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.     

The effect of sub-floor heating on house-dust-mite populations on floors and in furniture

It is well known that dehydrating conditions for house dust mites can be created by simply raising the temperature, causing loss of body water and eventually death. Thus, it can be expected that conditions for dust mites are less favourable on floors supplied with sub-floor heating. This was examined in a study of 16 houses with sub-floor heating and 21 without. The pattern of changes in air humidity and temperature on the floors was investigated and compared to known data of the tolerance of dust mites. Also the resident mite populations were compared. Floors with sub-floor heating had, on average, fewer mites, but the difference with unheated floors was small. It was remarkable that mite numbers were also lower in upholstered furniture. Another important observation was that some houses with sub-floor heating had high mite numbers, indicating that this type of heating is compatible with a thriving mite population. Temperature and humidity conditions of heated floors may allow mites not only to survive, but also to remain active in winter. A moderate increase in temperature, a moderate decrease inf (absolute) air humidity, or a combination of both, will suffice to keep the humidity all winter below the Critical Equilibrium Humidity, the level of air humidity that is critical for mite growth and reproduction, hence for allergen production. However, it is argued that measures to suppress allergen production by house dust mites are likely to be far more effective if taken in summer rather than in winter. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Allergenic mites (Acariformes, Pyroglyphidae) in house dust

Paper is the second part of the literature review on house dust mites (including 1985). It deals with the diagnosis of the dust mite allergy, the nature of the mite allergens, distribution and population density of the mites in various premises, seasonal population dynamics and population age structure of the dermatophagoid mites, life cycle and breeding of Dermatophagoides pteronyssinus and D. farinae on different food substrates. The methods of the house dust mite control are discussed. The original data on the house dust mite distribution in Moscow is shown. A comparative estimation of the results of mite antigens in the house dust discovering by the acarological and three immunological methods are given.     

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.     

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.     

Methods of assessment and control of house dust mites population and mite allergen exposure

The work is devoted to analysis of various methods of assessment and control of house dust mites population and mite allergens in city dwellings using own results and the literature data. Data about in-house dust mites biology and ecology, mechanisms of their migration and circulation in modern city conditions are presented. The comparison of several methods of mites number assessment and mite allergens exposure (classical acarological analysis, colorimetric method of guanine detection in house dust, immunochemical methods) has been performed and their advantages and disadvantages analyzed. As choice of adequate avoidance measures is one of the key question, various such measures (mechanical, physical and chemical) have been compared.     

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.     

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.     

Differences in development time,mortality and water loss between eggs from laboratory and wild populations ofDermatophagoides pteronyssinus (Trouessart, 1897) (Acari: Pyroglyphidae)

A total of four microcultures of adults ofDermatophagoides pteronyssinus, two each from laboratory and wild populations, were fed on separate diets of house dust and yeast granules. A total of 35 eggs of known age from each of the four microcultures were harvested and incubated at 15°C, 60% RH for 16 h/day and 30°C, 75% RH for 8 h/day to simulate diurnal microclimatic fluctuations in a bed. Eggs from females fed on yeast were larger and underwent more rapid rates of water loss, estimated by measurements of reduction in visible surface area (VSA), than eggs from females fed on house dust. There were no significant differences in mean egg development time between the four microcultures (range 6.0–6.88 days). Mortality of the eggs was as follows: from laboratory females fed on yeast, 31.4%; laboratory females fed on house dust, 11.5%; wild females fed on yeast, 2.9%; wild females fed on house dust, 0%. Thus diet and egg size at oviposition had no effect on mortality. Since the microclimates at which eggs from both populations were oviposited and incubated were identical, it is hypothesized that mortality was higer in eggs from laboratory cultures because the mites had become acclimated to the optimal conditions at which they had been kept and were less able to withstand the diurnal fluctuations in microclimate, similar to those imposed upon wild mites in their natural habitats.     

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.     

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.     

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.     

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.     

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.     

Epidemiology of dust-mite-related disease

For many years it has been suggested that allergens derived from the house dust mite played a major role in the pathogenesis of asthma, eczema and some cases of allergic rhinitis. Recently, house dust mite allergens have been purified and specific immunoassays developed with which exposure to house dust mites and their allergens can be more easily determined. Using these tools, epidemiological studies have provided confirmatory evidence that not only is house dust mite exposure associated with the majority of cases of asthma in children and young adults, but that it is causally related to the development of asthma.     

Seasonal changes in the population count of allergenic mites (Acariformes, Pyroglyphidae) in the dust of living quarters in the city of Moscow

The seasonal dynamics of allergenic mite quantity in house dust of three model apartments in Moscow has been observed during three years. Two periods of increase in mites' quantity have been revealed: wintry and summer-autumnal. Mite breeding takes place both in winter and in summer-autumnal period. The quantity variations of allergenic mites are cyclic and have individual traits peculiar to each population of these mites.     

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.     

Population growth and allergen accumulation of Dermatophagoides farinae cultured at 20 and 25 °C

House dust mites are cultured to obtain mite allergen material to produce allergen extracts (vaccines) for diagnostic tests, immunotherapy, and research purposes. Research laboratories and manufacturers have their own culturing protocols to grow these mites and these may vary between manufacturers and between research laboratories. The temperature at which mites are cultured may influence the allergen composition, allergen ratio of Der 1: Der 2 and endotoxin levels in the extracts produced from these cultured mites. In order to produce standardized and uniform extracts, across the industry and in various research laboratories, the influence of culture conditions must be understood. Here we determined how temperature affects mite population growth rates, dynamics of allergen production, Der f 1: Der f 2 ratio and endotoxin levels in extracts made from Dermatophagoides farinae mites cultured at 20 and 25 °C. We found that Der f 1 and Der f 2 accumulated exponentially in the cultures with Der f 1 accumulating faster than Der f 2. When the live mite populations peaked, the ratios for Der f 1: Der f 2 were 4.1 and 4.7 for cultures reared at 20 and 25 °C, respectively. Most of the Der f 1 and Der f 2 allergen in whole cultures is not in mite bodies and is lost when the mite material is washed. Thus, if the ratio of Der f 1 and Der f 2 is an important consideration for commercial and research extracts, then the temperature at which the mites are cultured and the collection procedure are important considerations.