|Year : 2019 | Volume
| Issue : 1 | Page : 14-18
An Indian perspective on dust mites
Department of Respiratory Medicine, School of Medical Sciences and Research, Sharda Hospital, Greater Noida, Uttar Pradesh, India
|Date of Web Publication||12-Jun-2019|
Dr. S N Gaur
Gaur Clinic, 130-A, Patparganj Village, Delhi - 110 091
Source of Support: None, Conflict of Interest: None
Dust mites are the most important group of indoor allergens. The dust mites have been classified as house dust mites and storage mites, however, with recent knowledge the different dust mite species are now labelled as “domestic mites.” The dust mites have been isolated at numerous Indian locations and their sensitization in Indian population has also been documented. In view of high sensitization in India, it is important to recognize the role of dust mites and their allergens in the precipitation of allergic diseases including allergic rhinitis and asthma. Allergies to dust mites can be confirmed by a classical clinical history of perennial, early morning and indoor symptoms substantiated by a positive skin prick test to these allergens. Further management of allergies to mites is possible using appropriate allergen avoidance measures and allergen immunotherapy. Multifaceted avoidance measures can be used, but, allergen avoidance by the means of an allergen impermeable bed encasings has the best evidence and is recommended in different guidelines. Allergen immunotherapy, the disease-modifying modality, has been proven to efficacious for house dust mite allergies.
Keywords: Allergen-impermeable bed encasings, domestic mites, immunotherapy, indoor allergens
|How to cite this article:|
Gaur S N. An Indian perspective on dust mites. Indian J Allergy Asthma Immunol 2019;33:14-8
| Introduction|| |
Allergy to dust mites has been strongly associated with the development of respiratory allergic diseases, such as asthma and allergic rhinitis. In addition to these, they have the potential to cause conjunctivitis, atopic dermatitis, and in rare cases anaphylaxis, which may result from ingestion of mite-infested food.
Dust mites are a potent source of indoor allergens; their specific biology allows them to thrive in indoor domestic conditions and also allows them (their allergens) to be in close contact with living persons. House dust has been considered as a trigger of asthma for >300 years; however, it was only in 1964 that house dust mites (HDMs) were reported as the actual source of house dust allergens. This review discusses the classification of the allergenic mites, diseases causes by them, with a focus on the Indian perspective in views of prevalence and distribution of dust mites in India, and finally evaluates the available management strategies against dust mites.
| Allergenic Dust Mites|| |
Mites are included in the subclass Acari along with the ticks, while the allergenic domestic mites belong to the order Astigmata. Being a part of Astigmata, means that they do not have external respiratory openings or stigmata.
Allergenic dust mites are broadly classified as HDMs and storage mites. The HDM predominantly include the two Dermatophagoides species, Dermatophagoides pteronyssinus and Dermatophagoides farinae. Although storage mites are commonly found in the storage facilities for grains, they are also found in the house dust. The best-recognized storage mites are Acarus siro, Blomia tropicalis, Glycyphagus domesticus, Lepidoglyphus destructor, and Tyrophagus putrescentiae.,
As both HDM and storage mites are found in the indoor environment, a new term “domestic mites” has been coined. Under the “domestic mites,” all the above-mentioned species which can be regularly found in the indoor environment, including bedding, sofas, and kitchen floors, are included [Figure 1].
Environmental conditions conducive for growth of dust mites
Temperature (25°C–30°C) and humidity (55%–75% RH) are required by the dust mites to thrive well. In addition, they require human or pet skin scales, which are colonized by fungi, yeasts, and bacteria. These factors along with the fact that they are light sensitive and photophobic probably explain their distribution – pillows, mattresses, carpets, soft toys, upholstered materials, and clothing., Among these beds are the best sources of food and conditions for mites to proliferate [Table 1]., Knowledge on the sources of dust mites is essential to implement targeted avoidance strategies.
Clinically relevant defined as a cutoff of >2 μg/g of dust, which can induce allergic sensitization and asthma.
Allergens of dust mites
The identified allergens from dust mites as mentioned on www.allergen.org are as follows:
- D. pteronyssinus: 23 allergens
- D. farinae: 32 allergens
- Euroglyphus maynei: 5 allergens
- A. siro: 1 allergen
- B. tropicalis: 14 allergens
- G. domesticus: 1 allergen
- L. destructor: 5 allergens
- T. putrescentiae: 8 allergens.
Many allergens from D. pteronyssinus and D. farinae show significant homology. The allergens from D. pteronyssinus have been identified as proteases Der p1, 3, 6, 9, 20), lipid-binding proteins Der p2, 7, 13, 14), contractile proteins Der p10, 11, 16, 17, 24), glycosidases and carbohydrate-binding proteins (Der f 4, 12, 15, 18, 23), glutathione S transferase Der p8), heat shock protein-70, and some allergens have unidentified function Der p5, 19, 21, and 22). Der p23 is a recently identified dust mite allergen, for which IgE is common – however, it represents only a small percentage of the total antidust mite IgE.
Among the HDM allergens, Group 1 and 2 bind to >50% of the amount of IgE that binds to HDM extracts (i.e., major allergens). Der p 23 also has similar IgE binding prevalence, but not all studies have found high titers. The medium or mid-tier allergens binding IgE in 30%–50% of mite-allergic patients are group 4, 5, 7, and 21.
It should also be noted that the sensitization to the different major and minor allergens has been found to comparable in patients from different geographical locations (Asia, Europe, and North America). Group 1 (Der p1, Der f 1) and Group 2 (Der p2, Der f 2) allergens are the major allergens in the different geographical locations. The major allergens (Group 1 – Der p1, Der f 1 and Group 2 – Der p2, Der f 2) from dust mites have been isolated from Indian homes and have also been estimated in the sera of Indian patients., In view of the available Indian data, these allergens can be considered as important.
| Diseases Associated With Dust Mites|| |
Diseases caused by the dust mites can be differentiated as per the method of exposure [Figure 2].
| Dust Mites in India|| |
Numerous Indian studies have documented the presence of the allergenic dust mites in different parts of the country [Table 2].,,,,,,,
Data from the different studies have shown the pan-Indian presence of the domestic mites. Clinicians should, therefore, be aware on the importance of the different mites and utilize the information appropriately. Among the different species, however, most work has been done on the Dermatophagoides species including data on sensitization, allergen avoidance, and allergen immunotherapy.
Dust mites have been recognized as an important sensitizer in the Indian populations. Like the studies on the presence of these mites in different geographical areas, a number of studies have also observed the sensitization to the different mite species [Table 3].,,,,,
From the available data as summarized in [Table 2] and [Table 3], it becomes evident that the two Dermatophagoides species (D. farinae and D. pteronyssinus) are the most important sensitizers across India and should be evaluated in all patients with perennial respiratory allergic diseases.
| Management of Allergies to Dust Mites|| |
Diagnosis of dust mite allergy is dependent on clinical history of the patient and documented sensitization for which skin prick tests are considered as the gold standard. Pointers of dust mite allergy on the clinical history include:
- Perennial symptoms (with possible seasonal exacerbations)
- Symptoms which are aggravated when the patient comes in contact with household dust and domestic/indoors activities
- Improvement in symptoms at high altitudes.
Standardized skin prick test allergens have recommended by various international authorities, and it becomes increasingly important for the diagnosis of dust mite allergens. As documented in the section on “allergens of dust mites,” there are numerous allergens in the dust mites. The presence of the important allergenic components is essential for appropriate diagnosis of patients. In an experimental research, Casset et al. evaluated the presence of the major and the important minor allergens amongst diagnostic extracts from different manufactures in Italy. Only two diagnostic extract manufacturers (including Merck) had the presence of the major (Der p1, Der p2) and the important minor allergens (Der p5, Der p7, Der p10, and Der p21). The other eight diagnostic extracts had either one or more missing minor allergens.
Recently, an Indian study evaluating the potency of dust mite allergen extracts has reported low potency of indigenously manufactured extracts. The authors had concluded that there is an urgent need for policymakers to institute stringent criteria for standardization of antigens in India.
Nasal provocation tests, currently not available in India, have also been used to confirm the diagnosis of allergy to dust mites.
Dust mites are ubiquitous allergens, and a number of interventions have been recommended to minimize exposure and thereby limit the symptoms due to exposure. It is important to note that household avoidance strategies are more likely to control or minimize allergic disease rather than prevent sensitization itself.
The avoidance strategies aim to reduce exposure and are targeted against the source of allergens or to reduce the environmental conditions conducive for the growth of dust mites [Table 4].,
Allergen immunotherapy (AIT) is the only disease modifying therapy for the treatment of allergic diseases. AIT has been recommended and is utilized for patients with HDM allergy. For AIT, the evidence is maximum and strongest for the two Dermatophagoides species. Limited data are available for the other mite species.
The Indian Guidelines on the practice of AIT also have recommended HDM as an important and potential target for the use of AIT.
Among the two routes of applications, subcutaneous immunotherapy (SCIT) and sublingual immunotherapy (SLIT), numerous trials and meta-analyses have been published. A summary of the available meta-analysis is provided in [Table 5].
|Table 5: Summary of meta-analysis for house dust mites allergen immunotherapy|
Click here to view
Importantly, the number needed to treat to have one asthmatic patient from deteriorating was calculated to be 6 for HDM SCIT.
It should be noted that while a dose of 5–20 μg of the major allergen is considered to be an effective dose in SCIT, corresponding data for SLIT are insufficient.
The expected benefits of AIT for HDM allergy are in line with the benefits for AIT and have been captured in [Box 1].,,
| Conclusion|| |
Dust mites are important sources of indoor allergens, and the clinicians should be aware of their presence in the Indian environment. Different allergenic mites have been isolated in India, and their corresponding sensitization rates have also been published. Indian clinicians should consider the role of dust mites in the development of respiratory allergies in their patients and should use appropriate diagnostic, avoidance, and immunotherapy schedules for optimal treatment outcomes.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]