Living in Your Stomach and Not Paying Rent: Common Intestinal Parasites

We humans might not be as far removed from the natural environment as we sometimes think. For the intestinal parasites and other species that can take up residence in our bodies, we’re just another feeding and breeding habitat.

The risk of parasitic intestinal infection is higher in rural or developing regions of the world than it is in the U.S. This is because, in poorer countries, food and drinking water may be contaminated and proper sanitation can be lacking.

This does not mean, however, that people in more developed countries are immune to various “stomach parasites.” In fact, we can get really sick from them. This article will discuss its risks, symptoms, and treatments.

Common Intestinal Worms in Humans

When it comes to intestinal parasites, flatworms and roundworms are ready suspects. These types of worms are found in many habitats–including the human intestinal tract.


These flatworms are transmitted to humans through infected food.  The tapeworm anchors itself to a host’s intestine using hooks on its head and begins to feed.

A tapeworm takes a few months to mature and reproduce, and it can survive up to 30 years inside the host. Eggs are excreted in the host’s feces and consumed by other animals; then the cycle begins anew.

Symptoms: nausea, weakness, diarrhea, weight loss, and dizziness. If the infection is invasive, symptoms can include headaches, masses or lumps, and seizures

Ascaris Worms

The largest of the intestinal nematodes (roundworms) affecting humans, they can reach 6-14 inches long. Like other intestinal worms, Ascaris worms are transferred through food.

The eggs hatch and penetrate the intestinal wall, enter the bloodstream, and from there travel to the lungs. They are coughed up and swallowed, returning to the gut.

While not common in the U.S., ascariasis does exist in other countries and can be contracted by travelers.

Symptoms: fever, tiredness, rash, vomiting, diarrhea, nerve problems, and coughing


Hookworms also are parasitic nematodes. They used to be prevalent in the U.S., but due to improved sanitation are less so today.

Like Ascaris, hookworms are soil-transmitted helminths, whose life cycle begins outside the body and is transmitted through contaminated soil (or food that grows there).

Larvae grow inside the body, where they attach to the wall of the intestine using hook-like appendages on their heads.

Symptoms: weakness, abdominal pain, nausea, diarrhea, and anemia. Many people have no symptoms

Pinworms or Threadworms

Pinworms, which cause enterobiasis, are tiny; adult females range from a quarter to half an inch in length and have a long, pin-shaped end–hence the name.

They live in the host’s intestines, but unlike many parasites,  do not pass into the blood and cannot survive for long in other parts of the body.

Pinworms lay eggs outside the host’s body, usually around the anus, causing itching; this helps spread the larvae through hand contact.

Symptoms: itching around the anus, parasites in stool, insomnia or irritability, and sometimes abdominal pain and nausea

Other Common Intestinal Parasites in Humans

Entamoeba Histolytica 

This single-celled organism causes amoebiasis (better known as amoebic dysentery) and predominantly infects humans and other primates.

Spread through feces, it can be found in water, damp environments, and soil; and it can contaminate fruits and vegetables. Amoebiasis causes more deaths than any other protozoan except malaria–nearly all in very young children.

Symptoms: abdominal pain, fever, weakness, and diarrhea. Many with this condition have no symptoms.

Giardia lamblia

This flagellate protozoan causes an infection of the small intestine known as giardiasis. When someone contracts giardiasis, it results in inflammation and other damage–reducing the gut’s ability to absorb nutrients, and thus causing diarrhea.

The parasite is very resistant to water treatment and can be found in drinking water.

Symptoms: gas, diarrhea, fatigue, nausea, weight loss, and abdominal pain


Causes include drinking or swimming in infected water. The spores can be difficult both to detect and to eradicate. During an outbreak, boiling tap water is recommended.

When someone is infected, the illness will usually run its course in under a month,

Symptoms: diarrhea, stomach cramps or pain, dehydration, nausea, vomiting, fever, and weight loss. Some people do not experience symptoms.

Get Rid of the Parasites

Nowadays, close to all types of parasites can be dealt with through medication prescribed by doctors or other therapies.

There are alternative ways to fight parasites, too–as well as the symptoms people can experience as the parasites “die off.” Microbe Formulas explains it here.

Stay Healthy!

For better or worse, parasites are part of the ecosystem that we all share. Still, you need to get rid of the gastro parasites that are making you sick–as most probably do, at least to some extent.

Even though many of the symptoms described in this article are common to a variety of conditions, you should contact your health care professional anyway. You still could be sick, even if it’s not intestinal parasites.

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