If the hairs on the back of your neck stand up when you hear the word “parasite,” you’re not alone. The media tends to push stories about giant worms being discovered in patients with mysterious symptoms all over the world. And the idea of a worm living inside your gastrointestinal tract can be really freaky.
But the truth is that parasites are pretty common; and typically, they’re nothing to be afraid of (even if they can cause some nasty symptoms.) Here’s what you need to know about intestinal parasites and whether or not you have one.
According to the Centers for Disease Control , parasites are living organisms that live on or in a host organism and get their food at the expense of the host. Parasitic infections are more common in the tropics and subtropics (think: the land around the equator) and impact rural and low-income countries at a higher rate.
That said, you can contract a parasite anywhere; in fact, parasites commonly go unnoticed in the United States—which means they can cause serious illness and chronic digestive issues in many people. You may have heard of the most common pathogenic parasites, called Giardia (or Giardiasis), which according to the Mayo Clinic , is one of the most common causes of waterborne disease in the U.S. and is often found in municipal water supplies, swimming pools and hot tubs, and wells.
According to Dr. Darcy McConnell , a board-certified family medicine doctor and functional medicine practitioner at Parsley Health in New York City, the most common intestinal parasite she sees aside from Giardia is Blastocystis hominis. “That’s definitely the top one I see among patients,” she says. This single-celled organism can live in the GI tract as a result of ingesting contaminated food and water. The interesting thing about Blastocystis hominis is that it can be either harmful or helpful, depending on the individual. If it does cause symptoms, they will most likely be watery diarrhea and nausea, according to the Mayo Clinic .
“The second most common is Dientamoeba fragilis,” says Dr. McConnell, explaining that this type of parasite lives in the large intestines and doesn’t always cause symptoms, either. In fact, both Blastocystis hominis and Dientamoeba fragilis are considered non-pathogenic parasites, meaning they don’t always cause health problems.
“They may just flow through you and conventional doctors don’t typically treat them,” she says. But it’s different in functional medicine , says Dr. McConnell. “When we see persistent non-pathogenic parasitic growth in the colon, especially in someone with chronic illness or IBS, we don’t take that lightly,” she says.
If you’ve ever dealt with food poisoning or a sudden onset of digestive issues, it may have been caused by a parasite. For some people, their body is able to easily fight it off and they recover quickly, but for others, it can take time. The strength of your immune system , gut microbiome, and even your diet can all impact how your body responds to a parasitic infection.
According to McConnell, she often suspects a parasite if the patient has recurrent GI symptoms, like IBS, or another chronic disease that’s not responding to other therapies.
But even if the parasite is non-pathogenic, Dr. McConnell says it could be disrupting the gut microbiome. “The parasite might be shifting things in a not-so-great direction when you consider all the fora, parasites, bacteria, and fungus in the GI tract.” In other words, it might not be a Giardia infection, but it could still be doing some harm.
Left untreated, intestinal parasites can lead to other issues such as nutrient deficiencies and immune-mediated intestinal conditions like celiac disease, inflammatory bowel diseases, and irritable bowel syndrome.
“The gold standard is a 3-day stool test,” says Dr. McConnell, explaining that the test consists of three consecutive days of stool collection by the patient. The samples are then looked at under a microscope to check for a parasite, its eggs, or even evidence from the immune system that a parasite is present. If any of those are found, it’s a positive parasite test.
Why three days, you ask? “The parasite has a life cycle and can go into hiding depending on the day,” she says.
At Parsley Health, high-tech specialty testing is used to assess gastrointestinal health if a gut issue is suspected, which may lead to uncovering undiagnosed parasitic infections. This can help catch them early before they lead to long-term health consequences—and is something you wouldn’t find in a conventional primary care practice.
The first rule of treating parasites is to prevent them in the first place by washing your hands and avoiding any sources of contaminated food or water. According to Mayo Clinic, this means avoiding food from street vendors, avoiding soft-cooked eggs and raw or undercooked meat and fish, and steering clear of moist food at room temperature, such as sauces at a buffet. Sticking to fruits and veggies that you can peel yourself—such as avocados and oranges—can also help reduce your risk.
If you already have a parasite, you’ll need to do a parasite cleanse protocol. At Parsley Health, parasites are treated using a combination of pharmaceutical medications, supplements , a parasite cleanse diet, and lifestyle interventions. “If a parasite is pathogenic and symptomatic, we treat it with a medication,” says Dr. McConnell. This would take the form of a prescription antiparasitic medication, such as metronidazole or ivermectin.
Next up in the parasite cleanse is a mixture of antimicrobial herbs. “Berberine, oil of oregano, and mugwort all have properties against parasites,” says Dr. McConnell, who explains that the purpose of herbs is not to kill the parasite but to rebalance the gut microbiome. “It’s about creating a gut flora that’s an unpleasant place for the parasite to live. It will end up leaving on its own because it’s no longer welcome,” she continues. Knowing this, it will come as no surprise that probiotics are also on the list of intestinal parasite treatments.
“Sometimes they’re easy to get rid of and sometimes they’re not,” says Dr. McConnell. Luckily, dietary changes that help you maintain a healthy gut microbiome can make the difference between getting rid of your parasite for good, or not. “In people with a healthy lifestyle and without any chronic disease it’s definitely easier,” explains McConnell.
The same applies for preventing parasites in the first place. “Some people get parasites and some don’t; the reason for this is a combination of bad luck, your immune system health, and your gut microbiome status,” says Dr. McConnell. “Making healthy food choices supports the microflora and makes it less likely that a parasite you accidentally ingest would make a home there,” she continues.
If you want to start supporting a healthy gut, start by incorporating gut healing superfoods like coconut oil, kefir, aloe vera, and leafy greens while eliminating unhealthy foods like sugar, refined carbs, and processed foods. Practices like intermittent fasting and drinking warm water with lemon are other ways to support your long-term gut health .
According to Dr. McConnell, the most important thing to know about parasites it that they’re both more common than you think—and also not as scary as you think. Most parasites are invisible to the naked eye and “anything larger than that is extremely rare,” she says. There are trillions of microorganisms—including molds, fungi, viruses, and yes, parasites—living in on and around us. “We have to get comfortable with it,” says McConnell.In fact, some parasites might even have certain health benefits, says Dr. McConnell. “They stimulate innate immunity, which is important for protecting against autoimmune disease ” she says. Until we know more, the best thing we can do to prevent parasitic infections from turning into a problem is to maintain a healthy gut.
Gretchen Lidicker is a writer, researcher, and author of the book CBD Oil Everyday Secrets: A Lifestyle Guide To Hemp-Derived Health & Wellness. She has a masters degree in physiology and complementary and alternative medicine from Georgetown University and is the former health editor at mindbodygreen. She's been featured in the New York Times, Marie Claire, Forbes, SELF, The Times, Huffington Post, and Travel + Leisure.