Mite is the common name given to arthropods of the order Acarina, belonging to the class Arachnidae, to which more than 30,000 known species belong, although there are possibly many unclassified others. House dust mites are visible only under the microscope and measure between 200 and 500 micrometers. However, in addition to land mites, there are also aquatic mites, including marine ones. They are mostly predators, but there are also plant eaters, detritivores and parasites. The order Acarina also includes ticks.
Habitat and reproduction
In houses, mites feed on human and animal skin scales. Per day, humans lose 1g of these pieces of skin. Mites are abundant on mattresses, wool blankets, feather pillows, carpets, rugs, sofas and stuffed toys and thrive in optimal conditions of above average humidity of 70 to 80% and temperature above 20°C. At altitudes of over 1200 m, mites no longer have good living conditions. For this reason, staying in high mountain regions can lead to the relief of certain allergies. They live 2 to 3 months, during which time they mate 1 to 2 times, laying 20 to 50 eggs. The most favourable time for mating is spring and autumn.
Mite droppings and dead mites disperse as fine dust, are inhaled and may cause allergies.
The mite allergens are well known. Major antigens are Der p1 (D. pteronyssinus), Der f1 (D. farinae) and Eur m1 (Euroglyphus maynei).
For sensitization to dust mites to occur, a Der p1 antigen level greater than or equal to 2 microns per gram of house dust is required. The prevalence of dust mite sensitisation in the general population is estimated to be around 10 to 20%. They are responsible for the majority of cases of perennial allergic rhinitis and asthma and also play an important role in atopic dermatitis. Some rare cases of anaphylaxis after eating food contaminated by large amounts of D. farinae (flour, pizzas, fish and vegetables, among others) have been described.
Preventive avoidance measures for house dust mites reduce clinical symptoms and are the first step in the treatment of dust mite allergic patients. These measures include:
– Daily aeration of rooms;
– Air and sun exposure of mattresses, quilts and pillows;
– Frequent washing of mattresses, duvets and pillows at 60°C;
– Regular and frequent vacuuming of mattresses and carpets using hoovers equipped with HEPA filters;
– Treat mattresses and carpets with acaricides;
– Use anti-dust mite covers on mattresses, duvets and pillows;
– Avoidance of domestic animals;
– Removal of carpets;
– Wash cuddly toys weekly;
– Maintain a dry atmosphere inside the houses (relative humidity at 50 to 60% and temperature between 18 and 20°C);
– Control the avoidance measures with the Acarext test (R), which estimates the number of dust mites present.
The effectiveness of ionisers and air purifiers, as well as mechanical ventilation, has not been demonstrated.
Specific immunotherapy with vaccines is recommended in sensitised patients when clinical symptoms are not controlled with avoidance and pharmacological treatment of symptoms.