Human Intestinal Parasites – Causes, Symptoms, Treatment, Prevention

What Are Intestinal Parasites?

The term parasite refers to organisms that infest another organism where it lives and feeds. Some of these parasites are microscopic and not visible to the naked eye whereas other parasites are relatively large. Human intestinal parasites are either one-cell organisms or intestinal worms that live in the small or large intestine and consume nutrients from the intestinal lumen or the blood flowing in the intestinal wall.

One-Cell Parasites – Protozoa

One-cell organisms, like Giardia lamblia, also called Giardia duodenale (Picture 1), Cryptosporidium (crypto) and Cyclospora, utilize nutrients from the stool. They belong to a living kingdom Protozoa (Gk. protos = first; zoa = animals). They may cause inflammation of the small intestine thus hampering absorption of nutrients. Entamoeba hystolytica lives predominantly in the colon.

Giardia under electron microscope

Picture 1. Parasite giardia from a stool sample,
as seen under the electron microscope (actual size:~0.01 mm)
(source: phil.cdc.gov)

Intestinal Worms (Helminths)

Intestinal worms (helminths), like roundworms (hookworms, whipworms, Ascaris and Trichinella), tapeworms and flukes, are few millimeters to several meters in size. These worms feed from the contents of the bowels or suck the blood from the intestinal wall and can cause about the similar symptoms as one-cell parasites. However, in most instances these intestinal worms cause little to no symptoms for months or years.

How Can One Contract Parasites?

Both protozoan and helminths (worms) are primarily contracted through ingesting contaminated food or water. The adult parasite or its eggs are shed in the stool of humans or animals. This can then contaminate water sources suahc as rivers and lakes as is the case with open sewage or poor water treatment practices. Drinking, bathing or irrigating crops with this contaminated water then allows the parasites to enter the body.

In some instances, parasites can be spread from person to person mainly when one person comes into contact with the fecal particles of a person who already has an infestation. This puts certain people at a greater risk. For example a caregiver changing diapers or cleaning soiled lined  of a person who already has an infestation or infection may therefore be at risk of contracting the infection.

Symptoms of Intestinal Parasites

Intestinal parasites can cause one or more of the following symptoms:

  • Mild diarrhea with waxing and waning course, appearing few days to several weeks after the travel into the country with poor hygiene, and lasting from several days to months (for comparison: bacterial diarrhea usually has a sudden and dramatic onset within some hours after a meal, and heals on its own in few days).
  • Mucus in the bowel movement
  • Bloating and flatulence
  • Weight loss is common.
  • Pale skin, tiredness, tingling (due to reduced absorption of minerals and vitamins).
  • Entamoeba histolytica may cause severe colitis with ulcers, abdominal cramps, blood in the stool with occasional pus – the disease is known as amebic dysentery (9). Entamoeba may invade liver, lung, brain, or other organs, where it forms cysts.
  • Worms, their parts or eggs can be sometimes found in the stool. Read more about intestinal worms.
  • Infection by either one-cell organisms or intestinal worms is often present without any symptoms.

Diagnosis of Intestinal Parasites

Diagnosis can be often suspected from history of prolonged bloating or diarrhea and can be confirmed by the following tests:

  • Ova and parasites (O&P) test of the stool. The test is often false negative so three stools from three different days (at least two days apart) should be tested.
  • Hemoccult test may reveal blood in the stool
  • Blood tests often reveal elevated eosinophils and IgE antibodies and lowered ferritin, hemoglobin or red cells
  • CT or biopsy are needed to find cysts in the liver, lungs or brain.

Treatment of Intestinal Parasites

Anti-parasitic drugs, like metronidazole, quinacrine, tinidazole and furazolidone are usually effective, but the exact treatment regime, as prescribed by your doctor, should be followed.

Paramomycin is not absorbed from the intestine into the blood, so it may be used in pregnancy (1). For cyclospora trimethoprim-sulfametoxazol can be used (2).

Intestinal parasites can be successfully eradicated, but may recur if the source of infection still exists. Delayed treatment can lead to a host of complications, some of which can be life threatening, as may be the case of severe dehydration in diseases like giardiasis.

Prevention of a Parasitic Infection

An infection by intestinal parasites can be prevented by:

  1. Hand washing with an antiseptic soap before eating and after using the toilet, particularly after a bowel movement, is imperative in preventing infections.
  2. Cooking food at high temperatures kills all parasites. Partially cooked meat or raw meat are high risk foods for passing on these parasites. Smoking or freezing does not destroy the parasites or eggs.
  3. Washing raw vegetables and fruits with a suitable disinfectant solution that is fit for consumption. Salt water may also be helpful to some extent. Clean running water should be used for rinsing.
  4. Consuming safe food and water is important to prevent infections. Travelers from western countries visiting Central or South America, Africa or South Asia should ingest only packaged, bottled or cooked foods and drinks and only fruits that they can peel by themselves.

Read more on food and water safety tips.

For How Long Is a Person with Parasitic Diarrhea Contagious?

Most parasites are transmitted through contact with the person’s feces and to a lesser extent with body fluids. It is usually not airborne so transmission cannot occur with droplets that become airborne from coughing or sneezing. A person may be infectious for prolonged periods of time, depending on the causative parasite.

Usually a person is contagious, or more specifically the stool contains the parasite, a short while after contracting the infection and for as long as the infection is active. Even without any symptoms being present a person may still be contagious. With some parasites like Entamoeba hystolitica a person can be contagious for months and even years thereafter.

Related Articles:

References:

  1. Incidence of intestinal parasites in homosexual men (ncbi.nlm.nih.gov)
  2. Intestinal protozoa (tulane.edu)
About Jan Modric (223 Articles)
Health writer

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