House Dust Mite allergy
Do you have a house dust mite allergy?
Species and way of life
For centuries, house dust has been known to induce allergy and asthma symptoms in people with particular sensitivity. The Flemish physician, John Babtista van Helmont, described such symptoms in one of his patients as early as 1662 "... as soon as a place is swept or the wind whirls up the dust, he immediately falls over and is close to suffocation."
In the 1960s, researchers in both the Netherlands and Japan were able to independently prove that house dust mites from the family Pyroglyphidae, particularly Dermatophagoides pteronyssinus and Dermatophagoides farinae, were the main sources of allergens in house dust.
Allergens from house dust mites are known to cause sensitisation in sensitive people, and this sensitisation is linked to the development of allergic asthma in both children and adults. In addition, it is well documented that there is a dose-response relationship between exposure to house dust mite allergens and an increase in the severity and risk of worsening allergic asthma.
Asthma is a major health problem worldwide, and both its prevalence and severity seem to be increasing
Source: ALK-Abelló
In the Western world, up to 30% of 13-year-old children are sensitised to house dust mites, and this sensitivity constitutes a significant independent risk factor for developing asthma
Two species of house dust mites in the family Pyroglyphidae, namely D. pteronyssinus and D. farinae, are the most important in temperate regions – both in terms of numbers and health. Clinically, they are important because most asthma symptoms in children and young adults are due to both an immediate allergic reaction to their allergens in the air as well as a familial propensity to develop atopic diseases.
The house dust mite D. pteronyssinus produces at least seven major allergens (as well as an additional seven minor allergens) that are officially recognized by the WHO/IUIS Allergen Nomenclature Subcommittee. The most important allergen, group 1, Der p 1, is the most widespread and thus also the most researched in Europe.
Large amounts of Der p 1 are found in the faeces of house dust mites – reflecting their digestive processes, in which food and cell debris are enclosed by a peritroic membrane (a non-cellular membrane that surrounds the food item in the mite's middle intestine and makes a selective filtration: It acts as an ultra-filter or a semi-permeable membrane that allows the passage of small, digested nutrient molecules, especially from skin flakes, while retaining larger particles and potential pathogens.
House dust mites are about 1/3 mm long, colourless and rarely visible to the naked eye. They develop from eggs to adult house dust mites through several larval and nymph stages.
This development can take from a few weeks to many months, depending on the surrounding environment. When house dust mites thrive best, they produce 20-40 faeces particles a day.
The lifespan is 3-4 months and the female lays 20-40 eggs once or twice in her life.
House dustmites' food consists of epidermal material (hair and scales) from humans and animals, and well-being also depends on a suitable temperature and humidity. The development occurs fastest at 25ºC and a relative humidity (RH) of 70%.
Allergens
The main allergens are found in the excrement of house dust mites. Amino acid sequences show only a few differences between species.
For Dermatophagoides pteronyssinus, the structure of nine allergens is now known, Der p 1, Der p 2, Der p 3, etc.
The allergens are quite stable under normal housing conditions. Thus, the important Der p 1 allergen is not affected by heating to 60ºC, and the allergen activity is unchanged after storage for four years at 5-25ºC.
Mite occurrence
Source: ALK-Abelló
In our bed environment, sweat and evaporation from the skin will increase the humidity and enable house dust mite growth - even in cases where the moisture content of the air in the middle of the room is significantly below the requirements of the house dust mites. Therefore, the highest concentration of house dust mites in the home is most often found in the bed environment.
We lose several grams of skin scales every night in bed, enough to feed a clinically significant house dust mite population.
The environment, especially mite residues and faeces, from dust mites in upholstered furniture is similar to that of the bed, while carpets, in addition to housing an independent house dust mite population, can act as a reservoir for allergens in bed or furniture.
The house dust mites are found in small quantities in our clothes and can thus be transported from one home to another.
If there are suitable growth conditions, significant dust mite growth can occur in a new home after just 1-2 years, and if you just replace the mattress without other measures, the mites can cause symptoms again after just four months.
The same applies to clothes that are washed infrequently and stored in places where there are dust mites, such as in damp cupboards, basements or holiday homes.
Sleeping animals can also harbor many house dust mites.
In practice, it is the humidity that determines whether a house dust mite population can be established in a home or not. Homes where there is a relative humidity of less than 45% during the winter months have a very low dust mite incidence.
The humidity indoors is highest in late summer and autumn, and correspondingly, the concentration of house dust mites and house dust mite allergen is highest in the autumn months, although with very large variations from home to home.
In Denmark, significant house dust mite growth (more than 100 house dust mites/g mattress hesitation) was found in 24% of randomly selected bedrooms, while the frequency in bedrooms in a non-allergic group was as high as 48% in 1992.
Source: ALK-Abelló
We now see significant exposure to house dust mite allergens (more than 2 mg/g mattress hesitation) in two-thirds of children who are predisposed to atopy (hereditary predisposition to develop certain types of allergies) as early as six months of age and in 52% of all adults.
House dust mite allergens are widespread in the home and are found especially in carpets, furniture, mattresses, pillows, duvets, rugs, curtains, soft toys, clothes, furry animals – and can even be detected to a lesser extent in head hair, on the skin and in umbilical cord blood.
A large study from New Zealand showed that dust samples from floors, beds and seats in hotels, hospitals, nursing homes, primary and secondary schools, cinemas, churches, ski huts, banks and airplanes, the level of P 1 was significantly lower in these public places compared to the home environment.
Although the level was significantly lower, it was found that carpets in public spaces are still an important source of dust mite allergens, and that lower Der p 1 level is related to how often cleaning is done.
Allergen-proof covers like AllerGuard significantly reduced dust mite allergens on all types of bedding (5, 16, and 76 times for pillows, duvets, and mattresses, respectively). The reduction of Der p 1 in the air was more moderate, but still up to a sixfold increase
