Intestinal Disorders Parasites

A number of parasites can infect the human digestive system. The majority of them take up at least temporary residence in the intestines. The following is a list of parasites that can wreak havoc in the human intestinal tract.

Pinworm (Enterobius vermicularis)

Pinworm, also known as seatworm or threadworm, is one of the most prevalent intestinal parasites in the United States, with approximately 40 million Americans infected. Worldwide, about 200 million people are infected with pinworm. Pinworm can infect anyone, but children are at the highest risk; an estimated 30 percent of the world’s children are infected with pinworm.

Pinworms are small, white worms, about half an inch in length. Infection occurs with the accidental ingestion of eggs. Symptoms usually appear about two to four weeks after ingestion when the female pinworms migrate to the rectum where they lay about 15,000 eggs each day. The main symptom of pinworm is irritation around the anus and vagina. The itching may also result in sleep disturbances.

A diagnosis of pinworm is made by seeing the worms or by microscopic detection of the eggs, obtained by a “cellophane tape test.” Pinworm is normally treated with a single dose of anti-worm medication, although a second dose may be given.

Giardia (Giardia lamblia)

Giardia is one of the most common intestinal parasites in the United States, second to only pinworm. Giardia is believed to infect approximately 2.5 million Americans each year.

Giardia is primarily a waterborne parasite. Most infections occur due to the ingestion of contaminated water. Eating raw or undercooked food may also result in giardiasis, but the occurrence is much less common. Symptoms normally appear one to two weeks after infection. The primary symptom of a giardia infection is diarrhea, but other symptoms such as flatulence, stomach cramps and nausea may be present.

To diagnose giardiasis, the doctor collects several stool samples to check for the parasites. Once the parasitic infection has been diagnosed, the doctor prescribes one of several prescription medications to treat giardia infection.

Coccidia (Cryptosporidium)

Coccidia are single-celled parasites that cause diarrhea. Many strains of coccidia occur in pets and are not infectious to people, but a few strains, such as Cryptosporidium sp., are.

Infection occurs due to the accidental ingestion of food or water contaminated with Crytosporidium. Symptoms normally appear about seven days after the infection. Some people may not exhibit symptoms of infection; others may experience symptoms such as watery diarrhea, weight loss, fever, abdominal pain, nausea and vomiting.

A diagnosis of cryptosporidiosis is made through an examination of stool samples. No real treatments exist for this parasite, as most people recover on their own. The patient is generally advised to drink plenty of fluids to prevent dehydration as the infection runs its course.

Hookworm (Necator americanus)

Hookworm is an intestinal parasite predominantly found in tropical and subtropical regions of the world. Approximately one billion people (one fifth of the world’s total population) are infected with hookworm. Many species of hookworm exist, but the most common species in the US is Necator americanus.

People are infected by either ingestion of the larvae or direct contact with soil that contains hookworm larvae. The larvae are able to penetrate the skin and enter the bloodstream, eventually making their way to the small intestine. Children are at especially high risk because of their tendency to play in the soil or walk around barefoot.

Symptoms of a hookworm infection include irritation at the site of penetration, weight loss, anemia, abdominal pain and diarrhea. This human parasitic infection is diagnosed by checking stool samples for hookworm eggs. Once diagnosed, medication is prescribed to treat the parasite. If the patient is suffering from anemia, iron supplements are also given.

Protozoan Infections: Entamoeba histolytica

Amebiasis is a disease caused by the parasite, Entamoeba histolytica. The disease is not very common in the US and is normally found in immigrants and people who have recently traveled to developing countries.

Infection occurs through ingestion of contaminated food or water, or by putting anything contaminated by Entamoeba histolytica in the mouth. Most people infected by Entamoeba don’t exhibit symptoms, but some who are infected typically display mild cases of loose stools and stomach pain. Symptoms occur anywhere from one to four weeks after infection.

Diagnosis of amebiasis is made through the examination of a stool sample, but this method is not always accurate; Entamoeba histolytica resembles another much more common (and harmless) amoeba, Entamoeba dispar. When examined under the microscope, Entamoeba dispar may be mistaken for Entamoeba histolytica. A blood test may be performed to accurately diagnose the disease. Oral anti-parasitics are the primary form of treatment for amebiasis.

Roundworms (Ascaris sp.)

Ascaris infection is the most common parasitic infection in the world, and is primarily found in tropical and subtropical regions. Roundworms are rare in the US, with most of the cases occurring in rural areas. Children are at a higher risk of infection by roundworms than adults.

Infection occurs with accidental ingestion of roundworm eggs. Most people infected with roundworms show no symptoms whatsoever. People with more severe infections may experience abdominal pain and slower weight gain. Occasionally, people with a severe case of roundworms may have blocked intestines.

Diagnosis of Ascaris is made by examining stool samples for roundworms and roundworm eggs. Once the diagnosis has been made, medications are prescribed to treat the infection.

Strongyloidosis (Strongyloides stercoralis)

Strongyloides stercoralis are unique worms in that they have two separate life cycles: a parasitic one and a free-living one. In the parasitic life cycle, Strongyloides are very similar to hookworms. In the free-living life cycle, the worms are able to survive and reproduce in the soil, without the need for a host.

People are infected through direct contact with soil containing larvae. The larvae can penetrate the skin and make their way to the small intestine. Larvae hatched from eggs within the intestine may also go through a process called “autoinfection” where the larvae penetrate the intestinal walls and go through the entire process of infection as if they had just penetrated the skin.

Most people with strongyloidosis display no symptoms, although moderate and severe infections may result in abdominal pain, nausea, vomiting, diarrhea and constipation. Examination of stool samples and blood tests are used in the diagnosis. A variety of medications may be prescribed to treat the infection.

Tapeworms (Dipylidium caninum)

Tapeworms are most common in dogs and cats, who acquire the parasite by swallowing fleas infected with tapeworm larvae. The risk of a tapeworm infection for humans is fairly low: The only way to become infected is to swallow an infected flea.

Most people with tapeworm infections do not display any symptoms although small particles that look like rice will be seen in the stool. To treat a tapeworm infection, a medication called praziquantel is prescribed to dissolve the tapeworms in the intestines.

Toxocariasis (Toxocara canis and Toxocara cati)

Toxocariasis is a zoonotic disease caused by parasitic worms found in the intestines of dogs (Toxocara canis) and cats (Toxocara cati). Humans contract the disease by accidentally ingesting Toxocara eggs, which are expelled with the animal’s stool.

Toxocariasis may occur in one of two forms:

  • ocular larva migrans (OLM): OLM is an eye disease that occurs when a worm enters the eye. OLM may result in visual impairment.
  • visceral larva migrans (VLM ): VLM is a result of severe or repeated toxocariasis infections. VLM causes swelling of organs. Symptoms include coughing and fever.

Diagnosis of toxocariasis is performed through blood tests. Treatment depends on the type of toxocariasis. For cases of VLM, anti-inflammatory medications are prescribed. For OLM, treatment is focused on preventing permanent damage to the eyes.

Trichinosis (Trichinella spiralis)

Trichinosis is an infection by a roundworm, Trichinella spiralis. The infection is acquired by ingestion of raw or undercooked meat, predominantly pork.

Most patients with trichinosis display no obvious symptoms, although patients with a moderate or severe infection may experience abdominal pain and aching muscles and joints.

The infection is diagnosed by blood tests or a close examination of the patient’s muscle tissue, where larvae are known to exist. Medications are prescribed to treat the infection if the problem is caught in the early stages. Once the worms encyst themselves in the muscle fibers, they are difficult to eradicate and symptomatic treatment is employed to alleviate patient suffering.

Whipworms (Trichuris trichiura and Trichuris vulpis)

Whipworms get their name from their appearance: long and whip-like. Over sixty species of whipworms exist, but very few species can infect humans. Trichuris trichiura is the human whipworm while Trichurisvulpis is the canine whipworm. Trichurisvulpis is mainly found in dogs, but very occasionally it is found in humans.

Like many other parasitic infections, whipworms are acquired by accidental ingestion of the eggs. Children are at highest risk of infection. Most people experience no symptoms, but severe cases of whipworm can cause abdominal pain, diarrhea and bloody stools.

A whipworm infection is diagnosed by examining stool samples. If eggs are present in the stool sample (female whipworms can lay as many as 10,000 eggs a day), then a whipworm infection is confirmed. Prescription medication is the most common form of treatment.

Resources

Arnold, L.K. (updated 2005). Trichinosis.

Beers, M.H.