Parasites are organisms that live in and feed off a living host. There are a variety of parasitic worms that can take up residence in humans. Among them are flatworms, roundworms, and thorny-headed worms (spiny-headed worms).

The risk of parasitic worm infection is higher in rural or developing regions. The risk is also greater in places where food and drinking water may be contaminated and sanitation is poor.

Read on to learn more about parasitic worms, plus how to avoid becoming an unwitting host.

When it comes to parasitic infection, flatworms and roundworms are the likely culprits. These two types of parasitic worms can be found in a variety of habitats. They’re not always visible to the naked eye.

Tapeworms

You can get a tapeworm, which is a type of flatworm, by drinking water contaminated with tapeworm eggs or larvae. Raw or undercooked meat is another way tapeworms can find their way into people.

Tapeworms embed their heads into the intestinal wall and remain there. From there, certain types of tapeworms can produce eggs that mature into larvae that migrate to other parts of the body.

A tapeworm looks like a long, white ribbon. They can grow up to 80 feet long and live in a human for up to 30 years.

Flukes

Flukes are another type of flatworm. Animals are more likely than people are to develop an infection from flukes.

Raw watercress and other freshwater plants are the main sources of flukes in humans. You can also get them when you drink contaminated water.

They make their home in the intestines, blood, or tissues. There are many varieties of flukes, and none reach more than a few inches in length.

Hookworms

The hookworm is a type of roundworm transmitted through feces and contaminated soil. The most common way to make contact with this type of roundworm is to walk barefoot on soil that contains hookworm larvae. The larvae can pierce the skin.

Hookworms live in the small intestine, where they attach themselves to the intestinal wall with a “hook.” They’re usually less than half an inch long.

Pinworms (threadworms)

Pinworms, also called threadworms, are tiny, fairly harmless roundworms. When fully matured, they live in the colon and rectum. The female lays eggs around the anus, usually during the night.

The eggs can survive on bedding, clothing, and other materials. People contract a pinworm infection when they touch the eggs and end up putting them in their mouths. The eggs are so small you can even breathe them in if they become airborne.

Pinworm infections are more common in children. They transmit easily among children and caregivers or in institutions.

Pinworm infections are usually harmless and easily treatable. However, there have been a few cases of people having pinworms in the appendix.

According to a 2019 literature review, pinworms are an uncommon cause of acute appendicitis. A 2011 case report noted that pinworms in the tissues of a surgically removed appendix are an infrequent finding, with the researchers also stating that parasitic infections only rarely cause acute appendicitis.

This research suggests that the symptoms of an intestinal parasitic infection may mimic symptoms one would see in acute appendicitis, although appendicitis may or may not actually be occurring.

Trichinella

Trichinella roundworms are passed among animals. The most common way humans get trichinosis, the disease caused by this roundworm, is by eating undercooked meat that contains larvae.

The larvae mature in the intestines. As they reproduce, those larvae can travel outside the intestines into muscle and other tissue.

It may be hard to believe, but you don’t always know when you have an uninvited guest inside you. You may not have any symptoms, or they may be quite mild.

The symptoms you may notice include:

Tapeworms

In addition, tapeworms can cause:

Flukes

It may take weeks or months to notice additional symptoms of fluke infection. These may include fever and fatigue.

Pinworms (threadworms)

Pinworms can sometimes cause anal itching.

Hookworms

Additional symptoms of hookworms include:

Trichinella

As Trichinella worms travel through the bloodstream and enter other tissue or muscles, they can cause:

If you’re experiencing any unusual symptoms, especially if you’re returning from a trip to a different country, speak with a doctor. They’ll work with you to determine the cause of your symptoms.

Diagnostic tests will be necessary to identify the culprit.

  • Fecal test. A fecal test involves submitting a stool sample and having it checked for parasites, larvae, or eggs. This test is noninvasive and is usually the only test needed.
  • Blood test. A blood test can be used to detect some types of parasites in the blood.
  • Imaging tests. Imaging tests such as CT scans, MRIs, or X-rays can be used to detect organ injury caused by parasites.
  • Tape test. A tape test involves placing clear tape around the anus. The tape can be examined under a microscope for the presence of pinworms or their eggs. Sometimes you may be able to see evidence of pinworms around a child’s anus, even with the naked eye, within the first few hours of them falling asleep.
  • Colonoscopy. It’s rare that a colonoscopy is used to help diagnose a parasitic infection. However, it might be performed if you took medications and your symptoms persisted.

The main treatment is prescription antiparasitic medications. This family of drugs can kill parasites and help pass them through your system.

Examples include:

  • albendazole (Albenza)
  • ivermectin (Stromectol)
  • mebendazole (Enverm)
  • triclabendazole (Egaten)

The antiparasitic medication you’ll receive, dosage schedule, and duration of treatment will depend on the type of parasitic infection you have. Don’t stop taking the medication in the middle of the course, even if you feel better.

In very severe cases in which parasites affect other parts of the body, additional treatments such as surgery and other medications to address additional problems caused by the parasites may be necessary.

Ask the doctor if you should follow a special diet or take nutritional supplements during this time. Follow up with the doctor as advised.

Most people respond well to treatment and feel better within a few weeks. A full recovery can be expected in most cases.

It may take longer to recover if you have a severe case, compromised immune system, or coexisting health condition.

The following tips can often help prevent parasitic worm infection:

  • Avoid or limit your consumption of raw or undercooked meat, fish, or poultry.
  • Avoid cross contamination during food prep by keeping meat separate from other foods.
  • Disinfect all cutting boards, utensils, and countertops that touched raw meat.
  • Don’t eat watercress or other freshwater plants raw.
  • Don’t walk barefoot in places where soil may contain feces.
  • Clean up animal waste as soon as possible.

Also, be sure to give your hands a good scrubbing with soap and water at these times:

  • before eating
  • before food prep
  • after touching raw meat
  • after using the toilet
  • after changing a diaper or caring for someone who’s sick
  • after touching an animal or animal waste

When you’re traveling

It’s more difficult to prevent parasitic worm infection when you’re traveling, especially to regions where sanitation is inadequate. That’s when you should be extra vigilant.

When traveling, take these steps:

  • Be aware of how your food is prepared.
  • Drink only bottled water.
  • Carry hand sanitizer. Soap and water is best, but if you don’t have access to soap and running water, it can help prevent parasitic worm infection.

The best hand sanitizers

Read our reviews of the best hand sanitizers on the market, and discover which one is ideal for travel.