Your Guide To Intestinal Parasites: Types, Signs, Treatment, And More

Few medical diagnoses strike fear in people like hearing you have a parasite, but it happens more often than most think. Parasites are responsible for a range of different illnesses in the world, including in the U.S., and they’re not just of the tapeworm variety. But, while having a parasite can be scary, there are proven ways to treat most forms. Here’s everything you need to know. 

While parasites like tapeworms get a lot of attention, there is actually a broad range of these organisms that can cause a variety of illnesses. “They’re all going to cause different symptoms,” says Amesh A. Adalja, M.D., senior scholar at the Johns Hopkins Center for Health Security. The word “parasite” is actually an umbrella term for many different organisms, but there are three main classes parasites that causes disease in humans can fall into:

Protozoa are one-celled organisms1 that can live on their own or be parasites. Just a single organism can multiple in your body and cause serious infection. Protozoa can live in your intestine, blood, tissue, or other areas of your body. More common protozoan infections include Giardia, Plasmodium, and Cryptosporidium.

Helminths (which get their name from the Greek word for worms) are usually the parasites that get the most attention. These are large, multicellular organisms1 that you can actually see in their adult stages. Once they reach adulthood, they can’t multiply in your body. Tapeworms, thorny-headed worms, and roundworms are all helminths.

Ectoparasites are organisms that feed off your blood1. They typically attach or burrow into the skin and stay there for weeks to months. Ticks, fleas, lice, and mites are ectoparasites. 

Once a parasite gets into your body, it can manifest in a number of different ways. Some, like cryptosporidium5, can settle into your small intestine and cause watery diarrhea6, while others, like malaria, enter your bloodstream7, causing fever, chills, body aches, and an enlarged liver. 

Intestinal parasites tend to get the most attention, and with good reason: They can cause some pretty intense symptoms:

By nature, intestinal parasites take root in your gastrointestinal (GI) tract. “That’s going to cause your immune system to react and you’re going to get different symptoms based on the organism,” Adalja says. Watery diarrhea, bloody diarrhea, bloating, gas, and constipation can all be symptoms of parasites, he says.

A parasitic infection can be hard on your body, and that can lead to feelings of fatigue and exhaustion, Bhanot. But certain intestinal parasites, like Giardia, can actually cause chronic fatigue syndrome—causing deficiencies and malabsorption of certain nutrients like iron and B12.

Unexplained rashes, hives, rosacea, or eczema can be a result of an intestinal parasitic infection, Romero says. The mechanism behind it is a little complex: Intestinal parasites can stimulate the production of immunoglobulin E (IgE), antibodies made by your immune system. That can then produce allergic reactions in your body, including skin problems, Romero says.

Some intestinal parasites can work your way into your muscles8, causing aches and pains, Romero says. “It can affect the muscle because it’s actually in there,” he explains. Trichinosis, which is caused by a type of roundworm, is one of them. You can get trichinosis by eating undercooked meat9.

Certain infections caused by hookworms and whipworms can cause blood loss, leading to iron-deficiency anemia3. The worms actually feed on your blood, causing the anemia, Adalja says. 

People always joke about how they must have an intestinal parasite if they feel hungry all the time, but this can be a real symptom of an infection. Tapeworms, for example, hatch in the stomach and feed on what you eat10, Romero says. 

The release of IgE in your body after contracting a parasite infection can cause itching, but specific parasites like pinworms can cause localized itching, Romero says. (With pinworms, you’ll likely feel itching around your anus, he says.)

Some intestinal parasites like the worm Ascaris can move through your body, Romero says. That includes relocating to your chest11, where it can cause a cough. 

An intestinal parasite can cause extra gas to build up12 in your GI tract, leading to bloating. The parasite giardia can cause this, along with a distended stomach. 

It’s entirely possible to have a parasite and have no symptoms, Bhanot says. People infected with the parasitic worm Ascaris, for example, usually have no symptoms11. 

If you suspect you have a parasite, it’s important to talk to your doctor. Your medical provider will need to test you to confirm that you do, in fact, have a parasite and to try to determine what it is. There are a few different ways to test for a parasite:

A stool test involves taking a sample of your stool and analyzing it for the presence of a parasite. Your doctor will probably give you specific instructions, but the Centers for Disease Control and Prevention13 (CDC) recommends collecting your stool in a dry, clean, leak-proof container and giving it to your doctor. (You will likely need to give at least three different stool samples, taken on different days.) Your doctor will then send the samples to a lab for testing.

An endoscopy13 is a procedure where a tube is inserted into your mouth to examine your intestine. A colonoscopy is similar, but the tube is inserted into your rectum. These tests look for the presence of a parasite in your GI tract.  

Some parasites can be detected through a blood test that looks for a specific infection. Note: There isn’t a universal test13 for all parasitic infections—your doctor will test for a specific one they may suspect that you have. Your doctor may order either a serology test to look for antibodies or parasite antigens in your blood, or a blood smear (which analyzes a drop of blood under a microscope).

Ultimately, every parasitic infection is slightly different, and each can cause a variety of symptoms. Whether you’re traveling or close to home, experts recommend being wary of uncooked or undercooked meats and washing your hands well14 with soap and water before handling food to lower your risk of contracting an infection. And, of course, if you suspect you may have a parasitic infection, call your doctor.