Mite allergy and mite exposure in Iceland.

In this overview of investigations into mite allergy in Iceland and of the current understanding of the sources of exposure, 2 major categories of mite-induced allergies were encountered. The first was house dust mite allergy due to house dust mites from unknown sources, and the second was barn allergy caused by mites connected with the degradation of stored hay. Characteristics of these diseases have been obtained from surveys where skin prick tests were made with commercially available extracts of mites and from zoological investigations where mites had been found in different kinds of dusts relevant for the tested persons. The investigations uncovered a discrepancy between the capital Reykjavik and countryside farms. While the frequencies of sensitization to house dust mites and barn mites are rather similar in the capital area and in the rural area, the exposure to these mites is unexpectedly low in the capital area. Thus, sensitization appears to take place preferably in the rural area.

House-dust mites in our homes are a contamination from outdoor sources.

Avoidance advices for house-dust mite sensitized persons are currently based upon the idea, that the mites (Dermatophagoides spp.) are part of the indoor fauna. A closer look at development stages in the house-dust samples shows, however, that only the mites' active stages are present there and that the stages between them, the inactive moulting stages, are absent. Therefore the mites probably do not carry out their life cycles in our dwellings, but are more likely contaminations from the open. Findings of low level concentrations can be explained by mites coming from outdoors and sedimented in accordance with known physical laws. The occasional finding of higher concentrations is the result of synchronized populations of the mites developing outdoors and being passively transported into our homes by wind and dust. The hypothesis explains why we find mites in our homes but nonetheless have no effect of avoidance measures. The verification of the entire hypothesis or part of it may have great impact on the management of the disease house-dust mite allergy.

A controlled intervention study concerning the effect of intended temperature rise on house dust mite load.

In epidemiological studies, increased indoor temperature--producing a lower relative humidity--is associated with low house dust mite (HDM) load. Twenty-eight dwellings were allocated for either intervention (12/15 completed) or control (11/13 completed). In the intervention group, participants were asked to increase the bedroom temperature by at least 3 degrees C compared to the self-assessed temperature of the previous winter. Dust samples were repeatedly collected from mattress and floor, and bedroom temperature and relative humidity were recorded hourly throughout one year. Dust was analysed for allergen (Der f 1 + Der p 1 + Der m 1 = Der 1) by ELISA and HDMs were counted. Changes in mite and in mite allergen concentration were the same in the control and intervention groups, and measured temperatures did not differ during intervention period in the groups (18 degrees C and 19 degrees C). Groups turned out not to be comparable with respect to initial (self-assessed) bedroom temperature (lowest in the intervention group). There was a significant seasonal variation, with doubled Der 1 concentrations in dust collected in July-November compared to January-May samples. No effect was obtained on mites or mite allergens, but this may be due either to a general lack of effect of increase in bedroom temperature, or to an insufficient increase in temperature in our intervention group. Seasonal variations in HDM and HDM allergens must be accounted for when data on exposure are interpreted.

Decay of house-dust mite allergen Der f 1 at indoor climatic conditions.

BACKGROUND: The decay of house-dust mite allergens is important for the outcome of avoidance measures for house-dust mite-allergic patients. OBJECTIVE: To quantify the stability of Der f 1 from mattress dust when exposed to domestic conditions. METHODS: Three samples of mattress dust were individually homogenized and divided into 64 subsamples. Mites were killed by freezing for 48 hours at -30 degrees C. The subsamples were exposed in eight homes, three storerooms, and one greenhouse, where temperature and relative humidity were recorded. Der f 1 was determined in extracts of subsamples (enzyme-linked immunoadsorbent assay) at 0, 3, 12, and 24 months. RESULTS: In the three samples of mattress dust, the initial concentrations of Der f 1 (mean +/- standard deviation; STD) were: 169 (12), 3.9 (0.4), and 31 (2.6) microg/g, respectively. Median half-life of Der f 1 in the mattress dust samples was 10 years in the exposure homes, 18 years in the store rooms, and 1.0 year in the greenhouse. No correlations among preserved Der f 1 and temperature, relative humidity, and absolute humidity in homes were found (Spearman rank correlation test). CONCLUSION: Natural decay of Der f 1, with an estimated half-life of 10 years at housing conditions, has no practical consequence in reducing allergen exposure. Therefore, avoidance measures should include an active removal of the allergens.

House dust mites and their allergens in Danish mattresses -- results from a population based study.

The purpose of this study was to identify the level of house dust mites (HDMs) and their allergens in mattresses, not selected on their owners atopic status, and to find associated factors. Dust was collected from 68 mattresses. The recruitment was population-based and conducted during the screening phase of a HDM intervention study. The visited persons declared to have had a "cold" bedroom the previous winter. HDMs were counted and dust was analysed by ELISA for Der 1 (= Der f 1+ Der p 1+ Der m 1). Multiple regression analysis was carried out to find housing conditions associated with high HDM levels. Type of housing, mattress age and self-assessed winter bedroom-temperature explained 47% of Der 1. Median concentrations were 3.77 microg Der 1/g and 1 HDM/0.1 g dust. Both immunochemically and microscopically Dermatophagoides farinae was dominant; D. pteronyssinus less frequent but important; and D. microceras insignificant. In 62% of these suburban homes the mattress dust exceeded 2 microg Der 1/g; and measurement of both Der f 1 and Der p 1 was necessary and sufficient to evaluate HDM allergen exposure. The association with a high HDM level was highest and most consistent for one-family houses.