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

Prevalence of allergic sensitization to storage mites in Northern Europe

BACKGROUND

Allergic sensitization to storage mites has mostly been related to occupational exposures like farming, grain/cattle handling, whereas for non-occupational settings, storage mite sensitization has been attributed to cross-reactivity with house dust mite (HDM) allergens.

OBJECTIVE

We aimed to describe the prevalence of allergic sensitization to storage mites, co-sensitization to HDM allergens and respiratory symptoms in Denmark, Iceland, Norway and Sweden.

METHODS

The population comprised of 1180 participants born 1945-1972 of the third follow-up of the population-based cohort European Community Respiratory Health Survey (ECRHS) in Aarhus, Bergen, Reykjavik and Uppsala. A clinical examination included skin prick tests (SPT) to Lepidoglyphus destructor, Tyrophagus putrescentiae, Acarus siro and common inhalant allergens, as well as standardized interviews.

RESULTS

8% were sensitized to HDM and 10% to storage mite, with some variation by study centre: Reykjavik 13%, Bergen 8% and Aarhus 7%. In Uppsala, only L destructor (3%) was measured. Storage mite sensitization was higher among men (11%) than women (8%). Among storage mite sensitized, 44% were also sensitized to HDM. Storage mite sensitization was associated with asthma and nasal allergies, but not with age, education, pet keeping or place of upbringing.

CONCLUSIONS AND CLINICAL RELEVANCE

In this Northern European population-based study, allergic sensitization to storage mite was as common as HDM sensitization. Storage mite sensitization was, independently of HDM sensitization, associated with respiratory symptoms and asthma. Our findings suggest that storage mite sensitization should be evaluated with regard to inclusion into the common inhalant allergen panel in Northern Europe.

Exhaled nitric oxide in a middle-aged Icelandic population cohort

The prevalence of atopy and asthma is relatively low in Iceland. The purpose of this study was to describe exhaled nitric oxide (FeNO) levels in the general population in correlation with demographic characteristics, smoking status, asthma, rhinitis, atopic status and lung function tests. Altogether 403 subjects, from the European Community Respiratory Health Survey (ECRHS) III who answered the main questionnaire and were checked by FeNO measurements, lung function testing, skin prick testing and measurement of total IgE and specific IgE were included. The geometric mean (95% CI) of FeNO was 16.2 ppb (15.2-17.1) and the prevalence of higher FeNO (⩾25 ppb) was 19.5% in the random sample. Subjects with higher FeNO levels were less likely to be current smokers and more likely to have asthma and rhinitis. Having higher FeNO values was also associated with higher total IgE, having specific IgE to at least one allergen and being skin prick test positive. Current smokers had significantly lower levels of FeNO, geometric mean (95% CI) 9.6 ppb (8.4-11.0), than ex-smokers 18.2 ppb (16.6-20.0) and never smokers 17.3 ppb (16.1-18.5). In multivariable models, having asthma (OR (95% CI) 2.10 (1.20-3.67)), having a specific IgE (OR 2.30 (1.25-4.23)) and being skin prick test positive (OR 2.06 (1.18-3.60)) were independently positively associated with a higher FeNO (⩾25) whereas current smoking was independently negatively associated with a higher FeNO (OR 0.19 (0.06-0.63)). Higher levels of FeNO (⩾25 ppb) were found in one out of five Icelanders; FeNO was positively associated with asthma and allergy and negatively with smoking.

Immunological aspects of the immune response induced by mosquito allergens

Allergies caused by mosquito bites may produce local or systemic reactions. The inhalation of mosquito allergens may also cause asthma and/or allergic rhinoconjunctivitis in sensitized individuals. The mechanisms implicated in the development of these immune responses involve IgE antibodies, different subtypes of IgG and proinflammatory cytokines as well as basophils, eosinophils and mast cells. Several allergenic components have been identified in the saliva and bodies of mosquitoes and some of these are present in different mosquito species. The most common species implicated in allergic reactions belong to the genera Aedes, Culex and Anopheles. Several Aedes aegypti allergens have been cloned and sequenced. The recombinant molecules show IgE reactivity similar to that of the native allergens, making them good candidates for the diagnosis of mosquito allergies. Allergen-specific immunotherapy with mosquito extracts induces a protective response characterized by a decreased production of IgE antibodies, increased IgG levels, a reduction in the severity of cutaneous and respiratory symptoms and the need for medication. The aims of this review are to summarize the progress made in the characterization of mosquito allergens and discuss the types of immune responses induced by mosquito bites and the inhalation of mosquito allergens in atopic individuals.

Respiratory allergy caused by house dust mites: What do we really know?

The house dust mite (HDM) is a major perennial allergen source and a significant cause of allergic rhinitis and allergic asthma. However, awareness of the condition remains generally low. This review assesses the links between exposure to HDM, development of the allergic response, and pathologic consequences in patients with respiratory allergic diseases. We investigate the epidemiology of HDM allergy to explore the interaction between mites and human subjects at the population, individual, and molecular levels. Core and recent publications were identified by using "house dust mite" as a key search term to evaluate the current knowledge of HDM epidemiology and pathophysiology. Prevalence data for HDM allergen sensitization vary from 65 to 130 million persons in the general population worldwide to as many as 50% among asthmatic patients. Heterogeneity of populations, terminology, and end points in the literature confound estimates, indicating the need for greater standardization in epidemiologic research. Exposure to allergens depends on multiple ecological strata, including climate and mite microhabitats within the domestic environment, with the latter providing opportunity for intervention measures to reduce allergen load. Inhaled mite aeroallergens are unusually virulent: they are able to activate both the adaptive and innate immune responses, potentially offering new avenues for intervention. The role of HDM allergens is crucial in the development of allergic rhinitis and asthma, but the translation of silent sensitization into symptomatic disease is still incompletely understood. Improved understanding of HDMs, their allergens, and their microhabitats will enable development of more effective outcomes for patients with HDM allergy.

Arthropod allergens in urban homes

Dust mites, cockroaches, and pets (cats, dogs) are common in homes worldwide, and many species are the source of potent allergens which cause allergic diseases. These diseases are influenced by genetic predisposition and environmental exposure. Generally, the levels of house dust mite (Der p 1 and Der f 1) and cockroach (Bla g 1, Bla g 2) allergens are used as markers of indoor exposure to arthropods.This article reviews the findings of allergens Der p 1, Der f 1, and Bla g 1 in randomly selected urban households in Zagreb (Croatia) measured from 2006 to 2010 and compares them with exposure to arthropod allergens in other countries. In short, house dust mite allergen levels in Croatian homes are low, but exposure is common; Der p 1 was found in 73 % and Der f 1 in 83 % of the households. By contrast, exposure to cockroach allergen Bla g 1 was both low and uncommon (13 %). Exposure to multiple allergens associated with sensitisation and asthma was not frequent in urban homes in Croatia. However, further studies should include monitoring of both arthropod and pet allergens in high-risk populations in inland and coastal Croatia. They should also investigate a complex dose-response relationship between exposure and sensitisation/asthma development, especially in early childhood.

A long-term follow-up of allergic diseases in Iceland

INTRODUCTION

Allergic disorders are an increasing health problem in many countries, in particular among children. We have evaluated the prevalence and manifestations of allergy in a cohort of young Icelanders for more than two decades. Variations in the epidemiology and clinical expression of allergy in different communities may help to identify etiological factors contributing to these disorders.

METHODS

A cohort of 179 children has been monitored for allergic manifestations for two decades, at the ages of two, four, eight, and 15 years, and most recently at the age of 21 years involving 120 of the participants.

RESULTS

Cumulative prevalences of 40%, 45%, and 29% have been observed, respectively, for rhinoconjunctivitis, eczema, and asthma during the study period. None had developed rhinoconjunctivitis at the age of about 2 years, but the point prevalence gradually increased to 33% at the age of 21 years. Conversely, the prevalence of eczema was 31% at the age of 2 years, but gradually declined to 8% at the age of 21 years. The prevalence of asthma peaked at 28% at the age of 4 years, but declined thereafter and has remained stable at about 13% from the age of eight to 21 years.

DISCUSSION

The prevalence of allergic diseases is high in Iceland among children and young individuals. Asthma and atopic eczema are very common in childhood, but decreases with age while the prevalence of rhinoconjunctivitis increases markedly. The very high and increasing prevalence of rhinoconjunctivitis among 15- to 21-year-old individuals is noteworthy.

Indoor environment in three North European cities in relationship to atopy and respiratory symptoms

BACKGROUND

In the European Community Respiratory Health Survey (ECRHS) I, the lowest prevalence of asthma and atopy was found in Reykjavík (Iceland) and Tartu (Estonia). The aim of this study was to compare home environments in Reykjavík and Tartu to a town with a higher prevalence of asthma and atopy (Uppsala, Sweden) in an attempt to identify factors in the indoor environment that could explain these differences.

METHOD

A random sample of 129 ECRHS II participants was included in this analysis at each of the three study centres. The subjects answered a questionnaire, blood was analysed for specific immunoglobulin E, a methacholine test was performed and home indoor measurements were taken.

RESULTS

The prevalence of atopy was 11.9% in Reykjavík, 35.5% in Uppsala and 28.2% in Tartu (P < 0.04). The level of indoor cat allergen was significantly lower in Reykjavík compared with Uppsala (P = 0.05). No mite allergens were identified in the 41 homes investigated in Reykjavík, while this was the case in 16% and 72% of the households in Uppsala and Tartu, respectively (P = 0.001). A positive association was found between asthma symptoms and cat allergen levels [odds ratio 1.53 (95% confidence interval 1.04-2.24)], while the levels of viable moulds were significantly associated with increased bronchial responsiveness.

CONCLUSIONS

Indoor exposure to allergens, moulds and bacteria was lower in Reykjavík than in the Swedish and Estonian centres. This finding indicates that the lower prevalence of allergic sensitization in Reykjavík may partly be related to lower indoor allergen exposure.

What can we learn about asthma and allergy from the follow-up of the RHINE and the ECRHS studies?

OBJECT

The international population-based studies RHINE and ECRHS have provided new insight in the epidemiology and management of asthma, allergy and rhinitis in young adults. The aim of the present review is to focus on longitudinal results with regard incidence and net change of asthma and asthma-like symptoms, risk factors and management of asthma, with special reference to the Nordic-Baltic countries.

RESULTS

Asthma and rhinitis are common conditions that are important in a public health perspective. There are gender differences in incidence and remission. A socio-economic gradient that non-atopic asthma is more strongly related to poverty seems to have developed in the last decade. These findings will challenge our welfare states in the future. In addition, occupational, as well as indoor and outdoor environmental exposures, influenced the onset of asthma. The population-attributable risk for adult asthma because of occupational exposures is equivalent to an incidence of new-onset asthma of 250-300 cases per million per year. Genetic factors, allergic sensitisation, gastro-oesophageal reflux, habitual snoring, diet and other factors may also contribute to the onset of asthma and rhinitis. Even though management of asthma has improved, there are still great variations throughout Europe. These findings highlight the key role doctors and nurses play in educating and reviewing management of patients.

Major mite allergen Der f 1 concentration is reduced in buildings with improved energy performance

BACKGROUND

Environmental conditions play a crucial role in mite growth, and optimal environmental control is key in the prevention of airway inflammation in chronic allergic rhinoconjunctivitis or asthma.

OBJECTIVE

To evaluate the relationship between building energy performance and indoor mite allergen concentration in a cross-sectional study.

METHODS

Major allergen concentration (Der f 1, Der p 1, mite group 2, Fel d 1 and Bla g 2) was determined by quantitative dot blot analysis from mattress and carpet dust samples in five buildings designed for low energy use (LEB) and in six control buildings (CB). Inhabitants had received 4 weeks prior to mite measurement a personal validated questionnaire related to the perceived state of health and comfort of living.

RESULTS

Cumulative mite allergen concentration (with Der f 1 as the major contributor) was significantly lower in LEB as compared with CB both in mattresses and in carpets. In contrast, the two categories of buildings did not differ in Bla g 2 and Fel d 1 concentration, in the amount of dust and airborne mould collected. Whereas temperature was higher in LEB, relative humidity was significantly lower than in CB. Perceived overall comfort was better in LEB.

CONCLUSIONS

Major mite allergen Der f 1 preferentially accumulates in buildings not specifically designed for low energy use, reaching levels at risk for sensitization. We hypothesize that controlled mechanical ventilation present in all audited LEB may favour lower air humidity and hence lower mite growth and allergen concentration, while preserving optimal perceived comfort.

Group 1 and 2 Dermatophagoides house dust mite allergens in the microenvironment of cats

House dust mite allergens (HDMAs) are some of the most common allergens associated with allergic diseases in humans and dogs. The purpose of this study was to determine whether HDMAs could be detected in cat-associated household microenvironments. From 50 cat-only households with 95 cats, dust samples were collected by vacuuming for 2 min m(-2) from three areas where cats slept or rested regularly from September to October 2006. Relative humidity and temperature were measured in each household using a data logger. Each owner completed a questionnaire on potential factors that might influence the prevalence of house dust mites (HDMs). Dust samples were analysed utilizing an ELISA for Der p 1, Der f 1 and HDM group 2 allergens. In 38 of 50 households there was greater than 2 microg g(-1) of dust for at least one HDMA. Using stepwise logistic regression, factors associated with increased HDMA levels included: free-standing houses, number of humans in household, longhaired cats and age of the cat. Factors associated with decreased HDMA concentrations included: forced air heating and central air conditioning, less than 50% carpeting of the home, use of flea control, cats suffering from dermatological disease and the average temperature of the household. Many sleeping/resting areas utilized by cats contain sufficiently high levels of HDMAs to be potential sources of sensitization. This finding should lead to further determination of the role of HDMs in cats suffering from putative allergic conditions such as atopic dermatitis or asthma.

Mite sensitization among Latina women in New York, where dust-mite allergen levels are typically low

In New York (NY), Latinos often have greater asthma morbidity than other ethnicities, and dust-mite sensitization is common despite low allergen levels. We investigated mite allergen exposure and sensitization in atopic and/or asthmatic women, the majority being Puerto Rican. Women (n = 274) recruited for a birth cohort study were visited postnatally. Dust from their homes was analyzed for mite allergens (Der f 1, Der p 1, and Blo t 5). Serum was analyzed for total and allergen-specific IgE. Thirty-seven percent were sensitized to Dermatophagoides pteronyssinus, 34% to Dermatophagoides farinae, and 21% to Blomia tropicalis. Only 5% of NY homes had levels of Der f 1 >2 microg/g; none had Blo t 5 or Der p 1 above this level. Caribbean or Latin American birthplace (a proxy for childhood exposure) was not associated with mite sensitization. Sensitization to D. pteronyssinus and D. farinae was associated with a report of doctor-diagnosed asthma [Odds ratio (OR) = 3.27, P = 0.003; OR = 2.81, P = 0.010, respectively]; sensitization to any mite was associated with asthma medication use in the past 12 months (OR = 3.12, P = 0.004). These associations held even after adjustment for cockroach, mouse, and cat sensitization.

PRACTICAL IMPLICATIONS

Despite the low concentrations of mite allergen in our community, many of the women in the atopically enriched cohort were sensitized to mites, even Blomia tropicalis which is typically found only in tropical environments.

High prevalence of allergic diseases and sensitization in a low allergen country

BACKGROUND

The prevalence of adult atopic diseases in Iceland is lower than in other West European countries, despite an affluent lifestyle, but limited data are available on children. The main aim of this study was to investigate the prevalence of atopic diseases and sensitivity to common allergens in 10- to 11-year-old Icelandic schoolchildren as part of phase II of the International Study of Asthma and Allergies in Children (ISAAC).

METHODS

Nine hundred and forty-six children and their parents answered a questionnaire about atopic diseases. Skin prick tests with six allergens were performed on 773 children and they were examined for signs of atopic dermatitis (AD).

RESULTS

The 12-month prevalence of allergic rhinoconjunctivitis and asthma was 11.5% and 8.9% respectively. The reported prevalence of AD was 27%, but only 9.2% had signs when inspected. A positive skin prick test (SPT) was found in 24.4% of the children, that is 18.8% to grass, 12.9% to cat, 3.6% to trees, 3.0% to Dermatophagoides pteronyssinus, 1.4% to D. farinae and 0.5% to Alternaria.

CONCLUSION

The high prevalence of atopic diseases in children at 10-11 years is surprising, as the prevalence in adults is low in Iceland. The findings resemble those in developing countries. Iceland has had an affluent lifestyle for a considerable time, but the absence of dust mites, low pet ownership and relatively low pollen counts in the country raise doubts about the role of exposure levels in the development of sensitization and atopic diseases.

What characterizes house dust mite sensitive individuals in a house dust mite free community in Reykjavik, Iceland?

BACKGROUND

Previous studies show that 6-9% of young adults in Reykjavik are sensitised to the house dust mite (HDM) Dermatophagoides pteronyssinus (D. pteronyssinus). However, only negligible amounts of HDM and HDM allergens were detected in their homes. The study investigates what characterizes these individuals.

METHODS

We investigated all participants in the European Community Respiratory Health Surveys I and II (ECRHS I and II) with D. pteronyssinus specific IgE, in the years 1991-92. A grass positive but D. pteronyssinus negative control group was recruited from the same cohort. A detailed questionnaire was administered and the specific IgE (Pharmacia CAP system) against six D. pteronyssinus cross-reactive allergens was measured.

RESULTS

Of 601 ECRHS I participants with available IgE results, 88% returned for ECRHS II, 8.4 years later. Of 49 individuals with D. pteronyssinus specific IgE in ECRHS I, 24 had become negative in ECRHS II. Compared with controls, HDM sensitive subjects were more often men who had lived on farms or kept aquaria fish in childhood. Of those with specific IgE against D. pteronyssinus in ECRHS I and II, 75% had detectable IgE antibodies (>or=0.35 kU/l) to cross-reactive allergens compared with none in the control group (p<0.0001): Lepidoglyphus destructor (L. destructor) (67%), shrimp (58%), cockroach (33%), mosquito (17%), tropomyosin (17%) and blood worm (4%).

CONCLUSIONS

Icelanders with specific IgE to D. pteronyssinus are more often men who spent time on farms in childhood and today have high prevalence of IgE antibodies cross-reactive to D. pteronyssinus.