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

Diesel dust can carry house dust mite (HDM) allergens into lungs

Ultra-fine diesel particles from traffic can carry toxic metals, grass pollen and house dust mite allergens deep into lungs.


In many major cities around the world the outdoor air contains ultra-fine diesel particles capable of travelling deep into lungs. Some of the particles can carry toxic metals and allergens on their surfaces. House dust mite allergens and grass pollen have been found on exhaust from diesel vehicles.

In the world's major cities, such as London, diesel particles account for up to 90% of total particle mass in outdoor ambient air. Of this mass the ultra fine particles (approximately 2.5 microns in diameter) are commonly made of half carbon and half salts in content. These fine particles are known to travel deep into the lungs and are capable of carrying cargo such as allergens from house dust mites, pollen and metals that can cause reactive damage to cells. Healthy lungs can neutralise or dispose of dirt and toxic materials but if overloaded or impaired by disease or malfunction the adverse effects from ultra fine diesel exhaust can result in inflammatory responses. Poor health associated with excessive exposure to diesel particles include exacerbations of asthma, chronic bronchitis, respiratory tract infections, heart diseases and strokes.


Lung

The Human Lung Sectioned

Self cleaning the lungs

Larger particles that are breathed in and land on the upper regions of the lungs (the trachea and bronchi) are caught and pushed upwards toward the throat by the sweeping action of cilia (tiny waving strands) located on top of lung cells. Once in the throat these particles can be swallowed or spat out for removal. Ultra fine particles that reach the delicate oxygen exchange area are removed by scavenging cells called macrophage. Once encased by the scavengers the non-biological particles and any biological debris attached to them are transported either up for cilia clearance or taken through the cell wall to lymph nodes to be stored or transported into the blood for removal.

The Mite's Faeces

Structurally, house dust mite droppings consist of 3 to 5 separate particles bound together by mucus and surrounded by a 1 to 2 micron semi-permeable membrane. One mite can excrete up to 20 pellets a day ranging in size from 10 to 50 microns. Each dropping can contain 14 fully identified allergens as well as guanine the mite's natural waste product. In moisture it takes two minutes for 90% of the major house dust mite allergen (Der p1) to escape the mite's dropping. Der p1 is an active digestive enzyme and a major cause of allergy and asthma.

The scavenging cells that protect the delicate gas exchange area of the lung have been found to produce nitric oxide upon exposure to Der p1. Nitric oxide is a marker of asthma.


References

'Mechanisms of particulate matter toxicity', S Salvi, and S T Holgate 'Clin. & Exper. Allergy', 1999, Vol. 29 pp1187-1194

Airborne house dust particles and diesel exhaust particles as allergen carriers. Ormstad H. Johansen BV Gaarder PI 'Clin. Exp. Allergy, 1998; 28 (6):702-8

'Nitric oxide production by alveolar macrophages in response to house dust mite faecal pellets and the mite allergens, Der p 1 and Der p2.' Peake et al. 'J. Aller. Clin. Immunol.'; 2003, 112:531-7