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What is the allergy causing house dust mite

The house dust mite 'Dermatophagoides pteronyssinus' is a tiny scavenger with a preference for eating mouldy old discarded human skin scales, but will also eat pollen grains, insect scales, bacteria and plant fibres. It has no sight, no respiratory system, cannot control its body temperature and lives by absorbing moisture and oxygen from the atmosphere. Mite droppings, which contain digestive enzymes, are a major cause of allergy and allergic disease worldwide. A single dropping can contain up to 14 separate and fully identified allergens.

The house dust mite is an ancient creature that has developed a clever method of recycling its food. It uses its droppings as 'food parcels'. Powerful enzymes in the tiny droppings break down hard-to-digest food for later nourishment. The house dust mite will not bite, but enzymes in its droppings can act like a bite. The enzymes cause and trigger allergies in humans by breaking down delicate living tissue. Recent research suggests that, at some stage in its evolutionary process, the house dust mite was once a mange-like parasite living on the skin of warm blooded animals with an existence similar to the sheep mange mite P ovis. This may explain the mite's preference for discarded skin scales and some of its active digestive enzymes designed to dismantle defence cell structures in warm-blooded animals.

The mite can produce up to twenty droppings a day, which means approximately 2000 during its active lifetime of up to 3 to 4 months. From eggs to breeding adults, mites pass through six stages of life. The adult female can lay from 60-100 eggs depending upon living conditions, which ideally for breeding mites are warm dark and damp. Most modern conventional beds provide perfect breeding conditions. An important fact to note; the house dust mite's biological make-up is 75% water. It must maintain this moisture content to breed. Reducing moisture is a threat to its existence.

References

The Biology of Allergenic Domestic Mites, An Update', Barbara J. Hart,1995 'Clinical Reviews in Allergy and Immunology ', Vol.13, pages 115 to 133. Humana Press Inc,

'A Major House Dust Mite Allergen Disrupts the Immunoglobulin E Network by Selectively Cleaving CD23, Innate Protection by Antiproteases', Hewitt CRA, Brown AP, Hart BJ, Pritchard DI, 'J.Exp.Med.'; 1995, 182, pages 1537 to 1544

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