The following correction was printed in the Guardian's Corrections and clarifications column, Wednesday September 7 2005
In the article below, we said that Schistosoma mansoni, which causes bilharzia, was a nematode worm that lived in red blood cells. Schistosoma mansoni is not a nematode - it is a trematode. Bilharzia parasites do not live in red cells. They live in the blood vessels.

Irish scientists may have a drastic answer to the great asthma epidemic. It is called bilharzia. They think one of the world's nastiest parasitic infections could help combat the scourge of the affluent society.

The British Isles have the highest levels of allergy in the modern world.

Around 30% of schoolchildren in Ireland show symptoms of asthma.

The disease, however, is less common in the world's poorest countries - and those children more heavily infected with the nematode worm Schistosoma mansoni that causes bilharzia are the ones with the lowest allergic reactions, Padraic Fallon, of Trinity College Dublin, will tell the British Association meeting in Dublin today.

There are an estimated 250 million people in the tropics infected by bilharzia parasites that live in the red blood cells. Many have anaemia and kidney damage. They do not, however, suffer from asthma or anaphylaxis.

Health experts call this the hygiene hypothesis. The theory is that an immune response evolved to cope with parasitic infections. In a cleaner, healthier world, the parasites are few, so the immune system responds instead to cats, peanuts or dust mites.

Dr Fallon and colleagues experimented with laboratory mice genetically engineered with a tendency to asthma and anaphylaxis. They then infected the mice with schistosomes.

"These animals did not develop difficulty in breathing. The presence of the worms blocks pulmonary inflammation," Dr Fallon said. "We believe that this research will lead us to develop new ways of preventing and treating asthma and anaphylaxis, which can then be extended to treat inflammatory bowel disease and arthritis."

Tapeworms have been tested, in the US, as a treatment for inflammatory bowel disease. Doctors are unlikely ever to treat wheezing children with parasites. But the next step will be to identify the biochemical machinery that might keep the asthma and other allergic reactions at bay.

The reasoning is that the infectious nematode deliberately exploits the human immune response for its own survival. So scientists also reason that they may be able to exploit the worm for the benefit of the uninfected, too.

"Ultimately we can find out what molecules in the worm induce this protective response. Ideally, we will use those therapeutically," Dr Fallon said.