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Friday, 12 May, 2000, 00:25 GMT 01:25 UK
Dust 'protects against asthma'
Getting rid of all the dust may not be the best way
Children living in houses with low levels of a substance found in dust are more likely to have wheezing attacks, scientists found.

It is further evidence that exposing very young children to substances blamed for causing allergic reactions may actually partly protect them from allergies.

This has led to research into possible "dust vaccines" against asthma and other allergic conditions.

The research, carried out in the United States and reported in the Lancet medical journal, looked at 61 infants aged between nine and 24 months who had suffered from wheezing attacks.

They found 10 of these children were found to be sensitive to at least one allergen, or allergy-triggering substance.

When their homes - in Denver, Colorado - were tested, and compared to those of children who were not sensitised, much lower concentrations of one particular ingredient of house dust were found.

This may be an important clue in the search for effective and safe asthma prevention

Andrew Liu, researcher
House dust endotoxin is derived from the cell walls of bacteria living in the dust.

Asthma and other allergies happen when the body's defence mechanisms recognise endotoxin, or other substances as intruders, and try to attack them.

One of the body's ways of attacking causes inflammation in the surrounding area - in asthma, this causes the typical narrowing of the airways, making it difficult to breathe.

The research suggested endotoxin exposure at a young age has the protective effect because it triggers a difficult immune response - the type I response.

Reducing inflammation

This replaces the more harmful type II response, which involves the harmful inflammation.

The study's authors suggest this is the first direct evidence that exposure to endotoxin in early life may protect against developing allergies which may last a lifetime.

Andrew Liu, principal investigator for the study, said: "This potential allergy-protective effect of environmental endotoxin may help to explain why children growing up in rural settings in developing countries and on farms, close to animals, are less likely to develop allergies and asthma.

"This may be an important clue in the search for effective and safe asthma prevention."

The precise causes of asthma are still unclear, although genetic factors play a major role in determining who is most likely to develop it.

Rates of asthma have rocketed in the Western world over the past few decades, and some have blamed the lack of exposure to allergens in modern, centrally-heated, ultra-clean homes.

In February, Italian scientists writing in the British Medical Journal, said there was a much higher rate of asthma and respiratory allergies among male air force cadets who came from ultra-clean homes.

Cadets who had been more exposed to orally-transmitted microbes, in the household environment or food, were less likely to develop these conditions.

One path being explored by researchers is to devise a vaccine from soil microbes that would prime the immune system and prevent predisposition to allergies.

Dr Kevin Jones, a Gateshead GP and lecturer in primary care at Newcastle University, said: "I'd be surprised if there is a message for the general public from this yet.

"It's yet to be shown in terms of actual symptoms that you can lower dust mites enough by cleaning to make a difference."

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09 May 00 | Health
Your bedding could make you ill
15 Jun 99 | Medical notes
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