What is the role of dust mite aeroallergens in the etiology of allergic diseases?

Updated: Jul 07, 2019
  • Author: Bhumika Patel, MD; Chief Editor: Michael A Kaliner, MD  more...
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Answer

Dust mite debris is the major source of allergens in house dust. [1, 2] This microscopic arthropod primarily feeds on organic materials, including skin scales, fungi, and bacteria.  Dust mites lack an organized respiratory system and their water supply is derived from the ambient air. Seasonal changes in relative humidity can affect the concentrations of dust mite allergen, and these fluctuations can contribute to allergic symptoms in the sensitized individual. [11]

In the home, mites typically infest objects that contain fabrics; for example, higher concentrations of mites are found in pillows, box springs, mattresses, bedding, carpets, throw rugs, drapery, stuffed animals, and upholstered furniture. Higher concentrations are usually found in older homes, in regions of high humidity, and in homes with heating units other than forced air. [3] Cold, dry air at high altitudes is not conducive to dust mite growth.

Both the mite bodies and fecal pellets are major sources of mite allergens, which become airborne when disturbed. [2] Dust mite allergens are predominately contained on aerodynamic particles 10 µm or larger in diameter and remain in the air for 30 minutes or less. In contrast, cat allergens are predominately carried on smaller particles, with an average size of 5 µm, and can remain in undisturbed air for days.

Allergens are named according to the first 3 letters of the genus and the first letter of the species (eg, the allergen for Dermatophagoides pteronyssinus is classified as Der p and Dermatophagoides farinae [see the image below] is classified as Der f). Allergens are grouped according to biologic function and homology. The major sources of dust mite allergens are the group 1 allergens Der p 1 and Der f 1.

Electron photomicrograph of Dermatophagoides farin Electron photomicrograph of Dermatophagoides farinae.

The concentration of dust mite allergens (an indirect assessment of exposure) is measured in micrograms per gram (μg/g) of settled dust from samples obtained by vacuuming a defined area of a carpet or mattress. The proposed threshold concentration of allergen exposure required to sensitize to dust mites is 2 μg of group 1 allergen (Der p 1 and Der f 1) per gram of dust. Levels of 10 μg/g of dust induce allergic symptoms or asthma in sensitized persons, but lower levels may also cause symptoms. [98]

Evidence that sensitization may occur at even lower levels also exists; hence, an individual genetically predisposed to develop allergic diseases may not have a safe level of exposure. More than 80% of homes in the United States and 85% of daycare facilities have detectable levels of dust mite allergens. [3] Furthermore, half of US homes have levels higher than the proposed threshold levels for sensitization; about 25% have levels at or higher than those required to induce asthma. [3]


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