Parental farming protects children against atopy: longitudinal evidence involving skin prick tests

Occupational endotoxin exposure in association with atopic sensitization and respiratory health in adults: Results of a 5-year follow-up

The objective of the present longitudinal study was to investigate the effects of occupational endotoxin exposure on respiratory health and atopic sensitization in adults. Health outcomes and personal endotoxin exposure estimates were determined for 234 farmers and agricultural workers both at baseline and 5 years later. A questionnaire was used to assess respiratory symptoms, spirometry tests were performed and total and specific IgE levels were measured in serum. A twofold increase in personal endotoxin exposure was associated with less hay fever (OR 0.68, 95%CI 0.54-0.87) and grass IgE positivity (OR 0.81, 95%CI 0.68-0.97) at both time points ("persistent" versus "never"). Although not statistically significant, a consistent protective pattern was observed for an increased loss of hay fever symptoms (OR 2.19, 95%CI 0.96-4.99) and grass IgE positivity (OR 1.24, 95%CI 0.76-2.02), and for less new-onset of hay fever (OR 0.87, 95%CI 0.65-1.17), grass IgE positivity (OR 0.83, 95%CI 0.61-1.12) and atopic sensitization (OR 0.75, 95%CI 0.55-1.02). Endotoxin exposure was not associated with changes in lung function. We showed that occupational endotoxin exposure is associated with a long-term protective effect on hay fever and grass IgE positivity. Results on longitudinal changes in hay fever, atopy and grass IgE positivity in adulthood were consistent with a protective effect of endotoxin exposure, but results need to be confirmed in larger cohorts. An effect of endotoxin exposure on lung function decline was not found.

Is the "farm effect" hypothesis still current? Atopy and allergic diseases in rural and urban children in Poland

OBJECTIVE

The prevalence of allergic diseases has reached epidemic proportions in the Western world. Although farm-living has been associated with a lower prevalence of asthma and atopy, a marked increase in atopy among rural populations after accession to the European Union has been recently reported in Poland. Here, we aimed to investigate the effect of living environment on the prevalence of atopy and allergic diseases in Polish children.

METHODS

400 schoolchildren aged 10-14 years from the capital city (223) and from traditional rural part of the country (177) were recruited from June to November 2011. Data on allergic diseases and symptoms were collected by means of questionnaire and physical examination. Atopy was assessed based on skin prick tests (SPTs) reactivity to inhalant allergens in 350 children.

RESULTS

A high discrepancy between the prevalence of allergic symptoms (46.7%) and doctor-diagnosed allergic diseases (25%) was demonstrated (p < 0.0001). Urban children had a higher overall prevalence of allergic diseases and atopy than children living in rural areas, 29.3% versus 17.1% (p = 0.007) and 33.5% versus 20% (p = 0.0045), respectively. However, no significant differences in the rates of particular allergic diseases were noted (p > 0.05). There was higher SPT positivity to trees, grass, corn, weeds, animal dander, and molds in urban children (p < 0.05).

CONCLUSIONS

Our data support the protective effect of farm-living on the prevalence of atopy and overall allergic diseases, albeit not on particular allergic diseases, in children in Poland. The underlying mechanisms are not identified, but current socioeconomic changes may be responsible.

High exposure to endotoxin in farming is associated with less new-onset pollen sensitisation

OBJECTIVES

Little is known about risk factors for new onset and loss of atopic sensitisation in adulthood. The aim is to examine the longitudinal effect of quantitatively assessed endotoxin exposures on changes in specific allergen sensitisation in young adults.

METHODS

The cohort consisted of 1113 young Danish farmers and rural controls, with a mean age of 19 years at baseline. Sensitisation to birch pollen, grass pollen, cat dander and house dust mite was measured by specific IgE levels in serum samples from baseline and at 15 years' follow-up. Changes in sensitisation were analysed in relation to cumulative endotoxin exposure during follow-up, considering early life farm exposure.

RESULTS

Endotoxin exposure during follow-up was significantly associated with less new onset of specifically grass and birch pollen sensitisation. For the highest versus lowest quartile of cumulative endotoxin exposure, the OR for new-onset IgE sensitisation was 0.35 (0.13-0.91) for birch and 0.14 (0.05-0.50) for grass. On the other hand, loss of pollen sensitisation showed a positive, although mostly non-significant, association with increased levels of endotoxin exposure. Endotoxin exposure was not associated with significant changes in cat dander and house dust mite sensitisation.

CONCLUSIONS

High exposure to endotoxin during young adulthood appears to protect against new onset of pollen sensitisation, independent of childhood farm exposure.

Farm Exposure and Atopy in Men and Women: The Saskatchewan Rural Health Study

Associations between farming exposures and atopy can vary by timing of exposure and sex. We examined associations between adult atopy, sex, and farm living in a rural Canadian population. In 2010, we conducted a baseline survey of 11,982 households located in four agricultural regions of Saskatchewan, Canada. Of the 7225 adults aged 18-75, 1658 underwent clinical assessments including skin testing. Of these, 1599 participants underwent skin prick testing to four common allergens. We defined atopy as >3 mm reaction to any of four allergens compared with saline control. Farming exposures were farm living in the first year of life and current farm living. All analyses were stratified by sex. The prevalence of atopy was 17.8% and was higher in men than women (P < .001). The most common allergy was to grasses (8.8%) followed by house dust mite (HDM) mixed (8.1%). Atopy was lower in those subjects with an early farm exposure (P = .08) and who were female (P = .03). After adjusting for education, age, and smoking status, both current and early farm exposures were associated with decreased sensitization to cat atopy in women that was stronger with current exposure (P < .05). Men had significantly decreased atopic sensitization to Alternaria with an early farm exposure and increased atopic sensitization to HDM with a current farm exposure. In this rural population, the protective effect of an early farm exposure for any atopy was weak overall. The impact of farming exposures on atopy was allergen dependent and varied by sex.

A clear urban-rural gradient of allergic rhinitis in a population-based study in Northern Europe

BACKGROUND

The protective effect of farm upbringing on allergic rhinitis is well known, but how upbringing in other environments influences the development of allergic rhinitis is scarcely investigated. The aim of this study was to investigate the association between place of upbringing and pet keeping in childhood and allergic rhinitis and nasal symptoms in adulthood.

METHODS

The population-based Respiratory Health in Northern Europe study includes subjects from Denmark, Norway, Sweden, Iceland, and Estonia born in 1945-1973. This paper analyses 13,376 participants of the third study wave. Six categories of place of upbringing were defined: farm with livestock, farm without livestock, village in rural area, small town, city suburb, and inner city. Pets in the home at birth and during childhood were recorded. Data were analysed using adjusted logistic regression models.

RESULTS

Livestock farm upbringing predicted less adult allergic rhinitis [odds ratio (OR) 0.68, 0.54-0.85] and nasal symptoms (OR 0.82, 0.68-0.99) than city upbringing, and an urban-rural gradient with decreasing risk per level of urbanisation was observed (OR 0.92, 0.88-0.94). Pets in the home at birth (OR 0.78, 0.68-0.88) and during childhood (OR 0.83, 0.74-0.93) were associated with less subsequent allergic rhinitis. Pet keeping did not explain the protective effect of place of upbringing.

CONCLUSION

Risk of allergic rhinitis and nasal symptoms in adulthood was inversely associated with the level of urbanisation during upbringing. Pets at birth decreased the risk further, but did not explain the urban-rural gradient. Persistent beneficial effects of microbial diversity in early life might be an explanation for the findings.

Association of living in a farming environment with asthma incidence in Canadian children

OBJECTIVE

The objective of this population-based 14-year follow-up study was to examine the effect of living in a farm environment on asthma incidence in children.

METHODS

A total of 10,941 children of ages 0 to 11 years who were free of asthma and wheeze at the baseline (1994-1995) in the National Longitudinal Survey of Children and Youth were considered in the study. Children's living environment was classified, based on interviewer's observation, into three categories: non-rural, rural non-farming, and farming. An incidence of asthma was obtained from health-professional diagnosed asthma reported either by the person most knowledgeable for children under 15 years or by the children themselves if they were of ages 16 years and over.

RESULTS

The 14-year cumulative incidence of asthma among children living in farming environments was 10.18%, which was significantly lower than that observed for children living in rural non-farming (13.12%) and non-rural environments (16.50%). After adjusting for age group, number of older siblings, allergy, parental history of asthma, dwelling in need of repairs and SES index, a dose-response relationship was observed with children living in rural non-farming and farming environments having significantly reduced risk of asthma [hazard ratio (HR): 0.77; 95% confidence interval (CI): (0.60, 1.00); p = 0.047 and HR: 0.56; 95% CI: (0.41,0.77); p < 0.001] in comparison to those living in non-rural environments.

CONCLUSION

This cohort study provides further evidence that living in a farming environment during childhood is protective of asthma incidence in adolescence and adulthood and this finding provides further support for the hygiene hypothesis.

The microbial environment and its influence on asthma prevention in early life

There is accumulating evidence to suggest that the environmental microbiome plays a significant role in asthma development. The very low prevalence of asthma in populations highly exposed to microbial environments (farm children and Amish populations) highlights its preventive potential. This microbial diversity might be necessary to instruct a well-adapted immune response and regulated inflammatory responses to other inhaled and ingested environmental elements, such as allergens, particles, and viruses. Like the internal gut microbiome, which is increasingly recognized as an important instructor of immune maturation, the external environmental microbiome might shape immune responses on the skin, airway mucosal surfaces, and potentially also the gut early in life. The diversity of the external microbial world will ensure that of the many maladapted pathways leading to asthma development, most, if not all, will be counterbalanced. Likewise, important contributors to asthma, such as allergen sensitization and allergic manifestations early in life, are being suppressed. Thus the facets of innate immunity targeted by microbes and their compounds and metabolites might be the master switch to asthma and allergy protection, which has been found in environments rich in microbial exposures.

Exposure to 'farming' and objective markers of atopy: a systematic review and meta-analysis

There is growing interest in the 'farm effect' on the spectrum of allergy. Evidence concerning the farm effect on asthma, eczema, and allergic rhinitis has been systematically synthesized, but without a specific focus on objective markers of sensitization. This focus is important, as farm exposures may be related to allergy but not to non-allergic phenotypes of disease. We aimed to systematically review and meta-analyse literature that has investigated associations between farm exposure at any age and objective measures of atopy, that is serum IgE or skin prick tests results. Using predefined inclusion and exclusion criteria, we identified 29 articles for review. IgE levels were measured in either childhood or adulthood by eighteen studies, while skin prick testing was performed in sixteen studies. Newcastle-Ottawa Scale quality assessments indicated that the majority of these studies demonstrated a representative sample of selected participants. Due to significant heterogeneity in study measures and methodology between studies, only few were meta-analysed. This meta-analysis showed a significant protective effect of farm exposure before 1 year of life on allergic sensitization (OR = 0.60 [0.52-0.70]). Farm exposure during childhood was also associated with a reduced risk of sensitization to cat or timothy (OR = 0.60 [0.51-0.70]; OR=0.46 [0.41-0.51]). Studies investigating the effect of farm exposure in adult life could not be meta-analysed, and their results were inconsistent. Insufficient studies investigated food sensitization as an outcome to allow synthesis. The majority of studies included in this review investigated childhood farm exposure, finding evidence to support a protective childhood 'farm effect' against subsequent atopy. There is inconsistent evidence on the association between farm exposure in adulthood and allergic sensitization. Further studies are needed to tease out the exact exposures and timing associated with farming environments that protect against allergic disease.

Allergen skin prick testing in early childhood: reproducibility and prediction of allergic symptoms into early adulthood

OBJECTIVE

To assess the predictive value of skin prick testing in early childhood on subsequent allergic symptoms up to adult age.

STUDY DESIGN

A cohort of 200 unselected healthy newborns was prospectively followed from birth to 20 years of age. Of them, 163 (82%) were reassessed at age 5 years, 150 (76%) at age 11 years, and 164 (83%) at age 20 years with a skin prick test that included 11 common allergens. On the basis of clinical examination and structured interview, the occurrence of atopic dermatitis, allergic rhinoconjunctivitis, recurrent wheezing, and symptoms of food hypersensitivity were recorded at each of the follow-up visits.

RESULTS

The reproducibility of skin prick test positivity at age 5 years was 100% at ages 11 and 20 years, ie, none of the skin prick-positive subjects turned negative during the follow-up. Gaining of new sensitizations to aeroallergens was common. Skin prick test positivity at age 5 years predicted allergic symptoms at ages 11 (sensitivity 28%, specificity 94%) and 20 years (sensitivity 23%, specificity 91%) but not atopic dermatitis.

CONCLUSIONS

Skin prick test positivity at age 5 years strongly predicts later skin prick test positivity and is associated with respiratory symptoms, ie, allergic rhinoconjunctivitis and recurrent wheezing, at ages 11 and 20 years. However, skin prick test negativity at age 5 years does not exclude sensitization and allergic symptoms at a later age.

Asthma and asthma related symptoms in 23,326 Chinese children in relation to indoor and outdoor environmental factors: the Seven Northeastern Cities (SNEC) Study

BACKGROUND

Both the levels and patterns of outdoor and indoor air pollutants have changed dramatically during the last decade in China. However, few studies have evaluated the effects of the present air pollution on the health of Chinese children. This study examines the association between outdoor and indoor air pollution and respiratory diseases among children living in Liaoning, a heavy industrial province of China.

METHODS

A cross-sectional study of 23,326 Chinese children aged 6 to 13 years was conducted in 25 districts of 7 cities in Northeast China during 2009. Three-year (2006-2008) average concentrations of particles with an aerodynamic diameter of ≤10 μm (PM10), sulfur dioxide (SO2), nitrogen dioxides (NO2), and ozone (O3) were calculated from monitoring stations in each of the 25 districts. We used two-level logistic regression models to examine the effects of yearly variations in exposure to each pollutant, controlling for important covariates.

RESULTS

The prevalence of respiratory symptoms was higher for those dwelling close to a busy road, those living near smokestacks or factories, those living with smokers, those living in one-story houses typically with small yards, and those with home renovation, bedroom carpet or pets. Ventilation device use was associated with decreased odds of asthma in children. The adjusted odds ratio for diagnosed-asthma was 1.34 (95% confidence interval [CI], 1.24-1.45) per 31 μg/m(3) increase in PM10, 1.23 (95%CI, 1.14-1.32) per 21 μg/m(3) increase in SO2, 1.25 (95%CI, 1.16-1.36) per 10 μg/m(3) increase in NO2, and 1.31 (95%CI, 1.21-1.41) per 23 μg/m(3) increase in O3, respectively.

CONCLUSION

Outdoor and indoor air pollution was associated with an increased likelihood of respiratory morbidity among Chinese children.

Epidemiology of Respiratory Allergies and Asthma

Asthma has puzzled and confused physicians from the time of Hippocrates to the present day. The word “asthma” comes from a Greek word meaning “panting” (Keeney 1964), but reference to asthma can also be found in ancient Egyptian, Hebrew, and Indian medical writings (Ellul-Micallef 1976; Unger and Harris 1974). There were clear observations of patients experiencing attacks of asthma in the second century and evidence of disordered anatomy in the lung as far back as the seventeenth century (Dring et al. 1689).

The relationship between pollen count levels and prevalence of Japanese cedar pollinosis in Northeast Japan

BACKGROUND

The prevalence of Japanese cedar (JC) pollinosis in Japanese children is increasing. However, few studies have reported the relationship between pollen count levels and the prevalence of pollinosis. To evaluate the relationship between JC pollen count levels and the prevalence of pollinosis in children, we investigated the sensitization and development of symptoms for JC pollen in two areas of Akita in northeast Japan with contrasting levels of exposure to JC pollen.

METHODS

The study population consisted of 339 elementary school students (10-11 years of age) from the coastal and mountainous areas of Akita in 2005-2006. A questionnaire about symptoms of allergic rhinitis was filled out by the students' parents. A blood sample was taken to determine specific IgE antibodies against five common aeroallergens.

RESULTS

The mean pollen count in the mountainous areas was two times higher than that in the coastal areas in 1996-2006. The prevalence rates of nasal allergy symptoms and sensitization for mites were almost the same in both areas. On the other hand, the rates of nasal allergy symptoms and sensitization for JC pollen were significantly higher in the mountainous areas than in the coastal areas. The rate of the development of symptoms among children sensitized for JC pollen was almost the same in both areas.

CONCLUSIONS

These results suggest that pollen count levels may correlate with the rate of sensitization for JC pollinosis, but may not affect the rate of onset among sensitized children in northeast Japan.

Research at the interface between human and veterinary health

Epidemiology is currently undergoing changes in its underlying philosophy and approach, as a result of the rapid global changes which are transforming the world in which epidemiologists live and work. This necessitates a multidisciplinary "population approach" involving "multilevel thinking" about the determinants of disease. These issues are of relevance to the interface between human and animal epidemiology, which has received considerable attention in recent years, particularly as a result of the arrival of H1N1 influenza, and the increasingly obvious need for coordinated systems of surveillance for human and animal infectious diseases. However, the need for coordination between human and veterinary epidemiology is broader than that, and there is no need to restrict the "one world one health" concept to communicable disease. In the current paper we will therefore consider the interface between human and animal health for the study of non-communicable disease, particularly those involving occupational and environmental risk factors. These issues are illustrated with two examples: one involving environmental health (asthma); and one involving occupational health (cancer). We will also discuss the potential to use animal health data as indicators for human environmental health risks.

Asthma and allergies: is the farming environment (still) protective in Poland? The GABRIEL Advanced Studies

BACKGROUND

Evidence exists that a farming environment in childhood may provide protection against atopic respiratory disease. In the GABRIEL project based in Poland and Alpine regions of Germany, Austria and Switzerland, we aimed to assess whether a farming environment in childhood is protective against allergic diseases in Poland and whether specific exposures explain any protective effect.

METHODS

In rural Poland, 23 331 families of schoolchildren completed a questionnaire enquiring into farming practices and allergic diseases (Phase I). A subsample (n = 2586) participated in Phase II involving a more detailed questionnaire on specific farm exposures with objective measures of atopy.

RESULTS

Farming differed between Poland and the Alpine centres; in the latter, cattle farming was prevalent, whereas in Poland 18% of village farms kept ≥1 cow and 34% kept ≥1 pig. Polish children in villages had lower prevalences of asthma and hay fever than children from towns, and in the Phase II population, farm children had a reduced risk of atopy measured by IgE (aOR = 0.72, 95% CI 0.57, 0.91) and skin prick test (aOR = 0.65, 95% CI 0.50, 0.86). Early-life contact with grain was inversely related to the risk of atopy measured by IgE (aOR = 0.66, 95% CI 0.47, 0.92) and appeared to explain part of the farming effect.

CONCLUSION

While farming in Poland differed from that in the Alpine areas as did the exposure-response associations, we found in communities engaged in small-scale, mixed farming, there was a protective farming effect against objective measures of atopy potentially related to contact with grain or associated farm activities.

The combined effects of family size and farm exposure on childhood hay fever and atopy

BACKGROUND

Exposure to farming environments and siblings is associated with reduced risks of childhood hay fever and atopy. We explored the independence and interaction of these protective effects in the GABRIELA study.

METHODS

Questionnaire surveys on farming, asthma, and allergies were conducted in four central European areas among 79,888 6-12-yr-old children. Aeroallergen-specific serum IgE was measured in a stratified sample of 8,023 children. Multiple logistic regression was used to compare gradients in allergy prevalence by sibship size across three categories of exposure to farming environments.

RESULTS

The prevalence of hay fever ranged from 2% (95% confidence interval 1.6%; 2.7%) among farmers' children with more than two siblings to 12% (11.2%; 13.0%) among children with no farm exposure and no siblings. Farming families were larger on average. More siblings and exposure to farming environments independently conferred protection from hay fever and atopy. There was no substantial effect modification between family size and exposure to farming environments. The odds ratios for hay fever per additional sibling were 0.79 among unexposed non-farm children, 0.77 among farm-exposed non-farm children, and 0.72 among children from farming families (2df interaction test: p = 0.41).

CONCLUSION

The inverse association of exposure to farming environments with hay fever is found in all sizes of family, with no substantial tendency to saturation or synergism. This suggests that different biological mechanisms may underlie these two protective factors. Combinations of a large family and exposure to farming environments markedly reduce the prevalence of hay fever and indicate the strength of its environmental determinants.

LPS-induced CD11b+Gr1(int)F4/80+ regulatory myeloid cells suppress allergen-induced airway inflammation

In humans, the bacterial product lipopolysaccharide (LPS) has been associated with protection from allergic diseases such us asthma. However, in mouse models of allergic asthma, differential effects of LPS have been noted based on the dose. A low dose of LPS promotes Th2 responses and allergic disease but a high dose has been associated with suppression of allergic airway inflammation. Our recent work has described the ability of LPS to increase the frequency of CD11b+Gr1(int)F4/80+(abbreviated as Gr1(int) cells) cells in the lung tissue of mice in a dose-dependent fashion that is dependent on TLR4 and the TLR adaptor protein, MyD88. Both phenotypically and morphologically, the cells were found to have similarities with mycloid-derived suppressor cells. Adoptive transfer of LPS-induced Gr1(int) cells suppressed allergen-induced airway inflammation suggesting regulatory functions of the cells in allergic asthma. Although the Gr1(int) cells are detectable in the lung tissue of LPS-treated mice, they are barely detectable in the lung-draining lymph nodes (Lns) or in the airway lumen. This causes selective enrichment of these cells over dendritic cells (Dcs) in the tissue which upon LPS stimulation migrate to lung-draining LNs. The Gr1(int) cells were found to blunt the ability of the lung DCs to upregulate GATA-3 or to promote STAT5 activation in primed Th2 cells, both transcription factors having critical roles in TH2 effector function. Thus, a complete understanding of the generation and regulation of the Gr1(int) cells would provide new avenues to either promote or delete these cells for disease-specific immunoregulation.

Indoor air pollution and childhood asthma: variations between urban and rural areas

Health effects of indoor pollution have been investigated overall in urban areas. To compare the potential effect of home air pollutants on asthma in urban and rural houses, two case-control populations, composed of children living in the city (32 asthmatics and 31 controls) and in the countryside (24 asthmatics and 27 controls) were included. During 1 week, nitrogen dioxide, fine particles, and volatile organic compounds (formaldehyde, acetaldehyde, benzene, toluene, ethylbenzene, and xylenes) were assessed at home. Urban dwellings were found to be more polluted than rural ones, with concentrations up to two times higher. In the whole population, exposure to acetaldehyde and toluene was significantly associated with a higher risk of asthma. In the urban population, the association with toluene was significant in children studied during winter, and with toluene, xylenes, and ethylbenzene when cases were restricted to current asthmatics. In rural settings, a relationship between asthma and formaldehyde exposure was observed (OR = 10.7; 95% CI 1.69-67.61). Our findings suggest that daily continuous exposures to pollutants may be implicated in asthma, even in the case of low exposure, as those found in rural areas. Our results could also indicate a specific effect of indoor pollution in the rural environment.

PRACTICAL IMPLICATIONS

Everyday exposure to indoor pollution was associated with a higher risk of childhood asthma. These findings suggest that even at low concentrations, pollutants could be implicated in asthma and reinforce the importance of establishing guideline values to improve indoor air quality by limiting sources or by optimizing ventilation. Specific effects could occur in rural environments where pollution differs from urban area.

Farm living: effects on childhood asthma and allergy

Numerous epidemiological studies have shown that children who grow up on traditional farms are protected from asthma, hay fever and allergic sensitization. Early-life contact with livestock and their fodder, and consumption of unprocessed cow's milk have been identified as the most effective protective exposures. Studies of the immunobiology of farm living point to activation and modulation of innate and adaptive immune responses by intense microbial exposures and possibly xenogeneic signals delivered before or soon after birth.

Pets keeping in home, parental atopy, asthma, and asthma-related symptoms in 12,910 elementary school children from northeast China

The effects of pet exposure and parental atopy on respiratory symptoms were investigated in 12,910 children residing in twelve districts of northeast China. Responses to a self-administered questionnaire completed by parents of children were used to ascertain children with persistent cough, persistent phlegm, doctor-diagnosed asthma, current asthma and current wheeze. Exposure to animals during pregnancy was positively associated with doctor-diagnosed asthma [adjusted odds ratio (ORs), 1.86; 95% confidence interval (CI) 1.35-2.57], current asthma (adjusted OR, 3.06; 95% CI, 1.95-4.81) and asthma-related symptoms. Pet exposure in the first year of life and currently having animals in household were also related to a significantly higher prevalence of doctor-diagnosed asthma and asthma-related symptoms in these children. Associations with respiratory symptoms strengthened with higher levels of animal exposure. Parental atopy increased the risk of asthma diagnosis (OR, 3.49; 95%CI, 2.84-4.30), current asthma (OR, 3.94; 95%CI, 2.81-5.54) and asthma-related symptoms. There was an interaction between parental atopy and pet exposure in persistent phlegm, but not in doctor-diagnosed asthma. We conclude that pet keeping and parental atopy increased the risk of respiratory symptoms in children. Parental atopy did modify the effect of pet exposure on persistent phlegm but not on doctor-diagnosed asthma.

PRACTICAL IMPLICATIONS

The relationship between exposure to animals and allergic respiratory diseases in childhood is controversial. Inconsistent with other cross-sectional studies mostly conducted in industrialized countries, our study indicates that exposure to animals may increase the occurrence of respiratory symptoms and diseases in children, and the associations with respiratory symptoms strengthened with higher levels of animal exposure parental atopy did modify the effect of pet exposure on persistent phlegm but not on doctor-diagnosed asthma. These findings support the view that measures should be taken to reduce animal exposure for children in China.

Changes in skin test reactivity among adults with atopic disease: a 3-year prospective study

BACKGROUND

Our knowledge about longitudinal predictors of atopy is limited.

OBJECTIVES

To describe changes in skin test reactivity during a 3-year period in a sample of adolescents and adults with atopic disease and to identify factors of importance for these changes.

METHODS

From a sample of 1,186 candidates, ranging in age from 14 to 44 years, who in a screening questionnaire reported symptoms suggestive of respiratory allergic disease, 344 individuals with a positive skin prick test (SPT) result concomitantly with asthma and/or rhinitis were clinically studied on 2 occasions, 3 years apart.

RESULTS

In total, 134 (39% of the study population) had a different SPT result at follow-up compared with baseline, based on a diagnostic criterion of 3 mm for a positive test result; 77 (22%) developed de novo sensitizations to 1 or more allergens, 45 (13%) had remission of 1 or more sensitizations, and 12 (4%) both gained and lost sensitizations. Female sex (odds ratio = 1.90 [1.02-3.57], P = .04) significantly predicted incidence of 1 or more sensitizations.

CONCLUSIONS

Four of 10 adults with atopic disease will have changes in SPT status during a 3-year period, and most will gain new sensitizations. Women with atopic disease are at increased risk of developing new sensitizations compared with men.

Familial aggregation of food allergy and sensitization to food allergens: a family-based study

BACKGROUND

The increasing prevalence of food allergy (FA) is a growing clinical and public health problem. The contribution of genetic factors to FA remains largely unknown.

OBJECTIVE

This study examined the pattern of familial aggregation and the degree to which genetic factors contribute to FA and sensitization to food allergens.

METHODS

This study included 581 nuclear families (2,004 subjects) as part of an ongoing FA study in Chicago, IL, USA. FA was defined by a set of criteria including timing, clinical symptoms obtained via standardized questionnaire interview and corroborative specific IgE cut-offs for > or =95% positive predictive value (PPV) for food allergens measured by Phadia ImmunoCAP. Familial aggregation of FA as well as sensitization to food allergens was examined using generalized estimating equation (GEE) models, with adjustment for important covariates including age, gender, ethnicity and birth order. Heritability was estimated for food-specific IgE measurements.

RESULTS

FA in the index child was a significant and independent predictor of FA in other siblings (OR=2.6, 95% CI: 1.2-5.6, P=0.01). There were significant and positive associations among family members (father-offspring, mother-offspring, index-other siblings) for total IgE and specific IgE to all the nine major food allergens tested in this sample (sesame, peanut, wheat, milk, egg white, soy, walnut, shrimp and cod fish). The estimated heritability of food-specific IgE ranged from 0.15 to 0.35 and was statistically significant for all the nine tested food allergens.

CONCLUSION

This family-based study demonstrates strong familial aggregation of FA and sensitization to food allergens, especially, among siblings. The heritability estimates indicate that food-specific IgE is likely influenced by both genetic and environmental factors. Together, this study provides strong evidence that both host genetic susceptibility and environmental factors determine the complex trait of IgE-mediated FA.

Living on a farm: impact on asthma induction and clinical course

Exposure to a farming environment protects individuals from respiratory allergy. The timing and duration of exposure seem to play critical roles. The largest reduction in risk of developing respiratory allergies is seen among those who are exposed prenatally and continuously thereafter. Contact with farm animals, at least in childhood, likely confers protection; other factors have not been completely identified. Also, the consumption of milk directly from the farm during childhood has been shown to be beneficial with respect to childhood asthma and allergies. Increased levels of microbial substances may contribute to the protective effects. The mechanisms by which such environmental exposures confer protection from respiratory allergies are not well understood. A number of gene-by-environment interactions have been observed with polymorphisms in genes of innate immunity receptors and exposure to farming environments. Increased levels of microbial exposures recognized by innate immune responses may affect adaptive immune responses resulting in decreased levels of atopic sensitization and asthma.

Housing characteristics, home environmental factors and respiratory health in 14,729 Chinese children

BACKGROUND

Very few studies have assessed the relative impact of housing characteristics and home environmental factors on asthma and asthma-related symptoms in Chinese children who have lower rates of asthma. To our knowledge few studies have assessed respiratory symptoms and allergies in this context.

METHODS

To assess the effects of housing characteristics, pet keeping, home decorations and other indoor environmental factors on respiratory health of Chinese children. We studied a population of 14,729 children (1-13 years old) from 12 districts in Liaoning province, Northeast China. Information on respiratory health, housing characteristics, and environmental pollutions were obtained by a standard questionnaire from the American Thoracic Society.

RESULTS

Housing conditions, house adjacent to traffic or not, house with or without pollution source nearby, pet keeping, presence of pests and mold/water damage in the home, home decorations and exposure to environmental tobacco smoke (ETS) were associated with doctor-diagnosed asthma and asthma-related symptoms both in boys and girls. The vulnerability towards exposure to housing conditions and environmental factors differed between males and females. Among boys, the risk of respiratory morbidity appeared to be reduced in households with larger surface areas and more rooms; use of a ventilation device was strongly protective against persistent phlegm (OR=0.68; 95%CI: 0.48, 0.96). Asthma-related symptoms were more associated with different pets among girls than among boys. The presence of a cat in the household was associated with doctor-diagnosed asthma (OR=1.89; 95% CI, 1.11-3.20), current wheeze (OR=2.64; 95% CI, 1.52-4.59), persistent cough (OR=1.84; 95% CI, 1.18-2.87) and persistent phlegm (OR=2.17; 95% CI, 1.21-3.87) only among girls.

CONCLUSION

Living within the vicinity of a source of pollution, traffic, pet keeping, home decorations, pests, mold and ETS are important determinants of children's respiratory health in China.

Effects of housing characteristics and home environmental factors on respiratory symptoms of 10,784 elementary school children from northeast china

BACKGROUND

Only few studies have assessed the relative impact of housing characteristics and home environmental factors on asthma and asthma-related symptoms in Chinese children, and to our knowledge, few studies have elaborated respiratory symptoms and allergies in this context.

OBJECTIVE

It was the aim of this study to assess the effects of housing characteristics, pet keeping, home decorations and other indoor environmental factors on respiratory health of Chinese children.

METHODS

We studied 10,784 children (6-13 years old) from 12 districts in Liaoning province, Northeast China. Information on respiratory health, housing characteristics and environmental pollution was obtained by a standard questionnaire from the American Thoracic Society.

RESULTS

Prevalence of asthma-related symptoms was higher for those living along the main stem of traffic, and for those with a house nearby a pollution source. Lower prevalence rates of respiratory morbidity were associated with households with a bigger area of residence and more rooms. Pet keeping was associated with doctor-diagnosed asthma (OR = 1.52; 95% CI 1.25-1.84). Home decorations also increased the risk of doctor-diagnosed asthma (OR = 1.72; 95% CI 1.45-2.04) and current asthma (OR = 1.43; 95% CI 1.06-1.93). Environmental tobacco smoke, pests and visible mold on walls were associated with the occurrence of asthma symptoms.

CONCLUSION

Home environmental factors are particularly important for the development of respiratory morbidity among children.

Skin sensitivity reactions to some allergens in different population groups of Ethiopian subjects

The prevalence of allergic diseases to a variety of allergens has only been studied in a few countries and it has never been studied in Ethiopia. This study was aimed at assessing the prevalence of skin sensitivity reactions to allergens in Ethiopian subjects. A total of 216 subjects were tested with a skin scratch test using five types of allergens and also for total and differential white blood cell counts. Positive reaction to one or more allergens was detected in 49.5% of the subjects, the most prevalent allergen being mite extract. Some 27% showed a positive reaction to multiple allergens. The mean eosinophil count was higher in the subjects reacting to at least one of the allergens compared to those with no reaction (p=0.038). The results demonstrate a high prevalence of allergic reactions to the few allergens tested. Further studies using several allergens are recommended to substantiate this finding.

Different effects of sensitization to mites and pollens on asthma symptoms and spirometric indices in children: a population-based cohort study

BACKGROUND

We have previously shown that long-term exposure of children to a highly polluted urban compared with a rural environment is associated with subclinical airway narrowing and increased prevalence of atopy.

OBJECTIVE

To test the hypothesis that sensitization to indoor perennial, compared with seasonal, aeroallergens has distinct effects on asthma symptoms and/or spirometric indices.

METHODS

We evaluated the respiratory health of 478 and 342 children aged 8 to 10 years living in an urban and a rural area, respectively, during a period of 8 years. Children were evaluated by parental questionnaire in 3 phases, 1995 to 1996 (phase 1), 1999 to 2000 (phase 2), and 2003 to 2004 (phase 3), and by spirometry and skin prick testing to 9 common local aeroallergens in phases 1 and 2.

RESULTS

Sensitization to pollens was associated with current wheezing in phase 1 of the study (odds ratio [OR], 3.36; 95% confidence interval [CI], 1.71 to 6.62; P < .001) but not with spirometric indices. Sensitization to mites was negatively associated with forced expiratory volume in 1 second (95% CI, -7.26 to -0.90; P = .01) and forced expiratory flow at 50% of forced vital capacity (95% CI, -10.80 to -1.33; P = .01) in study phase 1 but not in phase 2.

CONCLUSIONS

Our results indicate that sensitization to mites is associated with insidious involvement of large and small airways, whereas sensitization to pollens is associated with childhood wheezing at the age of 8 to 10 years. Subsequent loss of these associations implies that risk factors other than allergy influence airway disease at a later age.

Patterns of sensitization to food and aeroallergens in the first 3 years of life

BACKGROUND

There is a paucity of longitudinal studies of allergen sensitization in childhood.

OBJECTIVE

To investigate the pattern of sensitization in early childhood.

METHODS

A nested cohort of children (n = 543) were followed up from birth and given a skin prick test (SPT) at 1, 2, and 3 years of age. A detailed clinical history was obtained.

RESULTS

The prevalences of sensitization to aeroallergens were 1.3%, 6.4%, and 10.7% at 1, 2, and 3 years of age. The figures for food allergens were 2.8%, 3.9%, and 3.7%. There was a statistically significant increase in the prevalence of sensitization to >or=1 allergen between years 1 and 2 (P < .001) and years 2 and 3 (P = .032). Among those with a positive SPT at 1 year, 29% tested positive to additional allergens at 2 years (P = .0054). Sensitization to milk or egg at 1 year was a predictor for increased sensitization to peanut at 3 years (odds ratio, 34.8; P < .0001). Sensitization to egg at 1 year was associated with increased sensitization to aeroallergens at 3 years (odds ratios, house dust mite, 27.1, P < .001; cat, 8.9, P < .01; grass, 11.8, P = .005). For peanut and cat allergens, wheal size increases with the age of the child (P = .009 and P = .017, respectively).

CONCLUSION

Sensitization to allergens as demonstrated by positive SPT tends to increase with age, and this change can be detected in the first 3 years of life.

CLINICAL IMPLICATIONS

The high predictive value for early sensitization and a linear increase in SPT reactivity provide an opportunity for early intervention.

Increased sensitization in urban vs. rural environment--rural protection or an urban living effect?

In a population-based longitudinal cohort study, we tested the hypothesis that children growing up in a high-traffic polluted urban area (UA) in the Athens' basin have higher prevalence of allergies and sensitization when compared with those growing up in a Greek provincial rural area (RA). We recruited 478 and 342 children aged 8-10 living in the UA and the RA, respectively. Respiratory health was assessed by a parent-completed questionnaire in three phases: 1995-96 (phase 1), 1999-2000 (phase 2), 2003-04 (phase 3) and skin-prick testing to common indoor and outdoor aeroallergens was performed at phases 1 and 2. Reported asthma and eczema did not differ between the two areas, whereas reported hay fever was persistently more prevalent in the UA than in the RA (16.5%, 17.0%, 18.2% vs. 7.0%, 8.3%, 9.6%, respectively). Sensitization was more prevalent in the UA at both phases (19.0% vs. 12.1% in phase 1, 20.0% vs. 14.1% in phase 2). Residential area contributed independently to sensitization to >or=1 aeroallergens (OR: 0.29; 95% CI: 0.13-0.66; p = 0.003) and to polysensitization (OR: 0.28; 95% CI: 0.10-0.82; p = 0.020) in phase 1. These associations were independent of farming practices. No significant contributions were found in phase 2. Our results suggest that long-term exposure to urban environment is associated with a higher prevalence of hay fever but not of asthma or eczema. The negative association between rural living and the risk of atopy during childhood, which is independent of farming practices, implies that it is mainly driven by an urban living effect.

Contact with livestock--a protective effect against allergies and asthma?

BACKGROUND

A 'protective farm factor' possibly related to livestock exposure is hypothesized to reduce the risk for allergic sensitization.

OBJECTIVE

The purpose of this study was to determine whether 4-H club youth, who have opportunities for contact with livestock through club activities, have reduced risks of respiratory and allergic symptoms according to residence on a farm or exposure to livestock.

METHODS

A cross-sectional postal survey was completed by British Columbia 4-H members 8-20 years of age; a subset underwent skin prick testing as well. The association of farm residence and livestock exposure variables with symptoms were evaluated using logistic regression with adjustment for age, sex, cat and/or dog ownership, parental history of allergic disease, parental education, number of older siblings and exposure to smokers at home.

RESULTS

Questionnaires were completed by 1158 participants (response rate 50.3%); of these, a subset of 317 had skin prick tests (SPTs) (response rate 64.4%). Current residence on a farm was associated with a lower prevalence of ever having wheeze and asthma, as well as symptoms of atopic dermatitis. Variables relating to residence in a farm or rural area with livestock were more strongly associated with respiratory and allergic symptoms than were the livestock exposure variables such as frequency of contact and hours of barn use. The adjusted odds ratios for living in a farm residence in comparison with a rural non-livestock area were 0.49 (95% confidence interval (CI) 0.27-0.89) for diagnosed asthma, 0.51 (95% CI 0.30-0.85) for allergic rhinitis and 0.45 (95% CI 0.24-0.84) for atopic dermatitis.

CONCLUSION

Our findings suggest that some aspects of the farm environment, not just attributable to contact with livestock, were protective for respiratory and allergic conditions among 4-H youth.

In utero pesticide exposure and childhood morbidity

In humans, immune development begins early in embryonic life and continues throughout the early postnatal period. Although a number of pesticides have been observed to induce developmental immunotoxicity in mice, few human studies have examined the long term effects of in utero pesticide exposure on childhood morbidity. Empirical evidence suggests that the vulnerable period for toxic insults to the developing immune system extends from early gestation to adolescence in humans and animals. Using data from the Ontario Farm Family Health Study, we examined the relationship between farm couple exposures to pesticides during pregnancy and subsequent health outcomes in their offspring, including: persistent cough or bronchitis, asthma, and allergies or hayfever. No strong associations between pesticide exposures during pregnancy and persistent cough or bronchitis, or asthma were found. There was suggestive evidence that allergies and hayfever appeared to be more common in offspring, especially male offspring, exposed to certain specific pesticides during the period of pregnancy. Nevertheless, given the indirect indicators of pesticide exposure used in this study, and the scarcity of human studies on in utero exposure to pesticides and the development of allergies and other child health outcomes, these findings serve primarily to generate hypotheses for future research.

Respiratory allergy in agricultural workers: recent developments

PURPOSE OF REVIEW

To review recent evidence on the relationship between occupational exposure to allergens and asthmagens, and risk for developing allergy and asthma and the role of modifying factors in farmers and farm workers.

RECENT FINDINGS

Recent studies identified agents that have not been associated with allergy or asthma in farming populations before. The most intriguing findings, however, are those that suggest that the development of atopy and asthma might be influenced by exposure to pathogen associated molecular patterns (PAMPs), including endotoxin.

SUMMARY

The adverse and potentially protective effects of microbial exposures in the farm environment are discussed. Recent findings indicate that it is very likely that the protective effect of exposure to PAMPs such as endotoxin is not limited to childhood age. The protective effects that probably developed during childhood can still be observed at adult age. Furthermore, it even seems likely that exposures at adult age (in occupational environments), which stimulate the innate immune system, have an effect on allergy, independently of childhood exposure. It is hypothesized that reversal of atopy might occur as a result of high exposure to endotoxins and other PAMPs.

The influence of childhood infections and vaccination on the development of atopy: A systematic review of the direct epidemiological evidence

BACKGROUND

The 'hygiene hypothesis' has been used to justify a belief common among homeopaths, that the suppression of childhood infections and immunisation may lead to the development of chronic atopic diseases.

OBJECTIVES

To analyse the influence of childhood infections and immunisation on the development of atopy.

METHODS

Qualitative systematic review of direct epidemiological evidence (Medline 1993-2004) concerning the influence of childhood infections and immunisation on the development of atopy and discussion based on homeopathy.

CONCLUSIONS

(1) Childhood infections do not protect against atopy; on the contrary, they increase the risk of allergic diseases, in agreement to Hahnemann's observations, which included epidemic diseases among the factors capable of stimulating the development of chronic diseases. (2) Vaccination is not a risk factor for atopy, notwithstanding the allergenic effect of some vaccines.

Allergen-specific sensitization in asthma and allergic diseases in children: the study on farmers' and non-farmers' children

BACKGROUND

Farmers' children are less frequently sensitized to common allergens than the non-farmers' children, but less is known about their sensitization to other allergens and its association with clinical diseases.

OBJECTIVE

To examine the association of farm environment with atopic sensitization, allergic diseases, expression of allergen-induced symptoms, and the importance of specific sensitization against 'common' (timothy, dog, cat, birch, Dermatophagoides pteronyssimus, mugwort) and 'other' (cockroach, horse, Lepidoglyphus destructor, cow) allergens for asthma and allergic diseases in children.

METHODS

A cross-sectional study including 344 farmers' and 366 non-farmers' children aged 6-13 years in eastern Finland, using a self-administered written questionnaire and skin prick tests against the above-mentioned allergens.

RESULTS

Farmers' children had less asthma and allergic diseases and were less often sensitized against common allergens than the non-farmers' children. However, little difference was observed in sensitization against the other allergens between the farmers' (17.2%) and non-farmers (14.5%) children [adjusted odds ratios (aOR) 1.11 (0.71-1.72)]. Being sensitized against only other allergens, without sensitization against common allergens, was unrelated to asthma or allergic diseases. Among the single allergens, sensitization against pets or pollen, or against horse or cow, had the strongest association with asthma, hayfever, and atopic eczema; no such association was seen in D. pteronyssimus, mugwort, cockroach, or L. destructor. Farmers' children had significantly less often symptoms of allergic rhinitis in contact with dog (aOR 0.32%, 95% confidence interval (CI) 0.15-0.67), cat (aOR 0.45, 0.22-0.88), or pollen (aOR 0.58%, 95% CI 0.37-0.90) than the non-farmers' children.

CONCLUSION

Farm environment reduces the occurrence of asthma, allergic diseases, and atopic sensitization in children, and also the occurrence of allergen-induced rhinitis. Remarkable differences were observed between single allergens in their association with allergic disease, stressing the importance of allergen selection when defining atopy in epidemiological studies.

Another explanation for the low allergy rate in the rural Alpine foothills

A low allergy rate in coal and wood heated homes has been described in the small villages in the Alpine foothills and subsequently found to be associated with the farming environment. This was interpreted within the framework of the hygiene hypothesis but there are also alternative explanations. Lower air pollution could be one reason, which is, however, unlikely since the differences between the Bavarian countryside and the Munich municipal area were only weak. There could be genetic differences between the urban and rural population by previous isolation or by self-selection. The potential drop-out of allergy genes, however, will also not explain the absent increase of allergies in two generations. More likely, other lifestyle factors are important. Dietary habits are different in farmers and a less frequent vitamin D supplementation of newborns (otherwise expected to be allergy promoting) has been shown recently. The underlying cause for the "non-allergic farm child" remains speculative until the transfer of any farm-associated factor is leading to a similar risk reduction in the general population.

Indoor allergens, asthma, and asthma-related symptoms among adolescents in Wuhan, China

PURPOSE

Information on indoor allergen exposures among non-Western populations, which have lower prevalence of atopic illness, is scant. We examined whether exposures to common indoor allergens were associated with doctor-diagnosed asthma and asthma-related symptoms among Chinese adolescents.

METHODS

A cross-sectional study of 4,185 ninth grade students was conducted at 22 randomly selected schools in Wuhan, China. Information on respiratory health and exposures to indoor allergens was obtained by a self-administered questionnaire completed in class.

RESULTS

Having animals currently was associated with persistent cough [prevalence odds ratio (POR)=1.54, 95% confidence interval (CI ): 1.21-2.11] and wheeze (POR=1.41, 95% CI: 1.03-1.94). Early-life exposure to animals was also associated with doctor-diagnosed asthma (POR=1.95, 95% CI: 1.35-2.82). Associations with respiratory symptoms strengthened with higher levels of exposure and for exposure in both early childhood and in adolescence. Exposure to cockroaches and having mold/water damage in the home contributed especially to wheezing (POR=2.03, 95% CI: 1.41-2.90 for cockroaches; POR=2.49, 95% CI: 1.82-3.40 for mold/water damage).

CONCLUSIONS

Indoor allergen exposures were positively associated with asthma diagnosis and persistent respiratory symptoms among Chinese adolescents. Neither early-life nor current exposure to animals was protective for asthma or asthma-related symptoms.

Prognostic value of asymptomatic skin sensitization to aeroallergens

PURPOSE OF REVIEW

Asymptomatic skin sensitization to aeroallergens is frequently encountered in epidemiological studies and in everyday clinical life. Correct management of the condition is essential to avoid both progression into allergic disease and unnecessary intervention. Understanding immunological mechanisms in asymptomatic skin sensitization might provide new insights into the natural history and treatment of respiratory allergy.

RECENT FINDINGS

Research on asymptomatic skin sensitization is rare, and the present review unites previous studies with recent findings. It is a common condition affecting 8-30% of the population when using a local standard panel of aeroallergens. Clinically, immediate but not late-phase reactions are induced by allergen challenge. Absent eosinophil stimulation and migration and low IL-5 levels appear to be sentinel mechanisms. Prospective studies show that 30-60% become allergic, depending on allergens and follow-up period. No prospective intervention studies have been performed; however, allergen avoidance seems efficacious in reducing allergy development to occupational and domestic allergens. Asymptomatic skin sensitization due to an erroneously positive skin test must be ruled out before allergen avoidance measures are initiated.

SUMMARY

Surprisingly few papers exist on asymptomatic skin sensitization epidemiology and immunology, despite the intriguing question as to why symptoms do not develop in IgE-sensitized patients. It is a common condition and a risk factor for later development of respiratory allergic disease. Cross-sectional intervention studies suggest that allergy development is reduced by allergen avoidance. Immunologically, control of eosinophil stimulation and migration seems to be pivotal. How this control is maintained remains to be elucidated.

Childhood visits to animal buildings and atopic diseases in adulthood: an age-dependent relationship

BACKGROUND

Several studies reported protective effects of farming environments against atopic diseases. Therefore, we aimed to establish the relevant timing of exposure in early life.

METHODS

A cross-sectional study was carried out in a rural town. Overall, 4,537 inhabitants aged 18-44 years were eligible. Of these, 3,112 (69%) responded to a postal questionnaire on atopic diseases, life-time exposure to farming environments, and potential confounders.

RESULTS

Those with regular childhood exposure to animal buildings had a significantly reduced risk of nasal allergies. The greatest reduction in risk was seen for respondents starting regular visits to animal stables during the 1st year of life or between ages 3 and 5. Participants reporting start of exposure after age 5 remained at a lower risk for nasal allergies (0.70, 0.49-1.01).

CONCLUSIONS

The preventive effect of animal buildings' exposure against atopic respiratory diseases continues into adulthood. The magnitude of the effect appears to be age-dependent.

Trends in asthma, allergic rhinitis and eczema among Swedish conscripts from farming and non-farming environments. A nationwide study over three decades

BACKGROUND

Asthma and allergies are less common in children who have been raised in farming environments.

OBJECTIVES

To assess whether children who grow up in a farming environment have been protected against the general increase in atopic disorders in Sweden and whether other rural environments could also be protective.

METHOD

Linkage at an individual level of three national registers in Sweden: The Swedish Military Service Conscription Register (MSCR), the Register of the Total Population (RTP) and the Population and Housing Censuses (PHC). Asthma, allergic rhinitis and eczema at conscription were analysed in relation to area of residence, parental occupation, maternal age, family size and being the first born for 1 309 652 male conscripts in three successive cohorts born between 1952 and 1981.

RESULTS

Allergic rhinitis and eczema displayed a continuous increase throughout the study period, whereas the rise in asthma mainly occurred in conscripts born after 1961. Farming environments and rural living already provided protection from allergic rhinitis in conscripts born during the 1950s, but the protective effect was greater in later cohorts. An inverse association was observed between farm living and asthma, but mainly in conscripts born after 1970. The adjusted risk ratios for asthma in conscripts from farming vs. non-farming families were 1.00 (95% CI 0.93-1.07), 0.94 (95% CI 0.88-1.01) and 0.85 (95% CI 0.79-0.91) in conscripts born in 1952-1961, 1962-1971 and 1972-1981, respectively. Rural living per se had no effect on the occurrence of asthma. Eczema was less common in rural areas, but the time trend was similar in urban and rural areas.

CONCLUSIONS

Our findings suggest that environmental changes affecting the whole of society have promoted an increase in asthma, allergic rhinitis and eczema in both farming and non-farming environments. A lower risk of allergic rhinitis in conscripts whose parents were involved in farming was observed in all birth cohorts, whereas the protective effect of growing up on a farm on the risk of asthma appears to be a fairly recent phenomenon.

Environmental exposure to endotoxin and other microbial products and the decreased risk of childhood atopy: evaluating developments since April 2002

PURPOSE OF REVIEW

The hygiene hypothesis proposes an association between the change in exposure to microbes and the increased incidence of atopic diseases in recent decades. Exposure to microbes and childhood infections and their association with atopy has thus attracted much scientific interest. This review focuses on new developments in the field of epidemiology.

RECENT FINDINGS

Studies in adults confirm that exposure to orofaecal pathogens are associated with less asthma and allergies. In seropositive individuals, no increase in allergy prevalence over time was noted. Similarly, the generational increase in atopy and allergic rhinitis was not observed in individuals who were exposed to a farming environment in childhood. More than 20 studies have been published examining the effect of exposure to a farm environment in children and adults. Most consistently, the 'protective' farm effect was related to livestock farming and thus to microbial exposure. A dose-dependent inverse relationship between exposure to endotoxin in the mattress dust of children and the occurrence of atopic diseases was shown in rural environments in Europe. In addition, the blood cells of farmers' children were shown to express higher amounts of innate immunity receptors. Only a few farm studies have so far included an objective measure of the microbial environment. The examined exposure to endotoxin might partly be a surrogate measure of a much broader spectrum of immunomodulatory microbial compounds present in a rural environment.

SUMMARY

The 'hygiene hypothesis' has gained much credibility, but the results should be balanced against the benefits of established hygiene standards.

Asthma and atopy - the price of affluence?

Irrespective of improved knowledge of many aspects of atopic diseases, the unfavorable trends in their prevalence particularly among children could not have been reversed. A growing body of evidence suggests that something may lack from our societal affluence that has the capacity to provide protection against the development of atopic diseases. Much attention during the last years has been devoted to the hygiene hypothesis. This review outlines the impact of environment and lifestyle, particularly from the perspective of the East-West gradient, on the development of atopic diseases, with a special emphasis on the hygiene hypothesis in its broadest sense.

Asthma and atopy in rural children: is farming protective?

The prevalence of asthma and other atopic diseases has recently increased, especially in urban and modernized regions of the world. The majority of published prevalence surveys report that asthma and atopy are less common among children living in rural areas. While many exposures differ in rural and urban areas of the world, several recent studies have suggested that agricultural exposures in early childhood may decrease the risk of developing atopic disease. Livestock exposure, in particular, seems to be important, but additional research is needed to pinpoint the underlying mechanisms behind this apparent protective effect of rural and farm living. Additionally, prospective studies are needed to more closely examine the timing of farm exposures in relation to the onset of asthma and atopy, and to determine if the apparent protective effects of farming persist into adulthood.

Mucosal co-application of lactic acid bacteria and allergen induces counter-regulatory immune responses in a murine model of birch pollen allergy

Recent epidemiological studies and clinical trials suggest a possible role of certain lactic acid bacteria (LAB) strains in the prevention of allergic diseases. In this study, we aimed at evaluating the immunomodulatory potential of two LAB strains, Lactococcus lactis and Lactobacillus plantarum, for prophylaxis and therapy of allergic immune responses. Both LAB strains-induced high levels of IL-12 and IFN-gamma in naive murine spleen cell cultures. Intranasal co-application with recombinant Bet v 1, the major birch pollen allergen, prior or after allergic sensitization, led to increased levels of allergen-specific IgG2a antibodies and in vitro IFN-gamma production, indicating a shift towards Th1 responses. Successful immunomodulation by the mucosal pre-treatment was further demonstrated by suppression of allergen-induced basophil degranulation. We conclude that these LAB strains in combination with an allergen could be promising candidates for mucosal vaccination against type I allergy.