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.     

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.     

How relevant are house dust mite-fungal interactions in laboratory culture to the natural dust system?

Both house dust and house dust mitesDermatophagoides pteronyssinus contained a wider range of fungi than laboratory mite cultures. In total, nine species of fungi were isolated fromD. pteronyssinus in house dust, and these included three xerophilic species (Eurotium amstelodami, Aspergillus penicillioides andWallemia sebi) commonly found in laboratory cultures ofD. pteronyssinus. It is concluded that mites do interact with a similar range of fungi in natural dust and in laboratory culture, but that the diversity of fungal species in the laboratory is reduced and the density of individual fungal species in culture exceeds that of house dust. In a second experiment, dust samples were incubated at room temperature with 75% relative humidity. The diversity of fungi invariably declined from up to 13 genera to the few species recorded in laboratory culture. This suggests that the dominance of xerophilic fungi in laboratory mite rearings is mediated primarily by low relative humidity, and the exclusion of air-borne spores.     

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.     

Age structure and dynamics of house dust mite populations

Age structure—the relative numbers of eggs, immatures and adults—in populations of the house dust mitesDermatophagoides pteronyssinus andEuroglyphus maynei was investigated in four sequential monthly samples taken from mattresses in each of eight homes in Glasgow, Scotland. Additionally, age structure ofD. pteronyssinus was determined in samples taken bimonthly for 6 months from nine quadrats of a double mattress. It was found that although age structure varied considerably with time, forD. pteronyssinus in different homes the most common structure was one in which immatures were dominant, then eggs and then adults (31% of samples). Immatures or eggs were dominant in 75% of samples. ForE. maynei the age structure was quite different: the most common structure was one in which adults were dominant, then immatures and then eggs (69% of samples). In different quadrats of a double mattress, mean age structure ofD. pteronyssinus underwent a shift towards higher proportions of immatures and then eggs during the sampling period, which reflected the increase in population density detected during this period.Life and fecundity tables were constructed forD. pteronyssinus andE. maynei using previously-available in vitro data on fecundity and survivorship rates and hypothetical values based on means derived from a number of studies. From the tables the stable age distributions were calculated and compared with the age structures of the natural populations. It was found that mean age structure of natural populations ofD. pteronyssinus was fairly close to the predicted stable age distribution, but those ofE. maynei indicated the populations were in decline during the sampling period, a fact confirmed by abundance data. The concept that the rate of increase of house dust mite populations can be estimated by determining age structure of mites isolated from dust samples was explored using the hypothetical population parameters ofD. pteronyssinus. It was predicted that quite large differences in fecundity and mortality would not drastically alter the proportions of eggs, immatures and adults in stable populations.Eggs as components of the house dust mite population are considered seriously for the first time. Those ofD. pteronyssinus andE. maynei were identified and differentiated by allometry. It is stressed that forD. pteronyssinus, during the sampling period, half or more of the mites in a dust sample may be represented as eggs, and to ignore them is to deliberately make a less accurate estimate of population density than could be otherwise achieved.     

Identification of Glycycometus malaysiensis (for the first time in Brazil), Blomia tropicalis and Dermatophagoides pteronyssinus through multiplex PCR

Blomia tropicalis and Dermatophagoides pteronyssinus play an important role in triggering allergy. Glycycometus malaysiensis causes IgE reaction in sensitive people, but is rarely reported in domestic dust, because it is morphologically similar to B. tropicalis making the identification of these species difficult. The identification of mites is mostly based on morphology, a time-consuming and ambiguous approach. Herein, we describe a multiplex polymerase chain reaction (mPCR) assay based on ribosomal DNA capable to identify mixed cultures of B. tropicalis, D. pteronyssinus and G. malaysiensis, and/or to identify these species from environmental dust. For this, the internal transcribed spacer 2 (ITS2) regions, flanked by partial sequences of the 5.8S and 28S genes, were PCR-amplified, cloned and sequenced. The sequences obtained were aligned with co-specific sequences available in the GenBank database for primer design and phylogenetic studies. Three pairs of primers were chosen to compose the mPCR assay, which was used to verify the frequency of different mites in house dust samples (n?=?20) from homes of Salvador, Brazil. Blomia tropicalis was the most frequent, found in 95% of the samples, followed by G. malaysiensis (70%) and D. pteronyssinus (60%). Besides reporting for the first time the occurrence of G. malaysiensis in Brazil, our results confirm the good resolution of the ITS2 region for mite identification. Furthermore, the mPCR assay proved to be a fast and reliable tool for identifying these mites in mixed cultures and could be applied in future epidemiological studies, and for quality control of mite extract production for general use.

     

Seasonal abundance of xerophilic fungi and house-dust mites (Acarida: Pyroglyphidae) in mattress dust

Summary Arthropods and xerophilic fungi in dust from 5 mattresses and air-borne fungi were identified and counted every 4 weeks from January 1976 to October 1977.The arthropod fauna consisted mainly of the pyroglyphid mites Dermatophagoides pteronyssinus (58%) and Euroglyphus maynei (30%). The fungal flora consisted of Aspergillus restrictus (48%), A. glaucus (16%), Wallemia sebi (3%) and Penicillium spp. (25%). Air-borne fungi belonged to the same taxa but in different frequencies, 30, 7, 21 and 27%, respectively. Mattresses differed in quantities of mites and Penicillium.In July 1977, the highest population density of pyroglyphid mites was encountered: 69 specimens/g of dust. In the same month the numbers of A. restrictus rose significantly, reaching a maximum of 3.8×10⁴ diaspores/g of dust. Most air-borne fungi were isolated in the winter period of 1976/1977. No positive correlation was found between the numbers of air-borne and mattress-dust fungi. The summer of 1976 was exceptionally dry resulting in both a premature decline of the mite populations and a low level of A. restrictus diaspores.The seasonal peaks of A. restrictus and pyroglyphid mites correspond and suggest a synergistic cooperation which may result in an increased house-dust allergen production in the environment of asthmatic patients.Supported by grant no. 230 of the Dutch Asthma Foundation     

Seasonal prevalence of allergenic mites in house dust of Kolkata Metropolis,India

During the past few decades, house dust mites have attracted worldwide interest among medical entomologists and acarologists because of their importance in causing nasobronchial allergic disorders in human beings. House dust mites are present throughout the year; however, their relative densities differ in different seasons and habitats. Because the prevalence of house dust mite allergen is important epidemiologically and clinically, detailed knowledge on the seasonal abundance of important allergenic mites is of great importance for better understanding of the pathogenesis of the disease. In view of this, a systematic survey was carried out on the prevalence of total mites and four common allergenic mites in the city of Kolkata for two consecutive years. Both bed and bedroom floor dust were collected separately from homes inhabited by asthmatic patients situated in different corners of the city on monthly basis from January 2004 to December 2005. The population levels of total mites and four common allergenic mites, namely Dermatophagoides pteronyssinus, D. farinae, Austroglycyphagus geniculatus, and Blomia tropicalis separately, were highest during the pre-monsoon period (March–May), irrespective of habitat, whereas densities were low in all cases during winter (December–February). The study indicates that season had the most significant effect on the relative abundance of house dust mites except Dermatophagoides farinae, irrespective of habitat.     

Population growth and allergen accumulation of <Emphasis Type="Italic">Dermatophagoides pteronyssinus</Emphasis> cultured at 20 and 25°C

The house dust mites, Dermatophagoides pteronyssinus and D. farinae are cultured commercially and in research laboratories and material is harvested from these cultures to make extracts that are used for diagnosis, immunotherapy and research. Temperature and other climatic conditions can influence population growth rates, dynamics of allergen production, and the associated endotoxin, enzyme and protein levels of the mite material harvested from these cultures. Here we determined how temperature affected these parameters. Dermatophagoides pteronyssinus was cultured at 20 and 25°C at 75% relative humidity, and at 2-week intervals the concentrations of mites, Der p 1 and Der p 2 allergens, endotoxin, and selected enzymes were determined. Mite density increased exponentially but growth rate and final population density were greater at 25°C compared to 20°C. The combined allergen (Der p 1 + Der p 2) concentrations accumulated in the cultures at about the same rate at both temperatures. However, individual Der p 1 and Der p 2 accumulation rates varied independently at the two temperatures. Der p 1 accumulated faster at 20°C whereas Der p 2 accumulated faster at 25°C. The amount of Der p 1 in whole cultures was greater than the amount of Der p 2. The concentration of allergen for washed mites harvested from the cultures was much less than for the whole cultures. Our study demonstrated that temperature is an important factor in population growth and the dynamics of allergen production in cultured mites.     

Collective Migration in House Dust Mites

House dust mites (Dermatophagoides pteronyssinus) are widespread in the furniture and mattresses of homes throughout Eurasia. Because human occupation induces wide diurnal fluctuations in temperature and relative humidity, the most favourable locations for mites change constantly and they must migrate repeatedly. Here, we triggered and studied mites migration movements to a new area. Mites migrated from a starting arena to a second arena through a diamond‐shaped corridor offering a choice between two branches of equal length. In this article, we show that local air dryness and a distant water source were both necessary to trigger collective migration. Males and nymphs had a higher probability of migration than larvae and females. When migrating, although both branches initially appeared to be chosen equally, most mites eventually ended up choosing one particular branch. When about 50 or more mites had passed, there was an obvious choice of branch. We used a modelling approach to show that these data support the hypothesis that mites lay an attractive trail that is reinforced by followers. Consequently, the consistency of the collective choice is higher as the number of migrants grows. This article is the first to observe dust mite migration as a collective phenomenon.     

The fauna and distribution of house dust mites in residential homes of Bandar Abbas District,Southern Iran

This study was designed to determine the occurrence, distribution and abundance of house dust mites (HDM) in residential homes in Bandar Abbas (Hormozgan Province), because of numerous complaints of allergies in this oriental city. The study area was divided in five sampling zones based on population density and geographical distribution. In each sampling zone 10 houses were randomly selected. A total of 50 home dust samples were collected using a portable vacuum cleaner for 2 min from 1 m² of the surface of mattresses, carpets, sofas and furniture in residential houses. After collection, samples were immediately frozen. Mite species were identified and counted using standard methods and keys. Of the sampled houses 88% (44 houses) were contaminated with at least one HDM species. Three species were identified: Dermatophagoides pteronyssinus (63.1%), D. farinae (32.8%) and D. evansi (4.1%) (Pyroglyphidae). Our findings indicate a relationship between HDM density and moisture and temperature of residential places. The high contamination rate of residential houses (88%) and the favourable environmental conditions for these arthropods stress that they should be considered as important allergic causing agents.     

Skin-associated Bacillus, staphylococcal and micrococcal species from the house dust mite, Dermatophagoides pteronyssinus and bacteriolytic enzymes

Dust mites produce bacteriolytic enzymes, one of which belongs to the NlpC/P60 superfamily comprising bacterial and fungal proteins. Whether this enzyme is derived from the mite or from mite-associated microbes is unclear. To this end, the bacteriology of mites per se, and carpet and mattress dust from a group of asthmatic children and their parents was investigated. Dust from parents’ and children’s mattresses yielded significantly more colony forming units compared with dust from their corresponding carpets. Zymography demonstrated some dusts contained bacteriolytic enzymes, and in nine of the twelve dust samples from three of five houses examined, a prominent bacteriolytic band was obtained that corresponded to the mite band, although in one home, other lytic bands were detected. Fifty bacterial isolates were obtained from surface-sterilised, commercially obtained Dermatophagoides pteronyssinus. 16S rRNA, tuf and rpoB gene sequencing of nine Gram-positive isolates identified them as Bacillus cereus, B. licheniformis, Staphylococcus aureus, S. epidermidis, S. capitis and Micrococcus luteus, known human skin commensals. 16S rRNA sequence homologies of four of the nine isolates identified as B. licheniformis formed a distinct phylogenetic cluster. All species secreted lytic enzymes during culture although the lytic profiles obtained differed between the rods and the cocci, and none of the bands detected corresponded to those observed in dust or mites. In conclusion, mites harbour a variety of bacterial species often associated with human skin and house dusts contain bacteriolytic enzymes that may be mite-derived. The identification of a novel cluster of B. licheniformis isolates suggests an ecological adaptation to laboratory-reared D. pteronyssinus. It remains to be determined whether the previously described mite-associated 14 K lytic enzyme is derived from a microbial source.     

Population dynamics of mites of the family pyroglyphidae and micromycetes in laboratory cultures

Original data on the study of the population dynamics in allergenic house dust mites of the family Pyroglyphidae (Dermatophagoides pteronyssinus (Trouessart 1897) and D. farinae Hughes 1961) during long (37 weeks) joint cultivation with the micromycetes Aspergillus penicillioides Speg. in simple periodical cultures without addition of food (SPC) with different initial population density of mites are given. The micromycete A. penicillioides Speg., dominating in laboratory cultures of pyroglyphids, was cultivated in parallel without mites. It was found that during joint cultivation of A. penicillioides and mites, population dynamics of D. pteronyssinus and D. farinae in SPC depended on the initial population density of mites, which affected the duration of mite developmental stages and the degree of the maximal population density. Cultures of D. farinae developed more rapidly than cultures of D. pteronyssinus, independently of the initial population density (50 or 200 specimens per gram of the substrate). A high degree of the initial population density in both mite species resulted in the shortening of the lag-phase, in more rapid reaching of the maximal population density, and in the higher degree of the maximal population density. Population density of the fungus A. penicillioides did not depend on the presence of both mite species. On the basis of our own data and literary analysis, we assume that A. penicillioides can affect the ability of mites to explore the trophic substrate, the rate of the population development, and the degree of their maximal population density. Mites, in their turn, did not significantly affect the development of A. penicillioides in our experiments.     

Do the microorganisms from laboratory culture spent growth medium affect house dust mite fitness and microbiome composition?

The interaction of house dust mites(HDM)and microorganisms is the key factor in the survival of these mites in human-made environments.Spent growth medium(SPGM)provides the rest of the dict,along with dead mite bodies and microorganisms.SPGM represents a source of microorganisms for the recolonization of mite food and the mite digestive tract.An experiment was performed to observe how adding SPGM to the HDM diet affects HDM population growth,the microbiome composition and the microbial respiration in microcosms.We analyzed American house dust mite(Dermatophagoides farinae)and European house dust mite(Dermatophagoides pleronyssinus)originating from control diets and diets treated with an extract of SPGM from 1-and 3-month-old mite cultures.The microbiome was described using 16S and 18S barcode sequencing.The composition of the bacterial and fiungal microbiomes differed between the HDM species,but the SPGM treatment influenced only the bacterial profile of D.farinae.In the D.farinae microbiome of specimens on SPGM-treated dicts compared to those of the control situation,the Lactobacillus profile decreased,while the Candinium,Staphylococ-cus,Acinetobacter,and Sphingomonas profiles increased.The addition of SPGM extract decreased the microbial respiration in the microcosms with and without mites in almost all cascs.Adding SPGM did not influence the population growth of D.farinae,but it had a variable effect on D.pteronyssimus.The results indicated that the HDM are marginally influenced by the microorganisms in their feces.     

Clinical significance of dust mite allergens

Dust mites are an important cause of allergic diseases worldwide. The traces of Dermatophagoides farinae and Dermatophagoides pteronyssinus can be found all over the world, while Blomia tropicalis are more common allergenic mites in tropical areas. A variety of allergenic components in dust mites have been found, apart from the different positive rates of IgE reactions in dust mite allergic patients, their biological characteristics, effects on the innate immune system, and especially their distribution characteristics in patients are different. Studying the relationship between dust mite allergens and clinical significance will help for diagnosis of patients and formulation of corresponding Allergen Specific Immunotherapy.

     

Mites from house dust in Glasgow

Glasgow's mild, high-rainfall climate, combined with a deteriorating quality of housing and low standards of living in many parts of the city, makes it a particularly suitable place for thriving populations of house dust mites. The acarofauna in 124 samples of house dust from beds and carpets in seventy-four homes in Glasgow, Scotland, comprised thirty-one species of which the most abundant were Dermatophagoides pteronyssinus (Trouessart) (64.3%), Glycyphagus domesticus (De Geer) (16.7%), Euroglyphus maynei (Cooreman) (11.6%), Tarsonemus sp. (1.6%), Cheyletus eruditus (Schrank) (1.5%), C. trouessarti Oudemans (0.9%), Tarsonemus fusarii Cooreman (0.8%) and Glycyphagus destructor (Schrank) (0.7%). Mites were present in all the homes surveyed and the mean population density was found to be 97/100 mg of dust (range 2-1210). Over 47% of homes visited showed signs of disrepair associated with damp, especially unmodernized flats in old tenement buildings and 1960s council housing stock, many of which contain deprived occupants. There was a high incidence of hygrophilic species such as Glycyphagus spp., Tarsonemus spp. and Euroglyphus maynei in such homes. Samples from homes of atopic asthmatics were found to contain significantly fewer mites than those from normal volunteers (chi 2 = 54.7). This was partly due to the use of house dust mite avoidance measures (e.g. regular vacuum cleaning of mattresses as well as carpets) by some of the asthmatics.     

Identification of house-dust mites

The term house-dust mite usually refers to those species of the mite family Pyroglyphidae, that are known to commonly occur, although sometimes regionally, in the dust of human dwellings. These species belong to five genera:Dermatophagoides, Euroglyphus, Hirstia, andMalayoglyphus. Related species ofDermatophagoides have the most world-wide occurrence, the commonest being:D. farinae, D. microceras, andD. pteronyssinus. A correct taxonomic identification of house-dust mites is very important, not only from a biological stand point, but also regarding the consequences of their respective allergenical properties. Several immuno-chemical studies revealed differences between the products of two hard to distinguish sibling species. A preliminary practical taxonomic key for the most common and important house-dust mites is presented.