Intestinal worms, or parasitic worms, are simple organisms that feed off the human body. Many people recognize the more common varieties, such as tapeworms and hookworms, but they may be less aware of the other kinds.

Types of intestinal worms include tapeworm, hookworm, liver fluke, threadworm, Ascaris, which causes ascariasis, and Trichinella, which causes trichinosis.

Other common parasites are Giardia lamblia, which causes beaver fever, and Entamoeba histolytica, which causes amoebic dysentery. These are not worms, but they are intestinal parasites.

Intestinal worms can cause many symptoms, and some of these resemble the symptoms of other gut conditions. A prompt, accurate diagnosis can lead to early treatment and prevent complications. Most cases respond well to treatment, which usually involves medication.

This article looks at different types of intestinal worms, the symptoms they cause, who is at risk, and the treatment available.

Symptoms will vary between individuals and will depend on the type of worm present.

However, common signs and symptoms include:

Some types of worm, including some tapeworms, can affect the central nervous system (CNS), with potentially severe consequences.

Worms can enter the body in various ways, depending on the type. Sanitation problems often play a role, but intestinal worms can happen anywhere.

Common types in the United States are the pinworm Enterobius vermicularis and the hookworms Necator americanus (N. americanus) and Ancylostoma duodenale (A. duodenale).

Factors that increase the risk of infection due to a worm include:

  • having a weakened immune system, for example, due to older age or HIV
  • living in a hot or tropical climate
  • having a low income
  • having no access to potable water
  • being unable to read, which can affect health and safety awareness

Pinworms, the most common type of worms in the U.S., are more common in places where people live or spend time closely together, such as child care settings and residential care homes.

Pregnancy does not increase the risk of getting intestinal worms, but some antiparasitic medications may not be safe during this time. This may increase the risk of complications. A doctor can advise on a suitable approach if a person has worms during pregnancy.

Various types of intestinal worms can affect people. Below, we look at some of them.

Tapeworm

A tapeworm is a type of flatworm that lives in the intestine, where it attaches itself to the intestinal wall.

There are several types, including the following:

  • Taenia solium (T. solium) comes from raw or undercooked pork. It is more common in Latin America, Eastern Europe, sub-Saharan Africa, India, and Asia, but it also occurs in the U.S.
  • T. asiatica comes from beef or pig liver and mostly occurs in Korea, China, Taiwan, Indonesia, and Thailand.
  • T. saginata comes from beef or pig liver and occurs mainly in places where people eat raw beef, such as Eastern Europe, Russia, eastern Africa, and Latin America.

According to the World Health Organization (WHO), only T. solium has a significant impact on health.

Without treatment, T. solium larvae can cause cysts in the skin, eyes, muscles, and CNS. In the brain, they can lead to:

Experts believe that in areas where it occurs, it is responsible for up to 70% of epilepsy cases.

Tapeworm eggs can also be present in water and may enter the body if a person consumes contaminated water.

The Centers for Disease Control and Prevention (CDC) estimate that fewer than 1,000 new cases of tapeworms occur each year in the U.S.

Praziquantel (Biltricide) can remove a tapeworm. This drug paralyzes the worm, forcing it to detach from the intestinal wall. It then helps dissolve the worm so it can pass through the digestive system and leave the body during a bowel movement.

Hookworm

Hookworms live in the small intestine. Their name refers to how one end of the body tapers off into a needle or hook shape.

Two typesN. americanus and A. duodenale — only occur in humans.

Hookworms enter the body through the skin — for instance, if a person walks barefoot on contaminated soil. Once inside, they lay eggs in the small intestine. A person can pass them on through defecating outdoors, for example, in bushes or by using feces as fertilizer.

One kind can also enter the body if a person consumes the larvae, for instance, on food or the hands.

According to the CDC, hookworm affects around 576–740 million people worldwide. In the past, hookworm was common in the southeastern U.S., but numbers have fallen due to improvements in living conditions.

Most people with hookworm have no symptoms. Some individuals may have gastrointestinal symptoms, especially with a first-time infection. More serious complications include protein loss and anemia due to blood loss.

Doctors may prescribe medications such as albendazole and mebendazole to treat hookworm, usually for 1–3 days.

Fluke

Flukes are a type of flatworm. They can affect the lungs, intestines, liver, and other parts of the body. Liver flukes affect the liver, gallbladder, and bile duct.

Two types, Clonorchis and Opisthorchis, can enter the body when a person eats contaminated raw or undercooked:

  • fish
  • crabs
  • crawfish

Most people will not have symptoms, but an infection that lasts a long time can lead to severe symptoms and complications. Without treatment, infection can last for up to 25–30 years, which is the life span of these parasites.

If a person with Opisthorchis has symptoms, they may experience:

Another type, Fasciola, can occur anywhere there are sheep or cattle. The larvae can enter the body if a person eats contaminated watercress or other water plants.

Pinworm

A pinworm is a small, thin roundworm around the length of a staple.

Pinworms are relatively harmless and can live in the colon and rectum of humans. A person can pass the worms on to someone else through direct contact or by sharing a contaminated object with them, such as food, clothing, or bedding.

Pinworms commonly cause itching around the anus, which can affect sleep. When a person is asleep, female pinworms leave the anus to lay their eggs on the surrounding skin.

Many people with pinworm experience no symptoms or mild symptoms.

Prescription and over-the-counter (OTC) medications can remove pinworm. However, people should always seek medical advice before starting treatment. A person will need two doses, and one will be 2 weeks after the other. The whole household will need treatment.

Regular hand-washing and daily bathing can help prevent the spread.

Ascaris

Ascaris is one of the most common parasites, affecting up to 1.2 billion people globally. It causes the disease ascariasis.

Ascaris is similar to a hookworm but only a few inches (in) long. It lives in contaminated soil. It can enter the body when people ingest the eggs on fruits or vegetables that have not been carefully washed, peeled, or cooked.

Inside the body, it lives in the intestine. A person with Ascaris can pass on the eggs in feces.

Individuals with an ascariasis infection may have:

It can also affect growth in children.

Antihelminthic drugs, which aim to remove worms from the body, can treat ascariasis. A doctor may prescribe albendazole or mebendazole for 1–3 days.

Trichinella

Trichinella are a type of roundworm. A person can ingest them by eating undercooked or raw meats from animals that eat meat, such as pigs or wild boar. Contaminated meat contains live larvae. The larvae then grow in the intestines.

On reaching their full size, the Trichinella worms may leave the intestines and live in other tissues, such as the muscles.

Abdominal symptoms can appear 1–2 days after eating contaminated meat, and other symptoms can appear 2–8 weeks later.

Symptoms include:

Severe cases can be fatal.

Trichinella infection is rare in the U.S., but it can affect those who eat wild or game meat, including cured meats.

Prescription drugs can treat Trichinella infection. A person should seek medical help as soon as possible if they notice symptoms.

A person should seek medical advice if they:

  • have abdominal symptoms, such as diarrhea, lasting more than 2 weeks
  • lose weight unexpectedly
  • have itching around the anus
  • find a worm or piece of a worm on toilet paper or stool

A doctor may ask about:

  • signs and symptoms
  • dietary factors, such as whether a person may have recently eaten undercooked meat
  • recent travel

Various tests can help diagnose intestinal worms, such as:

  • stool tests
  • blood tests
  • a colonoscopy if stool tests do not show the cause of symptoms
  • imaging tests to check other organs for signs of damage
  • a tape test

A tape test involves touching the skin around the anus with a piece of transparent tape. A person should do this for 3 days on waking up. Signs of eggs, if present, will be visible on the tape.

Anyone who suspects that they have an intestinal worm should seek guidance from a healthcare professional.

Treatment will depend on the type of worm.

A doctor may recommend OTC or prescription medication. People should follow the guidelines for treatment to prevent the worm from coming back.

In some cases, a whole household may need treatment to ensure the worms are removed.

Intestinal worms can sometimes lead to complications. How these affect the body will depend on the worm, but possible complications include:

  • anemia and other nutritional deficiencies, due to difficulty absorbing nutrients
  • intestinal blockage
  • problems with lung and heart function
  • human cysticercosis, which can result in vision loss and seizures

In some cases, the complications stemming from untreated parasites can be life threatening.

People can take steps to reduce the risk of having worms.

Essential measures include:

  • washing the hands regularly, especially after using the bathroom and before handling food or eating
  • avoiding sharing clothing, bedding, and other personal items
  • avoiding defecating in fields and other open places, where possible

Many intestinal worms enter the body through the food that a person eats. Some safe food practices can help prevent infection:

  • Thoroughly cook pork, beef, and other red meats to an internal temperature of 145°F.
  • Always cook poultry, such as chicken and turkey, to an internal temperature of 165°F.
  • Ensure that cooked fish reaches an internal temperature of 145°F.
  • Never eat undercooked or raw meats.
  • Use separate cutting boards for meats and vegetables.
  • Thoroughly wash and peel all fruits and vegetables.
  • Use boiled or treated water for drinking and washing foods.
  • Freeze pork in pieces less than 6 in thick for 20 days at 5°F to kill worms.
  • Clean meat grinders thoroughly after use.
  • Note that freezing, salting, smoking, drying, and microwaving meat may not kill worms.
  • Avoid swimming in water that may be contaminated.
  • Always wear shoes when walking outdoors.

Below, we answer some questions people often ask about intestinal parasites, including worms.

What does poop look like when you have worms?

In some cases, a person may have diarrhea or constipation or notice a worm or part of a worm on feces. Often, however, there are no symptoms.

How do you treat intestinal parasites and get rid of worms?

A doctor will recommend medication after identifying which type of worm is present.

How do adults get worms?

Depending on the type of worm, people of any age can get worms from eating raw or undercooked meat or seafood, swimming in or drinking contaminated water, and walking barefoot in places where worms are present.

Sharing objects such as clothing or bedding and not washing the hands regularly also pose a risk.

What do intestinal worms feed on?

Intestinal worms and other parasites feed on nutrients inside the intestine. This can reduce the amount of nutrients a person’s body absorbs.

Do we all have intestinal worms?

No, this is a myth.

In 2016, researchers suggested that over 3.5 billion people had intestinal parasites, including worms, and that 4.5 million people had health problems as a result.

How do you get rid of intestinal worms naturally?

Scientists have not found any natural treatment that removes intestinal worms.

A person should consult a doctor about suitable medication. A 2017 mouse study suggests that wormwood might help. However, more research is needed.

Do we all need a parasite cleanse?

Intestinal worms are common worldwide, but different types occur in different places.

A person may be at risk of having worms for a number of reasons, such as consuming raw or undercooked meat or seafood, sharing personal items with others, drinking or swimming in contaminated water, walking barefoot outdoors, and not washing their hands regularly.

Some worms cause few or no symptoms, but some can cause severe complications over time.

Anyone who believes they may have an intestinal worm should contact a doctor as soon as possible for a diagnosis and prompt treatment. Effective treatment usually involves the use of medication.