Dust mites: update on their allergens and control

Indoor mites and forensic acarology

House dust mites (HDM) have been shown to produce allergens causing atopic allergies in human beings, known in medicine as house-dust-mite allergy or atopy. Over the past 25 years (1981-2006) a survey of dust samples from different places was made in the southern part of Poland, to determine the diversity of indoor acarofauna. In total, 1,532 samples were taken from dwellings, hospitals, libraries, research laboratories, drug-stores, and offices and other workplaces. More than 30 mite species were found of which the most abundant and common were HDM, especially Dermatophagoides farinae. Highest mite densities (g(-1) dust) were noted in dwellings. This survey revealed differences in the occurrence and prevalence of various species of domestic mites between and within (dwellings in) geographical areas. This knowledge may be useful in the field of forensic medicine.

Asthma in the inner city and the indoor environment

Inner-city residents continue to suffer disproportionate asthma morbidity despite recent progress in reducing asthma morbidity and mortality in other strata of the United States population. Studies over the past decade indicate that the indoor environment is a strong contributor to poor asthma control and asthma-related health care use in inner-city populations. Certain indoor exposures are more common and occur in higher concentrations in inner-city communities than in suburban communities. Identification of "asthmagenic" indoor exposures has paved the way for the development of intervention strategies aimed at reducing asthma morbidity. This article reviews the growing body of evidence that certain indoor environmental exposures contribute to the burden of asthma in the inner city.

Comparisons of the allergenic mite prevalence in dwellings and certain outdoor environments of the Upper Silesia (southwest Poland)

The occurrence of allergenic mites (pyroglyphid house-dust mites, acarid and glycyphagid storage mites and others) in dwellings and in synanthropic outdoor sites in a densely populated urban area was investigated. A total of 335 house dust samples were collected from dwellings at 7 different locations in Upper Silesia (Poland), including 84 samples from dwellings of Katowice. Mites were found in 188 of the samples examined (56.1%). A total of 4410 mite specimens were isolated and identified, including 4212 members of the family Pyroglyphidae (95.51%). Among them, Dermatophagoides farinae was predominant (75.3%), followed by D. pteronyssinus (18.6%) and Euroglyphus maynei (1.5%). Moreover, litter soiled with communal wastes was sampled. All 86 samples contained mites. A total of 7547 mite specimens were isolated including 6050 mites known as allergenic (80.5%). Among the astigmatid mites two acarids were dominant: Tyrophagus silvester and T. longior (28.7% and 25.1% of all mites). It should be stressed that 6 of the acarid mite species or genera found in outdoor environments are typical domestic mites (T. putrescentiae), or they have been collected from house dust samples (T. longior, Tyrolichus casei, Thyreophagus entomophagus, Mycetoglyphus fungivorus and Rhizoglyphus robini). The litter of synanthropic sites can therefore form a substantial source of infestation.

Mite allergens

There is an increasing awareness of the health implications of mite sensitivity, as it is closely related to asthma. Mite allergy constitutes a complex worldwide problem, with sanitary and economical implications. Not only are mite species present in house dust, producing potent allergens, but other, less studied species are also responsible for significant allergic reactions in occupational settings. In this review, we focus on the growing number of mite species that are implicated in allergic cutaneous and respiratory diseases in humans. Mite allergy is not restricted only to the human "indoor" environment, because numerous reports clearly demonstrate that many species that can induce sensitization and symptoms are encountered in occupational settings. An important component of allergy research is the evaluation of the allergenic cross-reactivity to verify to what extent different mite species have unique, species-specific, or cross-reactive allergens. The results of these investigations have important clinical consequences for the diagnosis and treatment of allergic diseases. Internationally standardized mite extracts are needed to compare sensitization rates around the world and clearly establish risk factors associated with sensitization and asthma. In spite of recent controversial results, a significant reduction in the exposure to mite allergens continues to be an important challenge and one of the main goals in the treatment of mite-induced respiratory symptoms. In many cases, this reduction must be achieved in the workplace as well as in the home environment.

[Dermatologic occupationally relevant type I allergies]

In Germany the most frequent initial report of occupational disease is due to occupational skin diseases ("Berufskrankheitenanzeige nach Nr. 5101 der Berufskrankheitenverordnung") defined as "severe or recurrent skin diseases that force the discontinuation of any activity that causes or that could be causing the development, the worsening, or the recurrence of the skin disease". The majority of these occupational skin diseases consists of irritant and allergic contact dermatitis. In contrast, work place- related Type I allergy (contact urticaria syndrome) is less frequent, but carries the risk of systemic reactions. The clinical manifestations and pattern of exposure to Type I allergens in the work place are described.

Dust mite allergens: mitigation and control

In recent years, greater attention has been given to the role of indoor allergens as a cause of sensitization and allergic respiratory diseases. Although indoor allergen control measures to reduce symptoms in individuals allergic to mites have produced controversial results, environmental allergen avoidance is today one of the four primary goals of asthma management recommended in several guidelines of asthma treatment. Exposure to high indoor aeroallergen levels, especially to house dust mite allergens, is an important environmental risk factor for allergic sensitization and the subsequent development and exacerbation of asthma. Therefore, effective aeroallergen avoidance is of use to prevent and treat allergic diseases. Although endotoxin exposure may be protective in early life, it has been demonstrated that the inhalation of endotoxin may exacerbate asthma in house dust mite sensitized patients. Mite-allergic asthmatic patients should be aware of the dangerous combination of mite allergen exposure associated with high endotoxin levels in house dust. These two immunologically active substances have been associated with severe asthma and seasonal exacerbation of symptoms. Effective house dust mite allergen avoidance will never be achieved using a single control measure; various methods are required to affect the multiple factors that facilitate high indoor allergen levels. Education of the patients and their families is also an important component of environmental control strategies.