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.
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
Parasites feed, grow or multiply in a way that harms your body.
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:
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:
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:
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.
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.
Common food sources of parasites include:
Common causes of parasitic infections include:
If you have symptoms of a parasitic infection, a healthcare provider may ask you questions, including:
Your provider will also order tests to confirm their diagnosis. These tests may include:
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 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).
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.
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:
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.
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:
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.
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.
The following tips can help prevent parasitic infections:
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.
Call your healthcare provider if you have signs of a parasitic infection or still have symptoms after treatment.
Go to the emergency room if your symptoms get worse quickly.
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.
Last reviewed by a Cleveland Clinic medical professional on 04/14/2023.
Learn more about our editorial process.