Parasite could help prevent asthma

Sep 5 2005

Asthma in Britain has reached epidemic proportions and the country now has one of the highest numbers of sufferers of the allergy in the world; in Ireland alone it is reported that as many as 30% of all schoolchildren have symptoms of the disease.

But Irish scientists think they may have found a possible response to the disease which at first glance seems rather dire because it involves a pretty nasty parasitic disease called bilharzia.

It appears that asthma has become very much an 'affluent 'disease, and is far less common in poorer countries where many children are infected with the nematode worm Schistosoma mansoni that causes bilharzia.

These children, according to Padraic Fallon, of Trinity College Dublin, have low allergic reactions.

Experts estimate that there are 250 million people in the tropics infected by bilharzia parasites which live in the red blood cells, which causes anaemia and kidney damage.

But it seems they do not suffer from asthma or anaphylaxis.

According to health experts the hygiene hypothesis is that an immune response has evolved to deal with parasitic infections, but in a cleaner, healthier world, parasites are few, so the immune system responds instead to cats, peanuts or dust mites.

In their research Dr Fallon and colleagues experimented with laboratory mice genetically engineered with a tendency to asthma and anaphylaxis, they then infected the mice with schistosomes.

Dr Fallon says the mice did not develop difficulty in breathing as the presence of the worms blocked pulmonary inflammation; he believes the research could help in the development of new ways to treat and prevent asthma and anaphylaxis.

It is also possible the treatment could be used to treat inflammatory bowel disease and arthritis.

Fallon says it is clear that the worm has evolved a way to control the human immune system, raising and lowering inflammation in its host, to just the right level to ensure its parasitic lifestyle can be maintained.

This is not the first time a parasite has been suggested as a cure for disease, as in the U.S. tapeworms have been tested as a treatment for inflammatory bowel disease.

Although it is unlikely that children with asthma would ever be treated with parasites, the researchers may be able to discover a biochemical device that might prevent the asthma and other allergic reactions occurring.

In a study in Gabon, Africa, schoolchildren that were infected with worms had lower allergic responses to house dust mites than children with no worms.

But when the worms were eradicated by drugs the children then developed increased allergic responses.

The scientists say that the infectious nematode deliberately exploits the human immune response for its own survival and they may also be able to exploit the worm for the benefit of the uninfected.

Dr Fallon says if they can find out which molecules in the worm induces the protective response. they may be able to use them therapeutically.