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Nov 11

Allergy to house dust mites
House dust mites are the most common cause of asthma, allergic rhinitis and sometimes eczema. In Malaysia, house dust mites are found in all localities surveyed with 80% homes containing several species of mite in high numbers. In one Malaysian study, millions of mites were found multiplying in the mattresses of most homes throughout the country. The two most prominent house dust mites found locally are Blomia tropicalis and Dermatophagoides pteronyssinus. These two species have unique allergens that do not cross-react and should preferably be tested separately in a patient suspected of house dust mite allergy. About 85% of patients allergic to dust mites react to both species but the other 15% react to one or the other species.

Dust mites feed mainly on skin scales (derived from humans or mammalian pets), fungi, hair/fur and body fragments of dead insects. The life span of the adult mite is about 2 to 3 months and during this period it will lay about 50 eggs per month. These eggs hatch and mature in about twenty-five days in the tropics. The major allergen of the house dust mite is derived from the fecal pellets (each dust mite defecates about 50 pellets daily) and dead dust mite parts. The fecal pellets are about 20 microns in size and can reach the upper airways of people breathing them. Fecal allergens contain enzymes that allow the allergen to penetrate mucosal surfaces rapidly and cause immune allergic sensitization.

Exposure to high levels of house dust mite allergens during infancy increases the risk of allergic sensitization and the development of asthma in later life. In Malaysia about 90% of children with asthma or allergic rhinitis are positive for house dust mites. In adults with asthma the prevalence rate of mite sensitization is close to 70%. Many adults with non-specific chronic cough are often positive to house dust mite allergens. Many patients with eczema also react to house dust mites. All patients with asthma or allergic rhinitis should undergo allergy tests for house dust mites to identify the causal factors for long term management of their clinical symptoms. Many studies have emphatically demonstrated that reduction of exposure to the mites in the home environment significantly lead to the improvement of allergic symptoms. One company in Malaysia has experience in home management of house dust mites. They also supply allergy products (mattress/pillow allergicovers, anti-dust mite sprays and air-filters.)