Soil-transmitted helminths refer to the intestinal worms infecting humans that are transmitted through contaminated soil (“helminth” means parasitic worm): Ascaris lumbricoides (sometimes called just “Ascaris“), whipworm (Trichuris trichiura), and hookworm (Anclostoma duodenale and Necator americanus). A large part of the world’s population is infected with one or more of these soil-transmitted helminths:

• approximately 807-1,121 million with Ascaris
• approximately 604-795 million with whipworm
• approximately 576-740 million with hookworm

Soil-transmitted helminth infection is found mainly in areas with warm and moist climates where sanitation and hygiene are poor, including in temperate zones during warmer months. These STHs are considered Neglected Tropical Diseases (NTDs) because they inflict tremendous disability and suffering yet can be controlled or eliminated.

Soil-transmitted helminths live in the intestine and their eggs are passed in the feces of infected persons. If an infected person defecates outside (near bushes, in a garden, or field) or if the feces of an infected person are used as fertilizer, eggs are deposited on soil. Ascaris and hookworm eggs become infective as they mature in soil. People are infected with Ascaris and whipworm when eggs are ingested. This can happen when hands or fingers that have contaminated dirt on them are put in the mouth or by consuming vegetables and fruits that have not been carefully cooked, washed or peeled. Hookworm eggs are not infective. They hatch in soil, releasing larvae (immature worms) that mature into a form that can penetrate the skin of humans. Hookworm infection is transmitted primarily by walking barefoot on contaminated soil. One kind of hookworm (Anclostoma duodenale) can also be transmitted through the ingestion of larvae.

People with light soil-transmitted helminth infections usually have no symptoms. Heavy infections can cause a range of health problems, including abdominal pain, diarrhea, blood and protein loss, rectal prolapse, and physical and cognitive growth retardation. Soil-transmitted helminth infections are treatable with medication prescribed by your health care provider.

Hookworm

An estimated 576-740 million people in the world are infected with hookworm. Hookworm was widespread in the southeastern United States until the early 20th century but is now nearly eliminated. Hookworm, Ascaris, and whipworm are known as soil-transmitted helminths (parasitic worms). Together, they account for a major burden of disease worldwide.

Ascaris

An estimated 807-1,221 million people in the world are infected with Ascaris lumbricoides (sometimes called just “Ascaris”). Ascaris, hookworm, and whipworm are known as soil-transmitted helminths (parasitic worms). Together, they account for a major burden of disease worldwide. Ascariasis is now uncommon in the United States.

Whipworm

An estimated 604-795 million people in the world are infected with whipworm. Whipworm, hookworm, and Ascaris are known as soil-transmitted helminths (parasitic worms). Together, they account for a major burden of disease worldwide.

The taxonomy of parasitic worms, all of which belong to the kingdom Animalia still contains many uncertainties. The pathogenic species are found in two phyla: the Nematoda, or roundworms, and the Platyhelminthes, or flat worms. The Nematoda is tentatively divided into two classes, one of which, Chromadorea, probably contains unrelated groups. The parasitic flatworms are contained within three classes of flatworm, of which two are important to humans, the trematodes and the cestodes.

Helminths, or parasitic worms, are multicellular eukaryotic parasites that depend heavily on virulence factors that allow them to gain entry to host tissues. For example, the aquatic larval form of Schistosoma mansoni, which causes schistosomiasis, penetrates intact skin with the aid of proteases that degrade skin proteins, including elastin.

To survive within the host long enough to perpetuate their often-complex life cycles, helminths need to evade the immune system. Some helminths are so large that the immune system is ineffective against them. Others, such as adult roundworms (which cause trichinosis, ascariasis, and other diseases), are protected by a tough outer cuticle.

Over the course of their life cycles, the surface characteristics of the parasites vary, which may help prevent an effective immune response. Some helminths express polysaccharides called glycans on their external surface; because these glycans resemble molecules produced by host cells, the immune system fails to recognize and attack the helminth as a foreign body. This “glycan gimmickry,” as it has been called, serves as a protective cloak that allows the helminth to escape detection by the immune system.

In addition to evading host defenses, helminths can actively suppress the immune system. S. mansoni, for example, degrades host antibodies with proteases. Helminths produce many other substances that suppress elements of both innate nonspecific and adaptive specific host defenses. They also release large amounts of material into the host that may locally overwhelm the immune system or cause it to respond inappropriately.

What is hookworm?

Hookworm is an intestinal parasite of humans. The larvae and adult worms live in the small intestine can cause intestinal disease. The two main species of hookworm infecting humans are Ancylostoma duodenale and Necator americanus.

How is hookworm spread?

Hookworm eggs are passed in the feces of an infected person. If an infected person defecates outside (near bushes, in a garden, or field) or if the feces from an infected person are used as fertilizer, eggs are deposited on soil. They can then mature and hatch, releasing larvae (immature worms). The larvae mature into a form that can penetrate the skin of humans. Hookworm infection is transmitted primarily by walking barefoot on contaminated soil. One kind of hookworm (Ancylostoma duodenale)can also be transmitted through the ingestion of larvae.

Who is at risk for infection?

People living in areas with warm and moist climates and where sanitation and hygiene are poor are at risk for hookworm infection if they walk barefoot or in other ways allow their skin to have direct contact with contaminated soil. Soil is contaminated by an infected person defecating outside or when human feces (“night soil”) are used as fertilizer. Children who play in contaminated soil may also be at risk.

What are the signs and symptoms of hookworm?

Itching and a localized rash are often the first signs of infection. These symptoms occur when the larvae penetrate the skin. A person with a light infection may have no symptoms. A person with a heavy infection may experience abdominal pain, diarrhea, loss of appetite, weight loss, fatigue and anemia. The physical and cognitive growth of children can be affected.

How is hookworm diagnosed?

Health care providers can diagnose hookworm by taking a stool sample and using a microscope to look for the presence of hookworm eggs.

How can I prevent infection?

Do not walk barefoot in areas where hookworm is common and where there may be fecal contamination of the soil. Avoid other skin-to-soil contact and avoid ingesting such soil. Fecal contamination occurs when people defecate outdoors or use human feces as fertilizer.

The infection of others can be prevented by not defecating outdoors or using human feces as fertilizer, and by effective sewage disposal systems.

What is the treatment for hookworm?

Hookworm infections are generally treated for 1-3 days with medication prescribed by your health care provider. The drugs are effective and appear to have few side effects. Iron supplements may be prescribed if you have anemia.

What is preventive treatment?

In developing countries, groups at higher risk for soil-transmitted helminth infections (hookworm, Ascaris, and whipworm) are often treated without a prior stool examination. Treating in this way is called preventive treatment (or “preventive chemotherapy”). The high-risk groups identified by the World Health Organization are preschool and school-age children, women of childbearing age (including pregnant women in the 2nd and 3rd trimesters and lactating women) and adults in occupations where there is a high risk of heavy infections. School-age children are often treated through school-health programs and preschool children and pregnant women at visits to health clinics.

What is mass drug administration (MDA)?

The soil-transmitted helminths (hookworm, Ascaris, and whipworm) and four other “neglected tropical diseases” (river blindness, lymphatic filariasis, schistosomiasis and trachoma) are sometimes treated through mass drug administrations. Since the drugs used are safe and inexpensive or donated, entire risk groups are offered preventive treatment. Mass drug administrations are conducted periodically (often annually), commonly with drug distributors who go door-to-door. Multiple neglected tropical diseases are often treated simultaneously using MDAs.

What is ascariasis?

Ascaris is an intestinal parasite of humans. It is the most common human worm infection. The larvae and adult worms live in the small intestine and can cause intestinal disease.

How is ascariasis spread?

Ascaris lives in the intestine and Ascaris eggs are passed in the feces of infected persons. If the infected person defecates outside (near bushes, in a garden, or field), or if the feces of an infected person are used as fertilizer, then eggs are deposited on the soil. They can then mature into a form that is infective. Ascariasis is caused by ingesting infective eggs. This can happen when hands or fingers that have contaminated dirt on them are put in the mouth or by consuming vegetables or fruits that have not been carefully cooked, washed or peeled.

Who is at risk for infection?

Infection occurs worldwide in warm and humid climates, where sanitation and hygiene are poor, including in temperate zones during warmer months. Persons in these areas are at risk if soil contaminated with human feces enters their mouths or if they eat vegetables or fruit that have not been carefully washed, peeled or cooked. Ascariasis is now uncommon in the United States.

What are the symptoms of ascariasis?

People infected with Ascaris often show no symptoms. If symptoms do occur they can be light and include abdominal discomfort. Heavy infections can cause intestinal blockage and impair growth in children. Other symptoms such as cough are due to migration of the worms through the body.

How is ascariasis diagnosed?

Health care providers can diagnose ascariasis by taking a stool sample and using a microscope to look for the presence of eggs. Some people notice infection when a worm is passed in their stool or is coughed up. If this happens, bring in the worm specimen to your health care provider for diagnosis.

How can I prevent infection?

• Avoid contact with soil that may be contaminated with human feces, including with human fecal matter (“night soil”) used to fertilize crops.
• Wash your hands with soap and warm water before handling food.
• Teach children the importance of washing hands to prevent infection.
• Wash, peel, or cook all raw vegetables and fruits before eating, particularly those that have been grown in soil that has been fertilized with manure.

Transmission of infection to others can be prevented by

• not defecating outdoors, and by
• effective sewage disposal systems.

What is the treatment for ascariasis?

Anthelminthic medications (drugs that rid the body of parasitic worms), such as albendazole and mebendazole, are the drugs of choice for treatment. Infections are generally treated for 1-3 days. The recommended medications are effective.

What is preventive treatment?

In developing countries, groups at higher risk for soil-transmitted helminth infections (hookworm, Ascaris, and whipworm) are often treated without a prior stool examination. Treating in this way is called preventive treatment (or “preventive chemotherapy”). The high-risk groups identified by the World Health Organization are preschool and school-age children, women of childbearing age (including pregnant women in the 2nd and 3rd trimesters and lactating women) and adults in occupations where there is a high risk of heavy infections. School-age children are often treated through school-health programs and preschool children and pregnant women at visits to health clinics.

What is mass drug administration (MDA)?

The soil-transmitted helminths (hookworm, Ascaris, and whipworm) and four other “neglected tropical diseases” (river blindness, lymphatic filariasis, schistosomiasis and trachoma) are sometimes treated through mass drug administrations. Since the drugs used are safe and inexpensive or donated, entire risk groups are offered preventive treatment. Mass drug administrations are conducted periodically (often annually), commonly with drug distributors who go door-to-door. Multiple neglected tropical diseases are often treated simultaneously using MDAs.

What is whipworm?

Whipworm (Trichuris trichiura) is an intestinal parasite of humans. The larvae and adult worms live in the intestine of humans and can cause intestinal disease. The name is derived from the worm’s distinctive whip-like shape.

How is whipworm spread?

Whipworms live in the intestine and whipworm eggs are passed in the feces of infected persons. If the infected person defecates outside (near bushes, in a garden, or field), or if the feces of an infected person are used as fertilizer, then eggs are deposited on the soil. They can then mature into a form that is infective. Roundworm infection is caused by ingesting eggs. This can happen when hands or fingers that have contaminated dirt on them are put in the mouth, or by consuming vegetables or fruits that have not been carefully cooked, washed or peeled.

Who is at risk for infection?

Infection occurs worldwide in warm and humid climates where sanitation and hygiene are poor, including in temperate climates during warmer months. Persons in these areas are at risk if soil contaminated with human feces enters their mouths or if they eat vegetables or fruits that have not been carefully washed, peeled or cooked.

What are the signs and symptoms of whipworm?

People with light infections usually have no signs or symptoms. People with heavy infections can experience frequent, painful passage of stool that contains a mixture of mucus, water, and blood. The diarrhea typically has an acrid smell. In severe cases growth retardation can occur. Rectal prolapse can also occur. In children, heavy infection may be associated with growth retardation and impaired cognitive development.

How is whipworm diagnosed?

Health care providers can diagnose whipworm by taking a stool sample. By using a microscope, providers can look for the presence of whipworm eggs.

How can I prevent infection?

• Avoid contact with soil that may be contaminated with human feces, including with human fecal matter (“night soil”) used to fertilize crops.
• Wash your hands with soap and warm water before handling food.
• Teach children the importance of washing hands to prevent infection.
• Wash, peel, or cook all raw vegetables and fruits before eating, particularly those that have been grown in soil that has been fertilized with manure.

Transmission of infection to others can be prevented by

• not defecating outdoors, and by
• effective sewage disposal systems.

What is the treatment for whipworm?

Whipworm infections are generally treated for 1-3 days with medication prescribed by your health care provider. The drugs are effective and appear to have few side effects.

What is preventive treatment?

In developing countries, groups at higher risk for soil-transmitted helminth infections (hookworm, Ascaris, and whipworm) are often treated without a prior stool examination. Treating in this way is called preventive treatment (or “preventive chemotherapy”). The high-risk groups identified by the World Health Organization are preschool and school-age children, women of childbearing age (including pregnant women in the 2nd and 3rd trimesters and lactating women) and adults in occupations where there is a high risk of heavy infections. School-age children are often treated through school-health programs and preschool children and pregnant women at visits to health clinics.

What is mass drug administration (MDA)?

The soil-transmitted helminths (hookworm, Ascaris, and whipworm) and four other “neglected tropical diseases” (river blindness, lymphatic filariasis, schistosomiasis and trachoma) are sometimes treated through mass drug administrations. Since the drugs used are safe and inexpensive or donated, entire risk groups are offered preventive treatment. Mass drug administrations are conducted periodically (often annually), commonly with drug distributors who go door-to-door. Multiple neglected tropical diseases are often treated simultaneously using MDAs.

Protecting Your Pets Protects Your Family

Worms that infect pets…

What are roundworms & hookworms?

You may already have heard that worms often infect puppies and kittens as well as older pets. The most common types of these parasitic worms are roundworms and hookworms. They live and grow inside the intestine of your pet. Roundworms* and hookworms develop from eggs into larvae (immature worms). The larvae later grow into adult worms.

Most pets show no signs of infection with these worms, but some may vomit, stop eating their food, or lose weight. Heavy infections in young puppies and kittens may lead to death.

* The word “roundworms” refers here to a group of worms known as ascarids. The word is sometimes used to include both ascarids and hookworms.

How do pets get worms?

Dogs and cats of any age may get roundworms and hookworms, but they are most vulnerable when they are very young. In fact, puppies of only 2–3 weeks of age can have many worms. That is because these worms are often passed from a mother to her puppies before the puppies are born. Sometimes they are passed shortly after the puppies are born, through a mother’s milk. Dogs and cats infected with these worms contaminate an area by passing worm eggs or larvae in their feces (poop). A dog or cat can be infected when they swallow dirt with dog or cat feces that has worm eggs or larvae.

…can infect people, too.

Can roundworms and hookworms infect people?

Yes. These worms, like other infections that humans can get from animals, are called zoonotic (zoe-o-NOT-ick) infections or zoonoses (zoe-o-NO-sees). By learning about these infections and how to prevent them, you can help protect your pets, yourself, and your family.

How do these worms infect people?

Dogs and cats with these worms pass worm eggs or larvae in their feces (poop). Because pets will pass feces anywhere, these eggs may contaminate a large area quickly. These worm eggs and larvae can survive for weeks and even years in areas such as parks, playgrounds, and yards.

• Roundworm infections usually happen when soil, sand, or plants that have been contaminated with infected animal feces are accidentally put in the mouth and ingested.
• Hookworm infections happen when larvae penetrate the skin. This usually happens when people sit or walk on contaminated soil or sand with bare feet.
• Children are more vulnerable to infection than adults because they play on the ground, may put dirty objects in their mouths, and may even eat dirt (eating non-nutritional items, like dirt, is sometimes referred to as “pica”).

How do roundworms harm people?

Roundworms enter the body when ingested as worm eggs that soon hatch into larvae. These larvae travel through the liver, lungs, and other organs. In most cases, these “wandering worms” cause no symptoms or obvious damage. However, in some cases they can cause damage to tissue. Sometimes they affect the nerves or even make their way to the eyes. In some cases, they may cause permanent nerve or eye damage, even blindness.

How do hookworms harm people?

Hookworm larvae typically move around within the skin causing inflammation and red, itchy tracks in the affected skin. This is called cutaneous (skin) larva migrans. One type of hookworm can make its way into deeper tissues and cause more serious damage to the intestines and other organs.

How can I protect my pets—and my family and myself—against worm infections?

• Have puppies and kittens dewormed by a veterinarian at an early age. Puppies and kittens may need to be dewormed more than once. Follow the veterinarian’s advice on how frequently puppies and kittens need to be tested and treated.
• Start or keep your pets on a drug program that prevents, treats, and controls these worms. A veterinarian can recommend treatments to eliminate and help prevent these worm infections. Since these products are available in many forms, you and the veterinarian can choose which one works best for your dog or cat. Ask for the product that is most effective against the worms that are most common in your area.
• Wash your and your children’s hands with soap and water after playing with pets or other animals, after outdoor activities, and before handling food or eating.
• Avoid touching soil, sand, plants, and other objects that might be contaminated by animal feces.
• Keep play areas, lawns, and gardens around your home free of animal feces.
  • Bag and throw away pet feces at least once a week.
  • Cover sandboxes when not in use.
• Obey leash laws.

Soil-transmitted helminths (STH) are intestinal worms (“helminth” means parasitic worm) infecting humans that are spread through contaminated soil. STH infection is found mainly in warm and moist climates where sanitation and hygiene are poor. STH are considered neglected tropical diseases (NTDs) because they inflict tremendous disability and suffering yet can be controlled or eliminated.

There are three types of STH that infect a large part of the world’s population: roundworm (Ascaris lumbricoides), whipworm (Trichuris trichiura), and hookworm (Ancylostoma duodenale and Necator americanus).

Key Facts

• Soil-transmitted helminths live in the intestine and their eggs are passed in the stool (poop) of infected people.
• Hookworm infections often occur in areas where human feces are used as fertilizer or where defecation onto soil happens.
• Hookworm infection is transmitted primarily by walking barefoot on contaminated soil.
• Ascariasis is the most common human worm infection, with 800 million to 1.2 billion people affected worldwide.
• Soil-transmitted helminths are more common in areas where people lack safe access to adequate sanitation.

Wormy Situation

A CDC laboratory technician holds a mass of Ascaris lumbricoides worms, which had been passed by a child in Kenya, Africa. Children seem to be infected more often than adults.

Eggs No One Should Eat

Ingesting whipworm (Trichuris trichiura) eggs leads to a whipworm infestation. These infections are more frequent among children, in areas with tropical weather, and poor sanitation practices.

Pigs Get Sick, Too

Ascaris lumbricoides is the primary parasite that infects humans, while Ascaris suum is the primary parasite that infects pigs. These two parasites are very closely related, and it’s often difficult to tell them apart. Ascaris suum can also make people sick (and pigs can become infected by Ascaris lumbricoides).

Prevention Tips

• Always wash hands with soap and water after working in the soil and before eating or handling food to help prevent infection from soil-transmitted helminths, especially in areas where sanitation and hygiene may be poor.
• Avoid ingesting soil that may be contaminated with human feces, including where human fecal matter (“night soil”) or wastewater is used to fertilize crops.
• Thoroughly wash and peel or cook fruits and vegetables grown in soil that has been fertilized with human fecal matter (“night soil”) or wastewater.
• The best way to avoid hookworm infection is not to walk barefoot in areas where hookworm is common and where there may be human fecal contamination of the soil. Also, avoid other skin contact with such soil and avoid ingesting it.