Parasites are organisms that depend on a host to survive and spread. There are three main types of parasites, and their symptoms vary. Treatment depends on the kind of parasite you have but may include prescription medications. Practicing good hygiene, thoroughly cooking meat and drinking clean water helps prevent many parasites.


What are parasites?

Parasites are organisms that live in, on or with another organism (host). They feed, grow or multiply in a way that harms their host. However, they need their host for their survival. For this reason, they rarely kill their host, but they often carry diseases that can be life-threatening.


Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

What do parasites do to your body?

Parasites feed, grow or multiply in a way that harms your body.

What are the three types of parasites?

The three main types of parasites that cause disease in people include:


An ectoparasite is a parasite that lives on the outside (exterior) of its host. They’re vectors (living things that carry diseases between animals and humans) that usually carry infections through blood. Many creatures that healthcare providers classify as vectors feed on your blood. They generally include:

  • Fleas. Fleas are small, wingless insects with strong back legs that they use to jump long distances. Infected fleas can spread disease when they bite their host or if a host accidentally swallows an infected flea.
  • Head lice and pubic lice (crabs). Lice are tiny, flat insects that travel by crawling. Head lice live on the hair on your head. Pubic lice live in your pubic hair, near your genitals. Both types of lice travel from person to person through close contact, which may include sexual intercourse or sharing personal items like sheets, pillows or towels.
  • Mites. Mites are small arachnids (eight-legged arthropods) that are relatives of spiders and ticks. They’re smaller than 1 millimeter (0.04 inches, about as tall as a stack of 10 sheets of paper). Certain types may cause scabies.
  • Ticks. Ticks are arachnids. Their bites usually don’t cause pain or itchiness. They typically bite you and then burrow into your skin. They’re common in wooded areas or grassy fields.

Helminths are parasitic worms that usually live in your gastrointestinal (GI) tract. Your GI tract is a series of hollow organs that connect to each other from your mouth to your anus, including your stomach, small intestine and large intestine. Helminths are visible to the naked eye in their adult stage — they range from greater than 1 millimeter to greater than 1 meter (a little longer than 39 inches, which is slightly smaller than the width of a doorway).

The main types of helminths that affect people include:

  • Flukes (Trematodes). Flukes are a type of flatworm. They can spread through contaminated water or aquatic animals, including snails, crabs and fish. There are many different types of flukes, and they may infect your blood, urinary bladder, liver, lungs, intestines and other organs.
  • Tapeworms (Cestodes). Adult tapeworms are long, flat worms that live in the intestines. They feed off the nutrients that their host gets from eating food. They spread by laying eggs in their host’s body. The eggs then leave the host’s body when the host poops. The eggs spread through infected food and water or undercooked meat.
  • Roundworms (Nematodes). Roundworms are small parasites that live in your intestines. They spread from infected poop or soil. There are many different types of roundworms.

Protozoans are one-celled organisms. You can’t see them without a microscope. They may live in your intestines or blood and tissues. They may spread through contaminated food or water, person-to-person contact or through the bite of a vector.

There are tens of thousands of different types of protozoans. Experts classify them according to how they move. The main types that affect people include:

  • Amoeba. Amoebas form temporary “false feet” (pseudopods) to move. The amoeba Entamoeba histolytica (E. histolytica) causes dysentery.
  • Ciliates. Ciliates use many short, hairlike structures (cilia) to move and gather food. Balantidium coli (B. coli) is the only ciliate that affects people. It causes dysentery.
  • Flagellates. Flagellates use one or many whip-like structures (flagella) to move and sense their surroundings. The flagellate Giardia intestinalis causes giardiasis, and Trypanosoma brucei causes sleeping sickness.
  • Sporozoans (apicomplexan). In their adult stage, sporozoans aren’t capable of moving. They eat the food their host is digesting or their host’s body fluids. The sporozoan Plasmodium causes malaria, and Cryptosporidium causes cryptosporidiosis.

How common are parasitic infections?

Parasites and parasitic infections are common. They affect millions of people throughout the entire world. Many people may not notice they have an infection because they have few symptoms. Others may have serious illnesses.

Symptoms and Causes

What are parasite symptoms in humans?

There are many different types of parasites, so their symptoms can vary. Common parasite symptoms may include:

You may have a parasite and no symptoms, or the symptoms may appear a long time after infection. You may also not have any symptoms and accidentally pass a parasite to another person who develops symptoms.

What foods cause parasites?

Common food sources of parasites include:

  • Raw or undercooked meat, including fish.
  • Raw or unwashed fruits and vegetables.
  • Raw aquatic plants, such as watercress.
  • Unpasteurized milk and juices.

How do people get parasites?

Common causes of parasitic infections include:

  • Spending time in areas with known parasites.
  • Contaminated water, foods, soil, blood or feces (poop).
  • Not washing your hands before eating or drinking.
  • Washing or bathing infrequently.
  • Having a weak immune system.
  • Contaminated bug bites.
  • Sexual contact.


Diagnosis and Tests

How do I know if I have parasites?

If you have symptoms of a parasitic infection, a healthcare provider may ask you questions, including:

  • When did your symptoms start?
  • Are your symptoms constant, or do they come and go?
  • Do any friends or family members you spend time with have similar symptoms?
  • Have you traveled recently?
  • Do you live near wooded areas or areas with tall grass?
  • Do you have pets that spend a lot of time outdoors?
  • Have you eaten any raw or rare animal meat?
  • Do you drink unpasteurized milk or juice?

Your provider will also order tests to confirm their diagnosis. These tests may include:

Physical examination

Your provider will examine your body. They’ll note any severe itching, bite marks or rashes. Depending on the type of parasite, they may also be able to see it on your hair, skin or clothing.

Fecal exam (stool culture)

Fecal exams help diagnose parasites that affect your intestines. Over the course of several days, you’ll collect three or more samples of poop for a provider to examine. The provider will send your samples to a lab, where technicians will look for parasites or eggs (ova).

Enteroscopy or colonoscopy

If a fecal exam can’t determine what kind of parasite you have, your provider may order an enteroscopy or colonoscopy. These exams use a long, thin, flexible tube with a small video camera at the end (endoscope) to look into your body. During an enteroscopy, the endoscope goes through your mouth and passes through to your small intestine. During a colonoscopy, the endoscope goes through your anus and passes through to your large intestine. A healthcare provider who specializes in conditions that affect your digestive system (gastroenterologist) performs these exams.

Blood tests

Your provider can diagnose some parasites through blood tests. Your provider will use a tiny needle (about the size of a standard earring post) to withdraw a small amount of blood. Your provider will then conduct one or both of the following tests:

  • Blood smear. Your provider will place a drop of your blood on a microscope slide and look at it under a microscope.
  • Serology. Your provider looks for antibodies or antigens in your blood sample that indicate the presence of specific parasites. Antibodies are proteins your body makes to fight infections. Antigens are foreign substances in your body that cause your immune system to react in order to get them out of your body.

Imaging tests

Some parasites may cause damage (lesions) to the structure of your intestines. Your provider may order X-rays, a magnetic resonance imaging (MRI) scan or a computed tomography (CT) scan to examine your organs for lesions.

Management and Treatment

How are parasites treated?

Your treatment depends on what type of parasite you have. Your healthcare provider may prescribe:

Carefully follow your provider’s instructions. If you don’t, your parasite may come back.

For treating ectoparasites such as lice, fleas and ticks, your provider may also recommend regularly:

  • Bathing with soap.
  • Washing your clothing, bedding and towels in hot water.
  • Vacuuming carpets, mattresses and furniture and emptying the vacuum bag into the trash outside.

Is there anything else I can do to get rid of parasites?

Along with prescribed medications, strengthening your immune system through diet and supplements may help your body get rid of parasites faster. Before trying any alternative therapies, check with a healthcare provider. They may affect other medications you take.

The following foods and supplements may help clear parasites from your digestive tract or prevent them from growing:

It’s also a good idea to drink plenty of water to help flush your system.

Do parasites go away on their own?

Some parasites go away on their own, especially if you have a healthy immune system and maintain a balanced diet. However, talk to a healthcare provider if you have signs of a parasitic infection. They can make an official diagnosis and help prevent the spread of the parasite to others.



Can parasitic infections be prevented?

The following tips can help prevent parasitic infections:

  • Regularly wash your hands with clean water and antibacterial soap. This includes before you eat, after handling raw meat and after handling poop, including dirty diapers or cleaning up after a pet.
  • Regularly bathe or shower. Wash with hot water and soap. Be sure to wash your hair, the backs of your arms and legs, between your toes, your genitals, your belly button and in and behind your ears.
  • Drink clean water. If you aren’t sure if the water is clean, drink bottled water. Don’t drink water from lakes, ponds or streams without bringing it to a rolling boil for at least one minute.
  • Cook meat to its recommended internal temperature. If you can’t, you should avoid it.
  • Regularly wash your personal items. Wash your clothing, bedding and other personal items in hot water with detergent. Dry them with a hot cycle in the dryer.
  • Protect yourself from insects. Wear long-sleeved shirts and pants when traveling through the woods or through grassy fields. Use DEET skin spray on your clothes and exposed skin.
  • Check yourself for insects after spending time outside. Check your hair, beltline and the backs of your legs, arms and back.
  • Regularly check your pets. Use a fine-toothed comb to remove insects. Ask your veterinarian what prevention products you should give your pets.
  • Practice safe sex. Wear condoms every time you have sex. Condoms help stop the spread of the parasite Trichomonas vaginalis, which causes trichomoniasis (trich).

Outlook / Prognosis

What can I expect if I have a parasite?

It depends on what type of parasite you have. With a proper diagnosis and treatment, most people make a full recovery. You may develop a serious infection with severe symptoms if you don’t get treatment.

Living With

When should I see my healthcare provider?

Call your healthcare provider if you have signs of a parasitic infection or still have symptoms after treatment.

When should I go to the ER?

Go to the emergency room if your symptoms get worse quickly.

What questions should I ask my healthcare provider?

  • What type of parasite do I have?
  • How did I get a parasite?
  • Do I have symptoms of a disease that the parasite spreads?
  • What treatment do you recommend?
  • What do I do if my symptoms don’t go away?
  • How do I prevent the spread of the parasite?

A note from Cleveland Clinic

Hearing that you have a parasite can give you the creeps. However, it doesn’t mean you’ve done anything wrong. Many parasites spread easily from person to person. If you have parasite symptoms, scheduling a visit with a healthcare provider for an official diagnosis and treatment is important. Be sure to follow their instructions to prevent others from getting the parasite and spreading it.

Medically Reviewed

Last reviewed on 04/14/2023.

Learn more about our editorial process.

Appointments 216.444.6503