What are intestinal parasites?
Intestinal parasites include worms and single-celled organisms that live in your intestines. A parasite is an organism that lives off another organism (host). Parasites use the host’s body for nourishment and shelter. They rely on the host as a vehicle to spread to the next potential host(s), where they can continue multiplying and spreading.
In return, intestinal parasites provide zero benefits. Instead, they can cause unpleasant symptoms and (in some cases) pose serious health risks.
What are the types of intestinal parasites?
Intestinal parasites include helminths (parasitic intestinal worms) and one-celled organisms called protozoa.
Helminths (parasitic intestinal worms)
Helminths include various roundworms (with round bodies) and flatworms (with flat bodies). Although they thrive and grow in your body, most helminths can’t reproduce there. Instead, they lay eggs that exit your body in your feces (poop). The species survive because other people (unknowingly) come into contact with the eggs and become new hosts.
Intestinal worms include:
- Pinworms (enterobiasis): These thread-like worms spread when you touch a surface contaminated with pinworm eggs and put your hands to your mouth. The eggs hatch in your small intestine. At night, female adults lay eggs around your anus (butthole). The process can cause anal itching. Scratching the area and touching a surface without washing your hands transmits the eggs.
- Ascaris (ascariasis): Through a microscope, these worms look like tiny earthworms. They spread if you ingest the eggs after coming into contact with contaminated soil. “Contaminated” means the soil contains poop with worm eggs in it. This can happen in places where people poop outside because of limited or no access to toilets. Ascaris also spreads in places where people use human feces as fertilizer to grow produce.
- Whipworms (trichuriasis): Whipworms get their name from their whip-like shape. As with Ascaris, whipworms spread when a host ingests eggs from contaminated soil.
- Hookworms (ancylostomiasis): Hookworms have hook-like heads they use to attach to your intestine walls and feed. Like Ascaris and whipworms, hookworms spread through contaminated soil. What’s different is that the eggs in the soil mature into larvae. If you walk on the soil barefoot, the hookworms can enter your body through your skin.
- Strongyloides (strongyloidiasis): These worms also spread through contact with contaminated soil. You can ingest them by mouth, or they can enter your body if you’re walking around barefoot. Unlike other helminths, Strongyloides can reproduce inside a host.
- Tapeworms (taeniasis): These segmented worms have bodies resembling ribbons. They live in the digestive tracts of human and animal (pigs, cows and fish) hosts. They spread when you ingest their eggs or larvae in undercooked pork, beef or fish. Or, you can get a tapeworm infection if you touch a surface contaminated with eggs and then touch your mouth.
- Trichinella (trichinosis): Transmission of Trichinella is similar to that of tapeworms. This type of roundworm spreads to humans who eat the raw or undercooked meat of an infected animal (usually pigs).
- Flukes: You can get a fluke infection from drinking contaminated water or eating infected aquatic plants or fish. The types that live in your intestines include Fasciolopsis buski, which causes an infection called fasciolopsiasis. Another type is Heterophyes, which causes heterophysiasis.
Protozoa
Like helminths, protozoa spread when you ingest trace amounts of poop that contain the eggs. They commonly spread through contaminated water or fruits and vegetables. But protozoa can also reproduce inside a human host.
Common types include:
- Giardia (giardiasis).
- Entamoeba histolytica (amebiasis).
- Cyclospora (cyclosporiasis).
- Cryptosporidium (cryptosporidiosis).
- Blastocystis species (Blastocystosis).
- Cystoisospora belli (cystoisosporiasis).
What is the most common intestinal parasite?
According to the World Health Organization (WHO), approximately 25% of the world’s population has an infection related to an intestinal parasite. In tropical and subtropical areas with limited access to clean water and sanitation, that number is as high as 50%. The most common intestinal parasite infection globally is ascariasis. It affects about 1 billion people worldwide.
In the U.S., the most common infections are from protozoa, especially the giardia parasite. Pinworms are the most common intestinal worm in the U.S.
