Ecological relationships between xerophilic fungi and house-dust mites (Acarida: Pyroglyphidae)

Summary At. 75 and 80% relative humidity (RH), on a wheat germ flake medium, Aspergillus penicilloides grew abundantly and suppressed the population growth of Dermatophagoides pteronyssiunus. At 71% RH, A. penicilloides grew moderately and was only antagonistic to D. pteronyssinus when the fungus was previously incubated on the medium.On a human dander medium and on mattress dust, A. penicilloides grew moderately at 71% and 75% RH and stimulated the development of D. pteronyssinus populations. Also a moderate growth of Eurotium repens on human dander positively influenced D. pteronyssinus. Wallemia sebi and Penicillium brevicompactum grew slightly or did not grow at all at 75% RH. No effect was observed on D. pteronyssinus.It appears that xerophilic fungi may stimulate, and occasionally may reduce, the growth of house-dust mite populations in the natural environment.     

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     

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.     

A review of biology and allergenicity of the house-dust miteEuroglyphus maynei (Acari: Pyroglyphidae)

Euroglyphus maynei is a commonly occurring mite species in house dust throughout the world, but studies of its biology and allergenicity have been relatively scarce because it is difficult to culture, and because species of the genusDermatophagoides have attracted most attention of research workers.Euroglyphus maynei has been inereasingly recognized as an important source of mite-derived allergens to which patients with house-dust mite allergy are exposed. There is a need for knowledge of its bilogy and allergenicity, in order to be able to grow it in vitro, and to establish whether or not it produces any unique allergens which do not cross-react with those ofDermatophagoides spp. and which may be of clinical significance. This article reviews published and unpublished data on taxonomy and identification, geographical and habitat distribution, seasonal population fluctuations, life-history and the effects of temperature and humidity, culture techniques and allergenicity ofE. maynei.     

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.     

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.     

Aspergillus penicilloides and Eurotium halophilicum in association with house-dust mites

Aspergillus penicilloides Speg., Eurotium halophilicum Christensen et al. and other xerophilic fungi were isolated from house dust. The isolates of E. halophilicum are described and compared with the type strain of this species. A. penicilloides appeared to be rather common. The species concept of this species is broadened to accomodate some variable forms with different colony characters and conidiophore structures. The role of both species is discussed in connection with house-dust mites, house-dust allergy and skin diseases.Supported by grant No. 230 of the Dutch Asthma Foundation.     

Effect of heat treatments on the house-dust mitesDermatophagoides pteronyssinus andD. farinae (Acari: Pyroglyphidae) in a mattress-like polyurethane foam block

The behaviour and survival of the house-dust mitesDermatophagoides pteronyssinus andD. farinae were studied under laboratory conditions in a mattress-like polyurethane foam block that was heated by an electric blanket. Mites obtained from a laboratory culture were introduced into the foam block which was sliced into seven horizontal layers and covered with an electric blanket. Measurements of temperature and relative humidity were taken between the layers and the number of living mites was established using the heat-escape method.     

Short communication. Clustering reduces water loss by adult American house dust mites Dermatophagoides farinae (Acari: Pyroglyphidae)

We investigated male clustering behaviour in large bulk cultures of the American house dust mite, Dermatophagoides farinae. Aggregation in the colony was restricted to males only. The water loss rates for individual males in isolation and as a group of six were determined. Males in a group of six retained water nearly twice as effectively (they had lower rates of net water loss) than individuals. Clustering is thus an adaptive behaviour to help reduce water loss. Because the clustering response was observed exclusively by males, this behaviour may serve an additional purpose that involves a pheromone system.     

Interference in foraging behaviour of European and American house dust mites Dermatophagoides pteronyssinus and Dermatophagoides farinae (Acari: Pyroglyphidae) by catmint, Nepeta cataria (Lamiaceae)

The European and American house dust mites, Dermatophagoides pteronyssinus and D. farinae, have a huge impact upon human health worldwide due to being the most important indoor trigger of atopic diseases such as asthma, rhinitis and atopic dermatitis. Preceding studies have shown that the behavioural response of house dust mites towards volatile chemicals from food sources can be assessed using a Y-tube olfactometer assay. In the current study, we used this assay to investigate, for the first time, the ability of the essential oil of the catmint plant, Nepeta cataria (Lamiaceae), known to repel other ectoparasites affecting human and animal health, to interfere with the attraction of D. pteronyssinus and D. farinae towards a standard food source (fish flakes). Two distinct chemotypes (A and B), enriched in the iridoid compounds (4aS,7S,7aR)-nepetalactone and (4aS,7S,7aS)-nepetalactone, and the sesquiterpene (E)-(1R,9S)-caryophyllene, were used. Initial assays with a hexane extract of fish flakes (FF extract) confirmed attraction of mites to this positive control (P < 0.001 and P < 0.05 for D. pteronyssinus and D. farinae respectively), but when presented in combination with either N. cataria chemotype, tested across a range of doses (10, 1, 0.1 and 0.01 μg), decreasing attraction of mites to their food source was observed as the dose augmented. Our study shows that N. cataria, enriched in iridoid nepetalactones and (E)-(1R,9S)-caryophyllene, exhibits potent repellent activity for house dust mites, and has the potential for deployment in control programmes based on interference with normal house dust mite behaviour.     

Effects of temperature and relative humidity on development times and mortality of eggs from laboratory and wild populations of the European house-dust miteDermatophagoides pteronyssinus (Acari: Pyroglyphidae)

As part of a study on passive physical control of house-dust mites, a total of 6000 eggs from a population ofDermatophagoides pteronyssinus (Trouessart, 1897) from 17-year-old laboratory cultures were incubated at 60 temperature and relative humidity combinations between 10–35°C and 55–100% RH. Eggs hatched at every combination, although mortality and development time increased between 10–20°C and 30–35°C and below 65% RH. Optimum conditions were 35°C and 80–85% RH. In temperate dry conditions, eggs from a wild population were found to be more resistant to mortality: they developed faster, with 7 times lower mortality than eggs from the laboratory population. This may have been because the laboratory population had become acclimated to the constant near-optimum conditions at which it was kept. Therefore it has been suggested that where laboratory cultures have been used in studies relating to passive physical control, caution should be taken in applying the conclusions to wild populations in the natural house-dust environment.     

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.     

Morphological observation on adult Dermatophagoides pteronyssinus (Acari: Pyroglyphidae) with scanning electron microscope

[目的]利用扫描电子显微镜(scanning electron microscopy,SEM)观察屋尘螨Dermatophagoides pteronyssinus 颚体、躯体、外生殖器及足等的形态结构.[方法]从床尘、枕尘中采集屋尘螨,分离出雌雄成螨,在体视显微镜下清洗处理活螨后,用SEM观察其外部形态特征.[结果]SEM照片显示,屋尘螨整肢钳状,须肢扁平;体表具细密皮纹,似指纹状,纹间距小于2 μm.外生殖器位于腹面正中,雌螨为产卵孔,雄螨生殖孔具1对叶状生殖盖.肛 门呈纵行裂孔,雄螨具2个肛吸盘.雌螨足跗节末端各具爪垫1个,雄螨跗节Ⅳ具2个吸盘.[结论]本研究观察结果为尘螨鉴定提供了更多依据.     

Contamination of Passenger Trains with Dermatophagoides (Acari: Pyroglyphidae) Mite Antigen in Japan

Passenger trains were surveyed for contamination with Dermatophagoides farinae Hughes and Dermatophagoides pteronyssinus (Trouesart) mites in Japan. A total of 492 dust samples were collected from upholstered seats in six commuter trains, one long-distance express train and three night trains in October, 1996 and January, April, and July, 1997. Mite antigen levels contained in fine dust fractions of these samples were measured by an enzyme- linked immunosorbent assay. Most samples obtained from commuter trains showed relatively high mite antigen levels of >10gm^–2 (corresponding to >100 mites). Express and night trains showed lower antigen levels per square meter, but higher mite antigen levels per gram of fine dust than commuter trains, indicating relatively high mite antigen densities. Seasonal comparisons indicated that commuter trains showed the highest mean antigen level per square meter in winter (January), whereas the highest antigen level per gram of fine dust was observed in summer (July) in express and night trains.     

Seasonal changes in the count of mites of the family Pyroglyphidae in houses in the city of Cheboksary

The results of human dwelling houses surveying for the presence of home dust mites and study of seasonal changes of their quantity in the town of Cheboksary are given. It has been found that the old wooden houses are inhabited by mites, in modern blocks of flats they are met rather seldom. The quantity of alive mites is maximum in September-October. The common number of mites is the greatest in December-January although the quantity of alive mites at this time is only 6.8%.