All you need to know about the house dust mite
For the Curious

Report on a historic house dust mite (HDM) avoidance study

In 1990 UK scientists designed a clinical study to identify 120 babies 'at risk from asthma' at birth. The infants came from parents with a history of asthma or allergic disease, or from families with a child already diagnosed with an allergic condition. To further identify the 'at risk' babies at birth, the scientists looked at the cord blood levels to measure total IgE antibodies.
The reason for this investigation was that high IgE antibody levels are an indication that an individual is very sensitive to the environment, even the environment found in the womb. This ultra sensitivity is known by doctors as atopy and is a risk factor for the development of allergy. In asthma more than 90% of patients are associated with an atopic status. Clearly identifying babies with high total IgE (potential for atopy) even before birth, and from families with a history of asthma or allergy, was an important beginning for the study.

Following identification the mothers and infants were randomly placed into one of two groups. The allergen avoidance group was called 'the prevention group'. Breastfeeding mothers in this group were told to avoid eating dairy products, eggs, soya, fish and shellfish, peanut and tree nut. Non-breastfeeding mothers were given an extensively hydrolysed formula feed for their infants. During the year-long regime considerable support was given by a specialist dietician, nurse and doctor to ensure that the mother's and baby's diets were nutritionally sound. Supplements were given to breastfeeding mothers who were on the avoidance diet. In addition to the manipulation of the diet, the prevention group practiced house dust mite avoidance using vinyl mattress covers and a mite killing spray in the bedroom and living room. At this time exposure to house dust mite droppings was considered a major risk factor in allergy and asthma. The second study group, the controls, were given standard medical advice offered by the NHS.

After twelve months the avoidance regime ended, medical notes were taken and a long series of follow-ups comparing the two groups began. All children were medically assessed at ages 1, 2, 4, 8, and 18 for the presence of asthma and atopy. In the prevention group outcomes, up to the age of 8, showed significant reductions in asthma, eczema and atopy. At age 18 there was no difference in atopy status between the two groups, however as the study scientists report, 'Comprehensive allergen avoidance in the first year of life is effective in preventing asthma onset in individuals considered at high risk due to heredity. The effect occurs in the early years, but persists through to adulthood' and 'further follow-up will determine whether our intervention has successfully prevented the onset of asthma or merely delayed it to later adult life.'

Study tests included, skin prick testing, spirometry, methacholine challenge and sputum induction. Further information was gathered from questionnaires and medical prescription records over the course of the study.

Asthma has dramatically increased over the past 50 years and is now estimated worldwide to affect over 300 million people. Scientists now recognise the environmental factors that influence the onset of asthma. They are named as: house dust mite exposure; dietary intake; microbial and viral exposures. This historic ground-breaking study from 22 years ago has led the way in recognising and reducing common asthma risk factors. It is up to other groups to follow their brave pathway.

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Interesting quotes that reflect positively on the study. 'Asking for a positive family history of asthma and atopic diseases is still a better predictor than those newly identified genetic markers or SNPs'. SNPs are single nucleotide polymorphisms which relate to known asthma genes.

'Allergic diseases and gene-environment interaction'. Erika von Mutius, The 9th Symposium on Specific Allergy 2012, 27-29 September, Berlin, Germany

Worrying new evidence suggests that a significant proportion of 4-6 month old infants already have established egg sensitisation and clinical reactivity (including anaphylaxis) prior to the 'first' introduction of egg, stressing the need to define the earlier pathways to sensitisation. Evidence that allergens can cross the placenta, breast milk and the cutaneous barrier provides potential pathways for the initiation of early sensitisation.'

'Early life development of the immune system', Susan L Prescott, The 9th Symposium on Specific Allergy 2012, 27-29 September, Berlin, Germany


References

1. 'Multifaceted allergen avoidance during infancy reduces asthma during childhood with the effect persisting until age 18 years', Martha Scott, Graham Roberts, Ramesh J Kurukulaaratchy, Sharon Matthews, Andrea Nove, S Hasan Arshad, 'Thorax', 2012; 67: 1046-1051