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5 Common Intestinal Parasites in Humans

Intestinal Parasites

Sure, we all know there are many types of parasites out there in our living environment. But have you ever stopped to think about whether those same parasites are making their home inside your body?

Intestinal parasites in humans are more common than may you think. In fact, there are hundreds of parasite species that can make their home in our intestinal tract, as well as many other places in the human body.

If you think you or somebody in your family has an intestinal parasite, here’s what you need to know in order to treat the problem safely and quickly. It may be wise to look into doing a parasite cleanse or colon cleanse.

1) Hookworms

There are two species of hookworms that commonly infect humans, Ancylostoma duodenale and Necator americanus. Of the two, Ancylostoma duodenale is a bit larger, at around eight to thirteen millimeters. Whereas Necator americanus usually reaches a length of seven to nine millimeters.

The life cycle of these two intestinal parasites begins with eggs that are passed in the stool. If conditions are just right (warm, damp, and shady) the eggs will hatch and release their larvae in a number of days. The larvae will continue to grow and mature in the soil until they come in contact with a human host. The larvae can then penetrate the skin to enter the human body and travel through the veins to the heart and then to the lungs. Once in the lungs the parasites travel up the bronchial tree to the pharynx where they will be swallowed.


Hookworms will then grow and mature while making their home in the small intestines. If you take no immediate action, most of these parasitic worms will eventually be purged from the system, but this process may take a number of years. Hookworms are the second most common intestinal parasite in humans through out the world. These parasites can be found worldwide in areas with a moist, warm climate. Both species of worms can be found in Africa, Asia and the Americas.

2) Schistosoma Species

Schistosomiasis is disease caused by the human intestinal parasite of the Schistosoma family. The three main species infecting humans are Schistosoma haematobium, Schistosoma japonicum, and Schistosoma mansoni.

The life cycle of these types of organisms begins when their eggs are eliminated from a host in feces or urine. The eggs then hatch and release larvae that can swim until it penetrates its next host, a specific species of snail. It will then grow and mature in the snail until it is excreted again. At this point, the Schistosoma parasite is ready to infect a human host.

Once contact is made with a human, the parasite will penetrate the skin of the human host and travel through the tissues until it makes its home in the veins surrounding the intestines. As the parasite reaches maturity, it can deposit eggs in the intestines that then move throughout the system to the bladder and the ureters until they are excreted with the feces and urine. And the whole cycle begins again.

Schistosoma parasites can reach a length of seven to twenty millimeters. These specific human intestinal parasites are typically transmitted via contact with contaminated water, either by drinking, swimming or bathing in it. Not common in North America, Schistosoma parasites are primarily located in parts of South America and the Caribbean, Africa, Asia, and the Middle East.

Intestinal Parasites in Humans

3) Cyclospora cayetanensis

Another human intestinal parasite is caused by the species Cyclospora cayetanesis. Its life cycle begins with the passing of eggs into the soil with feces or urine from a contaminated host. However, unlike many parasite species, direct fecal contact will not cause a Cyclospora infection. Instead, the human intestinal parasite will enter the body through the consumption of contaminated food and water.

Once in the body, Cyclospora parasites will invade the intestinal tract and mature and multiply within the system. Eventually, the eggs of the parasite will be shed in the waste of the human host, beginning the cycle anew. Cyclospora cayetanensis has been found in many countries throughout the world. Since the early 1990s, there have been at least eleven cyclospora outbreaks in North America alone, infecting approximately four thousand people.

4) Giardia intestinalis

The single-celled protozoan human intestinal parasite known as Giardia intestinalis, or Giardia lamblia, is responsible for the condition called giardisis. The life cycle of this parasite begins with the excretion of parasitic cysts in the waste of an infected host. The cysts may survive for several months in the environmental, until they are ingested by the human host in contaminated water, food, or contact with contaminated feces.


Once in the human body, Giardia will move into the small intestine and multiply. As the parasite continues moving through the system, it may become encysted near the colon. This cyst will then work its way out of the body via feces or urine. These human intestinal parasites are infectious when passed in the stool; therefore it is possible for one human to contract this condition from another. Giardia have a worldwide distribution, and they are found most frequently in warm, moist climates.

5) Pinworm

Enterobius vermicularis is the human intestinal parasite that is also known as human pinworm, as humans are the only known host of this parasite species. Pinworms typically lay their eggs on the skin surrounding the anal area. Therefore self-infection can occur when a contaminated individuals scratches the anal area and transfers the eggs on his hands to his mouth.

Human to human transmission is also possible via contact with contaminated clothes, toilet, surfaces, or bed linens. Pinworm eggs may also become airborne and infect a human via inhalation. Once inside the human body, pinworm eggs travel to the small intestine where they hatch and mature. Adult pinworms make their home in the human colon, where they can live for several months.

Once the female pinworms reach maturity, they will travel through the system and exit via the anus, where they will lay their eggs. These pinworm infections occur all over the world, most frequently in school-aged children or in overpopulated areas. This is the most common human intestinal parasite worm infection in the United States, with as estimated 40 million persons infected.

article written by: Dr. Edward F. Group III, DC, ND, DACBN, DABFM

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