Infectious Causes of Irritable Bowel Syndrome

Can Bacteria, Viruses, Yeast or Parasites Be Behind IBS?

Oct 19, 2009 Maija Haavisto

Several infectious causes have been suspected for triggering irritable bowel syndrome (IBS), including bacteria, viruses, fungi and parasites.

Irritable bowel syndrome (IBS) is a very common chronic condition that causes gastrointestinal symptoms. Like many illnesses, it is often blamed on stress and stress indeed tends to worsen IBS, but infectious agents may also play a role. Stomach ulcers were originally thought to be caused by stress, until Helicobacter pylori was discovered.

It is already well-known that IBS can be triggered by bacterial (Campylobacter jejuni, salmonella, shigella and E. coli) and possibly viral gastroenteritis (food poisoning and "stomach bugs"). This is known as post-infectious irritable bowel syndrome.

Does it make a difference whether IBS is caused by an infection? In case of post-infectious IBS, it may not, but some of the other forms may respond to antimicrobial treatment. In any case, it may be helpful for the person to understand that they are not at fault for their illness.

Bacteria

Besides post-infectious IBS, there is another bacterial cause of IBS known as small intestinal bacterial overgrowth (SIBO) or dysbiosis of the gut. Our intestines are normally full of beneficial bacteria, but in SIBO the balance is disturbed and non-beneficial bacteria dominate.

SIBO is usually diagnosed with a breath test, though there can be both false negatives and false positives. Probiotics can be helpful in milder cases, but usually SIBO is treated with antibiotics. A common choice is rifaximin (Xifaxan), which is not absorbed in the body and thus has few side effects.

SIBO has also been implicated in other conditions: in one study 96 out of 123 fibromyalgia patients were found to suffer from it and antibiotic treatment often helped their fibromyalgia symptoms, as well. Reportedly restless legs syndrome and interstitial cystitis can also respond to SIBO treatment.

Viruses

There is no clear evidence of viruses as the cause of IBS (save for post-infectious IBS), but studies have found chronic enteroviral infection present in the gut in patients with chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME) who also have IBS-like symptoms.

It may not be far-fetched to theorize a link between chronic enterovirus infection and IBS even in some patients without CFS/ME, but no studies have yet been done.

Candida

Candida albicans is a species of yeast normally present in the flora of human gut and other mucosa. When this flora is disturbed candida can cause infections like thrush and vaginal yeast infections. In alternative medicine a systemic yeast infection (candidiasis) is often blamed for dozens of different symptoms, but this is controversial.

Candida has also been associated for irritable bowel syndrome, especially the diarrhea-dominant form (IBS-D), but studies are scarce. In a 1985 study gastrointestinal yeast infection was associated with IBS symptoms triggered by "allergic or pseudo-allergic reactions" to certain foods.

Candida albicans infections can be treated with antifungal drugs. A common choice is nystatin, which is not absorbed into the body and thus rarely causes side effects. Alternative practitioners tend to recommend antifungal herbs like garlic and a so-called anti-candida diet, which is low on sugar and simple carbohydrates believed to feed the yeast.

Parasites

Giardia lamblia is a protozoal parasite that colonizes the small intestine, causing an illness called giardiasis. Acute giardiasis can resemble traveler's diarrhea, but it can also become chronic, often leading to weight loss. The chronic infection has been connected with irritable bowel syndrome in several studies.

Blastocystis hominis and the amoeba Dientamoeba fragilis are two other parasites suspected of causing IBS. Dientamoeba fragilis has particularly been connected to diarrhea-dominant IBS (IBS-D). These infections are common in developing countries, but epidemics have occurred in the Western world, too.

Gastrointestinal parasites are normally diagnosed from stool cultures or exam. If detected, they usually respond to treatment with an antibiotic called metronidazole (Flagyl). Metronidazole can be helpful for dysbiosis of the gut, as well. If Flagyl does not work, there are also other options depending on the parasite.

References:

Haavisto Maija. Reviving the Broken Marionette: Treatments for CFS/ME and Fibromyalgia. 2008.

Pimentel M. Review of rifaximin as treatment for SIBO and IBS. Expert Opin Investig Drugs. 2009 Mar;18(3):349-58.

Stark D, van Hal S, Marriott D, et al. Irritable bowel syndrome: a review on the role of intestinal protozoa and the importance of their detection and diagnosis. Int J Parasitol. 2007 Jan;37(1):11-20.

The copyright of the article Infectious Causes of Irritable Bowel Syndrome in General Medicine is owned by Maija Haavisto. Permission to republish Infectious Causes of Irritable Bowel Syndrome in print or online must be granted by the author in writing.

Giardia lamblia

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