The Truth about Human Parasites

What would you say if I told you that humans carry around parasites from other species? Well, according to the latest research, they do. And these parasites can cause serious health problems.

Parasites are tiny organisms that live inside or outside their human host. They feed off the host’s blood and tissue, causing damage to the body. Some parasites even affect brain function.

This article will cover everything about human parasites and how they can affect our overall gut health. It includes information on what a parasite is and how it affects our bodies. This article also covers how to get rid of parasites and prevention methods for parasitic infections. So let’s get started!

A Few Statistics on Parasites

The World Health Organization (WHO) classifies parasites as being among the six most dangerous diseases that infect humans. Parasites can even outrank cancer as the number one global killer. They are tied to many of the digestive issues that people suffer from.

The Center for Disease Control and Prevention (CDC) estimates that over 60 million people in the United States are likely to be infected with Toxoplasma gondii. It’s a parasite that’s associated with raw meat and contact with cat feces.

A Food Research Institute at the University of Wisconsin–Madison report on foodborne parasites estimates 2.5 million cases of food and waterborne Giardia lamblia and 3 million cases of Cryptosporidium parvum in the U.S. alone. Both of these protozoan parasites are found to be transmitted through drinking water that was contaminated with the fecal material of infected persons.

There are estimates that up to 50 million American children are affected by worm parasites, even though only a minimal number of cases are detected and reported. 

Why Are Parasites So Prevalent?

Your intestines provide the perfect breeding ground for parasites. Intestinal parasites enjoy making their homes inside impacted waste, as well as in the lining of colon walls.

Living inside our intestines, these microorganisms can take over by virtue of their sheer numbers – both in kind and in population. These parasites thrive because of how they’ve adapted their life cycles in unique ways to ensure their parasite species multiply within their hosts: us.

There are three major groups of parasites:

  • Protozoans (single-celled organisms)
  • Nematodes (roundworms)
  • Cestodes (tapeworms)

There are numerous parasite species that are common to North America that range from microscopic protozoans and Cyclospora cayetanensis, resulting from fecally-contaminated imported raspberries, – to macroscopic multicellular worms and nematodes, such as pinworm, hookworm, and whipworm.

Learn more about Tapeworm Symptoms and Prevention.

Symptoms of a Parasitic Infestation

There may not always be symptoms of a parasitic infection, but these are common signs to keep an eye out for to find potential evidence of parasites: 

  • Allergies to many different types of foods
  • Abdominal pain
  • Abdominal swelling
  • Anemia (low red blood count)
  • Bloating
  • Bloody stools
  • Diarrhea and inconsistent bowel habits
  • Flu-like symptoms such as coughing, wheezing, and a fever
  • Foul-smelling stools that get worse in the afternoon and evening
  • Fever
  • Gas and cramping
  • Itching around the anus, especially at night
  • Nausea
  • Vomiting
  • Weight loss with a ravenous appetite

Parasites Often Elude Diagnostic Testing

Parasites can range from several feet long to those that are invisible to the naked eye. While parasites often reside in the colon, it’s not the only place that parasites can be found. Almost any part of your body is vulnerable to infestation: the brain, blood, lungs, liver, esophagus, muscles, joints, skin, and even your eyes!

There are over 100 different types of parasites that can live inside human beings. 

To find parasites, there are many different laboratory methods that can be used, including parasite tests by the CDC. But unfortunately, there is not one uniform test that will cover all commonly known parasites. 

One type of test isn’t always conclusive and could require taking many different specimens.  Some parasites are identified on blood testing while others are found in a stool sample. 3 separate stool samples are recommended to increase the diagnostic yield of parasite testing. Testing can be time-consuming with repetitive tests needed.

4 Steps to Get Rid of Parasites

Dealing with parasites takes a multi-pronged approach. Here are the four steps to get rid of parasites and prevent them in the future: 

Step 1: Colon Cleansing

Step 2: Increase Your Fiber Intake

Step 3: Reverse Vitamin Deficiency

Step 4: Know the Sources of Parasites – Preventing Infection

Step 1: Colon Cleansing

Cleaning your colon means parasites will not have time or waste to hold onto. Flushing out impacted waste, passing stool more easily, and improving bowel transit times means parasites have nothing to feed on. 

Your body becomes an inhospitable host for parasites, meaning there’s less chance for a parasitic infection. 

Regular exercise, increased fluid intake and increased fiber will help keep waste moving through your colon. 

Step 2: Increase Fiber Intake

Making changes to your diet will help to keep your colon cleansed and clear of waste. That’s less opportunity for parasites to settle on impacted waste within your colon.

Increasing your dietary fiber intake helps keep your bowels regular, which keeps your colon clear of waste build-up.

You can increase your fiber intake by eating fiber-rich foods and a high-quality fiber supplement for low-fiber days. A dietary supplement containing psyllium is an easy way to increase fiber. A supplement can also produce less gas than some high-fiber foods.

Although some countries consume over 70 grams of fiber each day, the recommended daily allowance (RDA) for fiber in the United States is 25-30 grams. Increasing fiber creates softer, bulkier stool, which helps move stool through your digestive system more easily.

The result is a clean and toned colon that parasites would not want to move into and take over.

Step 3: Reverse Vitamin Deficiency

Parasites cause vitamin deficiencies in our body. Parasites feed off human blood to extract vital nutrients. They will also burrow into the intestinal walls, causing diarrhea or blood loss, which also makes it difficult for our bodies to absorb nutrients. 

Diphyllobothrium latum – commonly referred to as broad tapeworm or fish – will deplete your body of its vitamin B12. B12 is an essential vitamin for the proper functioning of your central nervous system, muscle coordination, and memory.

Unfortunately, many of us are already vitamin deficient due to the Standard American Diet of processed and junk foods. 

Vitamin supplements have become the foundation of good health. They will help reduce complications of parasitic infections by providing the vitamins our bodies need.

Step 4: Know How Parasites are Transmitted

To avoid a parasite infestation, it is important to understand parasites and how they operate, and then take the necessary precautions to avoid your body becoming a host to various parasites.

Learning how parasites are transmitted is important for parasitic disease prevention.  

Parasitic worms are transmitted from pets and other animals, such as beef and swine tapeworms. The Toxoplasma gondii parasite is found in cat feces, so cat litter boxes may pose a threat from toxoplasmosis.

Dogs carry Echinococcus, an intestinal tapeworm. Its eggs spread across a dog’s fur via its anus. Unhealthy human contact with infected dogs, such as kissing, can transport eggs into the human intestine, where they can eventually make their way to a host’s brain and liver.

Protozoa – such as Cryptosporidium and Giardia – are commonly transmitted through drinking water that is contaminated with fecal material from infected people.

They can be found in both running streams in nature and the tap water in many large cities served by surface water treatment plants. Outbreaks can potentially occur at public swimming pools and water parks. 

Schistosomes, such as the deadly Trematoda fluke, however, are only transmitted through skin contact with contaminated water.

One of the most common ways of contracting a parasitic infection is through eating food. Vegetables grown on farm soil that’s fertilized with infected human waste can easily transmit the eggs of various parasites. When swallowing contaminated food, parasites can be infectious. This can easily occur in homes and restaurants if the food is not properly washed. 

There are some parasites, like the roundworm nematode, that spend their immature egg stage in warm, moist soil, waiting to invade a new host. These parasites enter through the skin.

Walking bare foot or sitting on soil contanimated with feces can be an invitation to the eggs of hookworms or strongyloides. They can penetrate exposed skin and migrate through the body to the intestinal tract.

How to Prevent Parasite Infection

Here is a summary of the key ways to prevent infection of parasites.

  • Avoid known sources of parasites, such as contact with rodent feces, cat litter boxes, and inappropriate contact with dogs.
  • Use caution when drinking water that’s not clean and/or swimming in unfamiliar water sources.
  • Wash all fruits and vegetables thoroughly in clean water before eating to prevent roundworm and whipworm infection. You can add a few ounces of over-the-counter hydrogen peroxide and/or mild soap that’s safe for washing vegetables to increase the parasite-killing activity of water.
  • Wear slippers or shoes to prevent hookworm infection.
  • Do not use water that could be contaminated by septic tanks or other sources to wash your vegetables.
  • Contain all waste matter in the toilet; wash hands with soap and water after using the restroom and before meals.
  • Cornell Health:
  • Centers for Disease Control and Prevention:
  • National Library of Medicine:
  • National Library of Medicine:

Written and Medically Reviewed By

  • Sheila Jennings

    Sheila Jennings is a 4th-year medical student and also freelances as a content writer on gut health, nutrition, and food. She lives with IBS and has learned how to keep her symptoms at bay through a healthy diet and exercise. She wants to educate others on what they can do to take back control of their gut health and live like they used to.

  • Julie Guider, M.D.

    Dr. Julie Guider earned her medical degree from Louisiana State University School of Medicine. She completed residency in internal medicine at the University of Virginia. She completed her general gastroenterology and advanced endoscopy fellowships at University of Texas-Houston. She is a member of several national GI societies including the AGA, ACG, and ASGE as well as state and local medical societies.