House dust mites and their allergens at selected locations in the homes of house dust mite-allergic patients

BACKGROUND: Knowledge of the occurrence of house dust mites (HDM) and their allergens in domestic locations is important when planning intervention. OBJECTIVE: The aim of this study was to describe the distribution of HDMs and their allergens before intervention in multiple locations in the homes of newly diagnosed HDM-allergic patients with a known high Der 1 concentration in their mattress dust. METHODS: Dust was collected from ten locations in the homes of eight HDM-allergic patients. Dust was analysed for allergen content with ELISAs for Der f 1, Der p 1 and Der m 1; and HDM were counted. Total allergen concentrations ( micro g Der 1/g dust) were expressed as the sum of Der f 1, Der p 1 and Der m 1. RESULTS: On mattresses the median concentration was 86 micro g Der 1/g dust (range 30-288) and 188 mites/g dust (range 12-1910). Der 1 exceeded 10 micro g/g dust in mattresses (8/8), duvets/pillows (3/8), a bedroom carpet (1/1), a living room carpet (1/6), upholstered furniture (2/8) and a curtain (1/5). Uncarpeted floors, upholstered furniture, bookshelves and walls had significantly lower Der 1 concentration than the mattresses. The relative contribution of Der p 1, Der f 1 or Der m 1 to Der 1 was related to homes, rather than to the location. Der m 1 only occurred in minute amounts. CONCLUSION: For HDM intervention, our results indicate that priority should be given to the removal of allergens from mattresses, and in addition from carpets, duvets/pillows and upholstered furniture. Dust from walls, uncarpeted floors, bookshelves and curtains appear to contribute insignificantly to the domestic HDM allergen load.     

House dust mite control measures for asthma: systematic review

The major allergen in house dust comes from mites. We performed a systematic review of the randomized trials that had assessed the effects of reducing exposure to house dust mite antigens in the homes of people with mite-sensitive asthma, and had compared active interventions with placebo or no treatment. Fifty-four trials (3002 patients) were included. Thirty-six trials assessed physical methods (26 mattress covers), 10 chemical methods and eight a combination of chemical and physical methods. Despite the fact that many trials were of poor quality and would be expected to exaggerate the reported effect, we did not find an effect of the interventions. For the most frequently reported outcome, peak flow in the morning (1565 patients), the standardized mean difference was 0.00 (95% confidence interval (CI) −0.10 to 0.10). There were no statistically significant differences in number of patients improved (relative risk 1.01, 95% CI 0.80–1.27), asthma symptom scores (standardized mean difference −0.04, 95% CI −0.15 to 0.07) or in medication usage (standardized mean difference −0.06, 95% CI −0.18 to 0.07). Chemical and physical methods aimed at reducing exposure to house dust mite allergens cannot be recommended.     

Permeability of synthetic and feather pillows to live house dust mites and house dust

BACKGROUND: Previous studies have demonstrated significantly higher house dust mite (HDM) allergen levels from synthetic pillows, compared to feather pillows. Reasons for these differences could be lower permeability of feather pillow coverings to allergen in dust, greater HDM penetration of synthetic pillow covering, or both. OBJECTIVES: To determine the permeability of synthetic and feather pillow coverings to live HDMs and house dust. METHODS: Twenty live adult HDMs were seeded on top of two types of synthetic pillow covering (one standard polyester and one newer polyester/cotton type) and one type of feather pillow coverings with adequate food supply below in sealed culture dishes, kept at 23 degrees C and 70% relative humidity. After 24 and 48 h live HDM numbers remaining on top of the coverings were enumerated microscopically. Three aliquots of fine house dust (each in triplicate) were placed on top of the synthetic and feather pillow coverings, shaken gently for 30 min and penetrated dust was collected and weighed. RESULTS: After 24 h, all 20 HDMs had penetrated the standard synthetic pillow coverings, and no HDMs had penetrated either the feather pillow or the new synthetic pillow coverings after 24 or 48 h. Dust permeability (% of applied dust) for the standard synthetic, new type synthetic and feather pillow coverings were 0.88%, 0.07%, and 0.07%, respectively. This compared to 0.02% for a commercial occlusive pillow cover. CONCLUSIONS: These findings of total permeability of standard synthetic pillow coverings to live HDMs, and their greater permeability to house dust could explain their reported higher HDM allergen levels, compared to feather pillow coverings. Newer types of synthetic pillow coverings are similar to feather pillow coverings in their permeability to live HDMs and house dust.     

Usefulness of specific immunotherapy in patients with atopic dermatitis and allergic sensitization to house dust mites: a multi-centre, randomized, dose-response study

BACKGROUND: The effect of specific immunotherapy (SIT) on eczema in atopic dermatitis is not known. Therefore, a multi-centre, randomized dose-response trial, double-blind with respect to the efficacy of a biologically standardized depot house dust mite preparation was performed. METHODS: Eighty-nine adults with a chronic course of atopic dermatitis, SCORAD >or=40 and allergic sensitization to house dust mites [CAP-FEIA >or=3] were included, of whom 51 completed the study. Subcutaneous SIT with a house dust mite preparation (Dermatophagoides pteronyssinus/D. farinae) applying maintenance doses of 20, 2,000 and 20,000 SQ-U in weekly intervals for 1 year. The main outcome measures addressed the change of the SCORAD as average of the values after 9 and 12 months of SIT in comparison with the value at baseline. RESULTS: The SCORAD declined in the three dose groups in a dose-dependent manner (P = 0.0368, Jonckheere-Terpstra test) and was significantly lower in the two high-dose groups (2,000, 20,000 SQ-U) compared with the low-dose group of 20 SQ-U (P = 0.0379, U-test) after 1 year of SIT. The use of topical corticosteroids was significantly reduced with higher doses (P = 0.0007, Mantel-Haenszel chi-square test). CONCLUSIONS: Allergen-SIT for 1 year with a house dust mite preparation is able to improve the eczema in patients with atopic dermatitis who are sensitized to house dust mite allergens and reduces the need for topical corticosteroids. SIT may be valuable in the treatment of this chronic skin disease.     

Skin thymic stromal lymphopoietin promotes airway sensitization to inhalant house dust mites leading to allergic asthma in mice

Asthma is often preceded by atopic dermatitis (AD), a phenomenon known as 'atopic march'. It has been suggested that sensitization to common inhalant allergens, which is developed in a majority of patients with AD and often during the course of AD, may play a critical role in triggering the atopic march. Yet, what signal(s) delivered by AD skin could promote sensitization to inhalant allergens remains elusive. Here, by employing an experimental mouse asthma protocol, which is induced by airway sensitization and challenge to inhalant house dust mite (HDM), we demonstrate that the overproduction of cytokine thymic stromal lymphopoietin (TSLP) by AD skin promotes airway sensitization to HDM, thereby triggering subsequently an allergic asthma. Together, this study provides, for the first time, the experimental proof that TSLP represents an AD skin-delivered signal to promote sensitization to inhalant aeroallergen, which may account for one mechanism underlying the 'atopic march'.     

Birth month and sensitization to house dust mites in asthmatic children

Background: Early exposure to high quantities of allergen has an important role in the incidence of atopic sensitization. In fact, subjects sensitized to house dust mites (HDMs) have a significantly higher proportion of births in the season when HDMs are most abundant. Objective: The aim of this study was to investigate whether birth month patterns differ for asthmatic patients sensitized only to HDMs and for those sensitized to HDMs and other allergen(s). Methods: Among 2225 patients with asthma, aged 10–16 years, 1642 sensitized to HDMs were identified by skin prick testing. This group was composed of patients sensitized only to HDMs (n = 715) and patients sensitized to HDMs and other allergen(s) (n = 927). The birth month distributions of the group of HDM-sensitive asthmatics or its subgroups were compared with that of a reference population (total live births in the same years as the studied subjects). The risk ratio of a given birth month in relation to all the other months was calculated as an odds ratio (OR) with the corresponding 95% confidence interval (CI). Results: A significant difference in birth month distribution was observed for HDM-sensitive asthmatics (χ² = 23.6, P = 0.015), with higher rates of birth in August (OR: 1.23, 95% CI: 1.04–1.46) and September (1.24, 1.04–1.46). When the two subgroups were analyzed separately, significantly more births were noted in August (1.34, 1.06–1.71) and September (1.34, 1.05–1.70) for those sensitized only to HDMs, whereas no such birth month preference was observed for those sensitized to HDMs and other allergen(s). Conclusions: The HDM-positive asthmatics showed a greater proportion of births in August and September, which correspond to high HDM exposure. However, this birth month pattern was evident in asthmatic-sensitive only to HDMs, but was not observed in those sensitive to HDMs and other allergen(s).     

Allergen immunotherapy in atopic dermatitis

Introduction: Atopic dermatitis (AD) is a chronic relapsing skin disease, characterized by flare-up due to the exposure to allergens in patients sensitized to them. Currently, therapy of AD is mainly based on symptomatic treatment and avoidance of irritating/allergenic factors, house dust mites being particularly important. Allergen immunotherapy (AIT) is suggested to be the only etiologic treatment, to modify the natural history of the disease.

Areas covered: The aim of this review is investigating the putative role of AIT in AD through the evaluation of the most recent scientific literature. Several studies have been conducted since 1970, with promising results in improving the clinical outcome of AD, but they often lack the necessary scientific rigorousness. Moreover, heterogeneity of the studies makes it very difficult to compare and to analyze data in a systematic review or meta-analysis.

Expert commentary: As a result of the above-mentioned limitations, the treatment of AD with causative aeroallergen can nowadays be suggested only as an add-on therapy in selected patients who are non-responsive to the traditional therapy.     

Retrospective Analysis on the Effects of House Dust Mite Specific Immunotherapy for More Than 3 Years in Atopic Dermatitis

PurposeIn extrinsic atopic dermatitis (AD), house dust mites (HDM) play a role in eliciting or aggravating allergic lesions. The nature of skin inflammation in AD has raised a growing interest in allergen-specific immunotherapy (SIT). Thus, we assessed clinical improvement and laboratory parameters for evaluation of the benefit of long-term SIT.ResultsImprovement after SIT therapy was observed in 192 out of 217 patients (88.4%). Among these patients, 138 (63.5%) achieved excellent, near-complete or complete clinical remission. Significant reduction of pruritus, LOS, and the mean value of total serum IgE were observed (p<0.01). Better outcome was found in patients younger than 12 years of age (p=0.024). Patients with moderate to severe AD showed better treatment outcomes (p=0.036). Patients sensitized only to HDM had the better response to treatment, but SIT was also effective in multi-sensitized groups (p=1.051). No significant differences in baseline laboratory results were observed between good and poor responders (p>0.05).ConclusionWe emphasize the usefulness of long-term HDM SIT as a disease-modifying therapy for AD.     

The control of house dust mites in rugs through wet cleaning

Nine rugs from the bedrooms of seven private homes were cut into strips. Half of the strips were wet-cleaned according to a commercial procedure, and the others were kept as controls. Subsequently the cleaned and noncleaned strips were stitched together again and returned to their respective bedrooms. After 0, 1, and 3 months, parts of the strips were taken to the laboratory for tests. The tests were designed to measure the suitability of the rugs as a habitat for house dust mites. To do this, a number of house dust mites were introduced into fragments of the rugs, and the number of survivors and offspring after 4 weeks was determined. Immediately after cleaning, the habitat was markedly less suitable than before. After 1 month, the habitat suitability was partly but not totally recovered. After 3 months, no effect of cleaning could be discerned. (J ALLERGY CLIN IMMUNOL 1996;97:1214-7.)     

The use ofdomestic steam cleaning for the control of house dust mites

Background Control of dust mites using extremes of temperature is un alternative to the use of acaricides. In ihe past we have attempted control by freezing with liquiid nitrogen. The present paper deals with the opposite exlrcnic, the use of steam.
Objective To assess the feasibility inid effectiveness of a domestic steam cleaner for the control of dust mites. its effect on mite populations and concentrations of the allergen Der p I.
Methods A domestic steam cleaner was used to treat earpet squares that had been seeded in the laboratory with known numbers of dust mites ( Dermatophagoides pterpmussomis ). The number of live mites was monitored for a period of 4 months in eight treated earpet squares and eight controls. Dust samples were taken from 12 standardized areas of carpet in a tenement flat in Glasgow, UK., before and after steam cleaning treatmet. and the concentration of allergen Der p 1 was compared with 12 adjacent. control areas.
Results No live mites were found at any time in the treated carpet squares, whereas in the control squares geometric mean mite population density rose frotn 11 after 3 days to 39 after 1 month, 66 after 2.122 after 3 and 185 after 4 months. There was a mean reduetion of 8.7% in Der p I concentration (3.3-0.44 μg/g) compared with a reduction of 4.7% (2.22-2.l16μg/g) in control areas, a difference that was statistically significant at the 5% level.
Conclusion These data indicate that steam cleaning has considerable potential as an highly effective and efficient method of killing dust mites and reducing concentrations of Der p 1 in domestic premises.     

Sensitization to dust mites in children with allergic rhinitis in Singapore: does it matter if you scratch while you sneeze?

BACKGROUND: Previously published data established Blomia tropicalis, as the major source of allergic sensitization in asthmatic children in tropical Singapore. Objective To define the prevalence, clinical characteristics and risk factors of species-specific mite sensitization in paediatric allergic rhinitis (AR) patients in this unique environment. METHODS: We performed a prospective evaluation of newly diagnosed AR patients, from 1 May 2003 to 30 April 2004, from the otolaryngology and allergy outpatient clinics of the Kendang Kerbau Children's Hospital in Singapore. Patients included in the study showed evidence of sensitization to at least one respiratory allergen source and completed a detailed questionnaire. Relative risk of sensitization and associated risk factors were calculated using logistic regression analysis with the forward stepwise model. Multivariate regression analysis was performed to adjust for confounding interactions. Continuous values were compared using anova, SPSS 9.0 for Windows (SPSS Inc., 1999). RESULTS: One hundred and seventy-five patients were included, 119 (68%) males, 142 (81%) Chinese, age mean 7.9 years (range 2-16). Sixty-eight patients (39%) reported a concomitant diagnosis and/or clinical complaints of bronchial asthma and 84 (48%) of atopic dermatitis. Skin prick test results were positive for traditional house dust mites (Dermatophagoides pteronyssinus. and D. farinae mix) in 85% of patients and for B. tropicalis in 62%. Overall mite sensitization was 98%, household pets 10%, moulds 9% and food proteins 12%. By far the single most significant factor associated with Dermatophagoides sensitization in this group was the presence of allergic eczema (odds ratio (OR) 31.8%, 95% confidence interval (CI) 3.6-285, P=0.002). Allergic eczema was negatively associated with B. tropicalis sensitization (OR 0.26%, 95% CI 0.14-0.5). CONCLUSIONS: Children with AR and concomitant atopic dermatitis show a preferential sensitization to the Dermatophagoides mites. In our population, B. tropicalis sensitization is more prominent in children with pure respiratory allergy.     

The efficacy of sublingual immunotherapy for house dust mites respiratory allergy: results of a GA²LEN meta-analysis

Recent meta-analyses documented the efficacy and safety of sublingual immunotherapy (SLIT) in patients with allergic rhinitis (AR) and asthma (AA). Although SLIT appeared globally effective, the sub-analyses for single allergens provided uncertain results. This study is aimed to investigate the efficacy of SLIT with house dust mite (HDM) extracts in AR and AA through an updated reassessment of randomized controlled trials. Electronic databases were searched up to March 31, 2008, for randomized DBPC trials, assessing the efficacy of SLIT in AR and AA due to HDM sensitization. Outcomes were symptom scores and rescue medications use. For AR, eight studies fulfilled the selection criteria. A significant reduction in symptoms of AR (SMD −0.95; CI 95%−1.77 to −0.14 P  = 0.02) was found in 194 patients (adults and children) receiving SLIT compared to 188 receiving placebo. For AA, with nine studies, similar results were found for symptoms (SMD −0.95; CI 95%−1.74 to −0.15 P  = 0.02) in 243 patients (adults and children) receiving SLIT compared to 209 receiving placebo. A reduction in rescue medication use was found for AR (SMD −1.88; CI 95%−3.65 to −0.12 P  = 0.04) in 89 patients, and AA (SMD −1.48; CI 95%−2.70 to −0.26 P  = 0.02) in 202 patients. A relevant inter-study heterogeneity was detected. Promising evidence of efficacy for SLIT, using mite extract in allergic patients suffering from AR and AA, are herein shown. These findings suggest that more data are needed, derived from large-population-based high quality studies, and corroborated by objective outcomes, mainly for AA.     

Low-level exposure to house dust mites stimulates T-cell responses during early childhood independent of atopy

Background The imtnune responses which underlie the expression of allergic symptotns in childhood are believed lo be initiated in infancy and early childhood. The kinetics of this response have hardly been researched. Objective To analyse, in an environment with low house dust mite (HDM) exposure levels, the relationship between house dust mite (HDM)-specific T-cell reactivity as expressed by in vitro proliferation of blood mononuclear cells. Methods The study comprised a prospective analysis of patterns of allergen-specific T-cell reactivity in a cohort of 19 children, from whom blood samples were obtained in the spring during their second and third years of life. Blood mononuclear cell cultures were established in 200 μL AIM-V serum free medium. Crude house dust mite (HDM) and purified Der p 1 and Der p 2 extracts were used at optimal concentrations, i.e. 100μg/mL for HDM and 30μg/mL for the purified allergens. Tetanus toxoid (0.5 μglrnL) and ovalbumin (10 μg/mL) served as positive controls. A clinical diagnosis of allergy was verified with skin-prick tests. Dust samples were collected from a mattress and/or carpet or sofa in homes, day care centres and day care homes. Major mite allergen levels (Der p 1/Der f 1) in dust were analysed by an enzyme linked immunosorbent assay (ELISA). Results Specific T-cell responses were seen in the majority of the children against house dust mite (crude HDM extract. Der p 1 and Der p 2). The levels of the house dust mite allergens Der p 1 and Der f I were low, i.e. < 0.68 μg/g fine dust in the homes of the children and the day care centres that they were attending. This indicates that doses of mite antigen well below the suggested sensitization threshold level of 2 μg/g dust can induce mite-specific T-cell responses in young children. None of them showed clinical reactivity to house dust mites as indicated by negative skin-prick tests. Conclusions The findings suggest that active immunological recognition of environmental allergens and the ensuing initiation of allergen-specific T-cell responses, is a normal part of the ‘education’ of the immune system in early childhood and can occur even at very low exposure levels. Priming per se does not imply clinically significant sensitivity, however.     

House dust mite allergen (Der p 1) accumulation on new synthetic and feather pillows

BACKGROUND: We have previously demonstrated that synthetic pillows contain significantly more Der p 1 than feather pillows. The aim of this study was to compare the accumulation of Der p 1 allergen on new synthetic and new feather pillows. METHODS: Der p 1 was measured in dust samples from pairs of synthetic and feather pillows placed together on 12 beds over a 12-month period. RESULTS: After 12 months synthetic pillows contained higher concentrations of Der p 1 (19.28 microg/g; 95% confidence interval: 9.76-38.07) than feather pillows (6.45 microg/g; 2.96-14.05). There was a significant correlation between Der p 1 concentrations of pillows at 12 months and Der p 1 concentrations of the mattresses at the beginning of the study (r = 0.72; P = 0.008 for both types of pillows). CONCLUSIONS: Synthetic pillows accumulate Der p 1 more rapidly than feather pillows and the accumulation rate of Der p 1 on pillows is governed by the Der p 1 concentration in the immediate environment they are placed in.