Transient sensitization to house-dust mites a study on the influence of mite exposure and sex

This study aimed to evaluate the prognosis of a previous positive skin test to house-dust mites (HDM) in relation to environmental exposure. A total of 115 children, 50 from Stockholm and 65 from northern Sweden, all with a previous (average 2.5 years) positive Phazet (Pharmacia AB, Uppsala, Sweden) skin prick test (SPT) to extracts of Dermatophagoides pteronyssinus (Dpt) and/or D. farinae (Df) were included. Dust samples were collected from the children's mattresses, and the total (Dpt, Df, and D. microceras [Dm]) amount of major mite allergen was measured by ELISA (50 children) and expressed as microgram allergen per gram of dust, or was measured by microscopy (65 children). The results of microscopic mite counts were transformed to approximate allergen levels as 2 μg equals 100 mites per gram of dust. Of 115 originally SPT-positive children, only 48 (48%) remained positive at re test, while the majority (58%) were SPT negative after 2 years. Among the 67 converted children, 11 were still exposed to mite allergen, but only to low concentrations (only one converted child being exposed above the suggested threshold level [TLV] of 2 μg/g), compared to 15/48 children still SPT positive who were exposed above the TLV. This shows that continued mite exposure is a major risk factor (OR = 30, CI 4.8–184) for continued positive SPT to HDM. A minor risk factor for continued sensitization was sex, boys having a higher risk than girls (OR=2.2, CI 1.0–4.8). In conclusion, a surprisingly high rate of SPT conversion occurred, mainly as a result of a favorable indoor environment with low exposure to HDM and, to a lesser degree, as a result of sex. The present results support the view that the risk level of exposure is 2 μg mite allergen per gram of dust.     

Asthma, mite sensitization, and sleeping in bunks.

BACKGROUND: Mattresses and bedding are the main reservoirs of house dust mites. OBJECTIVE: Subjects sleeping in the bottom bunk may be exposed to house dust particles detached from bedding of the top bunk. Our aim was to ascertain whether this exposure could influence the development of mite sensitization and/or allergic symptoms in these individuals. METHODS: Symptoms of allergic respiratory disease were recorded and mite skin tests performed in 94 consecutive bunk-sleeping subjects (47 pairs of siblings) from an outpatient allergy clinic. Levels of Der p I, Der f I, and Der II were determined by enzyme-immunoassay in 16 randomly selected bedding dust samples (8 pairs of bunks). RESULTS: Mite sensitization rate and prevalence of allergic respiratory disease were similar for the top-bed and bottom-bed groups, whereas prevalence of asthma was significantly higher in the latter. Mite sensitization was significantly associated with family atopy background, whereas other factors such as house pets, indoor smoke exposure or types of mattress or bunks were not. Der p I levels higher than 2 microg/g dust were found in 12 of the 16 mattresses and the median of the 8-bed-bottom group was over 10 microg/g. CONCLUSIONS: Sleeping in bunks constitutes a greater risk of developing asthma for subjects sleeping in the bottom bed. Bunk sleeping should be discouraged in families with an atopic background and sensitized subjects should use the top bed.     

Nonlinear relations between house dust mite allergen levels and mite sensitization in farm and nonfarm children

BACKGROUND: Low sensitization rates to common allergens have been observed in farm children, which might be due to high exposure to microbial agents. It is not known how microbial agents modify the association between specific allergen exposure and sensitization. OBJECTIVE: To examine the relations between house dust mite allergen exposure and mite sensitization in farm and nonfarm children and to assess the effects of microbial agents levels on this association. METHODS: Major mite allergens of Dermatophagoides pteronyssinus (Der p 1) and Dermatophagoides farinae (Der f 1), endotoxin, beta(1,3)-glucans and fungal extracellular polysaccharides were measured in mattress dust of 402 children participating in a cross-sectional study in five European countries. Mite allergen (Der p 1 + Der f 1) levels were divided into tertiles with cut-offs 1.4 and 10.4 microg/g. Sensitization was assessed by measurement of allergen-specific immunoglobulin E against house dust mite. RESULTS: Prevalence ratios of mite sensitization for medium and high when compared with low mite allergen levels were 3.1 [1.7-5.7] and 1.4 [0.7-2.8] respectively. Highest mite sensitization rates at intermediate exposure levels were consistently observed across country (except for Sweden) and in both farm and nonfarm children. The shape of the dose-response curve was similar for above and below median mattress microbial agent levels, but the 'sensitization peak' appeared to be lower for above median levels. CONCLUSIONS: Our data suggest a bell-shaped dose-response relationship between mite allergen exposure and sensitization to mite allergens. In populations with high microbial agent levels and low sensitization rates, the curve is shifted down.     

A prospective study of the association between home gas appliance use during infancy and subsequent dust mite sensitization and lung function in childhood

BACKGROUND: Home gas appliance use has been associated with child respiratory illness but prospective data on the relationship between infant exposure and the development of child allergic disease has not been readily available. OBJECTIVES: (a) To determine if home gas appliance use is associated with increased risk of house dust mite (HDM) sensitization. (b) To examine whether any association between current home gas use and airway obstruction is influenced by HDM sensitization. METHODS: Design: an 8-year follow-up birth cohort study of children born during 1988 and 1989. Participants: a population-based sample (n = 498) of children who participated in the Tasmanian Infant Health Survey (TIHS) and resided in Northern Tasmania in 1997 (84% of eligible children). Main outcome measures: (a) Skin prick test reaction to nine allergens, including Dermatophagoides pteronyssinus (Der p 1) and Dermatophagoides farinae (Der f 1). (b) Spirometric lung function indices, including forced expiratory volume in one second (FEV(1)) and forced vital capacity (FVC). RESULTS: The relative risk for home gas appliance use at 1 month of age and HDM sensitization was 1.98 (1.04, 3.79) in a cohort analysis with confounder matching. Current home gas use was also associated with HDM sensitization (ARR 1.73 (1.43, 2.76)). Current home gas use was related to a stronger (P = 0.006) reduction in the FEV(1) : FVC ratio among HDM-sensitive children (adjusted difference - 6.2% (- 10.0 to - 2.4)) than non-HDM-sensitive children (adjusted difference - 0.3% (- 2.5 to 1.8)). CONCLUSION: Indoor pollutants from gas combustion may increase the likelihood of initial sensitization to HDM and play a role in the development of atopic asthma. HDM-sensitized children may be more vulnerable to indoor pollutant-induced airway obstruction. The ability of this study to detect such effects may partly reflect unflued gas appliance use among this sample.     

High prevalence of storage mite sensitization in a general adult population

Background and aim:  Occupational and nonoccupational storage mite (SM) allergy has received considerable attention in recent years. The study aimed to evaluate both the prevalence and factors associated with sensitization to SMs in a general adult population from a warm and humid area where mites are the predominant allergens.
Patients and methods:  An age-stratified random sample of 720 subjects was drawn from the population older than 18 years of A-Estrada (Galicia, Spain). From 697 eligible subjects, 469 (67%, median age 54 years, range 18–92 years, 44% males, 75% of cases from a rural environment) agreed to participate. Skin prick tests to SMs ( Lepidoglyphus destructor and Tyrophagus putrescentiae ), house dust mite ( Dermatophagoides pteronyssinus ), pollens, moulds and animal danders were performed in all cases. Wheals ≥ 4 mm were considered positive. Epidemiological data were assessed by questionnaire. A design-based analysis was performed and all calculations were weighted to give unbiased estimates.
Results:  Tyrophagus putrescentiae and L. destructor were the leading causes of allergic sensitization throughout all ages. SM sensitization was found in 104 cases (weighted value 24.4%, 95% CI 20.6–28.2). SM sensitization was inversely associated with age. Multivariate analysis showed that SM sensitization was not significantly associated with sex, smoking, educational level, farming profession, rural environment, indoor humidity, presence of pets, livestock or grain storage facilities near home.
Conclusions:  SMs ( T. putrescentiae and L. destructor ) are major aeroallergens in adults in the region studied, even in subjects without occupational exposure.     

House dust mite sensitivity: interaction of genetics and allergen dosage

Pairwise analysis of siblings from 21 families showed that house dust mite (HDM) sensitive children were exposed to higher concentrations of Der p I allergen in their mattress (P = 0.005) and bedding (P = 0.04), but not bedroom floor (P = 0.33), than their atopic sibling who was not sensitive to HDM antigens. There was no difference in the exposure to HDM numbers/100 mg of dust in the mattress (P = 0.61) or bedroom floors (P = 0.09). In contrast, pairwise analysis of siblings from 15 families showed that HDM sensitive children were not exposed to significantly different concentrations of Der p I in the mattress (P = 0.96), bedding (P = 0.11) or bedroom floor (P = 0.70) nor HDM numbers/100 mg of dust in the mattress (P = 0.12) and bedroom floor (P = 0.98) than their non-atopic siblings. These findings were identical when absolute allergen load was compared in these pairs. Genetic linkage studies in these families suggest the tendency to atopic IgE responses is conferred by a putative atopy locus on chromosome 11q. These results together suggest that differences in allergen levels in beds, among siblings with a comparable genetic tendency to atopy, play a significant role in determining the development of HDM allergy.     

Prevention of sensitization to house dust mite by allergen avoidance in school age children: a randomized controlled study

BACKGROUND: Sensitization to dust mites predisposes to asthma and allergic rhinitis, and prevention of this sensitization might reduce the rising prevalence of these disorders. OBJECTIVE: To test the effectiveness of dust mite avoidance measures on the development of sensitization to dust mites in children. METHODS: As part of a multicentre study (Study of Prevention of Allergy in Children of Europe), 242 children, aged 5-7 years, in three European countries (United Kingdom, Greece and Lithuania), were randomized to prophylactic group (n = 127) and control group (n = 115). At randomization these children were required to have a family history of atopy and positive skin test to an aeroallergen but not to house dust mite. Children in the prophylactic group were provided with dust mite impermeable mattress covers and advice on environmental measures to reduce exposure to dust-mite allergen. Control group children were given non-specific advice. After 12 months a standardized questionnaire was completed and skin prick tests were performed. RESULTS: Ten children in the prophylactic group and 19 in the control group were lost to follow-up. Three of 117 (2.56%) children in the prophylactic group and nine of 96 (9.38%) in the control group developed sensitization to dust mites. Logistic regression analysis confirmed an independent effect of prophylactic measures (adjusted odds ratio (OR): 0.14, 95% confidence interval (CI): 0.03-0.79, P = 0.03). Fifteen children need to be treated to prevent sensitization in one child. CONCLUSION: Dust mite sensitization can be reduced in school age children with simple mite avoidance measures.     

Association between KIR genes and dust mite sensitization in a Brazilian population

Background

Killer cell immunoglobulin-like receptors (KIRs), found on the surface of natural killer (NK) cells, play a key role in controlling the innate response. Such response depends on a series of cellular interactions between these receptors and HLA activating/inhibiting ligands. Atopic diseases have been associated with genes that regulate cytokine production and HLA genes, which may either protect or predispose to hypersensitivity.

Prevalence of sensitization to the predatory mite Amblyseius cucumeris as a new occupational allergen in horticulture

BACKGROUND: Protection against thrips, a common pest in bell pepper horticulture is effectively possible without pesticides by using the commercially available predatory mite Amblyzeius cucumeris (Ac). The prevalence of sensitization to Ac among exposed greenhouse employees and its clinical relevance was studied. METHODS: Four hundred and seventytwo employees were asked to fill in a questionnaire and were tested on location. Next to RAST, skin prick tests (SPTs) were performed with common inhalant allergens, the storage mite Tyrophagus putrescentiae (Tp) which serves as a temporary food source during the cultivation process and Ac. Furthermore, nasal challenge tests with Ac were carried out in 23 sensitized employees. RESULTS: SPTs positive to Ac were found in 109 employees (23%). Work-related symptoms were reported by 76.1%. Sensitization to Tp was found in 62 employees of whom 48 were also sensitized to Ac. Immunoglobulin (Ig)E-mediated allergy to inhalant allergens appeared to be an important risk factor for sensitization to Ac. Employees with rhinitis symptoms showed a significantly higher response to all Ac doses during the nasal challenge test compared with employees without rhinitis symptoms. CONCLUSIONS: The predatory mite Ac is a new occupational allergen in horticulture which can cause an IgE-mediated allergy in exposed employees. It is biologically active on the mucous membranes of the nose and therefore clinically relevant for the development of work-related symptoms.     

Atopy and house dust mite sensitization as risk factors for asthma in children

BACKGROUND: Recent evidence suggests that asthma is not invariably related to atopy. The aim of this study was to evaluate the frequency of atopy, asthma and sensitization to eight common allergens in a large group of children with allergic symptoms. METHODS: 1426 children referred to our Paediatric Asthma and Allergy Center because of allergic symptoms were examined. Bronchial asthma, allergic rhino-conjunctivitis, food allergy and atopic dermatitis were diagnosed with standardized methods. Atopy was diagnosed if at least one skin test was positive. RESULTS: Of the 1426 children examined, 629 (44%) were atopic and 769 (56%) were non-atopic. Asthma was diagnosed in the same proportion (i.e., 64%) of atopic and non-atopic children. However, after division into age groups, non-atopic asthma was significantly more prevalent (chi2 = 8.46) in children between 0 and 3 years old (group 1). On the other hand, atopy was significantly associated with asthma only in group 3 (odds ratio 1.85). Furthermore, a significant association with asthma symptoms was found for house dust mite (HDM) in group 3 (odds ratio 4.8). CONCLUSIONS: Asthma is related to atopy in pre-selected children only from the age of 7 years. House dust mite sensitization seems to be an important determinant of asthma in these "older" children.     

House dust mite sensitization in children and residential characteristics in a temperate region

House dust mite (Hdm) infestation used to be rare in Stockholm, but Hdm-sensitized children are now frequently observed, which probably indicates an increased infestation rate. This study was performed to elucidate determinants of Hdm sensitization in children living in the area. In a case-control study, 53 Hdm-sensitized children (cases), a group of non-Hdm-sensitized atopic children (N = 54), and a group of nonallergic neighborhood children (N = 53) were included. Mattress dust was analyzed with ELISA for content of Hdm allergens. Indoor humidity and temperature were measured, and questionnaire data were collected. Asthma was significantly more common in the Hdm-sensitized group than in the atopic control group. Hdm allergens were found in 40%, 19%, and 23% of the dust samples of the case group, atopic group, and neighborhood control groups, respectively. Only 15% of the dust samples of the Hdm-sensitized children contained Hdm allergens above the recommended threshold levels of sensitization of 2000 ng/gm of dust. Inadequate ventilation, which partly appeared to be a consequence of energy saving, appeared to be a risk factor for Hdm sensitization. This result may apply also to other temperate regions and suggests that the problem is preventable.