Parasitic worms may be an effective treatment for the inflammatory bowel disorder Crohn's disease, research in the US suggests.
Crohn's disease affects 100,000 people in Britain
A University of Iowa team found most of 29 Crohn's patients who swallowed a type of parasitic worm over a 24-week period showed an improvement.
It is thought that helminths, such as roundworms and threadworms, may prevent Crohn's in the developing world.
The research is published in the journal Gut.
Crohn's disease rates are relatively high in the developed world, where few people carry helminths.
But in the developing world, where it is relatively common for people to harbour these worms, rates of Crohn's are much lower.
In the developing world it is common for the worms' eggs to contaminate food, water, air, faeces, pets and wild animals.
And they are also found on toilet seats and door handles. Once inside the body, the eggs usually lodge in the bowel, where they hatch into worms.
Unlike other parasitic worms, such as tapeworms, they do not cause disease, and do not invade other parts of the body.
In the latest study, 29 adults with moderately active Crohn's disease swallowed 2,500 whipworm eggs of the species Trichuris suis - commonly found in pigs - every three weeks for 24 weeks in total.
Most of the patients had had their symptoms for around four years and standard treatment had not worked.
Five patients dropped out, but halfway through, 22 patients had experienced a significant improvement in their symptoms, with 19 of them having no symptoms at all.
By the end of the study, all but one had shown an improvement, with 21 reporting no symptoms.
There were no signs that the worms had caused any side effects, but people also taking drugs to suppress their immune system at the same time tended to fare better.
Crohn's disease is caused by an excessive immune response to normal gut bacteria, and the researchers say that helminths suppress the immune response and consequently dampen down inflammation.
As such they might provide a simple alternative to current medications, or could be used in combination.
They stress that the worms' eggs are shed in the stool, but cannot colonise another host until they have been incubated in the soil for several weeks, and so are unlikely to pose a public health risk.
However, they accept that larger trials are needed to confirm their results.
Dr Alastair Forbes, a consultant gastroenterologist at St Mark's Hospital, London, and spokesman for the National Association for Colitis and Crohn's Disease, said the research was interesting, but still at an early stage.
"It makes sense. What they are trying to do is to create a sort of anti-inflammatory response," he told the BBC News website.
"It seems remarkable that some people are prepared to be infected with worms, but the fact that they are says a lot about how poor current treatments are."
However, Dr Forbes said more work was needed to ensure the therapy was safe.
"People with Crohn's tend to have leaky bowels, so something that would not normally get into the circulation might do so in somebody with the disease," he said.