Allergy Asthma Immunol Res. 2016 Jul;8(4):312-318. English.
Published online Jan 22, 2016. http://dx.doi.org/10.4168/aair.2016.8.4.312
Copyright © 2016 The Korean Academy of Asthma, Allergy and Clinical Immunology
The Korean Academy of Pediatric Allergy and Respiratory Disease
No Concentration Decrease of House Dust Mite Allergens With Rising Altitude in Alpine Regions
Carina Grafetstätter1, Johanna Prossegger1, Herbert Braunschmid1, Renata Sanovic2, Penelope Hahne1, Christina Pichler1, Josef Thalhamer3, and Arnulf Hartl1
1Institute of Ecomedicine, Paracelsus Medical University, Salzburg, Austria.
2Institute of Physiology and Pathophysiology, Paracelsus Medical University, Salzburg, Austria.
3Department of Molecular Biology, University of Salzburg, Salzburg, Austria.
Several studies over the past 4 decades have indicated a significant reduction in house dust mite (HDM) and HDM allergen concentration in areas higher than 1500 m above sea level. These have served as basis of allergen avoidance therapies for HDM allergy and asthma. However, modern construction techniques used in the insulation, heating, and glazing of buildings as well as global warming have changed the environmental parameters for HDM living conditions. The present study revisits the paradigm of decreasing HDM allergen concentrations with increasing altitude in the alpine region of Germany and Austria.
A total of 122 dust samples from different abodes (hotels, privates and mountain huts) at different altitudes (400-2600 m) were taken, and concentrations of HDM allergens were analyzed. Humidity and temperature conditions, and numerous indoor environmental parameters such as fine dust, type of flooring, age of building, and frequency of cleaning were determined.
HDM allergen concentrations did not significantly change with increasing altitude or relative humidity. At the level of indoor parameters, correlations could be found for different flooring types and the concentration of HDM allergens.
In contrast to the widespread view of the relationship between altitude and HDM allergen concentrations, clinically relevant concentrations of HDM allergens could be detected in high-lying alpine regions in Austria and Germany. These results indicate that improvement in conditions of asthmatic patients sensitized against HDMs during a stay at high altitude can no longer be ascribed to decreased levels of HDM allergens, instead, other mechanisms may trigger the beneficial effect.
Keywords: Hypersensitivity; allergens; pyroglyphidae; asthma
Asthma and allergic rhinitis are chronic diseases with a steadily increasing prevalence. Worldwide, 300 million people suffer from asthma. In Germany alone, 7000 people die because of asthma each year. The mortality rate is rising in most countries, and allergy and asthma have become public health problems throughout the world . HDM allergens are one of the main causes of allergy and asthma, and increased exposure to indoor allergens has been suggested as a possible reason for the general rise in allergic diseases [2, 3]. The most frequent species are Dermatophagoides pteronyssinus (with the major allergens Der p 1 and Der p 2), and Dermatophagoides farinae (with the major allergens Der f 1 and Der f 2). Both comprise mite “group 1” and “group 2” allergens  and are common in European and American homes. Usually, HDMs colonize every part of a house, and HDM allergens are chemically stable for many years . The structure and sequence of Der p 1 and Der f 1 are almost identical, thus resulting in a high cross-reactivity and similar effects in patients .
Since early publications in the 1970s, allergologists have postulated a decreased HDM load and HDM allergen concentration with increasing altitude and decreasing humidity [7-10], however, some publications contradict this interpretation [11, 12]. Based on the assumption of a negative correlation of altitude and HDM concentration, allergen avoidance therapies for HDM allergy and asthma are offered in alpine regions. Clinical studies verified that a stay in high altitude improves relevant surrogate parameters for allergy and asthma, such as the reduction of specific IgE levels or improved clinical asthma markers [13-17].
The aim of the present study was to revisit the current hypothesis that altitude inversely correlates with the HDM allergen concentration. For that purpose, 122 dust samples were collected from different types of buildings (privates, taverns and mountain huts) located at altitudes of between 400 m and 2600 m in alpine regions of Germany and Austria and HDM allergen concentrations were measured.
As a second major parameter, relative air humidity (RH, %) was postulated to significantly influence HDM growth, and low indoor RH was recommended to reduce HDM [18-20]. However, in recent studies no association between HDM infestation and RH could be detected [21, 22].
Indoor allergens are usually attached to the surface of indoor particulate matter (PM), e.g. fine dust, which supports their transport to the respiratory tract and may also aggravate the allergenicity of indoor allergens and was therefore measured in all buildings included in this study [23, 24].
Allergen concentrations were related to fine dust pollution, temperature, humidity, and parameters of building characteristics and indoor environment (number of windows, type of flooring, age of building etc.).
No correlation could be measured between the concentrations of the allergens Der p 1 and mite group 2 with the altitude (Der p 1: r = 0.088, P = 0.334; mite group 2: r = -0.098, P = 0.285). Der f 1 showed a weak negative correlation with the altitude (Der f 1: r = – 0.319/P < 0.001), which may be due to a markedly higher concentration of Der f 1 in the altitude range below 1500 m compared to Der p 1 allergen levels (P = 0.001). There is a huge percentage disparity of Der p 1 and Der f 1 allergens below 1500 m altitude (Figure 1). Concentrations of Der p 1 and Der f 1 allergens do not differ in samples taken above 1500 m a.s.l. (P = 0.689).
Figure 1. Percentage of allergen concentrations of Der p 1, Der f 1 and Mite group 2 of samples taken in 400 – 1500 m a.s.l. (n = 65) and 1500 – 2600 m a.s.l. (n = 57). There are significant higher Der f 1 allergen levels compared to Der p 1 (p = 0.001) below 1500 m, but no concentration differences in higher altitude (p = 0.689).
No statistically significant difference could be found between the allergen concentrations of samples taken above and below 1500 m a.s.l. of both Der p 1 (P = 0.928) and mite group 2 allergens (P = 0.127) (Figure 2). Only Der f 1 gets reduced in higher altitude (P < 0.000).
Figure 2. Allergen concentrations of Der p 1, Der f 1 and Mite group 2 of samples taken above (n = 57) and below 1500 m a.s.l. (n = 65). There are significant lower Der f 1 allergen levels in high altitude compared to allergen levels below 1500 m a.s.l. (p = 0.000). For Der p 1 and Mite 2 allergens no concentration differences in higher altitude could be detected (Der p 1: p = 0.928; Mite 2: p = 0.127).
In general, mattresses represent a superior biotope for HDM compared to floors. Consistently, allergen concentrations of samples collected from mattresses were significantly higher than those taken from the floors (Der p 1: P = 0.001; Der f 1: P = 0.005; mite group 2: P = 0.017) reflecting a stoichiometric relationship of ~ 2:1.
One part of the samples (n = 37) was taken from buildings that were only used six months a year, at an altitude of 1750 – 2600 m, and were fully frozen during winter. The other part (n = 85) originates from buildings at altitudes of 420 – 1650 m, which were occupied all throughout the year. Despite the drastic differences in the living conditions for dust mites in these two groups, for Der p 1 and mite group 2 allergens no significant changes in allergen concentration could be detected (Der p 1: P = 0.832; mite group 2: P = 0.672). Only Der f 1 allergens show less concentrations in samples taken from buildings closed and unheated during the winter (Der f 1: P = 0.005).
There was a clear negative correlation of temperature to rising altitude (r = – 0.537; P < 0.001), but no relationship between temperature and the concentration of mite allergens could be measured (Der p 1: r = – 0.133, P = 0.201, Der f 1: r = 0.027, P = 0.799, mite group 2: r = – 0.077, P = 0.459).
RH also showed a clear negative correlation with altitude (r = – 0.635; P < 0.001). However, in contrast to previous studies, there was no correlation between allergen concentrations and RH (Der p 1: r = – 0.158; P = 0.129; Der f 1: r = – 0.047; P = 0.652; mite group 2: r = – 0.102; P = 0.328).
Indoor fine dust PM values (n = 111) showed no correlation with altitude or the weight of collected dust samples. A positive correlation was found for the weight of dust in the collected samples from floors and mattresses with concentration of mite allergens (Der p 1: r = 0.359, P < 0.001; Der f 1: r = 0.398, P < 0.001; Mite group 2: r = 0.406, P < 0.001). Concentration of mite allergens also showed weak negative correlations with most of the measured PM, indicating fine dust bound allergens hovering in the air (data not shown).
Interestingly, indoor environmental characteristics showed no association with the concentration of mite allergens. A non-significant difference could be measured with different types of floors. Stone floors displayed the lowest allergen concentrations (arithmetic mean: Der p 1: 20.93 ng/g, Der f 1: 11.44 ng/g, mite group 2: 10.86 ng/g), whereas vinyl floors showed the highest concentrations of Der p 1 and mite group 2 allergens (arithmetic mean Der p 1: 56.12 ng/g, mite group 2: 29.30 ng/g). Highest Der f 1 allergen concentrations were found on laminate floors (arithmetic mean Der f 1: 124.83 ng/g).
These results clearly indicate that the concentration of HDM allergens Der p 1 and mite group 2 does not significantly decrease at high altitudes. Moreover, no correlation between altitude, RH and HDM allergen concentrations could be found. Even in mountain huts at high altitudes that were not used in winter and thus were fully frozen at that time, HDM concentrations did not differ from buildings located at lower altitudes which were occupied throughout the year. Similarly, dwelling conditions did not significantly alter the allergen load. Only Dermatophagoides farinae shows a weak negative but significant correlation with rising altitudes. Due to this fact, we assume a higher sensitivity of the American HDM and poorer ability to adapt to changes.
Importance of the study
We provide evidence that HDM allergen levels are not significantly lower in the mountainous areas of the alpine region of Germany and Austria. The data indicate that recovery of asthmatics and allergy sufferers during a stay in a high-altitude region is not the result of lacking allergen (allergen avoidance), as has been postulated for several decades. Hitherto unknown mechanisms, possibly triggered by stationary effects or climatic conditions, seem to be responsible for mitigating the allergic immune response.
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