The HDM grazes on fungi and rotting skin scales and their digestive system may create up to 20 dung-pellets a day. The droppings are wrapped in a special film and contain undigested scraps of food which are broken down by powerful enzymes to provide nourishment for the mite later. In other words they can eat their own droppings up to three times over and still have a plentiful supply of food! The pellets, once disturbed in an unventilated room, can remain suspended in still air for 20 minutes. Unsuspecting and vulnerable people may easily breathe them in, causing asthma or asthma symptoms, allergic rhinitis and the exacerbation of eczema. The mite is also implicated in glue ear and conjunctivitis.
Allergic reaction
One of the mite's most powerful enzymes is known by scientists as Der p1. It is very important to understand the way this enzyme interferes with the human lung or nasal tissue in vulnerable people.
In the lungs
Once Der p1 is breathed in and released it breaks down the adhesion molecules binding cells together. Inside the delicate tissue of the lungs it 'clips off' important bits of cells. This action raises an alarm in the body's defence system. The resulting reaction causes damage to the lung as the body searches to destroy an invader/parasite. Der p1 is doing what it is designed to do. It is breaking down potential food for the mite. Sadly it is not supposed happen in our lungs!
The clipping action of a specific cell (B cell) is the same action taken by certain parasites. The ensuing chaos gives the parasite a chance to hide and not be detected! No wonder the body reacts with such fury! References: 1. Hewitt CRA. Brown AP, Hart BJ & Pritchard DI. A major house dust mite allergen disrupts the immunoglobulin E network by selectively cleaving CD23: innate protection by antiproteases', J. Exp Med. 1995, 182: 1537-1544
2. Shakib F, Schulz O, Sewell H, A mite subversive: cleavage of CD23 and CD25 byDer p1 enhances allergenicity; Immunology Today; 19,7 313-316
3. Pritchard DI. Immunity to helminths: is too much IgE parasite- rather than host protective? Parasite Immunology, 1993: 15: 5-9
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