Canine atopic dermatitis (CAD) is a prevalent inflammatory skin disease of dogs worldwide. Certain breeds such as the West Highland White Terriers (WHWT) are predisposed to suffer from CAD. Microbial dysbiosis is known to play a significant role in the pathogenesis of the disease, which is similar to its human counterpart, atopic dermatitis (AD). To date, no large cohort-study has been conducted in a predisposed dog breed to study the impact of the early-life microbiota on the development of CAD, as well as the possible implication of factors such as hygiene and access to the outdoors. in this study skin samples of 143 WHWT, including 109 puppies up to three weeks old and 34 parent dogs, from 17 breeders, were subjected to 16S rRNA gene and ITS2 amplicon sequencing to disclose the bacterial and fungal oral and skin microbiota, respectively. The oral samples served as a control group to confirm differences between haired and mucosal surfaces. The cutaneous microbiota differed between sample sites and age of the dogs. The season of sampling, geographical origin as well as hygiene status of the household and the access to the outdoors shaped the skin microbiota of the puppies significantly. However, we found that the individual early-life microbiota did not predispose for the later development of CAD. Among the inflammatory skin diseases occurring in dogs, canine atopic dermatitis (CAD) is prevalent with up to 10% of dogs affected worldwide 1,2. CAD is a genetically predisposed inflammatory and pruritic allergic skin disease with characteristic clinical features associated with IgE antibodies most commonly directed against environmental allergens 3. Across species, similarities in the clinical manifestations of atopic dermatitis have been observed and the disease is becoming more common 4. In contrast to humans who may develop respiratory signs, dogs usually remain in the cutaneous stage of the disease 5. Nevertheless, CAD is frequently discussed as a model for human atopic dermatitis (AD). AD has a strong genetic component 6 , but its occurrence seems to be increasing in recent years due to environmental factors 2. Among the discussions about protective and risk factors, the hygiene hypothesis 7 has been prominent for many years. It speculates that early microbial exposure reduces the risk for developing allergies and, consequently, the improvement of hygiene may explain a rise in allergic diseases. This hypothesis has been

Background Canine atopic dermatitis (cAD) is a common allergic skin disease that is known to affect individuals early in life; the natural history of its initial development has not been documented. Some breeds such as West Highland white terriers (WHWTs) are highly predisposed to cAD. Objectives To follow 100 WHWT puppies during their first three years and to record the onset of clinical signs of cAD. Animals One hundred and eight puppies from 29 litters were included and 90 were followed for three years. Methods and materials Puppies were examined initially while with their breeders. After adoption, the owners were contacted twice each year and dogs were examined by veterinarians if signs compatible with cAD were detected; diagnosis of cAD was by two different definitions. The onset, location of the clinical signs and severity of cAD, as well as co‐morbidities were recorded. Results The prevalence of cAD in the cohort was 52%. Most affected dogs (60%) developed signs of cAD during their first year of life and males were over‐represented. The location of clinical signs mirrored those of previous descriptions. The severity of cAD was mild in 36% and severe in 13% of affected WHWTs. Dogs with cAD often exhibited other atopic diseases, but only gastro‐intestinal signs were significantly different between WHWTs with and without cAD. Adverse reaction to foods was diagnosed in 24% of dogs. Conclusion and clinical importance This longitudinal study of puppies from a predisposed breed sheds new light on the early development of cAD in WHWTs.

Toxocara canis-specific IgE appears to be a major component of total IgE in dogs. Total and T. canis-specific IgE levels are higher in non-atopic compared to atopic dogs. It is speculated that T. canis infection may have a protective effect against the development of canine atopic dermatitis and/or that elevations in total serum IgE level are often not associated with atopic dermatitis.

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BackgroundThere is accumulating evidence in studies of allergic diseases in humans and dogs that environmental experiences during the first months of life can influence the development of allergic disease. No prospective study has evaluated this in veterinary medicine.Hypothesis/ObjectivesTo assess early‐life risk factors for canine atopic dermatitis (cAD) and estimate its heritability.AnimalsA West Highland white terrier birth cohort (n = 107) followed up to three years of age recording the development of cAD.Methods and materialsThe effect of environmental factors [house dust mites (HDM), hygiene, feeding, lifestyle] and early‐life determinants [breeder, mode of delivery, birth season, sex, litter size, early‐life immunoglobulin E (IgE) levels] were assessed, using Stata SE 15.1 statistical analysis. Heritabilities were estimated using the R program packages MCMCglmm and QGglmm.ResultsMaternal allergic status [P = 0.013, odds ratio (OR 3.3)], male sex (P = 0.06), mode of delivery (P = 0.12), breeder (P = 0.06), presence of HDM (P = 0.11) and environmental hygiene level (P = 0.15) were identified as possible influence factors by bivariate analyses. In the multivariate analysis the male sex was significantly associated with the development of cAD in the offspring (P = 0.03, OR 2.4). The heritabilities on the observed scale were 0.31 (direct), 0.04 (maternal genetic effects) and 0.03 (maternal permanent environmental effects).Conclusion and clinical importanceThese results suggest that several environmental factors could influence the development of cAD but clearly demonstrate the genetic influence of the individual and the dam. Further studies are needed to identify specific environmental factors, which could be potential targets for primary disease intervention.