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, flukes, and roundworms.

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 and aren’t always visible to the naked eye.


You can get a tapeworm by drinking water contaminated with tapeworm eggs or larvae. Raw or undercooked meat is another way these flatworms 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 migrate to other parts of the body.

A tapeworm looks like a long, white ribbon. They can grow up to 50 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 become infected with flukes. Raw watercress and other fresh water plants are the main sources of flukes in humans. You can also get infected when you drink contaminated water.

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


Hookworms are transmitted through feces and infected soil. The most common way to make contact with this type of roundworm is to walk barefoot on soil infested with hookworm larvae, which 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 are tiny, fairly harmless worms, but they’re quite common in children. These roundworms 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 get infected 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.

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 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 that 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
  • bacterial infection
  • 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

Learn more: Trichinosis »

If you’re experiencing any unusual symptoms, especially if you’re returning from a trip to another country, you should consult your doctor. They will 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.
  • An endoscopy or colonoscopy can be useful when stool samples turn up no evidence of parasites. They may also help eliminate other causes for your symptoms.
  • A blood test can be used to detect parasites in the blood.
  • Imaging tests like MRI, CT scan, or X-rays can be used to detect 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 pinworm eggs. But even with the naked eye, you may be able to see evidence of pinworms around a child’s anus first thing in the morning.

The main treatment is prescription antiparasitic medication. This family of drugs can kill parasites and help pass them through your system. In most cases, you’ll have to take the medication for several weeks. You shouldn’t stop taking it, even if you feel better.

In very severe cases in which parasites have invaded other parts of the body, additional treatments like surgery may be necessary.

Ask your doctor if you should follow a special diet or take nutritional supplements during this time. And 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, a compromised immune system, or a coexisting health condition.

The following tips can often help prevent parasitic worm infection:

  • Never eat raw or undercooked meat 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 fresh water plants raw.
  • Don’t walk barefoot in places where soil may be contaminated by feces.
  • Clean up animal waste.

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You should also give your hands a good scrubbing with soap and water:

  • before eating
  • before food prep
  • after touching raw meat
  • after using the toilet
  • after changing a diaper or caring for someone who is 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 those 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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Keep reading: Ringworm in babies: Diagnosis, treatment, and prevention »

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