The allergy causing house dust mite was once a parasitic-like animal

The House Dust Mite

Image courtesy of The London School of Hygiene & Tropical Medicine.

In making the changeover some of the mite's parasitic characteristics remained and became enhanced to deal with the new way of living. These characteristics include the mite's ability to make specialised enzymes that dissolve the 'glue' that binds defence cells together and others that break down discarded cuticles such as shells from dead animals or human nail clippings. It is these enzymes, plus others, help make up the 14 allergens found in house dust mite droppings, which can cause asthma, rhinitis, eczema, and conjunctivitis.

By looking in depth at just one of the enzymes, the destructive power of the mite becomes apparent, along with its ability to harm beyond allergy. Group one allergen (Der p1) is a digestive enzyme, similar to one used in the food industry (papain). Der p1's activity has been shown to dissolve proteins that bind defence cells together. Once in the body it continues its disruptive pathway by clipping immune molecules known to signal allergy. But perhaps it is at its most harmful state when the activity of Der p1 offers bystanders or opportunistic pathogens an entrance into the body.

The fact that the mite morphed from parasite to scavenger could change the public's perception of the mite from being a nuisance to a dangerous intruder in our homes threatening the health of the vulnerable, most of whom are mite allergic children.