The colonisation of new houses by house dust mites (Acari: Pyroglyphidae)

House dust mites,Dermatophagoides species (Acari: Pyroglyphidae), produce allergens, known for the provocation of asthma and other allergic reactions. To determine the time needed for complete colonisation of a new house by house dust mites, dust samples were collected from carpets of houses varying from 2 weeks to 2 years in age. In contrast to the expectation, no relation was found between age of the houses on the one hand and average levels of mite-allergensDer pI andDer pII and mite numbers on the other. However, presence of dogs appeared to be positively related to allergen levels. Furthermore, carpets in bedrooms appeared to contain more allergens than carpets in living-rooms. Finally, the age of the mattress was not related to allergen levels of bedroom floors.     

Optimisation of a screening procedure for house dust mite numbers in carpets and preliminary application to buildings

The relative performances of the mobility and heat escape methods for measuring house dust mite numbers in carpet has been evaluated. The optimum method was found to be the mobility method for 24 hours at ambient temperatures which exhibited a mite collection efficiency of approximately 30%. Measurements in three dwellings showed that the method should be applied to carpet at several locations in the living room and/or bedrooms as a general sampling procedure, or adjacent to loungeroom seating to determine the worst case scenario. Carpets using different types of fibre within the same dwelling should be assessed separately. For the limited number of dwellings investigated, wool carpets were found to exhibit higher mite numbers than nylon carpets, even when the former had been insect-resist treated. No house dust mites were found in the wool carpets of an office building which was mechanically ventilated and heated and achieved low indoor humidities in winter.     

A simple model for predicting the effect of hygrothermal conditions on populations of house dust mite Dermatophagoides pteronyssinus (Acari: Pyroglyphidae)

A simple mite population index (MPI) model is presented which predicts the effect on house dust mite populations of any combination of temperature and relative humidity (RH). For each combination, the output is an index, or multiplication factor, such that 1.1 indicates 10% population growth and 0.9 indicates 10% population decline. To provide data for the model, laboratory experiments have been carried out using lab cultures of Dermatophagoides pteronyssinus. The population change was observed for mites held in steady-state conditions at different combinations of temperature and RH over 21 days. From the results, a best-fit equation has been derived which forms the basis of the MPI model. The results also enable a new term to be defined: the Population Equilibrium Humidity, PEH, the RH for a given temperature at which house dust mite populations neither grow nor decline. It is similar to Critical Equilibrium Humidity, the RH below which house dust mites are unable to maintain water balance, but relates to a population of mites (rather than a physiological phenomenon) and is more able to take account of the observed effects of extremes of temperature and RH. Compared with previous population models, the MPI model is potentially more accurate and comprehensive. It can be combined with other simple models (described in previous papers), such as BED, which simulates the average hygrothermal conditions in a bed, given room␣conditions, and Condensation Targeter II, which simulates room conditions given a range of easily obtainable inputs for climate, house type and occupant characteristics. In this way it is now possible, for any individual dwelling, to assess the most effective means of controlling mite populations by environmental means, such as by improving standards of ventilation and insulation, or by modifying the occupant behaviour that affects the hygrothermal environment within a dwelling. Although the MPI model requires further development and validation, it has already proved useful for understanding more clearly how the different hygrothermal conditions found in beds and bedrooms can affect mite populations. It has also demonstrated that there is considerable scope for controlling mites by environmental means in cold winter climates such as the UK.     

Crystal structure and some properties of a major house dust mite allergen, Derf 2

Pyroglyphid house dust mites are a major source of allergens in house dust. Mite allergens sensitize and induce asthma, rhinitis, and eczema in a large portion of patients with allergic diseases. Here, the crystal structure of a major mite allergen, Derf 2, derived from Dermatophagoides farinae was solved by single isomorphous replacement method with anomalous scattering (SIRAS) at 2.1A resolution. The present study also demonstrated that the conformation of the allergen was critical in the determination of Th1/Th2 shift based on physicochemical and immunological analyses. This indicates that rigidly folded and singly dispersed structure is essentially required for the generation of Th2 type cells by the allergen, while conformational variant protein leads to Th1 skewing, irrespective of the same amino acid sequence. This structure/function relationship may allow us to develop a novel strategy for hyposensitization therapy in patients with allergic diseases triggered by house dust mite allergens.     

Abundance of house dust mites in relation to climate in contrasting agricultural settlements in Israel

The correlation between climatic conditions and mite numbers in houses from rural areas was studied in 13 agricultural communities (kibbutzim and moshavim) in nine geo-climatic subregions of Israel. Mites were present in 97% of the dust samples. The average number of mites per gram of dust in the different localities ranged between 84 and 2053. The maximum number of mites (7440/g dust) was found in a carpet from a house in Geva Carmel in the northern coastal region. The most prevalent species of mites were Dermatophagoides pteronyssinus and Dermatophagoides farinae, which were found in 85.6% and 71.3% of the samples, respectively. The house dust mites D. pteronyssinus, D. farinae and Euroglyphus maynei constituted 94.8% of the mites. Most of the mites were isolated from the carpets and sofas (37.0% and 33.7%, respectively), and a smaller number from beds (29.3%). The smallest number of mites (< or = 250/g dust) were found at a minimum relative humidity (RH) of 30% and lower, with a maximum temperature of 32 degrees C and higher, i.e. in the Jordan valley and Negev mountains. A greater number of mites (250-500/g dust) were found at a minimum ambient RH of 35-40% and a maximum temperature of 32 degrees C and higher, i.e. the Hula valley. A large number of mites (500-1000/g dust) were found at a minimum RH of 35-40% with a maximum temperature of 30 degrees C and lower, i.e. in the Judean and Samarian range, as well as in upper Galilee. The largest number of mites (1000-2000/g dust) was found at a minimum RH of 45% and higher, with a maximum temperature ranging between 30 and 32 degrees C. These conditions occur in the coastal strip, the coastal plain and in the Judean and Samarian foothills. A monthly examination of two houses in Zova, a kibbutz in the Judean hills next to Jerusalem, and two houses from Palmachim, a kibbutz in the coastal region, revealed that the highest prevalence of mites was found in the months April-November and May-November, respectively. In Zova, the highest number of mites were found during the months of June and July while the highest concentrations of D. pteronyssinus-antigen (Der p I) were measured during the month of September. A positive correlation between mite numbers and the quantity of Der p I in house dust was found.     

House-dust mite sensitivity among rural and urban asthmatics of West Bengal, India: a comparison

House-dust mite allergy is a fairly common problem in West Bengal among individuals sensitive to dust inhalation. House-dust mites belonging to the genusDermatophagoides are abundant in the homes of asthmatic patients residing in urban as well as rural areas of West Bengal. The frequency of positive skin reaction to different dust-related allergens tested was higher (χ²=5.4777, df = 1;P < 0.05) among patients of urban areas compared with that among the patients of rural areas. Urban patients showed more frequent skin reaction towards cockroach allergen, while rural patients are more sensitive to hay-dust allergen and these are very much related to their local environmental conditions. Analysis of radioallergosorbent test (RAST) results against house dust (HD) and mites reveal that 73 and 90% patients of both urban and rural areas responded positively towardsDermatophagoides pteronyssinus (DP) andDermatophagoides farinae (DF) antigens, respectively. The present study indicates no significant difference in house-dust mite sensitivity and mite levels in homes among the rural and urban asthmatics of West Bengal, India as evidenced from the results of analysis of dust samples, allergy skin test and detection of mite-specific IgE antibodies by RAST.     

House dust mite fauna in western Anatolia, Turkey

House dust mites play an important role in the pathogenesis of allergic diseases. Many factors may influence mite growth. The presence of mites is related to mean temperature and humidity as well as altitude. The aim of this study was to analyze the mite fauna in 5 regions of western Anatolia, Turkey, that have similar climatic properties with low mean temperature and humidity, but differ in altitude. During the period October-November 2004, house dust was collected from 290 homes in 5 different cities. House dust mites were isolated in 67 (23.1%) of 290 samples. The family Pyroglyphidae (Astigmata) was present in all positive samples. This study suggests that the selected western Anatolian regions that share similar environmental conditions host similar dust mite populations.     

Cross-reactivity between storage and dust mites and between mites and shrimp

Many patients have sensitivities to multiple species of storage and house dust mites. It is not clear if this is because patients have multiple sensitivities to species-specific mite allergens or if these mites share many cross-reacting allergens. Our objective was to further define the cross-allergenicity between several species of storage and house dust mites using crossed-immunoelectrophoresis (CIE), crossed-radioimmunoelectrophoresis (CRIE), immunoblotting, and ELISA. CIE and CRIE reactions revealed that storage mites shared two cross-antigenic molecules and one of these bound IgE in a serum pool from mite allergic patients. Antibody in anti-sera built to each species of mite recognized many SDS–PAGE resolved proteins of other mite species and this suggested the potential for other cross-reactive allergens. Among patient sera, IgE bound to many different proteins but few had IgE that bound to a protein with common molecular weights across the mite species and this suggested mostly species-specific allergens. Antiserum built to each mite species precipitated one protein in shrimp extracts that bound anti-Der p 10 (tropomyosin) and IgE in the serum pool. Anti-Der p 10 showed strong binding to shrimp tropomyosin but very little to any of the mite proteins. ELISA showed the mite extracts contained very little tropomyosin. The storage and dust mites investigated contain mostly species-specific allergens and very small amounts of the pan-allergen tropomyosin compared to shrimp and snail.     

Mites in house dust and human allergoses

The literary data on the study of the house-dust mites during the period from 1864 till 1983 are given. The methods of the house dust samples collection in flats and the methods of the house-dust mites isolation from the house dust are evaluated. The house-dust mites fauna including more than 130 species is described. The synantropic mites-pyroglyphides are the main part of the fauna, the stored products mites and predatory cheyletid and gamasid mites occur regularly. The rest part of the fauna consists of the different mites got into house by chance. The literary data on the influence of temperature and relative humidity on the development and growth of the mite population are given. The house-dust mites feeding and digestion processes bearing relation to the formation of the mite allergen are reviewed. The original data complete the literary data on the fauna and distribution of the house-dust mites in Moscow.     

Effectiveness of vacuum cleaning and wet cleaning in reducing house-dust mites,fungi and mite allergen in a cotton carpet: A case study

In order to evaluate the effect of continuous, thorough vacuuming on house dust organisms and mite allergen, a cotton carpet was vacuumed every other day, six times in total. Seven weeks later, the carpet was cleaned by means of spray extraction. Samples were taken before and after this wet cleaning.In total 1150 g of dust was collected, containing approximately 174 000 arthropods (dead and alive) and 9000×10⁶ fungal spores. In the course of the experiment, the amount of dust collected at each vacuuming decreased. The number of extracted house dust mites did not decrease significantly, but that of the predator miteCheyletus did. The number of extracted fungal spores showed a significant decrease (from 142 to 16×10⁶ spores/m² per minute vacuuming), as did the extracted mite allergen per m². After 7 weeks the number of mite eggs and complete house dust mites had increased enormously. After cleaning by spray extraction another increase in the number of complete mites and mite eggs was found, while the amount of mite allergen was diminished.The population growth of the house dust mite between the 6th and the 7th vacuuming is probably due to the decrease of their most important predator,Cheyletus. After the wet cleaning a number of extra eggs hatched, probably due to the high humidity in the carpet. The procedures used in this study to combat house dust mites may have an adverse effect in the long run.     

Synanthropic Mites of Kolkata, India: An Ecological Appraisal

Ecological observations were made on house dust mites of Kolkata as they form a major part of synanthropic mite community. Dust samples were collected with regard to the abundance of mite in relation to certain socio-ecological parameters like, habitat preference, location of house, construction pattern of house, types of mattresses used and the frequency of cleaning of mattresses. Among two different habitats examined, bed dust contained significantly higher mite population (p < 0.01) than the corresponding bedroom floor dust. The density of total mites and glycyphagids are significantly higher in rural houses in comparison to those of urban houses. In contrast, rural houses contained least number of pyroglyphids/g of dust. The density of total mites as well as pyroglyphid mites/g of dust are higher in mud house in comparison to concrete house. The density of total mites, pyroglyphids and glycyphagids are higher in cotton mattress in comparison to that of foam mattress. The frequency of cleaning has a significant effect on reducing mite densities i.e., the more the frequency of cleaning the lesser are the mite densities.     

Predicting the population dynamics of the house dust mite Dermatophagoides pteronyssinus (Acari: Pyroglyphidae) in response to a constant hygrothermal environment using a model of the mite life cycle

A generalised model of the life cycle of a house dust mite, which can be tailored to any particular species of domestic mite, is presented. The model takes into account the effects of hygrothermal conditions on each life cycle phase. It is used in a computer simulation program, called POPMITE, which, by incorporating a population age structure, is able to predict population dynamics. The POPMITE simulation is adapted to the Dermatophagoides pteronyssinus (Acari: Pyroglyphidae) (DP) mite using published data on the egg development period, total development period, adult longevity, mortality during egg development, mortality during juvenile development, and fecundity of individual DP mites held at a range of constant hygrothermal conditions. An example is given which illustrates how the model functions under constant hygrothermal conditions. A preliminary validation of POPMITE is made by a comparison of the POPMITE predictions with published measurements of population growth of DP mites held at a range constant hygrothermal conditions for 21 days. The POPMITE simulation is used to provide predictions of population growth or decline for a wide range of constant relative humidity and temperature combinations for 30 and 60 days. The adaptation of the model to correctly take account of fluctuating hygrothermal conditions is discussed.     

Effectiveness of education for control of house dust mites and cockroaches in Seoul, Korea

We evaluated the efficacy of health education in reducing indoor arthropod allergens in Seoul. The mite control measures comprised the use of mite-proof mattress and pillow coverings, regular washing of potentially infested materials, maintenance of a low humidity, removal of carpets, and frequent vacuum cleaning. Cockroach control measures included trapping, application of insecticides, and protecting food. Of 201 homes enrolled in October 1999, 63 volunteers were included in a 2-year follow-up survey between April 2000 and January 2002. Before intervention, the density of mites/g of dust varied greatly; 27.1/g in childrenos bedding, 20/g in adult bedding, 7.2/g on the floors of childrenos bedrooms, 6.8/g in sofas, 5.9/g on the floors of adultos bedrooms, 3.9/g on living room floors, 3.7/g in carpets, and 1.9 mites/g on kitchen floors. The predominant mite species and house percentages infested were; Dermatophagoides farinae 93%, D. pteronyssinus 9%, and Tyrophagus putrescentiae 8%. Comparing 1999 and 2001 infestations, before and after 25 mo of education, mite abundance was reduced by 98%, from 23.7 to 0.57 mites/g of dust. In 1999, cockroaches were detected in 62% homes: 36% Blattella germanica and 35% Periplaneta spp., including 9% double infestations of B. germanica and P. americana. Following intervention, cockroach infestation rates decreased to 22% of houses in 2000 and 23% in 2001. We conclude that continuous and repetitive health education resulted in the effective control of domestic arthropods.     

Distribution and abundance of house-dust mites (Acarina: Pyroglycphidae) in Rome,Italy

For the first time in Rome, house-dust mite infestation was studied in 90 randomly selected houses. In each house, mite infestation was assessed in three sites: mattress, bedroom and living room. In total, 87.8% of the sampled houses were positive for dust mites. In the houses infested, 11.4% showed densities of >100 mites/g of dust, 15.2% registered densities between 50 and 99, and in the remaining houses (73.4%), the densities were between 1 and 49 mites/g dust. The percentages of infested houses were positively correlated with the relative humidity (RH) values (r=0.89,P=0.02). At the lowest range of RH (between 46 and 50), the infestation was 50% and at the highest range of RH (between 73 and 78) it was 100%. The mattress was significantly the most infested (71.1%) of the tested sites. Only wool and spring mattresses were infested, and they did not show any significant differences in mite concentrations.Dermatophagoides farinae was the most abundant species (53.1%), followed byGlycyphagus domesticus (34.5%),D. pteronyssinus (5.2%), andEuroglyphus maynei (0.2%);D. farinae was also the most frequent species (56.9%). The remaining specimens (7.0%) were predator species commonly found in houses. The prevalence ofD. farinae in Rome is discussed.     

Allergen exposure and control

Allergens produced by the house dust mites (family Pyroglyphidae) are probably the single most important allergens associated with asthma world wide. If exposure to these allergens in houses could be sufficiently reduced, then asthma symptoms may be markedly reduced and even prevented from being initiated. Only about half of the many attempts to reduce mite allergens in houses have shown any clinical benefit. One reason may be that exposure was not reduced enough-however exposure to mite allergens has never been measured in any trial. This review summarises previous allergen control trials and then provides an outline of allergen exposure, including the nature of exposure, the analytical methods available and the recognised risks of allergen exposure. This provides a perspective to evaluate the individual methods used to kill mites and to reduce exposure to the allergens. The object is to provide a framework to improve and develop allergen avoidance as an effective component of asthma management.The author is supported by a project grant from the National Heath and Medical Research Council of Australia.     

Guanine as a hygienic index for allergologically relevant mite infestations in mattress dust

Since guanine is not only an essential constituent of vital nucleic acids, but also the main end product of nitrogenous waste excretion in arachnids, it is a potential candidate for a hygienic index for mite activity in house dust. The public health significance of these mites is based on their production of allergen in the home environment.In 101 mattress-dust samples, total number of mites and guanine content were positively correlated. The hygienic standard of 10 mites per 0.1 g dust (as derived from Danish investigations) was met in all samples with less than 0.06% guanine in the dry dust. Where the guanine content was more than or equal to 0.25% in the dry dust, mite numbers were higher than 10 mites per 0.1 g dust in 43 of the 44 samples. The three different groups (negligible mite content, possibly allergologically relevant mite concentration and allergologically unhygienic mite situation) could be easily discriminated on the color scale.The guanine-AZO-dye reaction in vacuum cleaner dust is a strong and promising candidate for an allergologically relevant hygienic index in the home.     

Specific measurement of a major mite allergen, Der f II, by an enzyme-linked immunosorbent assay system using monoclonal anti-Der f II antibodies.

An enzyme linked immunosorbent assay system using a monoclonal antibody, 15E11, specific for a major allergen Der f II in house dust mite, was developed. This system detected only Der f II in the presence of Der p II and other allergens. The Der f II contents in several house dust samples significantly correlated with the numbers of the mites in the same house dust samples (n = 14, r = 0.88, p < 0.001). These data showed that this system was useful for specific measurement of Der f II in house dusts.     

Induction of allergic contact dermatitis by astigmatid mite-derived monoterpene, alpha-acaridial

α-Acaridial [2(E)-(4-methyl-3-pentenyl)butenedial] is a novel monoterpene secreted from the house dust mites. Because of its molecular nature of a highly reactive, small lipidic compound, we addressed whether α-acaridial might function as a haptenic allergen that induced allergic contact dermatitis. Mice sensitized with α-acaridial were challenged by the same antigen on the ear skin. After 2 days, significant ear swelling with a prominent infiltration of CD4⁺ T lymphocytes was observed. In vitro, α-acaridial exhibited an outstanding ability to quickly interact with and chemically modify a reference protein. Virtually all cysteine residues and a sizable fraction of lysine residues were found to be selectively modified, suggesting that α-acaridial could potentially interact with any proteins. Previously, numerous mite-derived proteinaceous allergens have been associated with contact dermatitis. Our study now emphasizes that small lipidic compounds released from mites comprise a new class of mite allergens, and therefore, is of significant medical implications.     

Effectiveness of benzyl benzoate in elimination of house dust mites

The effect of elimination treatment with benzyl benzoate was examined in 30 adults with asthma caused by sensitivity to house dust mites. The patients were randomised into a control and an active group, who treated their mattresses with benzyl benzoate (Acarosan^®). The study lasted 12 months and the effect of the treatment was monitored by monthly dust sampling, analyzed for major allergens fromDermatophagoides pteronyssinus andfarinae by the ELISA method and for guanine by the Acarex^® method. The clinical effect was assessed by measuring lung function, daily peak flows, symptoms and medicine consumption as well as skin prick tests, and specific IgE to mite allergens. For both groups, a significant decrease was observed in house dust mite allergens, but there was no significant difference between the groups. No considerable differences were observed in clinical parameters within or between the groups. A good correlation was observed between ELISA and Acarex^®. but the latter showed a major variation in the different classes. In conclusion. treatment of mattresses with benzyl benzoate had no effect in a group of patients with asthma due to house dust mite allergy. Regular vacuum cleaning of the bed may reduce house dust mite allergen exposure.     

The effect of house design and environment on fungal movement in homes of bronchial asthma patients

The effect of house building design and environment on the fungal movement in the houses of 41 bronchial asthma (BA) patients has been investigated by examining house dust. The presence and composition of fungi were determined and compared in relation to building structure, house age, size of living room, main flooring material, presence of a living-room rug or air purifier, and frequency of vacuum cleaning. Among these elements, fungal CFU apparently varied only between building structure: wooden-board houses had significantly higher numbers of fungi than reinforced concrete houses (p < 0.01), and wooden mortar or iron-framed prefabricated houses had significantly higher numbers of fungi than reinforced concrete houses (p < 0.05). Classification of the types of fungi present in the house dust of BA patients showed that, regardless of the building designs, there were high levels of osmophilic fungi (group A) and fungi that survive at relatively dry conditions (group B), whereas fungi that survive in very wet conditions (group D) were present at low frequency. This revised version was published online in August 2006 with corrections to the Cover Date.