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

Early-life farm exposures and eczema among adults in the Agricultural Lung Health Study

Background

Several studies conducted in Europe have suggested a protective association between early-life farming exposures and childhood eczema or atopic dermatitis; few studies have examined associations in adults.

Objectives

To investigate associations between early-life exposures and eczema among 3217 adult farmers and farm spouses (mean age 62.8 years) in a case-control study nested within an US agricultural cohort.

Methods

We used sampling-weighted logistic regression to estimate odds ratios (ORs) and 95% confidence intervals (95%CIs) for associations between early-life exposures and self-reported doctor-diagnosed eczema (273 cases) and polytomous logistic regression to estimate ORs (95%CIs) for a 4-level outcome combining information on eczema and atopy (specific IgE≥0.35). Additionally, we explored genetic and gene-environment associations with eczema.

Results

Although early-life farming exposures were not associated with eczema overall, several early-life exposures were associated with a reduced risk of having both eczema and atopy. Notably, results suggest stronger protective associations among individuals with both eczema and atopy than among those with either atopy alone or eczema alone. For example, ORs (95%CIs) for having a mother who did farm work while pregnant were 1.01 (0.60-1.69) for eczema alone and 0.80 (0.65-0.99) for atopy alone, but 0.54 (0.33-0.80) for having both eczema and atopy. A genetic risk score based on previously identified atopic dermatitis variants was strongly positively associated with eczema, and interaction testing suggested protective effects of several early-life farming exposures only in individuals at lower genetic risk.

Conclusions

In utero and childhood farming exposures are associated with decreased odds of having eczema with atopy in adults.

A Childhood Farm Environment Protects from Allergic Sensitization until Middle Age but Not from New-Onset Sensitization in Adulthood: A 15 Year Longitudinal Study

Data are insufficient on the protective effect of a farm environment in childhood regarding sensitization in middle age and new-onset sensitization in adulthood. A skin prick test (SPT) and questionnaire data from the Northern Finland Birth Cohort 1966 study (NFBC66) were used to investigate sensitization at age 46 years related to childhood living environment. A subpopulation of 3409 participants was analyzed to study factors related to new-onset sensitization between ages of 31 and 46 years. Data on complete SPTs were available for 5373 cohort members at age 46. Professional farming by parents (odds ratio (OR) 0.54; 95% confidence interval (CI) 0.43–0.68) and keeping of farm animals (OR 0.53; 95% CI 0.43–0.66) in infancy were associated with a lower risk of sensitization at age 46. Sensitization (OR 0.58; 95% CI 0.47–0.72) and polysensitization (OR 0.43; 95% CI 0.32–0.57) were less common in those who lived in a rural area in infancy compared to a city area. The childhood living environment had no effect on new-onset sensitization between ages 31 and 46. We conclude that living on a farm or in a rural environment in childhood had a protective effect on sensitization even in middle age, but these factors did not protect from new-onset sensitization in adults.

Respiratory diseases and allergy in farmers working with livestock: a EAACI position paper

Farmers constitute a large professional group worldwide. In developed countries farms tend to become larger, with a concentration of farm operations. Animal farming has been associated with negative respiratory effects such as work-related asthma and rhinitis. However, being born and raised or working on a farm reduces the risk of atopic asthma and rhinitis later in life. A risk of chronic bronchitis and bronchial obstruction/COPD has been reported in confinement buildings and livestock farmers. This position paper reviews the literature linking exposure information to intensive animal farming and the risk of work-related respiratory diseases and focuses on prevention. Animal farming is associated with exposure to organic dust containing allergens and microbial matter including alive microorganisms and viruses, endotoxins and other factors like irritant gases such as ammonia and disinfectants. These exposures have been identified as specific agents/risk factors of asthma, rhinitis, chronic bronchitis, COPD and reduced FEV₁. Published studies on dust and endotoxin exposure in livestock farmers do not show a downward trend in exposure over the last 30 years, suggesting that the workforce in these industries is still overexposed and at risk of developing respiratory disease. In cases of occupational asthma and rhinitis, avoidance of further exposure to causal agents is recommended, but it may not be obtainable in agriculture, mainly due to socio-economic considerations. Hence, there is an urgent need for focus on farming exposure in order to protect farmers and others at work in these and related industries from developing respiratory diseases and allergy.

Analysis of variability of high sensitivity C-reactive protein in lowland Ecuador reveals no evidence of chronic low-grade inflammation

OBJECTIVES

C-reactive protein (CRP) is a central component of innate immune defenses, and high sensitivity CRP has emerged as an important biomarker of chronic inflammation and cardiovascular disease risk. Prior analyses of CRP variability have reported stable between-individual differences in CRP over time, but a limitation of current knowledge is that it is based on research conducted in post-epidemiologic transition populations.

METHODS

This study evaluated CRP variability among adults in the southeastern region of the Ecuadorian Amazon where rates of infectious diseases remain high. Blood samples were collected from 52 adults at four weekly sampling intervals and were quantified using a high-sensitivity immunoassay.

RESULTS

Median CRP concentration was 0.52 mg/l. About 34.6% of participants had CRP >3 mg/l at one time point, but no individuals had CRP >3 mg/l across two or more sampling intervals, and within-individual correlations revealed low levels of stable, between-individual differences in CRP. The application of current guidelines for the assessment of chronic inflammation failed to detect a single case of "high risk" CRP.

CONCLUSIONS

This study is the first to investigate CRP variability in a nonindustrialized, high infectious disease environment. It documents a pattern of variation over time that is distinct from prior research, with no evidence for chronic low-grade inflammation. These results may have substantial implications for research on inflammation and diseases of aging globally, as well as for scientific understandings of the regulation of inflammation.

Respiratory health effects of large animal farming environments

With increases in large animal-feeding operations to meet consumer demand, adverse upper and lower respiratory health effects in exposed agriculture workers are a concern. The aim of this study was to review large animal confinement feeding operational exposures associated with respiratory disease with a focus on recent advances in the knowledge of causative factors and cellular and immunological mechanisms. A PubMed search was conducted with the keywords airway, farm, swine, dairy, horse, cattle inflammation, organic dust, endotoxin, and peptidoglycan, among items were published between 1980 and now. Articles were selected based on their relevance to environmental exposure and reference to airway diseases. Airway diseases included rhinitis, sinusitis, mucus membrane inflammation syndrome, asthma, chronic bronchitis, chronic obstructive pulmonary disease, hypersensitivity pneumonitis, and organic dust toxic syndrome. There is lower prevalence of immunoglobulin (Ig) E-mediated asthma and atopy in farmers and their children, but organic dust worsens existing asthma. Multiple etiologic factors are linked to disease, including allergens, organic dusts, endotoxins, peptidoglycans, and gases. Large animal confinement feeding operations contain a wide diversity of microbes with increasing focus on gram-positive bacteria and archaebacteria as opposed to gram-negative bacteria in mediating disease. Toll-like receptors (TLR) and nucleotide oligomerization domain (NOD)-like innate immune pathways respond to these exposures. Finally, a chronic inflammatory adaptation, tolerance-like response in chronically exposed workers occurs. Large animal confinement farming exposures produce a wide spectrum of upper and lower respiratory tract diseases due to the complex diversity of organic dust, particulates, microbial cell wall components, and gases and resultant activation of various innate immune receptor signaling pathways.

Comparative insights into the regulation of inflammation: levels and predictors of interleukin 6 and interleukin 10 in young adults in the Philippines

Inflammation is a central part of innate immunity, but its role in anti-pathogen defenses has been overshadowed by recent interest in the contribution of inflammation to a wide range of chronic degenerative diseases. Current research on chronic inflammation is conducted primarily in affluent populations with low levels of infectious disease; comparative research in different ecological settings is needed to advance understandings of the causes and consequences of variation in the regulation of inflammation. This article investigates the levels and predictors of interleukin-6 (IL-6) and interleukin-10 (IL-10)-two cytokines important to the regulation of inflammation-in a large, population-based study in the Philippines. Concentrations of IL-6 and IL-10 were determined in N = 1,569 healthy young adults (20-22 years) in Metro Cebu, Philippines. IL-6 and IL-10 concentrations were positively correlated, and body mass index and symptoms of infectious disease were both associated with higher concentrations of IL-6 and IL-10. Median concentrations of IL-6 (1.0 pg/mL) and IL-10 (7.56 pg/mL) were substantially lower and higher, respectively, than levels reported for other populations based on a systematic review of prior research. This study contributes to a growing body of research in human ecological immunology, and suggests that there may be substantial population differences in the regulation of inflammation that has implications for the association between inflammation and disease.

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.

Effects on pulmonary health of neighboring residents of concentrated animal feeding operations: exposure assessed using optimized estimation technique

Potential adverse health effects of concentrated animal feeding operations (CAFOs), which were also shown in the authors' Lower Saxony Lung Study, are of public concern. The authors aimed to investigate pulmonary health effect of neighboring residents assessed using optimized estimation technique. Annual ammonia emission was measured to assess the emission from CAFO and from surrounding fields. Location of sampling points was optimized using cluster analysis. Individual exposure of 457 nonfarm subjects was interpolated by weighting method. Mean estimated annual ammonia levels varied between 16 and 24 μg/m³. Higher exposed participants were more likely to be sensitized against ubiquitous allergens as compared to lower exposed subjects (adjusted odds ratio [OR] 4.2; 95% confidence interval [CI] 1.2-13.2). In addition, they showed a significantly lower forced expiratory volume in 1 second (FEV₁) (adjusted mean difference in % of predicted -8%; 95% CI -13% to -3%). The authors' previous findings that CAFOs may contribute to burden of respiratory diseases were confirmed by this study.

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.

99th Dahlem conference on infection, inflammation and chronic inflammatory disorders: farm lifestyles and the hygiene hypothesis

About 15 years have gone by since Strachan first proposed the idea that infections and unhygienic contact may confer protection from the development of allergic illnesses. The so-called 'hygiene hypothesis' has since undergone numerous modifications in the field of epidemiology, clinical science and immunology. Three main areas of research have been brought forward: to explore the role of overt viral and bacterial infections for the inception of allergic diseases; to investigate the significance of environmental exposure to microbial compounds on the development of allergies; and to study the effect of both exposures on underlying innate and adaptive immune responses. A concept unifying these various aspects has not been found, but various pieces of a complex interplay between immune responses of the host, characteristics of the invading microorganism, the level and variety of the environmental exposure and the interactions between an exposed subject's genetic background and the environmental exposures becomes apparent. A natural experiment relating to the hygiene hypothesis is the recurrent observation of a protective effect of growing up on a farm for asthma and allergies. This has been shown in a large number of epidemiological studies across the world among children and adults. The timing and duration of exposure are likely to play a critical role. The largest reduction in risk has been demonstrated for those exposed prenatally and continuously thereafter until adulthood. The protective factors in these farming environments have not been unravelled completely. Findings from various studies suggest that the contact with farm animals, at least in childhood, confers protection. Also the consumption of unprocessed cow's milk directly from the farm has been shown to protect from childhood asthma and allergies. Increased levels of microbial substances may, at least in part, contribute to the 'farm effect'. However, only few studies have measured microbial exposures in these environments and the results obtained so far suggest that the underlying protective microbial exposure(s) have not been identified, but a number of studies using metagenomic approaches are currently under way. The mechanisms by which such environmental exposures confer protection from respiratory allergies are also not well understood. There is good evidence for the involvement of innate immune responses, but translation into protective mechanisms for asthma and allergies is lacking. Furthermore, a number of gene x environment interactions have been observed.

Exposure to farm crops, livestock, and farm tasks and risk of glioma: the Upper Midwest Health Study

Some studies of brain cancer have found an excess risk for farmers. The National Institute for Occupational Safety and Health previously found no increased glioma risk for ever (vs. never) being exposed to pesticides on a farm among 798 cases and 1,175 population-based controls (adult (ages 18-80 years) nonmetropolitan residents of Iowa, Michigan, Minnesota, and Wisconsin). For this analysis (1995-1998), 288 cases and 474 controls (or their proxies) who had lived on farms at age 18 years or after were asked about exposure to crops, livestock, and farm tasks. Logistic regression was used to calculate odds ratios adjusted for age, age group, sex, state, and education. Never immediately washing up (adjusted odds ratio (OR) = 3.08, 95% confidence interval (CI): 1.78, 5.34) or changing clothes (OR = 2.84, 95% CI: 1.04, 7.78) after applying pesticides was associated with increased glioma risk. Living on a farm on which corn, oats, soybeans, or hogs were raised was associated with decreased risk (corn-OR = 0.37, 95% CI: 0.20, 0.69; oats-OR = 0.63, 95% CI: 0.40, 1.00; soybeans-OR = 0.69, 95% CI: 0.48, 0.98; hogs-OR = 0.63, 95% CI: 0.43, 0.93). Negative associations may be due to chance or a "healthy farmer" effect. Farmers' increased risk of glioma may be due to work practices, other activities, or an inverse association with allergies (reported by other investigators).

Suppression of airway inflammation by a natural acute infection of the intestinal epithelium

Although chronic intestinal helminth infections may suppress allergen-induced airway pathology by inducing a combination of modified T-helper (Th) 2 and immunosuppressive cytokines, a similar capacity of natural acute intestinal infections has remained untested, despite their global prevalence. Here, we show that allergic airway phenotypes including eosinophilia, eotaxin mRNA, and Th2 cytokines are significantly suppressed in animals that were infected by and that have cleared the intestinal parasite Eimeria vermiformis. Unlike in helminth-infected animals, regulation requires temporal coincidence of infection with sensitization; depends on interferon-gamma; and is not associated with an enhanced antigen-specific immunoglobulin G1 response. Moreover, regulation was effective following allergen sensitization in different anatomical sites, and in young and adult mice. These data highlight a transient anatomical dissemination of "functional immunologic dominance" following infection of the gut mucosa. They strongly support the hypothesis that airway allergies are naturally suppressed by both acute and chronic mucosal pathogens, but by different mechanisms.

Allergen tolerance versus the allergic march: the hygiene hypothesis revisited

In addition to genetics, several environmental variables appear to impact allergic risk. Meta-analyses of epidemiologic studies presented in this article demonstrate a correlation between specific ambient exposures (eg, livestock, pets, endotoxin, and unpasteurized milk ingestion) and reduced allergic risk during childhood. Additional laboratory investigations discussed in this review characterized the intrinsic immunostimulatory activities of living environments. Considered together, results of these investigations suggest a novel paradigm by which early-life home exposures to microbial products and other allergen-nonspecific immunostimulants modify allergic risk.

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.

Prevalence of allergy, patterns of allergic sensitization and allergy risk factors in rural and urban children

BACKGROUND

We aimed to compare the prevalence of allergic diseases and sensitization in children living in urban and rural areas and to identify potential risk/protection factors associated with allergy.

METHODS

School children 12-16 years old, from urban community (n = 201) and rural area (n = 203) were recruited. The data obtained by questionnaire were referred to doctors' diagnosis, skin prick tests (SPTs), and serum specific and total IgE assessment.

RESULTS

The prevalence of allergic diseases in urban children was significantly higher as compared with rural children [asthma 16.42%vs 1.97% (P < 0.001) allergic rhinitis 38.81%vs 10.84% (P < 0.001)]. Positive SPTs to at least one allergen was found in 63.7% of urban and 22.7% rural children (P < 0.001). Significantly higher percentage of allergic rural than urban children were monosensitized or sensitized to 2-4 allergens, but almost a fourfold higher percentage of allergic urban children was found to be sensitized to five or more allergens (P < 0.0001). The history of frequent upper respiratory factor (URT) infections, antibiotic therapy, tonsiltectomy/adenoidectomy were positively associated with development of atopy and sensitization.

CONCLUSION

Our findings confirm that residence of rural area is associated with a significant lower prevalence of allergic sensitization and symptoms in school children. Several risk and protective factors related to environment and style of life could be identified in both environments.

Reduced risk of atopic sensitization among farmers: the Humboldt study

BACKGROUND

It needs to be clarified whether farming is associated with a reduced risk of atopy or allergic condition. There is a lack of consistent evidence for prevalences of atopy, respiratory allergy and asthma in adult farmers.

METHODS

A cross-sectional study of adults (n = 2,081) was conducted in the town of Humboldt, Sask. Allergy skin prick tests were conducted to determine atopic sensitization. Respiratory allergy and physician-diagnosed asthma were based on self-reporting. Logistic regression was used to assess the associations of atopy, respiratory allergy and asthma with farming practices, adjusting for other important variables.

RESULTS

Of 2,081 participants, 27.8% were farmers. Reduced risks of atopic sensitization, respiratory allergy and asthma were observed among farmers compared to non-farmers. After adjustment for sex and age, which are major confounders, the odds ratio for atopic sensitization was 0.79 (95% confidence interval: 0.65, 0.97) for farmers versus non-farmers. Asthma showed a similar trend; however, there was no statistically significant difference in either respiratory allergy or asthma rates observed between farmers and non-farmers.

CONCLUSIONS

The prevalence of atopy was lower in adult farmers than in non-farmers.

Allergies, infections and the hygiene hypothesis--the epidemiological evidence

The 'hygiene hypothesis' was first proposed by Strachan in 1989 suggesting that infections and unhygienic contact with older siblings or through other exposures may confer protection from the development of allergic illnesses. This hypothesis has evolved in various ways exploring the role of overt viral and bacterial infections, the significance of environmental exposure to microbial compounds, and their effect on underlying responses of innate and adaptive immunity. So far a truly unifying concept is still lacking, but various pieces of a complex interplay between a host's immune response, characteristics of the invading microorganism, the level and variety of the environmental exposure, and the interactions between a genetic background and a range of exposures become apparent. All these pieces eventually assemble to the clinical presentation of a complex syndrome namely of asthma and allergic illnesses. Even if today practical implications cannot directly be deduced from these findings, there is great potential for the development of novel preventive and therapeutic strategies in the future based on the concepts of the 'hygiene hypothesis'.

The many faces of the hygiene hypothesis

About 15 years have gone by since Strachan first proposed the idea that infections and unhygienic contact might confer protection against the development of allergic illnesses. The so-called hygiene hypothesis has ever since undergone numerous more or less subtle modifications by various researchers in the fields of epidemiology, clinical science, and immunology. Three major tracts have developed exploring the role of overt viral and bacterial infections, the significance of environmental exposure to microbial compounds, and the effect of both on underlying responses of the innate and adaptive immunity. To date, a truly unifying concept has not yet emerged, but various pieces of a complex interplay between immune responses of the host, characteristics of the invading microorganism, the level and variety of the environmental exposure, and the interactions between a genetic background and a range of exposures becomes apparent. These influences are discussed as determinants for a number of complex allergic illnesses in this review, while we attempt to pay attention to the importance of different phenotypes, namely of the asthma syndrome. Even if today practical implications cannot directly be deduced from these findings, there is great potential for the development of novel preventive and therapeutic strategies in the future.

Inverse association between farm animal contact and respiratory allergies in adulthood: protection, underreporting or selection?

BACKGROUND

It has been argued that the inverse association between exposure to farm animals and nasal allergies observed in children and adults might be because of self-selection.

AIMS

We aimed to assess the health-based selection out of farming in adults.

MATERIAL AND METHODS

A cross-sectional study was carried out in a rural region. Overall, 4053 inhabitants (63%) aged 18-44 years responded to a questionnaire on respiratory diseases, life-time exposure to farming environments and potential confounders. For 2678 of these, specific immunoglobulin E to common allergens was available. The outcome was: (i) sensitization and symptoms of nasal allergies (symptomatic sensitization); (ii) sensitization without symptoms of nasal allergies (asymptomatic sensitization).

RESULTS

Farm animal contact in childhood was associated with a decreased risk of symptomatic and asymptomatic sensitization. Continued exposure to farm animals in adulthood further decreased the odds ratio of symptomatic (odds ratio 0.2; 95% confidence interval 0.1, 0.4) but not asymptomatic sensitization (0.7; 0.4, 1.1). Starting farm animal contact in adulthood even increased the odds ratio of asymptomatic sensitization (2.4; 1.1, 5.2).

CONCLUSIONS

The preventive effect of childhood contact to farm animals against sensitization continues into adulthood. However, in adulthood self-selection based on symptoms and underreporting of symptoms might also play a role.

Exposure to farming environments in early life and type 1 diabetes: a case-control study

It has been hypothesized that a stimulation of regulatory cytokines by microbial compounds reduces autoimmune as well as atopic diseases. Farm-related contact to microbial compounds protects from allergies, but no data on the association between farm contact and type 1 diabetes is available. The aim of this study was to test this association. A case-control study was conducted in five children's hospitals. Regular contact to farm animals and potential confounders were assessed using a postal questionnaire. Eligible subjects were all prevalent cases with type 1 diabetes registered in the hospitals and hospital-based control subjects (response rate 91%). Included were children aged 6-16 years living in rural areas with German nationality (242 case and 224 control subjects). Regular contact to stables (adjusted odds ratio 1.2 [95% CI 0.5-2.7]) was not associated with type 1 diabetes. In addition, regular contact to specific farm animals was not associated with case status. There was a tendency for an inverse relationship between allergic rhinitis and type 1 diabetes (0.6 [0.3-1.1]; P = 0.11). There was no evidence that early exposure to farm animals largely decreases the risk in children for developing type 1 diabetes.

Effect of farming environment on sensitisation to allergens continues after childhood

AIMS

The farming environment in childhood has been reported to decrease the risk of sensitisation to allergens. The purpose of the present study was to explore whether later exposure to a farming environment also could affect this sensitisation.

METHODS

A population based sample of 202 women who did not live on a farm and 231 who did. The subjects filled in a questionnaire and underwent skin prick tests for several common and farming related allergens.

RESULTS

The prevalence of sensitisation to any of the allergens was similar in the two groups (37.1 v 34.6% (p = NS). However, compared with women who did not live on a farm, the women who lived on a dairy farm showed a low prevalence of sensitisation to pollens (4.4 v 17.3%, p = 0.01) and cats (3.5 v 10.4%, p = 0.047). The risk of sensitisation to pollens and pets was lowest among women with both a childhood and adulthood farming environment and was dose dependently associated with current contact with farm animals. However, this contact increased the risk of sensitisation to bovine dander.

CONCLUSION

The farming environment may reduce sensitisation to common allergens also after early childhood. However, it may also increase sensitisation to farm allergens.

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.

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.