Systematic review: Exposure to pets and risk of asthma and asthma-like symptoms

Early childhood environment related to microbial exposure and the occurrence of atopic disease at school age

BACKGROUND

There is a growing body of evidence that the early childhood environment with respect to day care attendance, older siblings, pet ownership, and early life airway infections may protect from developing atopic disease. Few studies have distinguished between atopic sensitization and symptoms, and none have evaluated independent contributions for all of these different environmental conditions.

OBJECTIVE

Examine independent effects on atopic sensitization and symptoms of day care attendance, older siblings, pet ownership, and early infancy's airway disease.

METHODS

A cross-sectional survey among 8-13-year-old school children with complete data for 1555 children.

RESULTS

After adjustment for confounders, atopic sensitization occurred less frequently in children that had attended a day care centre (OR: 0.73, 95% CI: 0.55-0.98) or had a cat or dog before 2 years of age (OR: 0.78, 95% CI: 0.61-0.99). Having older siblings yielded a nonsignificant trend towards protection (OR: 0.88, 95% CI: 0.70-1.11). For symptoms, there was no relation with having older sibs, day care attendance and pet ownership, although there was a trend towards protection for the combination of atopy and symptoms. In contrast, children with doctors' treated airway disease before age 2, more frequently reported recent symptoms of wheeze, asthma, rhinitis, or dermatitis (all P < 0.05).

CONCLUSION

Early life environmental exposure to day care, or pets may protect against atopic sensitization. Protection against symptoms only occurred if atopic sensitization was present as well.

Are influences during pregnancy associated with wheezing phenotypes during the first decade of life?

AIM

Recently, attention has focused on possible early life origins for asthma. We sought to identify whether factors present during pregnancy were associated with development of childhood wheezing phenotypes.

METHODS

A whole population birth cohort (n=1456) on the Isle of Wight, UK, was followed through to age 10 y. Where possible, information regarding environmental exposures and events during pregnancy was obtained from the maternity records (n=1238). Children were seen at ages 1, 2, 4 and 10 y, and wheezing symptoms were used to define wheezing phenotypes in the first decade (n=1034).

RESULTS

Risk of early-onsetpersistent wheeze (onset in the first 4 y, still present at age 10) was increased by environmental tobacco smoke exposure in pregnancy (OR=2.44; 95% CI: 1.37-4.34) plus maternal asthma (3.57; 1.84-6.94), but reduced by cat ownership (0.30; 0.13-0.62). Early transient wheeze (onset in the first 4 y, but not present at age 10) was increased by environmental tobacco smoke exposure (1.58; 1.02-2.45), male gender (1.68; 1.09-2.60) and low birthweight (3.65; 1.27-10.52). No environmental factors in pregnancy were associated with late-onset persistent wheeze (onset after age 4 y, still present at 10 y).

CONCLUSION

In addition to genetics, maternal exposures during pregnancy show association with childhood and especially early-life wheezing phenotypes.

Ontogeny of the Allergic Inflammatory Response

The ability to produce allergic responses begins early in fetal life along with the development of other elements of the immune system. Among the most interesting questions related to the development of allergic disease are whether the fetus in utero commonly is exposed to sufficient allergen to induce IgE production and how much the mother's immune responses affect the developing fetal immune system. After birth, it seems that many factors, including the frequency and severity of infections and the timing and intensity of allergen and animal exposures, continue to influence immune development.

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.

Symptoms of asthma and the home environment. The ISAAC I and III cross-sectional surveys in Münster, Germany

BACKGROUND

The indoor home environment has been shown to be associated with the presence of respiratory symptoms and atopic disease.

METHODS

Two cross-sectional surveys (1995-2000) were conducted, using data from the ISAAC phase I and III surveys, collected in Münster, Germany (n = 6,996, response 81.8%). We analyzed the prevalence ratio (PR) for several indoor exposures and asthma-related outcomes in 6- to 7-year-old children, adjusting for potential confounders.

RESULTS

Positive associations were observed regarding exposure to molds, environmental tobacco smoke, cooking with gas and space heating with fossil fuels, but most associations were not statistically significant. Surprisingly, presence of a carpet was negatively associated with most respiratory conditions. When restricting the analysis to participants without avoidance of a carpet due to a history of atopic disease, the protective associations disappeared. Mostly, present pet ownership did not show positive associations with respiratory symptoms. However, ownership at different times in life revealed positive associations, particularly in regard to birds owned in the first year of life (PR 1.51, 95% CI 1.11-2.06, for sleep disturbance due to wheeze and PR 1.28, 95% CI 1.01-1.63, for wheeze during the last 12 months, respectively).

CONCLUSIONS

Only few indoor factors were positively associated with the studied outcomes. The change of associations in participants that reported allergy-related avoidance of carpets suggests that the observed effects are a result of asthmatics' changed behavior. The effect of allergy-related change in behavior and the results observed concerning the ownership of pets at different ages underline the need of establishing a precise temporal relationship between disease and exposure.

Early life risk factors for current wheeze, asthma, and bronchial hyperresponsiveness at 10 years of age

STUDY OBJECTIVES

We sought to identify early life factors (ie, first 4 years) associated with wheeze, asthma, and bronchial hyperresponsiveness (BHR) at age 10 years, comparing their relative influence for these conditions.

METHODS

Children were seen at birth, and at 1, 2, 4, and 10 years of age in a whole-population birth cohort study (1,456 subjects). Information was collected prospectively on genetic and environmental risk factors. Skin-prick testing was performed at 4 years of age. Current wheeze (in the last 12 months) and currently diagnosed asthma (CDA) [ie, current wheeze and ever-diagnosed asthmatic subject] were recorded at 10 years of age when BHR was measured at bronchial challenge. Independent significant risk factors for these outcomes were identified by logistic regression.

RESULTS

Independent significance for current wheeze occurred with maternal asthma (odds ratio [OR], 2.08; 95% confidence interval [CI], 1.27 to 3.41) and paternal asthma (OR, 2.12; 95% CI 1.29 to 3.51), recurrent chest infections at 2 years (OR, 3.98; 95% CI, 2.36 to 6.70), atopy at 4 years of age (OR, 3.69; 95% CI, 2.36 to 5.76), eczema at 4 years of age (OR, 2.15; 95% CI, 1.24 to 3.73), and parental smoking at 4 years of age (OR, 2.18; 95% CI, 1.25 to 3.81). For CDA, significant factors were maternal asthma (OR, 2.26; 95% CI, 1.24 to 3.73), paternal asthma (OR, 2.30; 95% CI, 1.17 to 4.52), and sibling asthma (OR, 2.00; 95% CI, 1.16 to 3.43), recurrent chest infections at 1 year of age (OR, 2.67; 95% CI, 1.12 to 6.40) and 2 years of age (OR, 4.11; 95% CI, 2.06 to 8.18), atopy at 4 years of age (OR, 7.22; 95% CI, 4.13 to 12.62), parental smoking at 1 year of age (OR, 1.99; 95% CI, 1.15 to 3.45), and male gender (OR, 1.72; 95% CI, 1.01 to 2.95). For BHR, atopy at 4 years of age (OR, 5.38; 95% CI, 3.06 to 9.47) and high social class at birth (OR, 2.03; 95% CI, 1.16 to 3.53) proved to be significant.

CONCLUSIONS

Asthmatic heredity, predisposition to early life atopy, plus early passive smoke exposure and recurrent chest infections are important influences for the occurrence of wheeze and asthma at 10 years of age. BHR at 10 years of age has a narrower risk profile, suggesting that factors influencing wheezing symptom expression may differ from those predisposing the patient to BHR.

[Environment and asthma in children: controversies]

The increase in asthma prevalence over the past 20 years could be due to modification of exposure to environmental factors (environmental theory) or to the lost of protective factors (hygienist theory). Among environmental factors this paper reviewed the controversial role of exposure to house dust mite (HDM). If exposure to HDM is deleterious in asthmatics known to be sensitised to this allergen, the effect of HDM exposure on asthma incidence has been challenged recently, based on longitudinal studies showing no correlation between level of exposure to HDM and asthma incidence. Exposure to animal dander may have protective effects. This review has shown that, even if some studies have shown potential protective effect of early exposure, the protection seems to be better in families with a low risk of atopy; almost all studies tend to show a deleterious effect of current exposure; exposure to dog dander may be more protective than cat. These studies cannot give definite conclusions to change current advices of early eviction of HDM and animal dander, especially in families with a high risk of atopy. The deleterious effect of passive smoking on asthma prevalence and severity is undisputable and our efforts should concentrate on obtaining effective eviction of passive smoking.

Exposure to pets, and the association with hay fever, asthma, and atopic sensitization in rural children

BACKGROUND

An increasing number of studies report pet exposure to be associated with lower risk of asthma and allergies. This 'protective pet effect' has been suggested to result from a modified T-helper (Th)2-cell response, or because of increased microbial load in homes where pets are kept. We examined the associations between pet contact and the occurrence of asthma and allergies in children of the rural Allergy and Endotoxin (ALEX) population, taking farm animal contact, endotoxin and cat allergen levels in mattress dust into account.

METHODS

Information about contact with pets and farm animals, asthma and allergy were collected for 812 children by a standardized parents' questionnaire and an interview. Mattress dust endotoxin and cat allergen levels as well as specific IgE and IgG4 antibodies to Fel d1 were determined.

RESULTS

Current contact with dogs was inversely associated with diagnosed hay fever (OR 0.26, 95% CI 0.11-0.57), diagnosed asthma (OR 0.29, 95% CI 0.12-0.71), sensitization to cat allergen (OR 0.48, 95% CI 0.23-0.99) and to grass pollen (OR 0.55, 95% CI 0.33-0.94), but not with increased IgG4 levels. Early and current contact with cats were associated with reduced risk of wheezing (OR 0.48, 95% CI 0.23-1.00, and OR 0.49, 95% CI 0.26-0.92, respectively) and grass pollen sensitization. Adjustment for farm animal contact but not for endotoxin and cat allergen exposure attenuated these associations and the effect of pet was stronger among farmers' children.

CONCLUSION

Although pet exposure was very frequent in this rural population, the inverse relation between current dog contact, asthma and allergy was mostly explained by simultaneously occurring exposure to stable animals or was restricted to farm children. In addition, a subtle form of pet avoidance may contribute to the protective effect of pet.

Cutaneous and serological responses to cat allergen in adults exposed or not to cats

BACKGROUND

The relationship between pet ownership and the risk of developing respiratory allergic sensitization to pet allergens is still controversial.

OBJECTIVE

To determine the degree of cutaneous immediate hypersensitivity and the levels of specific IgE and IgG4 antibodies to cat allergen in cat sensitized patients directly or indirectly exposed to this animal.

METHODS

We studied 112 adolescents and adults sensitized to cat allergens (43 with and 69 without a cat at home). There were also 52 control subjects, 27 atopic non-sensitized to cat and 25 non-atopic. The degree of immediate hypersensitivity was assessed by using, in duplicate, skin prick test with four five-fold dilutions of cat hair allergen extract with the content of its major allergen Fel d 1 quantified in micrograms plus positive (10 mg/ml histamine chlorhydrate) and negative (saline solution) controls. The resulting wheal areas were analysed by means of Parallel Line Assay. A blood sample was collected from every patient and control subjects for the evaluation of serological cat specific IgE and IgG4 antibodies.

RESULTS

Patients with cat at home had a lower cutaneous response than patients without this pet. The difference in the skin sensitivity was estimated in 3.4 times (P<0.01). There was no statistical difference between the levels of cat specific IgE antibodies in the two groups of patients (P=0.065). The levels of Fel d 1 specific IgG4 antibodies showed a statistically significant association with the presence of cat at home, with higher levels in patients owing cat at home than in patients without this pet (P<0.001).

CONCLUSION

The results of this study demonstrate that direct cat exposure in adolescents and adults with respiratory allergy is associated with a lower cutaneous response to cat allergenic extract, assessed by SPT and compared with indirect exposure. In patients with cat at home mean levels of specific IgE are statistically comparable whereas the levels of IgG4 are higher in comparison with subjects not exposed to cats. The role of indirect exposure to cat allergens in airways sensitization also in adults is emphasized. Moreover, patients with cat at home show a cutaneous and serological sensitization to cat allergen not higher in comparison with subjects not exposed to cats.

Does exposure to dogs and cats in the first year of life influence the development of allergic sensitization?

PURPOSE OF REVIEW

The goal of the review is to place studies published after 1 June 2002, concerning the relationship between early life exposure to cats and dogs and the later development of allergy, within the context of the effects of other environmental exposures on allergic disease.

RECENT FINDINGS

Most of the recent studies have shown that exposure to cats and dogs early in infancy reduces the prevalence of allergic sensitization or allergic disease later in childhood. While this general trend is relatively consistent, there are differences in specific findings between studies, such as the effect of parental allergies. Other studies suggest that the association between cat and dog exposure and a lower risk of allergy is due to either differences in other environmental exposures or to genetic differences between exposed and non-exposed children. It is impossible to directly compare the results from all of these studies since there are often important differences in racial/ethnic backgrounds of the children, climate, housing conditions, and the family and social customs of those enrolled in different studies.

SUMMARY

The risk of a child developing any form of allergy appears to depend upon many factors including a child's genetic constitution, early environmental exposure to allergens and to other agents which interact with the immune system, and to allergen exposure later in life. It appears that exposure to something that is increased in homes with cats or dogs reduces the risk of allergic sensitization.

The utility of specific immunoglobulin E measurements in primary care

BACKGROUND

The identification of atopic patients may not be considered a necessary step in the diagnosis process in primary care. This study investigated the impact of the addition of a specific immunoglobulin E (IgE) antibody test on the current management by primary-care physicians of patients with respiratory and skin symptoms.

METHODS

The study had a prospective before-after design. It was conducted in two geographic areas of Italy and Spain and consisted of two parts, Part I and Part II. In each part patients were recruited according to inclusion and exclusion criteria. After the clinical examination, the patients were classified into one of the following categories using a physician's classification: allergic, nonallergic or uncertain. A blood sample was taken from each included patient for specific IgE antibody determination using a Pharmacia CAP System, including either Phadiatop Infant (0-5 years of age) or Phadiatop and food mix (fx5e) (>5 years of age). If a positive result was found, an additional 6-26 specific IgE tests were performed. In Part I the result of the specific IgE antibody determinations was not available before the physician's classification was made. In contrast, in Part II, the result of the IgE test was available at the time when the physician's classification was made. Between Part I and Part II an educational intervention for physicians to improve their knowledge of blood testing for IgE-mediated allergy was carried out.

RESULTS

A total of 721 patients were included in the study. The agreement between classifications based on clinical data and IgE antibody results changed from a kappa coefficient of 0.13 in Part I to 0.86 in Part II. With regard to the allergic status the proportion of uncertain cases was reduced from 26.3% in Part I to 4.1% in Part II. The proportion of patients that were advised to avoid allergens increased from 18% in Part I to 62% in Part II in the group of patients classified both by the clinician and the IgE test.

CONCLUSIONS

The use of specific IgE antibody determinations improves the clinical management of patients with allergy related symptoms in primary care, allowing advice to be given on specific allergen avoidance. However, the applicability of this diagnostic tool in different areas and countries should be further assessed in cost-effectiveness studies.

Presence and timing of cat ownership by age 18 and the effect on atopy and asthma at age 28

BACKGROUND

Asthma and allergic sensitization to cats frequently coexist, although recent studies show less atopic disease among people who had pets in infancy. However, no longterm evaluations have been performed thus far.

OBJECTIVE

We sought to evaluate the relationship between cat ownership at different age periods (< 18, > 18, and both periods and atopic disease at age 28.

METHODS

Australian school children aged 8 to 10 years were recruited in 1982 and participated in follow-up surveys until 2002. Cat ownership was defined by surveys in 1992 and 2002 as having a cat before age 18 only, after age 18 only, or in both periods of life. Health outcomes were defined at a mean age of 28.5 years.

RESULTS

Complete data were available for 224 subjects, 50 of whom had a cat before 18 years of age only, 14 after age 18 only, and 70 in both periods. Compared with 90 subjects that never had a cat, having a cat before age 18 protected against atopy to outdoor allergens, airway hyperresponsiveness (AHR) to histamine, current wheeze, and current asthma (P < .05). In contrast, subjects who acquired their first cat after age 18 showed a trend toward higher prevalence rates for asthma symptoms and AHR (P > .10).

CONCLUSIONS

Having had a cat before 18 years of age protects against adult asthma and atopy.

Early-life environmental risk factors for asthma: findings from the Children's Health Study

Early-life experiences and environmental exposures have been associated with childhood asthma. To investigate further whether the timing of such experiences and exposures is associated with the occurrence of asthma by 5 years of age, we conducted a prevalence case-control study nested within the Children's Health Study, a population-based study of > 4,000 school-aged children in 12 southern California communities. Cases were defined as physician-diagnosed asthma by age 5, and controls were asthma-free at study entry, frequency-matched on age, sex, and community of residence and countermatched on in utero exposure to maternal smoking. Telephone interviews were conducted with mothers to collect additional exposure and asthma histories. Conditional logistic regression models were fitted to estimate odds ratios (ORs) and 95% confidence intervals (CIs). Asthma diagnosis before 5 years of age was associated with exposures in the first year of life to wood or oil smoke, soot, or exhaust (OR = 1.74; 95% CI, 1.02-2.96), cockroaches (OR = 2.03; 95% CI, 1.03-4.02), herbicides (OR = 4.58; 95% CI, 1.36-15.43), pesticides (OR = 2.39; 95% CI, 1.17-4.89), and farm crops, farm dust, or farm animals (OR = 1.88; 95% CI, 1.07-3.28). The ORs for herbicide, pesticide, farm animal, and crops were largest among children with early-onset persistent asthma. The risk of asthma decreased with an increasing number of siblings (ptrend = 0.01). Day care attendance within the first 4 months of life was positively associated with early-onset transient wheezing (OR = 2.42; 95% CI, 1.28-4.59). In conclusion, environmental exposures during the first year of life are associated with childhood asthma risk.

Housing characteristics and children's respiratory health in the Russian Federation

OBJECTIVES

We studied housing characteristics, parental factors, and respiratory health conditions in Russian children.

METHODS

We studied a population of 5951 children from 9 Russian cities, whose parents answered a questionnaire on their children's respiratory health, home environment, and housing characteristics. The health outcomes were asthma conditions, current wheeze, dry cough, bronchitis, and respiratory allergy.

RESULTS

Respiratory allergy and dry cough increased in association with the home being adjacent to traffic. Consistent positive associations were observed between some health conditions and maternal smoking during pregnancy, many health conditions and lifetime exposure to environmental tobacco smoke (ETS), and nearly all health conditions and water damage and molds in the home.

CONCLUSIONS

Vicinity to traffic, dampness, mold, and ETS are important determinants of children's respiratory health in Russia.

Asthma, allergy, and upper airway disease

The practitioner must be aware of the strong interrelationship between asthma, allergy, eczema, otitis media, viral upper respiratory infection, and sinusitis. When allergy, eczema, otitis media (particularly after the age of 2 years), viral upper respiratory infection, or sinusitis is present in a patient, asthma must be considered as possible sequelae. If a patient has symptoms of intermittent or persistent asthma, consideration must be given to the presence of allergy, eczema, otitis media, viral upper respiratory infection, or sinusitis as comorbid conditions or possible triggers for the asthma symptoms. Failure to evaluate the entire upper and lower airway for these interrelated conditions will result in incomplete treatment and incomplete symptom relief [61]. This article reviews the strong association between diseases of the upper and lower airway [62,63]. Treatment and control of upper airway symptoms is essential for control of asthma symptoms. Control of allergy, eczema, otitis, sinusitis, and viral symptoms result in improved outcomes for asthma patients. Reduction of these asthma triggers and comorbid conditions is also likely to reduce asthma medication requirements while improving symptoms status.

Focus on cat allergen (Fel d 1): immunological and aerodynamic characteristics, modality of airway sensitization and avoidance strategies

The increasing frequency of pet ownership (especially cats) in many industrialized countries has raised the level of exposure to the allergens produced by these animals. Moreover, it is likely that modern energy-saving systems and the wide use of upholstered furniture has resulted in closer contact between cats (and their allergens) and humans. Many different methods have been developed to quantify the main cat allergen (Fel d 1) in settled dust and in ambient air. The threshold levels of cat allergen inducing sensitization or triggering respiratory symptoms in sensitized patients have been calculated in settled dust, but airborne amounts of Fel d 1 probably represent a more reliable index of allergen exposure. Noticeably, the amount of Fel d 1 may be relatively high also in confined environments where cats have never been kept. It has been demonstrated that clothes of cat owners are the main source for dispersal of allergens in cat-free environments. This fact may be of relevance, because recent studies have shown that allergic sensitization to cats is more likely to develop in children exposed to moderate levels of this allergen than in children exposed to high amounts of Fel d 1. The ubiquity of cat allergen may justify the common observation that allergen avoidance is often insufficient to reduce the risk of developing allergic sensitization and/or symptom exacerbation in highly susceptible patients. Further efforts are needed to improve the efficacy of Fel d 1 avoidance strategies to try to reduce the risk of allergic sensitization to this allergen.

Resource costs for asthma-related care among pediatric patients in managed care

BACKGROUND

In 1998, the economic burden of asthma in the United States was estimated to be 12.7 billion dollars. Yet few studies have examined the relationship between the total costs of asthma-related care and measures of asthma morbidity. Understanding the relationship between total costs of asthma-related care and morbidity can assist in designing the most cost-effective asthma care strategies to improve patient outcomes and minimize total costs.

OBJECTIVE

To investigate correlates of asthma costs for children with mild-to-moderate persistent asthma and, specifically, to characterize how closely the percentage of predicted forced expiratory volume in 1 second (FEV1) and symptom days were correlated with costs of illness.

METHODS

A total of 638 parents and children with mild-to-moderate persistent asthma in 4 managed care delivery systems in 3 different US geographic regions were enrolled. Symptom burden and annual resource utilization were determined from reports of physician visits, hospitalizations, emergency department visits, medication use, and parental missed workdays. Spirometry was conducted on children who were 5 years and older. To characterize the relationship between symptom days and the percentage of predicted FEV1 with costs, we specified a multivariate regression model.

RESULTS

The median total annual asthma-related cost for the group was 564 dollars (interquartile range [IQR], 131 dollars-1602 dollars). Indirect costs represented 54.6% of total costs. Medicines accounted for 52.6% of direct costs. The mean percentage of predicted FEV1 was 101.6% (range, 39.3%-183.5%; IQR, 91.6%-111.3%), with 91.4% of patients with a percentage of predicted FEV1 of more than 80%. Based on multivariate modeling, increasing asthma severity, use of peak expiratory flow rate meters, younger age, low-income status and nonwhite race, and longer duration of asthma were significantly associated with increasing cost. Symptom days (P < 0.001) predicted annual costs better than percentage of predicted FEV1 (P < 0.16) in this group of children.

CONCLUSIONS

For the large number of children with mild-to-moderate persistent asthma and normal or near-normal lung function, symptom days are predictive of health care costs. For these insured children receiving care from 3 large managed care providers, low-income status and nonwhite race were the strongest correlates for increased asthma-related costs.

Allergy markers in adults in relation to the timing of pet exposure: the EGEA study

BACKGROUND

Studies suggest that early childhood exposure to pets may protect from the development of atopy, but limited information is available on adults. The association of allergy markers in adulthood with current and childhood exposure to pets was studied considering retrospectively the window of exposure.

METHODS

Immunoglobulin E (IgE), skin prick tests (SPT), eosinophils were related to exposure to pets in 187 adult asthmatic cases and 243 controls from the Epidemiological Study on the Genetics and Environment of Asthma, bronchial hyperresponsiveness and atopy (EGEA) study. Analyses were redone after exclusion of subjects who removed pets or experienced symptoms to animals to take into account selection in that retrospective study.

RESULTS

In asthmatic cases, current exposure to pets was unrelated to SPT positivity (+), whereas childhood exposure was significantly related to less SPT+ to any allergen, and to cat in particular, with an association restricted to those exposed before 2 years of age [OR = 0.30 (CI 0.12-0.76)]. Considering the relative timing of exposure in relation to asthma onset showed that the protective effect of exposure to pets occurs for pet exposure starting before asthma onset [OR for SPT+ = 0.19 (CI 0.08-0.48)].

CONCLUSION

Results support the hypothesis that exposure to pets in early life, and in particular before asthma onset, may protect against allergen sensitization in adulthood.

Pet-keeping in childhood and adult asthma and hay fever: European community respiratory health survey

BACKGROUND

Whether pet-keeping early in life protects against or promotes allergy remains unclear.

OBJECTIVE

Our aim was to examine the effects of childhood pet-keeping on adult allergic disease in a large international population-based study, including information on sensitization, adult pet-keeping, and pet prevalence in the populations.

METHODS

We used information from structured interviews (n = 18,530) and specific IgE to common aeroallergens in blood samples (n = 13,932) from participants in the European Community Respiratory Health Survey (ECRHS) to analyze the associations between keeping pets and adult asthma and hay fever.

RESULTS

Keeping cats in childhood was associated with asthma only among atopic subjects, an association that varied between centers (P =.002) and was stronger where cats where less common (< 40% cats: odds ratio(wheeze) [OR(wheeze)] = 1.84, 95% CI = 1.31-2.57; 40%-60% cats: OR(wheeze) = 1.33, 95% CI = 1.10-1.61; > or =60% cats: OR(wheeze) = 0.98, 95% CI = 0.73-1.33). Dogs owned in childhood or adulthood were associated with asthma among nonatopic subjects (childhood: OR(wheeze) = 1.28, 95% CI = 1.13-1.46; adulthood: OR(wheeze) = 1.31, 95% CI = 1.14-1.51; both: OR(wheeze) = 1.69, 95% CI = 1.40-2.04). In atopic subjects, those who had owned dogs in childhood had less hay fever (OR = 0.85; 95% CI = 0.73-0.98) and no increased risk of asthma (OR(wheeze) = 1.01, 95% CI = 0.87-1.17). Respiratory symptoms were more common in subjects who had owned birds during childhood (OR(wheeze) = 1.12; 95% CI = 1.02-1.23) independent of sensitization.

CONCLUSIONS

The effects of pet-keeping in childhood varied according to the type of pet, the allergic sensitization of the individual, and the wider environmental exposure to allergen. Cats owned in childhood were associated with more asthma in sensitized adults who grew up in areas with a low community prevalence of cats. Dogs owned in childhood seemed to protect against adult allergic disease but promote nonallergic asthma.

Early sensitisation and development of allergic airway disease - risk factors and predictors

The development and phenotypic expression of allergic airway disease depends on a complex interaction between genetic and several environmental factors, such as exposure to food, inhalant allergens and non-specific adjuvant factors (e.g. tobacco smoke, air pollution and infections). The first months of life seem to be a particularly vulnerable period and there is evidence that sensitisation is related to the level of allergen exposure during early life. At present, the combination of atopic heredity and elevated cord-blood IgE seems to result in the best predictive discrimination as regards development of allergic disease at birth. Early sensitisation, cow's milk allergy and atopic eczema are predictors for later development of allergic airway disease. Exposure to indoor allergens, especially house dust mite allergens, is a risk factor for sensitisation and development of asthma later in childhood in high-risk infants and infants with early atopic manifestations.

A dual long-term effect of breastfeeding on atopy in relation to heredity in children at 4 years of age

BACKGROUND

The long-term effect of early feeding on atopic sensitization is still unsolved. The aim of this study was to evaluate the long-term effect of breastfeeding on atopy in groups of 4-year-old children stratified by atopic heredity.

METHODS

We collected four groups of 4-year-old children from a birth cohort: two groups with differing backgrounds of atopic heredity, all exclusively breast-fed for at least 3 months; and two groups with differing atopic heredity, but all fed with cow's milk-based formula during their first weeks. The data were collected with a questionnaire, skin prick testing, and measurement of serum total and allergen-specific IgE levels.

RESULTS

Breastfeeding significantly decreased the risk of allergic rhino-conjunctivitis [odds ratio (OR) 0.41, 95% confidence interval (CI) 0.18-0.95] and sensitization to furred pets, as measured by skin prick results, in children with atopic heredity, whereas in children without atopic heredity, breastfeeding was related to an increased risk of symptomatic atopy (OR 2.57, 95% CI 1.16-5.70), and high serum IgE values. A significant interaction was found between heredity and breastfeeding.

CONCLUSIONS

The long-term effect of breastfeeding was dual: in children with atopic heredity, breastfeeding protected against atopy, whereas in children without atopic heredity, it increased the risk of atopy.

Controlling indoor allergens

PURPOSE OF REVIEW

Epidemiological surveys indicate that there has been a notable increase in the prevalence of asthma and other allergic diseases in children and adults. The purpose of this review is to report and comment on recent studies about the role of allergen in primary prevention and to seek new insights on the effects of allergen control in allergic patients.

RECENT FINDINGS

This paper deals with allergen reduction in primary prevention, the effect of early exposure to pets on atopic diseases and the development of new occupational activity improving allergen control in allergic patients.

SUMMARY

The role of allergen dose involved in the onset of atopy is controversial. Studies hypothesizing that a reduction of allergen dose might reduce atopy failed to confirm the data from the Isle of Wight study and found no effect on the frequency of immunoglobulin E sensitization. This effect might nonetheless occur later in life. Other studies indicate that high doses of allergen early in life have a protective effect against cat and dog sensitization. Only one retrospective study found that cat exposure was protective against cat sensitization. A German prospective study suggested, however, that it is more probable that cat allergen exposure is harmfully related to sensitization, by increasing IgE synthesis. The effect of high doses must be clarified by further prospective studies. Accordingly, we must be very careful when giving advice on primary prevention, particularly about the protective effect of cat and dog allergens. Secondary prevention may be dramatically improved with the help of a new occupational activity: the medical indoor environment counsellor.

Heredity, pet ownership, and confounding control in a population-based birth cohort

BACKGROUND

The association between pet ownership in childhood and subsequent allergic disease is controversial. Bias related to selection of pet exposure has been suggested as a reason for contradictory study results.

OBJECTIVE

The purpose of this investigation was to elucidate how pet exposure depends on family history of allergic disease, smoking, and socioeconomic factors in a prospective birth cohort.

METHODS

Parents of 4089 two-month-old children answered a questionnaire that included detailed questions about family history of asthma (maternal, paternal, and sibling), rhinoconjunctivitis, atopic eczema/dermatitis syndrome, pollen and pet allergy, smoking habits, parental occupation, and family pet ownership (cat and dog). Dust samples collected from the mothers' beds were analyzed for Fel d 1 and Can f 1 in a subgroup of the cohort.

RESULTS

Cats were less frequently kept in families with parental asthma, rhinoconjunctivitis, or pet or pollen allergy (3.5% to 5.8%) than in families without parental allergic disease (10.8% to 11.8%). Dogs were less common in families with (3.3%) than in families without (5.9%) parental atopic eczema/dermatitis syndrome. Families with smoking mothers and those with low socioeconomic index kept cats and dogs more frequently. Cat allergen levels were lower in homes with than in homes without maternal pet allergy, and this tended to hold true even for homes without a cat. Cat ownership decreased from birth to 2 years of age, especially in families with parental history of allergic diseases.

CONCLUSION

There seems to be a selection of pet exposure based on parental history of allergy, maternal smoking, and socioeconomic factors. This has to be taken into consideration in evaluations of risk associations between pet exposure and allergic disease in childhood.

Familial and environmental determinants for wheezing and asthma in a case-control study of school children in Palestine

BACKGROUND

Our prevalence study on Palestinian school children aged 6-12 years showed lower rates for asthma and asthma symptoms than economically developed and industrialized countries. Reasons for such differences are largely unknown, and could possibly be related to different environmental and lifestyle factors.

OBJECTIVE

To investigate familial, early life exposures and indoor environmental determinants for asthma in children in Palestine.

METHODS

From the population of our previous study, a group of 273 children with wheeze in the past 12 months (of whom 99 children had physician-diagnosed asthma) were matched with an equal number of non-wheezing controls. This case-control study involved a parental questionnaire; skin prick testing (SPT) with mixed house dust mites, cat and dog dander, mixed grass, mixed trees pollen, Alternaria tenuis, olive tree and cockroach extracts; and serum for total and specific IgE for the same eight allergens.

RESULTS

Paternal asthma and maternal hayfever significantly tripled the risk for their children to have wheezing. Previous diagnoses of bronchial allergy, bronchitis, pneumonia, or whooping cough, and positive SPT for house dust mites and cockroaches were significantly more likely among wheezing and asthmatic children than controls. Specific IgE levels for house dust mites and cat allergens showed significantly higher risk for reported wheezing. After adjustment for several environmental and sociodemographic factors using multivariate logistic regression analysis, paternal asthma, maternal hayfever, damp houses, cat and cockroach SPT positivity proved to be strong predictors for wheezing symptoms.

CONCLUSION

Our study confirmed that familial 'atopic' diseases are significant predictors of childhood asthma in Palestinian children. Moreover, indoor environment such as presence of cats and domestic moulds also appear to play a role. Our findings are consistent with studies in Canada, New Zealand, Estonia and Sweden, and show promise to explore further gene-environment interaction in the genesis of asthma.

Exposure to pets and atopic dermatitis during the first two years of life. A cohort study

The aim of this study was to assess the association between keeping pets in early childhood and the occurrence of atopic dermatitis in an ongoing birth cohort followed up to the age of 2 years. We analyzed data of 4578 children in the intervention and observation part of an ongoing cohort study. The children were recruited at birth in the two study regions Wesel and Munich between January 1996 and June 1998. Information on atopic diseases and pet ownership was obtained by questionnaire at the child's first and second birthday. The logistic regression model showed a negative association between 'keeping any pet' and in particular 'keeping dogs' in the 1st year of life and the development of atopic dermatitis in the 1st and the 2nd years of life. The protective effects remained statistically significant after adjusting for several possible confounding variables (1st year(any) pet OR 0.71, 95% CI [0.55;0.92], 1st year(dog) OR 0.62, 95% CI [0.39;0.98], 2nd year(any) pet OR 0.74, 95% CI [0.57;0.97], 2nd year(dog) OR 0.63, 95% CI [0.40;0.98]). Ownership of small furred pets (hamster, rabbit and guinea pig) also showed a borderline protective effect for the 1st year. We assume an association between keeping pets and undefined environmental factor(s) that contribute protectively to the development of atopic dermatitis in early life, presumably by effects on the maturation of the immune system.

Is prevention of childhood asthma possible? Allergens, infections and animals

What we know: Epidemiological studies have identified a number of factors associated with increased incidence of asthma. These include allergen sensitisation and exposure, reduced exposure to infections and to farm animals in early childhood, and maternal smoking. These factors may represent "true" risk factors for asthma or may be merely associated factors that do not in themselves cause asthma. The "hygiene hypothesis" has been proposed as one mechanism by which infections may protect against asthma. Current recommendations for the primary prevention of asthma include exclusive breastfeeding for the first six months of life, avoidance of maternal smoking during pregnancy and infancy, and reducing the levels of house-dust mite in some environments. What we need to know: What are the mechanisms by which specific risk factors and prevention strategies lead to or protect from asthma? How do genetic and environmental factors interact to increase the risk of asthma?

The development of childhood asthma: lessons from the German Multicentre Allergy Study (MAS)

Epidemiological surveys have indicated that there has been a notable increase in the prevalence of both asthma and other allergic symptoms in children and young adults. Since it seems unlikely that genetic factors would contribute to the rising trend, environmental factors might play a major part in the development of childhood asthma. In a prospective birth-cohort study, we assessed the relevance of different exposures such as mite and cat allergen exposure, environmental tobacco smoke (ETS) exposure, early infectious diseases and vaccinations for the development of childhood asthma up to the age of 10 years. Data up to 7 years of age have been evaluated. Of 1314 newborn infants enrolled in five German cities in 1990, follow-up data at age 7 years were available for 939 children (72%). Assessments included repeated measurements of specific IgE to food and inhalant allergens, measurement of indoor allergen exposure at 6 months, 18 months and 3 years of age and yearly interviews by a paediatrician. At age 7 years, pulmonary function was tested and bronchial responsiveness was determined in 645 children. At age 7, the prevalence of wheezing in the past 12 months was 10% (94 out of 938), and 6.1% (57 out of 939) parents reported a doctor's diagnosis of asthma in their children. Sensitisation to indoor allergens was associated with asthma, wheeze and increased bronchial responsiveness. However, no relationship between early indoor allergen exposure and the prevalence of asthma, wheeze and bronchial responsiveness was seen. During the first 3 years of life, intra-uterine tobacco and consistent ETS exposure have an adjuvant effect on allergic sensitisation that is transient and restricted to children with a genetic predisposition for allergy. Children sensitised to any allergen early in life and sensitised to inhalant allergens by the age of 7 years were at a significantly increased risk of being asthmatic at this age (odds ratio (OR) = 10.12; 95% confidence interval (CI) = 3.81-26.88). Children with repeated episodes (> or =2) of runny nose before the age of 1 year were less likely to develop asthma by the age of 7 years (OR = 0.52; 95% CI = 0.29-0.92). Our data do not support the hypothesis that exposure to environmental allergens directly causes asthma in childhood but that induction of specific IgE responses and the development of childhood asthma are determined by independent factors. Indoor allergen avoidance is recommended as first line treatment in secondary and tertiary prevention; however, conclusions should be drawn with caution about the possible effect of primary preventative measures. Since allergic asthma seems to be a Th2-disease, immunomodulating factors such as early childhood infections, LPS-exposure or other factors influencing gene-environment interaction and individual susceptibility seem to be relevant for the development of childhood asthma.

Pets, parental atopy, and asthma in adults

BACKGROUND

Studies of exposure to pets and the risk of asthma have provided conflicting results.

OBJECTIVE

We conducted a population-based incident case-control study to assess the relationship of current and previous pet keeping with the risk of adult-onset asthma. We also investigated whether genetic propensity as a result of parental atopy modifies these relations.

METHODS

From the source population of 441,000 inhabitants of a geographically defined area in South Finland, we systematically recruited, during a 2.5-year period, all new cases of asthma in 21- to 63-year-old adults and randomly selected control subjects. The clinically diagnosed case series consisted of 521 adults with newly diagnosed asthma and a control series of 932 control subjects. Information on current and past exposure to hairy pets was collected by using a self-administered questionnaire.

RESULTS

In logistic regression analysis the risk of asthma was lower among subjects with pets during the past 12 months (adjusted odds ratio [OR], 0.74; 95% confidence interval [CI], 0.57-0.96) but higher among subjects with pets more than 12 months previously (adjusted OR, 1.39; 95% CI, 1.05-1.84). Parental atopy increased the risk of asthma (OR, 1.88; 95% CI, 1.47-2.41), but there was no interaction between parental atopy and pet exposure.

CONCLUSIONS

The present results are consistent with the hypothesis that both keeping furry pets and parental atopy increase the risk of asthma development in adulthood. Parental atopy does not modify the effects of pet exposure. The negative association between current pets and the risk of asthma is consistent with selective avoidance of these pets by symptomatic individuals.

Do animals on the farm and in the home reduce the risk of pediatric atopy?

Recent evidence suggests that proximity to pets and farm animals early in life may decrease the risk of developing atopy. Studies investigating the etiology of atopy and asthma have been especially challenging due to difficulties in ascertaining and classifying incident cases. Nevertheless, cross-sectional and cohort studies described in this paper reported across various populations, among children and adults, tended to demonstrate inverse associations between the presence of indoor cats and dogs or frequent exposure to livestock during the first years of life and sensitization to pet and pollen allergens, hay fever, and to a lesser degree, asthma. The biological mechanisms of this protection is unknown, as are the factors associated with pet keeping and livestock farming that may play a role. In the meantime, it appears that counseling prospective parents that avoidance of exposure to animals in the first years of life will prevent atopy may not be sage advice.