Using Component-Resolved Diagnosis to Characterize the Sensitization to Specific Cat and Dog Allergens in Patients with Allergic Respiratory Diseases in Catalonia, Spain.

INTRODUCTION: Sensitization to cat and dog allergens is common in patients with allergic respiratory diseases. The study objective was to determine the prevalence of immunoglobulin E (IgE) sensitization to specific cat and dog allergens using component-resolved diagnosis (CRD) in patients with allergic respiratory diseases plus cat and/or dog sensitization. METHODS: We included 87 patients aged 8-62 years, diagnosed with allergic asthma and/or rhinitis plus cat and/or dog sensitization, and attended at the allergy section of a tertiary hospital in Badalona (Catalonia, Spain). We used CRD to determine IgE sensitization to specific cat/dog allergens and skin prick tests (SPTs) to determine differences between diagnostic test results. RESULTS: Patients were monosensitized to cats (20.7%) or dogs (3.4%) or sensitized to both (75.9%). The highest positive allergen rates were for Fel d 1 (91.7%) and Fel d 4 (41%) in patients sensitized to cat allergens and for Can f 5 (80%) and Can f 1 (70%) in those sensitized to dog allergens. CRD and SPT results differed somewhat: 16.1% and 27.6% of patients CRD positive for cat or dog sensitization, respectively, were SPT negative, and 6.9% SPT positive for dog sensitization were CRD negative. Few statistically significant relationships were found between any allergen components and any respiratory disease characteristic or contact with furry animals. CONCLUSIONS: CRD may be used to determine the prevalence of IgE sensitization to specific cat and dog allergens in patients with allergic respiratory diseases plus cat and/or dog sensitization. As SPT may not correctly identify all patients sensitized to cats and dogs, our results support the use of CRD.

Sensitization to molecular dog allergens in an adult population: Results from the West Sweden Asthma Study.

BACKGROUND: As the prevalence of dog allergy rises, component resolved diagnosis might improve the diagnosis, understanding of the clinical outcomes and the effectiveness of immunotherapy. Considering the paucity of data in adults, the current study characterized the patterns of sensitization to dog molecular allergens in an adult population. METHODS: Data were derived from the West Sweden Asthma Study, a population-based and representative sample of adults from western Sweden. Of the 2006 subjects clinically examined, 313 participants sensitized to whole dog allergen extract were measured for specific immunoglobulin E (sIgE) levels to Can f 1, Can f 2, Can f 3, Can f 4, Can f 5 and Can f 6 using ImmunoCAP™. Polysensitization was defined as sensitization to ≥3 components. Overlapping sensitization was defined as having concomitant sensitization to at least two dog molecular allergen families (lipocalin, albumin or prostatic kallikrein). RESULTS: Of 313, 218 (70%) subjects tested positive to at least one dog allergen component. Sensitization to Can f 1 (43%) was the most common, followed by Can f 5 (33%) among molecular allergens, while sensitization to lipocalins (56%) was the most common among component families. Polysensitization was found in 22% of all participants and was more common in participants with than in those without asthma. Subjects with asthma were less likely to be monosensitized to Can f 5 than those without asthma. Subjects with asthma had higher IgE levels of Can f 3, Can f 4 and Can f 6 than those without asthma. Overlapping sensitizations also differed between those with asthma and allergic rhinitis and those without. CONCLUSION: Increased knowledge about the sensitization patterns of dog allergen components can aid in defining their role in asthma and rhinitis. In complex clinical cases of dog allergy, a detailed analysis of dog allergen components can provide additional information on the nature of sensitization.

Recombinant multimeric dog allergen prevents airway hyperresponsiveness in a model of asthma marked by vigorous TH 2 and TH 17 cell responses.

BACKGROUND: Allergy to dogs affects around 10% of the population in developed countries. Immune therapy of allergic patients with dog allergen extracts has shown limited therapeutic benefit. METHODS: We established a mouse model of dog allergy by repeatedly administering dog dander and epithelium extracts via the intranasal route. We also assessed the efficacy of a recombinant multimeric protein containing Can f 1, f 2, f 4 and f 6 in preventing inflammatory responses to dog extracts. RESULTS: Repeated inhalation of dog extracts induced infiltration of the airways by TH 2 cells, eosinophils and goblet cells, reminiscent of the house dust mite (HDM) model of asthma. Dog extracts also induced robust airway hyperresponsiveness and promoted TH 17 cell responses, which was associated with a high neutrophilic infiltration of the airways. scRNA-Seq analysis of T helper cells in the airways pinpointed a unique gene signature for TH 17 cells. Analysis of T-cell receptors depicted a high frequency of clones that were shared between TH 17, TH 2 and suppressive Treg cells, indicative of a common differentiation trajectory for these subsets. Importantly, sublingual administration of multimeric Can f 1-2-4-6 protein prior to sensitization reduced airway hyperresponsiveness and type 2-mediated inflammation in this model. CONCLUSION: Dog allergen extracts induce robust TH 2 and TH 17 cell-mediated responses in mice. Recombinant Can f 1-2-4-6 can induce tolerance to complex dog allergen extracts.

Allergic sensitization to lipocalins reflects asthma morbidity in dog dander sensitized children.

Background: Sensitization to dog is an important risk factor for asthma in children, but the clinical relevance of IgE to available dog- and furry animal allergen molecules is uncertain. Methods: Spirometry, methacholine challenge, fraction of exhaled nitric oxide, nasal challenge with dog extract and questionnaires were performed in 59 dog-sensitized children (age 10-18 years). Serum IgE to dog-, cat-, horse extracts and the allergen molecules Can f 1-6, Fel d 1, Fel d 2, Fel d 4 and Equ c 1 were evaluated. Results: Median numbers of positive IgE results to furry animal allergen molecules among children without asthma was 3, with asthma 5.5 and with troublesome asthma 9 (asthma vs. no asthma; p = 0.039; troublesome asthma vs. no asthma; p = 0.009). The odds ratio for asthma if sensitized to any lipocalin was 7.2 (95% confidence Interval: 1.44-35.9). Children with troublesome asthma had higher IgE levels to the lipocalins Can f 2, Can f 4 and Can f 6 compared to the rest of the study population (44 vs. 4.1 kUA/L, p = 0.015; 5.8 vs. 0.9 kUA/L, p = 0.018 and 1.3 vs. 0.7 kUA/L, p = 0.03 respectively). Furthermore, a positive nasal challenge was more common among children with troublesome asthma (83% vs. 36%, p = 0.036). Conclusions: Polysensitization to furry animal allergens and lipocalins is associated with asthma in dog-sensitized children. Children with troublesome asthma have higher IgE levels to several dog lipocalins than other dog sensitized children. Key message: Polysensitization to furry animal allergens and high IgE levels to the dog lipocalins Can f 2, Can f 4 and Can f 6 is associated with asthma severity in dog dander sensitized children. Molecular allergy diagnostics may thus help the clinicians to evaluate the impact of allergic sensitization on asthma morbidity.

Single-cell characterization of dog allergen-specific T cells reveals TH2 heterogeneity in allergic individuals.

BACKGROUND: Allergen-specific type 2 CD4+ TH2 cells are critically involved in the pathogenesis of IgE-mediated allergic diseases. However, the heterogeneity of the TH2 response has only recently been appreciated. OBJECTIVE: We sought to characterize at the single-cell level the ex vivo phenotype, transcriptomic profile, and T-cell receptor (TCR) repertoire of circulating CD4+ T cells specific to the major dog allergens Can f 1, Can f 4, and Can f 5 in subjects with and without dog allergy. METHODS: Dog allergen-specific memory CD4+ T cells were detected ex vivo by flow cytometry using a CD154-based enrichment assay and single-cell sorted for targeted gene expression analysis and TCR sequencing. RESULTS: Dog allergen-specific T-cell responses in allergic subjects were dominantly of TH2 type. TH2 cells could be phenotypically further divided into 3 subsets, which consisted of TH2-like (CCR6-CXCR3-CRTH2-), TH2 (CCR6-CXCR3-CRTH2+CD161-), and TH2A (CCR6-CXCR3-CRTH2+CD161+CD27-) cells. All these subsets were nonexistent within the allergen-specific T-cell repertoire of healthy subjects. Single-cell transcriptomic profiling confirmed the TH2-biased signature in allergen-specific T cells from allergic subjects and revealed a TH1/TH17 signature in nonallergic subjects. TCR repertoire analyses showed that dog allergen-specific T cells were diverse and allergic subjects demonstrated less clonality compared to nonallergic donors. Finally, TCR and transcriptomic analyses revealed a close relationship between TH2-like, TH2, and TH2A cells, with the last ones representing the most terminally differentiated and highly polarized subtype. CONCLUSIONS: Our study demonstrates heterogeneity within allergen-specific TH2 cells at the single-cell level. The results may be utilized for improving immune monitoring after allergen immunotherapy and for designing targeted immunomodulatory approaches.

Cross-reactivity of Can f 1 with Syrian hamster and Fel d 1 in children.

Introduction and objectives: With increasing pet allergies among pediatric patients, the need for precise environmental care is increasing. We investigated the clinical, immunological, and environmental characteristics of pediatric patients sensitized to a dog to evaluate the cross-antigenicity of canine lipocalin Can f 1 with feline lipocalin Fel d 1 and Syrian hamster extract.Materials and methods: The protein fractions of the processed and commercial Syrian hamster extracts were compared using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). An enzyme-linked immunosorbent assay (ELISA) inhibition test was performed on Can f 1, Fel d 1, and processed Syrian hamster extract, and the antigen-specific immunoglobulin E (IgE)-binding capacity for each antigen was analyzed using serum samples from patients.Results: Twelve of 19 patients with a median age of 40.5 months were symptomatic when exposed to dogs. Eleven (91.7%) patients showed a positive IgE response to Can f 1. Two patients were positive for Fel d 1-specific IgE antibody, and one was positive for hamster-specific IgE antibody. SDS-PAGE confirmed the presence of different patterns of protein bands between the commercial and processed hamster extracts. There was no cross-antigenicity among Can f 1, Fel d 1, and processed Syrian hamster extract.

Cross-reactivity of Can f 1 with Syrian hamster and Fel d 1 in children

Introduction and objectives: With increasing pet allergies among pediatric patients, the need for precise environmental care is increasing. We investigated the clinical, immunological, and environmental characteristics of pediatric patients sensitized to a dog to evaluate the cross-antigenicity of canine lipocalin Can f 1 with feline lipocalin Fel d 1 and Syrian hamster extract. Materials and methods: The protein fractions of the processed and commercial Syrian hamster extracts were compared using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). An enzyme-linked immunosorbent assay (ELISA) inhibition test was performed on Can f 1, Fel d 1, and processed Syrian hamster extract, and the antigen-specific immunoglobulin E (IgE)-binding capacity for each antigen was analyzed using serum samples from patients. Results: Twelve of 19 patients with a median age of 40.5 months were symptomatic when exposed to dogs. Eleven (91.7%) patients showed a positive IgE response to Can f 1. Two patients were positive for Fel d 1-specific IgE antibody, and one was positive for hamster-specific IgE antibody. SDS-PAGE confirmed the presence of different patterns of protein bands between the commercial and processed hamster extracts. There was no cross-antigenicity among Can f 1, Fel d 1, and processed Syrian hamster extract. Conclusions: Since the standard commercial hamster extract did not contain Syrian hamster antigens that were diverse enough, caution should be taken when using it. In children allergic to cats and dogs, sensitization to isolated Can f 1 or Fel d 1 is unlikely to cause cross-reactivity to Syrian hamster hair and epithelium (AU)

Analysis of allergen profile in patients sensitized to canine allergen and potential Can f 5 cross-reactivity with human PSA.

Can f 5 allergy and possible cross-reactivity with human semen in which there are significant amounts of prostate-specific antigen (PSA) are particularly interesting aspects of allergy to dog. The objective of the study was to confirm cross-reactivity between human PSA and Can f 5 in a study of canine sensitised women. A total of 100 women (aged 18-73, 41 on average) with a positive history of animal fur allergy or positive skin prick tests to canine allergens were selected. Levels of Immunoglobulin E (IgE) specific to Can f 1, Can f 2, Can f 3, Can f 5 were determined. Patients with increased concentration of sIgE Can f 5 were selected for further inhibition testing using polystyrene microplate ELISA test coated with human PSA. In the studied population, allergy to Can f 5 dominated (52.3% of patients with increased concentration of canine-specific IgE were allergic to this allergenic component). In all analyzed cases, the concentration of IgE Can f 5 decreased after incubation on the ELISA plate coated with human PSA. The minimum decrease in concentration was 10.44%, the maximum was 37.73%, the average decrease was 21.6%. No statistically significant influence of the presence or absence of allergenic sIgE Can f 5 in blood serum on the occurrence of symptoms after intercourse was found. The study confirmed the moderate ability of Can f 5 to cross-react with human PSA sIgE, which may be clinically significant in some women. At the same time, symptoms of an allergy to male semen do not constitute a typical clinical presentation of allergy to Can f 5.

Unusual and Unexpected Allergic Reactions Can Be Unraveled by Molecular Allergy Diagnostics.

The fifth class of immunoglobulin, immunoglobulin E (IgE) was discovered in 1967 and has had immense importance for the understanding, diagnosis, and treatment of allergic disease. More than 50 years have passed and efforts to characterize, standardize, and refine allergens with the aim to improve clinical diagnosis and allergen-specific immunotherapy are still ongoing. Another important breakthrough was made in 1999 with the introduction of component-resolved diagnostics (CRD), making it possible to quantify IgE antibodies against individual allergen proteins for diagnostic purposes at a molecular level. The progress and developments made in allergy diagnosis often originate from clinical observations and case studies. Observant physicians and health-care personnel have reported their findings in the medical literature, which in turn has inspired researchers to become involved in clinical research. Allergists continuously encounter new allergies and are often asked by their patients how to prevent new reactions. In the current article, we focus on recent clinical observations that can now be explained by CRD. The examples taken concern allergic reactions toward peanuts, tree nuts, lemon kernels, health drinks, meat, insects, dog dander, cannabis, and semen. We now have an improved understanding of why patients may react in a serious or unexpected way, as illustrated by these examples, yet many other clinical observations remain unexplained. The aim of this review is to highlight the importance of clinical observations among allergic patients, focusing on systemic, or unusual and unexpected allergic reactions, where component-testing has further refined the diagnosis of IgE-mediated allergy.

IgE recognition profile of aeroallergen components in young children sensitized to dogs.

BACKGROUND: Pet ownership is increasing rapidly and as growing numbers of dogs in household, clinicians are facing more allergic patients and so as in young children. OBJECTIVE: This study aims to profile the IgE recognition patterns to aeroallergen components in young children sensitized to dogs. METHODS: Through retrospective chart reviews, we evaluated the clinical, environmental, and laboratory findings of patients sensitized to dogs in early life. We further evaluated specific IgE to dog component allergens (Can f 1, Can f 2, and Can f 3) and other aeroallergens using a microarray. RESULTS: The median age of 28 patients sensitized to dogs (dog-specific IgE ≥ 0.35 kU/L; 0.38-101 kU/L) was 61 months and underlying diseases included doctor diagnosed atopic dermatitis (n = 17), asthma (n = 7), and allergic rhinitis (n = 5). Twenty patients (71.4%) had experienced self-reported dog allergy and 70.0% of them were symptomatic after exposed to dogs from others. Component-resolved diagnosis was performed on 18 patients. Can f 1 positivity was the most common (77.8%) but had no value in symptom prediction. The most common cosensitized aeroallergen was house dust mites (44.5%). The symptomatic group tended to be poly-sensitized to Can f 1, Can f 2, and Can f 3. CONCLUSION: Can f 1 was dominantly detected and poly-sensitized to Can f 2 and/or Can f 3 simultaneously tend to develop hypersensitivity to dogs in young children. Most of them were exposed to dogs not living with.

Children Monosensitized to Can f 5 Show Different Reactions to Male and Female Dog Allergen Extract Provocation: A Randomized Controlled Trial.

BACKGROUND: Dog dander consists of several allergenic molecules including Can f 5, which is a protein expressed in the prostate of male dogs. OBJECTIVE: To investigate whether children monosensitized to Can f 5 show different reactions to provocation tests with male versus female dog dander in a double-blind randomized clinical trial. METHODS: Twenty-two children (15-18 years) with a history of dog sensitization were enrolled from the COpenhagen Prospective Studies on Asthma in Childhood2000 mother-child cohort. Skin prick test, specific IgE levels to dog dander (e5), and dog components Can f 1, 2, 3, and 5 were first assessed. We subsequently performed skin prick test and conjunctival allergen provocation test using dog dander collected separately from male and female dogs. RESULTS: Seven of the 22 children were monosensitized to Can f 5. Eight were sensitized to a mix of the dog components, and 7 were no longer sensitized to dog. Of the children monosensitized to Can f 5, all had a positive skin prick test result to male dog extract and 1 of 7 was also positive to female dog extract (P = .01). Furthermore, 5 of 7 had a positive conjunctival allergen provocation test result to male dog extract and 1 of 7 also reacted to the female dog extract (P = .03). There was no difference between reactions to male and female dog extract provocation in children sensitized to a mix of the dog components. CONCLUSIONS: Children monosensitized to Can f 5 show different reactions to male and female dog extract provocation using both skin prick test and conjunctival allergen provocation test, suggesting tolerance to female dogs.

Frequency of allergic sensitization to Can f 5 in North East Italy. An analysis of 1403 ISACs 112 (Component Resolved Diagnosis) collected retrospectively.

Summary: Recent studies have shown the increasing relevance of allergic sensitization to Can f 5, a prostatic kallicrein expressed in the prostate and detectable only in male dogs. The aim of the present study was to establish the frequency, level of sensitization and association with other dog allergens of Can f 5, as assessed by Component Resolved Diagnosis (CRD- ISAC 112, ThermoFisher Scientific, Uppsala, Sweden), in North East Italy. A total of 1403 CRD ISAC 112 were examined retrospectively. Five-hundred twenty subjects (37 %) had a positive IgE response to at least one of the available animal allergens. Among these 520 subjects, 268 (51.5 %) showed at least one sensitization to dog allergens. Among dog-sensitized individuals, 183 (69.02%) showed IgE against Can f 5, and 106 (57.92%) were sensitized exclusively against Can f 5. The average Can f 5 specific IgE was 8.810 ISU-E, with 77.6 % of individuals showing medium or high values of specific IgE according to manufacturer's specifications. In conclusions, our data confirmed that there is a high number of sensitized patients to Can f 5, which have a high degree of allergic sensitization. These results should be taken into account by allergists managing dog allergic patients. In fact, clinical consequences of this sensitization regard respiratory allergy (burden of rhinitis/asthma), systemic reactions (anaphylaxis during sexual intercourse from cross-reaction with human prostatic antigen), allergen immunotherapy-AIT (likely ineffective in patients with exclusive sensitization), and preventive measures (possibility to own a female dog and a likely reduction of allergen passive transport). Further studies are needed to better explore these aspects in "real life".

Dog allergy: can a prevalent or exclusive sensitization to Can f 5 be considered a lucky or negative event in real life?

Summary: Recent studies have shown the increasing relevance of allergic sensitization to Can f 5 (a prostatic kallikrein), which is an androgen-regulated protein expressed in the prostate and detectable only in male dogs. Can f 5 can be a prevalent or exclusive sensitizing agent in a considerable percentage of dog-allergic patients. Its specific allergenic characteristics are able to induce possible negative as well as positive clinical effects in individuals sensitized to dogs. In the present article we pointed out the possible pros or cons of sensitization to this allergen in real life. Further studies should be carried out to correctly assess some peculiar characteristics of Can f 5, in order to support the most of positive aspects and remedy at best the negative effects.

Critical aspects in dog allergen immunotherapy (DAI). May Component Resolved Diagnosis (CRD) play a role in predicting the efficacy?

We hypothesize that a pivotal condition determining the efficacy of dog allergen immunotherapy (DAI) might be the mono-sensitization to dog lipocalins (Can f 1-2) in individuals not directly or indirectly exposed to other furry animals. In fact, the concomitant sensitization to lipocalins and/or albumins, especially in those patients directly exposed to furry animals, may potentially stimulate patient's airways by inducing persistent inflammation and, thus, clinical symptoms. In these conditions, it is likely that DAI alone could be inadequate to reduce airway inflammation mediated by inhalation of dog allergens in patients with simultaneous exposure to other furry animals. Can f 5 has been found as exclusive allergen in about one third of dog-sensitized individuals. Considering the presence of different allergenic materials in extract of mammalian origin, it is evident that a standard DAI is not likely to be effective in Can f 5 prevalent or mono-sensitized individuals. Moreover, we would underline the need of collecting detailed information on the possible exposures to furry animals (other than the common pets), an information that usually is neglected in clinical practice. Furthermore, a detailed clinical history exploring the real significance of dog sensitization (mono or poly-sensitization, induction of clinical symptoms after exposure etc.) should be performed before prescribing DAI. In some patients, with potential high susceptibility to animal allergens, the use of CRD is essential to verify the presence of concomitant allergic sensitization to lipocalins and/or albumins belonging to other furry animals. The availability of CRD introduced the possibility of a better targeted prescription of DAI because it might be useful for point out the primary allergens and for the exclusion of cross-reactive ones.

Canis familiaris allergen Can f 6: expression, purification and analysis of B-cell epitopes in Chinese dog allergic children.

Dog allergy is common worldwide. However, the allergenicity of dog allergy is still unclear in China as well as in special group, such as children. In this study, we chose Can f 6, a major dog allergen which belongs to the lipocalin to study its allergenicity in Chinese dog allergic children. Can f 6 gene was subcloned into pET-28a vector and transformed into E. coli BL21 (DE3) cells for expression. The recombinant Can f 6 was purified by nickel affinity chromatography, identified by SDS-PAGE, and tested for its allergenicity by Western blot with sera and basophil activation test. Secondary structures, B cell epitopes and homology modeling of Can f 6 were predicted by using a series of bioinformatical approaches. And the verification of B cell epitopes was detected by ELISA. The recombinant allergen showed an explicit band with the molecular weight of 20 kDa by SDS-PAGE. Sera from 56.3 % (18/32) of dog-allergic children patients reacted with Can f 6. The induction of the expression of CD63 and CCR3 of dog allergic children in passively sensitized basophils was up to approximately 5.0 times higher than healthy subjects. The secondary structure of Can f 6 contains 3 α-helices, 9 ß-sheets and random coils. Five B cell epitopes of Can f 6 were predicted and were confirmed successfully by ELISA. The results showed Can f 6 is a major allergen in Chinese children, which provides a basis for further study of Can f 6 in diagnosis and treatment of symptoms in children in China. The structural information of Can f 6 will help to form a foundation for the future design of vaccines and therapies for Can f 6 related allergies.

The cat lipocalin Fel d 7 and its cross-reactivity with the dog lipocalin Can f 1.

We investigated the prevalence of sensitization to the cat lipocalin Fel d 7 among 140 cat-sensitized Swedish patients and elucidated its allergenic activity and cross-reactivity with the dog lipocalin Can f 1. Sixty-five of 140 patients had IgE to rFel d 7 whereof 60 also had IgE to rCan f 1. A moderate correlation between IgE levels to rFel d 7 and rCan f 1 was found. rFel d 7 activated basophils in vitro and inhibited IgE binding to rCan f 1 in 4 of 13 patients, whereas rCan f 1 inhibited IgE binding to rFel d 7 in 7 of 13 patients. Fel d 7 and Can f 1 showed high similarities in protein structure and epitopes in common were found using cross-reactive antisera. Fel d 7 is a common allergen in a Swedish cat-sensitized population that cross-reacts with Can f 1, and may contribute to symptoms in cat- but also in dog-allergic patients.

Can the presence of cat/dog at home be considered the only criterion of exposure to cat/dog allergens? A likely underestimated bias in clinical practice and in large epidemiological studies.

An important aspect of allergic sensitization to furry animals is the association of dog and cat exposure in early childhood with the incidence of respective allergies later in life. This topic is very controversial, because some authors have found a "facilitating" effect, while others have noticed a "protective" or even no significant effect in individuals living in urban areas. It is likely that some biases could be responsible of these contradictory findings. Cat/dog ownership or their presence in indoor environments are considered usually the main criteria to assess the exposure to these pets in studies' questionnaires. Even in clinical practice "are there animals at home?" is the common query usually done when collecting anamnestic data. In our opinion, these commonly used questions should not be considered the main index of exposure to pet allergens, because they can lead to erroneous interpretation of the clinical significance of positive skin prick tests for pet allergens as well as of the real risk of exposure to allergens of dog/cat in epidemiological studies. Consequently, we suggest a new, more realistic, classification of modalities of exposure to pet allergens in "real life" based on five possible conditions.

Dog and cat exposure and respective pet allergy in early childhood.

BACKGROUND: The association of dog and cat exposure in early childhood with the incidence of respective allergies has remained controversial. The aim of the study was to obtain population-based evidence on the association of early exposure to dog or cat, or both, with dog and cat allergies. METHODS: The study population was identified from the nationwide population register comprising all children aged 1-4 yr (N = 4779) born between 2001 and 2005 and living in the province of South Karelia, Finland. Cross-sectional questionnaire data on pet exposure in infancy and physician-diagnosed pet allergies were obtained from 3024 participants and merged with longitudinally accumulated data on sIgE and skin prick tests indicating allergic sensitization abstracted from all patient records in the area. RESULTS: The adjusted relative incidence of positive test results (with 95% confidence intervals) was 2.69 (1.45-5.02) for dog and 5.03 (2.47-10.2) for cat allergens among children exposed to a respective pet alone compared with children without such exposure. The corresponding adjusted prevalence odds ratios for diagnosed dog and cat allergies were 1.75 (0.77-3.79) and 5.13 (2.30-11.4), respectively. The association between pet exposure and the incidence of positive test results was independent of parents' allergies. CONCLUSIONS: Early exposure to dog and cat at home is associated with a higher incidence of respective pet allergy during the first four years of life. Further evidence from population-based studies with longer follow-up is required to justify any recommendation concerning early pet contacts with a view to preventing pet allergies later in life.