Hookworm infection

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at February 29, 2016
StartDiseasesHookworm infection

Hookworm infection is one of the most common parasitic infections in humans, and although many infected people don't experience symptoms, a hookworm infection can cause serious complications if left untreated.

Almost all hookworm infections are originally caused by the skin coming into contact with soil that is contaminated with human feces. Fortunately, hookworm infections are easy to treat, and are easily preventable with proper sanitary precautions.


Definition & Facts

Hookworm infections can be caused by a number of species of hookworm, most notably Ancylostoma duodenale and Necator americanus. The former is the most common species throughout India, the Middle East, and North Africa, while the latter is predominant in the Americas, China, Southeast Asia, and sub-Saharan Africa. Both species are grayish or pinkish-white, hook-shaped, and about one centimeter long and very thin.

Hookworm was once widespread in the United States, but hygiene measures have nearly eradicated it. The Rockefeller Sanitary Commission, formed in 1909, is credited with the rapid decrease in hookworm infections, improving education, medication, research, field work, and public health in eleven southern states. However, up to 740 million worldwide still suffer from hookworm, mostly poor people in less-developed countries.

Those in warm and moist climates are at much higher risk. It has been estimated that one-third of all pregnant women living in developing countries have a hookworm infection, which is a huge problem due to anemia and other complications that result.

Symptoms & Complaints

Many people who have a hookworm infection have no symptoms, especially if the infection is not severe. However, if left untreated, the infection can cause serious complications. The first sign of a possible hookworm infection is an itchy rash on the foot. This is caused by the hookworm larvae penetrating the skin.

Once the infection has progressed further, if other symptoms are present, they can include coughing, chest pain, fever, stomach pains, digestive problems, nausea and vomiting, loss of appetite, and fatigue.

Children tend to get hookworm infections more often than adults. Unfortunately, repeated infections can lead to mental disability and physical disability. When a pregnant woman has a hookworm infection, it makes her more likely to have an underdeveloped fetus, give birth prematurely, or have a child with a low birth weight. Hookworm in children also increases the risk of other dangerous infections.

The hookworm organism attaches itself to the gastrointestinal wall. This causes blood loss at the site of attachment, leading to complications. Continual blood loss can lead to anemia which occurs in about 10% of hookworm infection cases. Nutrient deficiencies can occur as well, including severe protein loss which causes fluid buildup in the abdomen. Additionally, the intestinal membrane can be damaged by the parasites.


The hookworm infection cycle begins when a person walks barefoot in soil that is contaminated with hookworm larvae. The larvae enter the body by penetrating the skin of the foot. They then migrate through the vascular system until they reach the lungs. Once inside the lungs, they migrate up to the trachea. They are then swallowed, and are able to enter the digestive system. They migrate to the small intestine, where they mature and reproduce. Female hookworms can lay up to 30,000 eggs per day, and these eggs exit the body via the person's feces.

In poor areas of the world with little sanitation or available toilets, the infected person is likely to defecate outside on the ground. The eggs are thereby reintroduced to the soil, perpetuating the cycle of hookworm infections. Other risk factors include using human feces as fertilizer for crops. Walking barefoot in gardens or fields that contain hookworm larvae is likely to cause infection.

Diagnosis & Tests

Hookworm infections are diagnosed by examining stool samples. This is only possible during the later stages of infection, when the worms have already began to release eggs. The eggs must be searched for with a microscope, as they are not visible to the naked eye. Because the egg develops as it makes its journey down the gastrointestinal tract, by the time the eggs are released in the stool they have separated into four to eight blastomeres, which are cells produced by cell division after the egg has been fertilized.

The eggs of different worm species are indistinguishable, so they must be cultured in a lab so that the larvae will hatch. Examination of the larvae will determine which species the eggs belong to. This is important because different species of worm require different treatment and have different complications. In addition to a stool sample, blood tests to determine any nutrient or vitamin deficiencies are also useful.

Treatment & Therapy

Treating a hookworm infection is relatively simple. In the case of anemia caused by a hookworm infection, dietary supplements are given to correct the problem. The parasite infection itself is treated with an antihelmintic drug, such as albendazole or mebendazole. These drugs are classified as benzimidazoles, which essentially work by binding to certain proteins, rendering the hookworm unable to maintain its cytoskeleton, thus killing the worm. Multiple courses of medication may be needed in order to be sure that the infection has been completely eradicated. Some anthelmintic drugs may pass into the breastmilk of a nursing mother, causing unwanted effects for the infant.

Prevention & Prophylaxis

The main preventative measure that individuals can take against hookworm infection is to avoid contact with human feces. In most developed countries, the risk of accidentally coming into contact with human feces is quite low.

In these places, wearing shoes whenever you go outdoors is enough to eliminate any chance of hookworm infection. However, in countries with lower standards of sanitation where there may be human feces in the soil, other measures can be taken.

For example, all vegetables should be thoroughly washed and cooked before eating. Governments can greatly reduce the rate of hookworm infection by implementing effective sewage disposal systems; in fact, this is the most effective and important preventative measure.