House dust mite allergy – Indian perspective

Background: Although the prevalence of allergic diseases are more common in westernized and developed countries, the incidence is increasing in a rapid pace in developing countries like India too, becoming doubled, tripled and even quadrupled in the last few decades. However, data in this regard is still fragmentary except few scattered information in Indian context. In a rough estimate, In India, 250 million people are suffering from one or more allergic manifestations.

Methods: During last more than 20 years, studies on different aspects of house dust mite allergy have been carried out on Kolkata population including entomological, clinical and immunological parameter through identification of allergenic mites, allergy skin tests and estimation of total IgE level, and identification of allergen specific IgE antibodies.

Results: An inventory of house dust mite fauna of Kolkata, India has been prepared. A total of 53 species belonging to 34 genera, 12 families and 3 orders have been identified, of which 18 species have been recorded for the first time from India and 7 species were identified as new to science. The genus Dermatophagoides alone constituted 60% of the total acarine fauna, predominated by D.pteronyssinus (47%) followed by Blomia tropicalis, D. farinae and Austroglyciphagous geniculatus. Both D. pterinyssinus (DP) and D. farina (DF) co-existed in the same habitat and maximum number of mites isolated from an individual dust sample was 13750/gm of dust. Seasonal trend indicates mite count were higher in pre-monsoon and minimum during winter. Preliminary screening through Skin Prick Test showed 83% patients reacted positively towards allergens of mites (either DP or DF), 92% patients had elevated levels of serum IgE and the mean value higher than control sera (p<<0.001). 85% patients of the study group showed allergen specific IgE antibodies against house dust and Dermatophagoides mites.

Conclusions: The study confirms that DF is the main source of allergen in house dust of Kolkata Metropolis followed by DP. Increased use of heavy curtains, blankets, padded furnitures, sofa sets, soft toys and use of foam mattress instead of conventional cotton mattress favours the growth and multiplication of house dust mites, which ultimately increases the chances and duration of exposure to those indoor allergen. Metamorphic changes in life style including diet and dietary habits, acquisition of Western lifestyle, low standard of indoor environment, increasing air pollution and over all intolerable psychological stress are blamed for such an increased occurrence and frequent recurrences in India.