Sensitization to house dust mites in Reykjavik, Iceland, in the absence of domestic exposure to mites.

BACKGROUND: House dust mites are common sources of indoor allergens. In Reykjavik, Iceland, 9% of the young adult population had serum-specific IgE to Dermatophagoides pteronyssinus. Sensitization to mites is usually assumed to be due to exposure to house dust mites in the indoor environment. This investigation was carried out to measure the concentrations of house dust mite allergens and to investigate which species of mites were present in beds in Iceland. METHODS: A total of 197 randomly selected adults were visited at home using the European Community Respiratory Health Survey (ECRHS) II Indoor protocol. Dust samples were collected from mattresses for measurement of house dust mite allergen concentrations and to estimate the number and type of house dust mites. Additional samples from mattresses and floors were collected from the homes of 10 patients with positive skin prick tests (SPT) to D. pteronyssinus. House dust mite allergen concentrations were measured using ELISA and examination of mite species was carried out using microscopy. Climatic parameters were assessed using psychrometer readings in the bedrooms and outdoors. RESULTS: We found two single mite specimens, both D. pteronyssinus, in two dust samples. Mite allergen analyses indicated that two other dust samples had Der f 1 results close to the cut-off of 0.1 microg/g of dust. No samples were positive for Der p 1. In an additional collection of dust from the homes of 10 SPT-positive patients no Dermatophagoides spp. were found. CONCLUSIONS: Reykjavik citizens are exposed to extremely low amounts of house dust mite allergens in their homes. Possible alternative sources for sensitization are discussed, such as bird nests, exposure from travelling abroad, or other mites or invertebrates that cross-react with house dust mite allergens. Our findings suggest that exposures other than to house dust mites indoors are possible sources of mite allergen exposure.

House dust mites and their allergens at selected locations in the homes of house dust mite-allergic patients.

BACKGROUND: Knowledge of the occurrence of house dust mites (HDM) and their allergens in domestic locations is important when planning intervention. OBJECTIVE: The aim of this study was to describe the distribution of HDMs and their allergens before intervention in multiple locations in the homes of newly diagnosed HDM-allergic patients with a known high Der 1 concentration in their mattress dust. METHODS: Dust was collected from ten locations in the homes of eight HDM-allergic patients. Dust was analysed for allergen content with ELISAs for Der f 1, Der p 1 and Der m 1; and HDM were counted. Total allergen concentrations ( micro g Der 1/g dust) were expressed as the sum of Der f 1, Der p 1 and Der m 1. RESULTS: On mattresses the median concentration was 86 micro g Der 1/g dust (range 30-288) and 188 mites/g dust (range 12-1910). Der 1 exceeded 10 micro g/g dust in mattresses (8/8), duvets/pillows (3/8), a bedroom carpet (1/1), a living room carpet (1/6), upholstered furniture (2/8) and a curtain (1/5). Uncarpeted floors, upholstered furniture, bookshelves and walls had significantly lower Der 1 concentration than the mattresses. The relative contribution of Der p 1, Der f 1 or Der m 1 to Der 1 was related to homes, rather than to the location. Der m 1 only occurred in minute amounts. CONCLUSION: For HDM intervention, our results indicate that priority should be given to the removal of allergens from mattresses, and in addition from carpets, duvets/pillows and upholstered furniture. Dust from walls, uncarpeted floors, bookshelves and curtains appear to contribute insignificantly to the domestic HDM allergen load.

Chemical control of Penthaleus major (Acari: Prostigmata) in hayfields in Iceland.

The plant parasitic mite Penthaleus major (Dugès) occurs as a pest on perennial grasses in hayfields in Iceland, northern Norway, and southern Greenland. In these areas it appears as a summer phenomenon, contrary to more southern locations, where it appears as a pest on winter crops. Up to 500 individuals of P. major were collected per day in pitfall traps. Spring application of 44 ml/ha of permethrin and 5 ml of deltamethrin significantly reduced but did not eliminate the populations of P. major the following weeks. In addition to this immediate effect, spring application also decreased the mite populations in the fall and even the following spring. Additional effects might be obtained by earlier spring application. Despite a significant reduction in mite populations and reduction in visible plant damage, significant differences on dry matter yield were rarely registered. A side effect of application was a small but significant reduction in potassium-content of the yield, and the reduction in mite population was accompanied by a corresponding reduction in the number of spiders.

Pitfalls in evaluating mite exposure from house-dust samples.

Results from vacuum collected samples from a patient's environment may support the diagnosis of mite allergy. High estimates of mites or mite allergens do show that a patient is exposed. Low estimates are harder to interpret. Estimates may be low due to dust dynamics or to the behaviour of the mites, which, according to their biology, can be present or almost absent in the samples. A survey is given of the nature of these obstacles to proportionality between sample results and the exposure which might be experienced by a patient during a period of time. To reduce the problems of false-negative estimates of exposures from single samples, series of samples collected weeks apart may improve the significance of diagnoses.

Peak expiration flow variations may reflect house-dust-mite exposure and patient reactivity.

Peak expiration flow records from patients allergic to house-dust mites (Dermatophagoides spp.) may show a characteristic variation from week to week due to the general life cycle of these mites in dwellings. This was demonstrated from the combined records of 10 patients recorded in their own homes, covering a period of 30 consecutive weeks and comprising 973 peak flows. The levels of house-dust mites were predicted from published data for floor-dust samples from Danish dwellings. Peak flow increased or decreased in accordance with weekly changes in the concentration of mites, rather than as an immediate reaction to the current concentration of live, active mites. A dose-response relation was demonstrated. This suggests that the patients' peak flow variations might be linked to molting in mites. As such, peak flow measurements have a potential as a tool for the specific diagnosis of, monitoring of, and research in asthma caused by domestic mites.

Does guanine concentration in house-dust samples reflect house-dust mite exposure?

Using specific ELISA extracts, we analyzed samples of pure mite cultures and house dust for group I allergens from Dermatophagoides pteronyssinus, D. farinae, and D. microceras. Correspondingly, we measured the concentration of guanine and xanthine by rigorous chemical methods. The pure mite cultures were used to correlate allergen levels with guanine levels. The house-dust samples one-sidedly contained more guanine than expected. This suggests that considerable amounts of guanine originate from non-house-dust mite sources and implies that guanine quantifications are of limited clinical value.

Annual fluctuations of mites and fungi in Danish house-dust: an example.

For one year dust was sampled monthly from a single mattress. Until August mite counts were at background levels. In September and October there was a burst in the counts for the house-dust mite, Dermatophagoides farinae and for the house mite, Glycyphagus domesticus. Their occurrence might be interpreted as a response to large densities of an unidentified yeast in September. This yeast appeared when the indoor absolute humidity exceeded 9 g H2O/kg dry air. The mite Tarsonemus rakowiensis reached its maximum in October, and might be a possible house-dust mite predator, although the evidence is far from conclusive. An aliquot of ten grams of mattress dust sampled from a mite-free location on top of the mattress hardly became infested, although the environmental conditions were ideal. Obviously, the mattress dust from the dry room was not optimal for either the yeast or the mites.

Tarsonemid mites in Danish house dust.

From a study of 98 typical Danish city apartments it was found that pyroglyphid and tarsonemid mites dominated the housedust acarofauna. Both groups of mites show a remarkable similarity in their occurrence and dependence on the microclimate. Room air humidities above 7 g water/kg dry air involved the highest densities. Below this limit only background contamination appeared. At least 14 distinct forms of tarsonemid mites were found, with Tarsonemus floricolus Can. & Fanz., 1876 as the dominating species. As tarsonemid mites were found regularly rather than occasionally, it is suggested that these mites may be responsible for at least a part of the cases of housedust allergy that cannot be ascribed to the content of Dermatophagoides mites in the housedust.