Image caption Macaque monkeys suffer from a similar bowel condition to humans

Chronic diarrhoea could be treated using parasitic worms, a study of monkeys has suggested.

Research published in PLOS Pathogens, suggests the treatment restores gut bacteria to a healthy state.

Other work in mice has already suggested conditions such as ulcerative colitis could be treated in this way.

A UK expert said parasitic worms were being investigated for a range of conditions, including multiple sclerosis and allergies.

Captivity

Inflammatory bowel diseases, like colitis, are often fuelled by a wrongly targeted response by the immune system to gut bacteria.

Such diseases are more common in developed countries - and scientists suggest this is because people in developing countries have more exposure to parasitic worm (helminth) infections and therefore have a natural protection that has evolved as people and worms learnt to co-exist.

THE WONDER OF WORMS Parasitic worms are "old friends" and humans have lived with them for as long as we have existed. And while people in developing countries still do so - and have low levels of inflammatory disease, the opposite is true in developed countries. It appears our immune systems came to rely on parasitic worm infections as part of the way our body defended itself. And when they are no longer there, it appears that may upset our immune systems. Now researchers are looking at how the worms' effects can be harnessed to treat conditions ranging from multiple sclerosis to allergies. Hookworms and pig whipworms are amongst those being investigated. Results are promising. But those squeamish about dealing with worms or their eggs may not have to worry - it is more likely drugs will be developed that mimic their effects.

Recent studies have used parasitic worms to successfully treat inflammatory bowel disease in humans, but it is unclear exactly how they do this.

This latest study looked at monkeys because young macaques kept in captivity often develop chronic diarrhoea that can be hard to treat.

Five macaques with diarrhoea were treated with parasitic worms called whipworms.

Tissue samples were taken before and after treatment and it was found the balance of gut bacteria was restored to required levels.

And four out of five animals had less diarrhoea and started to gain weight.

Dr P'ng Loke, of the New York University Langone Medical Center, who led the study, said: "The idea for treating colitis with worms is not new, but how this therapy might work remains unclear.

"Our findings suggest that exposure to helminths may improve symptoms by restoring the balance to the microbial communities that are attached to the intestinal wall."

The researchers now plan a study in humans to look at how pig helminth eggs might help alleviate the symptoms of colitis.

Compensating

Prof Graham Rook, of the centre for clinical microbiology at University College London, said a number of research teams were investigating the effects of parasitic worms in various conditions.

"This is not part of the hygiene hypothesis [which says exposure to bacteria strengthened the immune system]. It's the "old friends" hypothesis.

"We co-evolved with these things, so they had to be tolerated. We found ways of suppressing the immune systems, and in some way have come to depend on them."

And he said the field of research as a whole would be "hugely significant".

He added: "With helminths, if you get the dose right, you can probably live with worms and not have symptoms.

"But it may well be there is going to be a battery of molecules you could be dosed with to compensate for not meeting our 'old friends'."