Intestinal Parasites

Intestinal parasites include worms and one-celled organisms that rely on human hosts (their guts in particular) to hatch, grow and thrive. They spread when an unsuspecting host unknowingly ingests their microscopic eggs. Antiparasitic medicines and antibiotics can clear most infections.


What are intestinal parasites?

Intestinal parasites include worms and single-celled organisms that live in your intestines. A parasite is an organism that lives off another organism (host). Parasites use the host’s body for nourishment and shelter. They rely on the host as a vehicle to spread to the next potential host(s), where they can continue multiplying and spreading.

In return, intestinal parasites provide zero benefits. Instead, they can cause unpleasant symptoms and (in some cases) pose serious health risks.

What are the types of intestinal parasites?

Intestinal parasites include helminths (parasitic intestinal worms) and one-celled organisms called protozoa.

Helminths (parasitic intestinal worms)

Helminths include various roundworms (with round bodies) and flatworms (with flat bodies). Although they thrive and grow in your body, most helminths can’t reproduce there. Instead, they lay eggs that exit your body in your feces (poop). The species survive because other people (unknowingly) come into contact with the eggs and become new hosts.

Intestinal worms include:

  • Pinworms (enterobiasis): These thread-like worms spread when you touch a surface contaminated with pinworm eggs and put your hands to your mouth. The eggs hatch in your small intestine. At night, female adults lay eggs around your anus (butthole). The process can cause anal itching. Scratching the area and touching a surface without washing your hands transmits the eggs.
  • Ascaris (ascariasis): Through a microscope, these worms look like tiny earthworms. They spread if you ingest the eggs after coming into contact with contaminated soil. “Contaminated” means the soil contains poop with worm eggs in it. This can happen in places where people poop outside because of limited or no access to toilets. Ascaris also spreads in places where people use human feces as fertilizer to grow produce.
  • Whipworms (trichuriasis): Whipworms get their name from their whip-like shape. As with Ascaris, whipworms spread when a host ingests eggs from contaminated soil.
  • Hookworms (ancylostomiasis): Hookworms have hook-like heads they use to attach to your intestine walls and feed. Like Ascaris and whipworms, hookworms spread through contaminated soil. What’s different is that the eggs in the soil mature into larvae. If you walk on the soil barefoot, the hookworms can enter your body through your skin.
  • Strongyloides (strongyloidiasis): These worms also spread through contact with contaminated soil. You can ingest them by mouth, or they can enter your body if you’re walking around barefoot. Unlike other helminths, Strongyloides can reproduce inside a host.
  • Tapeworms (taeniasis): These segmented worms have bodies resembling ribbons. They live in the digestive tracts of human and animal (pigs, cows and fish) hosts. They spread when you ingest their eggs or larvae in undercooked pork, beef or fish. Or, you can get a tapeworm infection if you touch a surface contaminated with eggs and then touch your mouth.
  • Trichinella (trichinosis): Transmission of Trichinella is similar to that of tapeworms. This type of roundworm spreads to humans who eat the raw or undercooked meat of an infected animal (usually pigs).
  • Flukes: You can get a fluke infection from drinking contaminated water or eating infected aquatic plants or fish. The types that live in your intestines include Fasciolopsis buski, which causes an infection called fasciolopsiasis. Another type is Heterophyes, which causes heterophysiasis.

Like helminths, protozoa spread when you ingest trace amounts of poop that contain the eggs. They commonly spread through contaminated water or fruits and vegetables. But protozoa can also reproduce inside a human host.

Common types include:

What is the most common intestinal parasite?

According to the World Health Organization (WHO), approximately 25% of the world’s population has an infection related to an intestinal parasite. In tropical and subtropical areas with limited access to clean water and sanitation, that number is as high as 50%. The most common intestinal parasite infection globally is ascariasis. It affects about 1 billion people worldwide.

In the U.S., the most common infections are from protozoa, especially the giardia parasite. Pinworms are the most common intestinal worm in the U.S.


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Symptoms and Causes

Symptoms of intestinal parasites can include abdominal pain and anal itching
Depending on the infection, intestinal parasites can cause various unpleasant symptoms that affect your digestive system.

What are the symptoms of intestinal parasites?

Some infections don’t cause symptoms, so you won’t know you have a parasite. When there are symptoms, they vary depending on the type of infection.

Symptoms of intestinal parasites include:

Do intestinal parasites show up in poop or in the toilet?

Usually, it’s the eggs — not the intestinal worms — that show up in poop. They’re so small that you need a microscope to see them.

Tapeworms are the exception. Segments of the tapeworm sometimes break off into poop along with the eggs. What you see in the toilet may look like small grains of white rice embedded in poop.

What causes intestinal parasitic infections?

Transmission routes vary depending on the parasite. But most people get intestinal parasites by ingesting eggs that get passed along through poop. The eggs are microscopic, so there’s no way to know you’re swallowing them.

You can get intestinal parasitic infections from:

  • Consuming contaminated water: Water sources include public and private drinking water sources, pools, rivers and lakes.
  • Eating contaminated foods. This includes eating produce washed in contaminated water or grown in contaminated soil. You can get parasites from eating raw or undercooked meats with the parasite.
  • Touching your fingers to your mouth. Some parasite eggs can survive on surfaces for a long time. If you touch the surface and then touch your mouth, you can get infected. Depending on the parasite, these surfaces include bed linens, pet fur or even human skin.
  • Walking on contaminated soil barefoot. The larvae of some intestinal worms can enter through your skin if you walk barefoot on the soil they’re living in.

Risk factors

Your risk of getting (and spreading) a parasite depends on where you live and common practices.

You’re more likely to get an infection in places with:

  • Warm and humid climates, especially tropical and subtropical areas, including sub-Saharan Africa, Asia, Latin America and the Caribbean (Strongyloides is more common in rural areas in the Southeastern U.S. and Appalachia).
  • Limited access to clean water.
  • Inadequate public sanitation.
  • Many people living close together.
  • People living in close contact with livestock.

Practices that increase your risk include:

  • Pooping outside (because of inadequate public sanitation facilities).
  • Using human feces (poop) as fertilizer.
  • Walking outside barefoot in a high-risk area.
  • Engaging in unprotected oral-anal or penis-in-anus sex in a high-risk area.


What are the complications of intestinal parasites?

You may experience severe symptoms if you have a heavy parasitic load (lots of parasites). You’re at greater risk if you have a weakened immune system or if you’re pregnant. Depending on the parasite, untreated infections can lead to:

Diagnosis and Tests

How are intestinal parasites diagnosed?

Your healthcare provider will ask about your symptoms and perform a physical exam. They’ll perform stool tests to look for parasite eggs in your poop. Often, that’s the only test you’ll need.

Other diagnostic tests include:

  • The Scotch™ tape test: This test can help your provider see if you or your child has pinworms. You place sticky tape around your anus to pick up any eggs that may be there. Your provider will look at the tape beneath a microscope to check for eggs.
  • Blood tests: Blood tests can show if you have low red blood cells (anemia) or too many white blood cells (eosinophilia). This is a sign of some types of parasitic infections. Some tests detect antigens or antibodies. These tiny proteins can indicate the presence of a particular parasite.
  • Imaging: Your provider may order an X-ray, ultrasound, MRI (magnetic resonance imaging) or CT scan (computed tomography scan) to identify adult worms in your intestines.
  • Colonoscopy: This test can show any damage inside your intestines related to an intestinal infection.


Management and Treatment

What is the treatment for intestinal parasites?

Some infections clear on their own, but most people need prescription antiparasitic drugs to get rid of intestinal parasites. These drugs work by paralyzing parasites, stopping their growth, or killing the parasite or its eggs. The specific medicine you need depends on the parasite you have and how severe your symptoms are.

Common parasitic drugs include:

  • Pyrantel pamoate for pinworms.
  • Mebendazole or albendazole for soil-transmitted intestinal worms.
  • Metronidazole, tinidazole or trimethoprim/sulfamethoxazole (TMP-SMX) for protozoa infections.

Depending on the medicine, you may only need one dose to clear the infection. For others, you may need to take one or more doses daily for anywhere between three days up to three weeks. Some, like pinworm treatments, require you to take the medicine and wait a while before retaking it. Follow your provider’s instructions so you’re taking medicines exactly as prescribed.

You should notice symptom improvements once the medicine has wiped out the parasite and its eggs.


Can these infections be prevented?

Access to clean water and waste facilities is the best solution for preventing most intestinal parasite infections. But you can reduce your risk of intestinal parasites by:

  • Drinking clean water. Avoid drinking water in lakes, rivers and ponds. And if you’re unsure if a water source is safe, use bottled water instead.
  • Washing your hands regularly. Use clean water and antibacterial soap to keep your hands free of parasite eggs. Wash your hands after going to the bathroom, before handling food or eating, and after cleaning up after children (dirty diapers) or pets.
  • Eating carefully prepared produce in high-risk areas. Avoid eating raw produce if you’re in an area where intestinal parasites are common. Only eat fruits and vegetables washed in clean water, peeled and cooked.
  • Wearing shoes and gloves. Footwear that doesn’t leave your feet exposed can prevent whipworm infections. Wear gloves if you’re working in the dirt.
  • Cooking meats until they’re at a safe temperature. Cook whole cuts to 145 degrees Fahrenheit (62.8 degrees Celsius) and ground meat to 160 (about 71 degrees Celsius) degrees Fahrenheit.
  • Practice safe sex. Use a condom or dental dam when having sex to reduce the likelihood of transmission.

Outlook / Prognosis

What can I expect if I have intestinal parasites?

Medications kill most intestinal parasites quickly. Once the parasites are gone, symptoms usually go away, too.

It can be harder to clear infections if you have a weak immune system or if you’re pregnant. In these instances, your healthcare provider will monitor you closely to ensure the treatments are working to get rid of the parasite.

Living With

How do I take care of myself?

While you’re waiting for the infection to clear:

  • Stay hydrated: Drink clean water, sports drinks or broth to prevent dehydration.
  • Get adequate nutrition: Eat uncontaminated foods, so you’re getting enough daily nutrition. If you have an upset stomach, try eating small portions of food instead of large meals.
  • Prevent reinfection (if possible): Medicines can clear current infections, but they can’t prevent you from getting parasites in the future. Sometimes, prevention means showering and washing linens daily during treatment (pinworms). Sometimes, it means consistently wearing shoes and gloves when you’re working outside. Take steps to prevent getting another parasite.

When should I see my healthcare provider?

See your healthcare provider if you have symptoms of an intestinal parasite, especially if you live in or traveled to a high-risk region or suspect you ate undercooked food.

When should I go to the ER?

Go to the ER if you have signs or symptoms of dehydration, including:

A note from Cleveland Clinic

Most people get intestinal parasites when they consume parasite eggs (usually in poop). This scenario may seem impossible. After all, most of us like to think we’re in complete control of what goes in our mouths. But this thinking doesn’t apply when it comes to parasite eggs. They’re impossible to see with the naked eye. And if you’ve gotten eggs on your fingertips, you can spread them absent-mindedly — when you touch objects, food and, yes, even your mouth.

But awareness is important. Understanding how intestinal parasites spread can make you think twice before skipping handwashing or eating undercooked food. If you do get infected, don’t delay seeing a healthcare provider. Antiparasitic medicines can evict your unwelcome guests before they settle in and pose health risks.

Medically Reviewed

Last reviewed on 02/23/2024.

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