With so much research into the effects of its microbes on our health, the gut has begun giving up more its secrets.

But some things remain a mystery – like the causes of irritable bowel syndrome, the chronic, often hard to treat gut problem thought to affect as many as one in five people (especially women) at some point in their lives.

Abdominal bloating, cramping, pain or discomfort, constipation or its opposite – loose, frequent motions – and food sensitivities are typical symptoms.



Genes, diet, stress, gut microbes or infections are thought to play a part. But now there may be two other culprits – infection by one of two gut parasites that most people have never heard of: Dientamoeba.fragilis and Blastocystis hominis.



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Although many of us have had gut-wrenching gastro caused by other parasites such as Giardia and Cryptosporidium, Blastocystis and D.fragilis are unfamiliar names. Yet they may contribute to IBS symptoms, according to Professor Kerryn Phelps, a GP and adjunct professor of medicine at the University of Sydney and the University of NSW.

Supplied Dr Kerryn Phelps believes two parasites whose names are unfamiliar to many of us may contribute to irritable bowel syndrome symptoms.

"One reason we're seeing more of these parasites is because there's now a more sensitive test that makes them easier to detect," she says.

"The question people ask is how did I get this parasite? It's difficult to know but possibilities include contaminated waterways or swimming pools, unwashed contaminated fruit and vegetables, bathroom fixtures, nappy change tables, close contact with children and sexual contact," says Phelps whose new book, The Mystery Gut, is a guide to how the gut works and how to deal with its many problems

But diagnosing these parasites is controversial – many doctors say there's not enough evidence to conclude they cause gut symptoms, especially with Blastocystis.

"There's a lot of debate about whether Blastocystis can cause problems – but it's likely that there are different subtypes, some of which are pathogenic and others which aren't. It may also be that the overall balance of other bugs in the gut determines whether we develop symptoms," Phelps says.

Last year, a report from the Australasian Society for infectious Diseases published in The Medical Journal of Australia said that testing using the new PCR (polymerase chain reaction) test for these two parasites was leading to unnecessary treatment with antimicrobial medication and recommended that doctors not test for them.

"We do need more research into these parasites, but there's sufficient evidence to convince me that they should be treated if they're found in people with gut symptoms," she says.

"It's true that you can have these parasites in the gut without having any problems – but then you don't test people who don't have symptoms. The real controversy is that you have people with gut symptoms who test positive for D. fragilis and Blastocystis who are told that they're not sick and can't be treated. "

Although there's evidence that both parasites, especially D. fragilis, have the potential to cause problems, we need more research to know exactly how they might contribute to gastrointestinal symptoms, says Dr Damien Stark, a senior scientist in the microbiology department of St Vincent's Hospital in Sydney who is part of team that's been studying D.fragilis.

"We've known about D.fragilis for 100 years and we see it in people of all ages from children right through to the elderly. While it's more common than other similar parasites such as Giardia or Cryptosporidium, there are still many unanswered questions about it.

"It's more common in children but that's likely to be because they're more prone to pick up pathogens that can be transferred to the mouth from faeces. But there are still so many unanswered questions because it's difficult to get funding for research – it's not considered important," he says, adding that while some small studies have shown treatment improves symptoms in some people, we need larger, randomised controlled trials to determine which are the best drugs to use.

In the meantime, what if you're plagued by unexplained IBS symptoms like bloating and diarrhoea – and your doctor has ruled out more serious causes such as inflammatory bowel disease or bowel cancer?

Phelps suggests asking your doctor to arrange a stool PCR test and if it's positive, he or she should recommend appropriate antibiotics and probiotics or refer you to a doctor with a special interest in gut problems.

"If your doctor won't order a PCR test, find one who will," she says.

The Mystery Gut by Professor Kerryn Phelps with Dr Claudia Lee and Jaime Rose Chambers is published by Macmillan, AU$34.99.