What Are Helminths?

Helminths are parasitic worms that can infect humans and other animals. There are three types of helminths: flukes (trematodes), tapeworms (cestodes), and roundworms (nematodes).

When these worms get into the human body, they can cause parasitic infection, which appears as intestinal worms. This infection is known as helminthiasis, although it's sometimes called helminthosis or simply a worm infection. 

Helminths are most common in areas that have moist, warm climates and poor sanitation. When worms are in someone's intestines, that person passes eggs through their stool. As the feces come into contact with soil, the eggs can spread.

People can contract the infection if the infested soil reaches their mouths, often through dirty hands. In the case of hookworm, the parasite matures in the soil and is passed when a person walks over the soil with bare feet.

Some people with helminthiasis have no symptoms. However, as the infection becomes severe, people may experience abdominal symptoms, including diarrhea and vomiting. Intestinal worms are treatable, but the condition can lead to physical and cognitive growth problems if left untreated.

Types of Helminths

Three types of helminths infect humans. A fourth type primarily infects animals but can infect humans in rare cases. They are:

• Roundworms: These helminths, which have the scientific name nematodes, have a cylindrical body similar to earthworms. They can lead to infection in the intestines or elsewhere in the body. 
• Flukes: These helminths, or trematodes, have a flat body and leaf-shaped head with a sucker that helps them attach. They generally infect the bile ducts (thin tubes from the liver to the small intestine), liver, or blood. 
• Tapeworms: Tapeworms, or cestodes, are long, segmented flatworms found in or around the intestines. 
• Thorny-headed worms: These helminths, or acanthocephalans, have a round body and barbs around their head. They mainly infect animals, and human infection is very rare.

 Symptoms

People with mild infections of helminths might not have any symptoms. However, if the infection persists it can lead to more severe symptoms that often include abdominal discomfort. The symptoms of helminthiasis, or an intestinal worm infection, include:

• Abdominal pain 
• Diarrhea
• Blood loss, including blood in the stool
• Weakness or exhaustion
• Weight loss and malnutrition
• Restricted growth
• Cognitive effects (changes in thinking and memory)
• Rectal prolapse (the rectum protrudes beyond the anus)

Diseases Caused by Helminths

When helminths infect a person, they can lead to diseases. Although infections are rare in the United States, about 24% of people globally have a helminth infection. The three most common intestinal worm infections are:

Ascariasis

Ascariasis is the most common type of helminthiasis in humans. It’s caused by the roundworm Ascaris lubricoides. Ascaris larvae and adult worms live in the intestines.

Many people with ascariasis don’t have symptoms, but a severe infection can lead to abdominal symptoms. Ascariasis can also migrate outside the intestines, leading to cough and other symptoms as the worms spread.

Whipworm

Whipworm is an infection caused by a type of roundworm. Whipworms live in the large intestine and generally cause a more severe infection than ascariasis.

The symptoms of whipworm include painful bowel movements, diarrhea that contains blood or mucus, and frequent defecation. As whipworm progresses, a person can experience anal prolapse, anemia (reduced ability of the blood to carry oxygen due to low red blood cells or low hemoglobin), and stunted growth.

Hookworm

Hookworm infections are caused by the helminths Ancylostoma duodenale and Necator americanus. These worms infect the small intestine.

Unlike other helminth infections that are passed by ingesting eggs, hookworm is most often contracted by walking barefoot on contaminated soil. Hookworm larvae in the soil can enter the body through the feet and travel to the intestine. 

After the hookworm enters the foot, a person might experience itchiness or a rash. With mild infections, there may be no symptoms after that. More severe infections will lead to diarrhea, abdominal pain, loss of appetite, weight loss, and anemia.

Treatment

Helminth infection is diagnosed through the analysis of a stool sample. If you display symptoms of a helminth infection, particularly if you have traveled to an area where these infections are common, your doctor will have the lab look for worms in your stool. 

If you have a worm infection, your doctor will likely prescribe antihelmintic medications. These medications, including Albenza (albendazole) and Emverm (mebendazole), rid the body of parasitic worms. They come as a chewable tablet that’s taken twice daily for three days.

Summary

Three types of helminth (parasitic worm) infections seen in humans are caused by roundworms, tapeworms, and flukes. They can cause abdominal pain, diarrhea, bloody stool, and other symptoms. They occur more often in tropical climates where there is poor sanitation.

Ascariasis, whipworm, and hookworm are some of the more common helminth infections. Helminth infections are treated with anthelmintic medications.

A Word From Verywell

Helminth infections have a strong “ick” factor. Although it’s unpleasant to think about parasitic worms, remember that worm infections are incredibly common, affecting up to 24% of people. Luckily, they’re very easy to treat with a three-day course of medication.

However, if left untreated, the infection can get worse, so be sure to reach out to your doctor if you’re concerned.