominal pain, loss of appetite, and diarrhea.
Severe, chronic infections can cause loss of blood and anemia that is sometimes severe enough to cause fatigue and, in children, heart failure and widespread swelling.
Doctors diagnose the infection by identifying hookworm eggs in a stool sample.
The infection is treated with medications used to treat worm infections.
Helminths are parasitic worms that can infect humans and animals. There are 3 types of helminths: flukes (trematodes), tapeworms (cestodes), and roundworms (nematodes). Hookworms are roundworms.
Worldwide, approximately 406 to 480 million people are infected with hookworms. The infection is most common in tropical areas where sanitation is inadequate. Hookworms thrive in warm, moist places.
Two species of hookworm cause most infections in people:
Ancylostoma duodenale
Necator americanus
Both species are present in moist, hot areas of Africa, Asia, and the Americas. Ancylostoma duodenale is present in the Middle East, North Africa, and southern Europe. Necator americanus is present mainly in the Americas and Australia. It once was common in the southern part of the United States and is still present in areas in that region where there is unsanitary disposal of human waste. These species are always present on islands of the Caribbean and in Central and South America.
Another species of hookworm called Ancylostoma ceylanicum infects animals such as dogs, cats, and hamsters. It is present in parts of Asia and some South Pacific islands. Ancylostoma ceylanicum can complete its life cycle in humans and on occasion causes hookworm infection in people.
When people are infected with a large number of one of these 3 species or are infected for a long time, they may develop anemia. Anemia is a condition in which the number of red blood cells or the level of hemoglobin is low.
(See also Overview of Parasitic Infections.)
Other hookworm infections
Other hookworm species usually cause infections only in cats, dogs, or other animals. However, people are occasionally infected. In people, these hookworms cannot mature and reproduce and do not cause blood loss that leads to anemia. However, after larvae of some Ancylostoma species penetrate the skin, they wander in the skin, causing an itchy rash called cutaneous larva migrans.
Rarely, larvae of an animal hookworm called Ancylostoma caninum penetrate a person's skin and travel to the intestine. They may not cause any symptoms or they may cause abdominal pain and a condition called eosinophilia. Eosinophilia is a higher than normal number of eosinophils in the blood. Eosinophils are a type of disease-fighting white blood cell that play an important role in the body's response to allergic reactions, asthma, and infection with parasitic worms. When eosinophilia occurs in the intestine, the condition is known as eosinophilic enteritis. Although Ancylostoma caninum larvae may cause some symptoms in people, they do not mature and reproduce and do not cause blood loss and anemia.
Transmission of Hookworm Infection
Hookworm eggs are passed in stool. They eggs hatch after 1 to 2 days if they are deposited in a warm, moist place on loose soil. Larvae emerge and live in the soil. The larvae can survive 3 to 4 weeks in the environment if conditions are favorable. After 5 to 10 days of development, larvae are able to cause infection and can penetrate the skin.
A person can become infected by walking barefoot on or otherwise coming into direct contact with contaminated soil.
Once larvae enter the body, they move through the bloodstream to the lungs. The larvae pass into the air spaces of the lungs and move up the respiratory tract. They are coughed up into the throat and swallowed and eventually reach the small intestine. Once inside the small intestine, the larvae develop into adults. They attach themselves by their mouth to the lining of the upper small intestine, where they produce eggs, feed on blood, and produce substances that keep blood from clotting. As a result, the person loses blood and may develop anemia.
Adult worms may live 2 or more years.
Image from the Centers for Disease Control and Prevention, Global Health, Division of Parasitic Diseases and Malaria.
Symptoms of Hookworm Infection
Many people with hookworm infection do not have symptoms. However at the start of a hookworm infection, an itchy, red, raised rash (ground itch) may develop where the larvae penetrate the skin. The movement of the larvae through the lungs can cause fever, coughing, eosinophilia, and wheezing.
When adult worms first attach in the intestine, they can cause pain in the upper abdomen, loss of appetite, diarrhea, and weight loss.
Over time, severe infections cause anemia as blood is lost, and people become deficient in iron, which is needed to produce red blood cells. Iron deficiency anemia causes fatigue, weakness, shortness of breath, a rapid heartbeat, and paleness.
In children, continuing blood loss can lead to severe anemia, heart failure, and widespread tissue swelling. In pregnant women with severe anemia, the fetus may not grow normally.
Diagnosis of Hookworm Infection
Examination of a stool sample
Blood tests
Hookworm infection is diagnosed by identifying hookworm eggs in a sample of stool. Stool should be examined within several hours after defecation.
For people who have recently traveled to an area where hookworm infection is common, a blood test may be done to check the number of eosinophils (a type of white blood cell). This blood test can be an early way to detect possible hookworm infection, because the number of eosinophils increases weeks before eggs are found in the stool.
Blood tests for anemia and iron deficiency are also done.
Cutaneous larva migrans is diagnosed based on the appearance and location of the rash.
Treatment of Hookworm Infection
Medications used to treat worm infections (anthelmintics)
For iron deficiency anemia, iron supplements
To treat intestinal hookworm infection, a doctor prescribes albendazole, mebendazole, or pyrantel pamoate. These medications are known as anthelmintics, and they are taken by mouth.
Because of possible negative effects on the fetus, only pyrantel pamoate is used in pregnant women.
Iron supplements are given to people with iron deficiency anemia.
Cutaneous larva migrans eventually goes away on its own. However, because symptoms can last 5 to 6 weeks, people are usually treated with albendazole or another anthelmintic called ivermectin. These medications eliminate the infection.
Prevention of Hookworm Infection
Hookworm infection prevention involves the following:
Using sanitary toilet facilities
Preventing the skin from directly contacting soil (for example, by wearing shoes and using a tarp or other barrier when sitting on the ground) and anywhere dogs or cats have defecated
Treating dogs for hookworms and treating cats for hookworms to prevent them from spreading animal hookworms to people
In areas where human hookworm infection is common, public health officials sometimes periodically treat people who are likely to be infected with hookworms.
