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What are parasitic worms?

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, thorny-headed worms, and roundworms.

The risk of parasitic infection is higher in rural or developing regions. The risk is great 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 likely culprits. These two types of parasitic worms can be found in a variety of habitats. They aren’t always visible to the naked eye.


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 are a type of flatworm. People are less likely than animals to contract 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 your intestines, blood, or tissues. There are many varieties of flukes. None reach more than a few inches in length.


Hookworms are transmitted through feces and contaminated soil. The most common way to make contact with this type of roundworm is to walk barefoot on soil infested with hookworm larvae. They can pierce through 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 are tiny, fairly harmless worms. They’re more common in children. These roundworms, when fully matured, 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 them 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. They’re easily passed among children and caregivers or in institutions.

Although pinworm infections are usually harmless and easily treatable, there have been less common cases of pinworms in the appendix that, when present, are usually in children and rarely in adults. One journal article found pinworms to be a rare cause of acute appendicitis.

Another journal article noted that pinworms in the tissues of a surgically removed appendix are an infrequent finding, and researchers also state that parasite infections only rarely cause acute appendicitis.

However, these articles note that the symptoms of an intestinal parasite infection may mimic symptoms one would see in acute appendicitis, although appendicitis may or may not actually be occurring.

Trichinosis worms

Trichinosis roundworms are passed among animals. The most common way humans get trichinosis is by eating undercooked meat that contains the larvae. The larvae mature in your 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 could have include:

  • nausea
  • lack of appetite
  • diarrhea
  • abdominal pain
  • weight loss
  • general weakness

In addition, tapeworms can cause:

  • lumps or bumps
  • allergic reaction
  • fever
  • neurological problems such as seizures

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

  • fever
  • fatigue

Additional symptoms of hookworms include:

  • itchy rash
  • anemia
  • fatigue

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

  • fever
  • swelling of the face
  • muscle pain and tenderness
  • headache
  • light sensitivity
  • conjunctivitis

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

Diagnostic tests will be necessary to identify the culprit:

  • A fecal test involves checking a stool sample for parasites, larvae, or eggs.
  • A colonoscopy can be useful when stool samples turn up no evidence of parasites as a cause of diarrhea. They may also help eliminate other causes for your symptoms.
  • A blood test can be used to detect some types of parasites in the blood.
  • Imaging tests like MRI, CT scan, or X-rays can be used to detect organ injury caused by parasites.
  • 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. But even with the naked eye, sometimes you may be able to see evidence of pinworms around a child’s anus within the first few hours of falling asleep.

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

The antiparasitic medication you’ll receive, doses schedule, and duration of treatment will depend on the type of parasite 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 have invaded other parts of the body, additional treatments like surgery and other medications to address additional problems caused by the parasites may be necessary.

Ask your doctor if you should follow a special diet or take nutritional supplements during this time. Follow up with your 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
  • a coexisting health condition

The following tips can often help prevent parasitic worm infection:

  • Never eat 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 be contaminated by feces.
  • Clean up animal waste.

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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

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

When traveling, be sure to:

  • 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.

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