Update on the role of genetic factors, environmental factors and allergens in canine atopic dermatitis.

BACKGROUND: Canine atopic dermatitis (cAD) is a common, complex and multifactorial disease involving, among others, genetic predisposition, environmental factors and allergic sensitisation. OBJECTIVE: This review summarises the current evidence on the role of genetic and environmental factors and allergic sensitisation in the pathogenesis of cAD since the last review by ICADA in 2015. MATERIALS AND METHODS: Online citation databases and proceedings from international meetings on genetic factors, environmental factors and allergens relevant to cAD that had been published between 2015 and 2022 were reviewed. RESULTS: Despite intensive research efforts, the detailed genetic background predisposing to cAD and the effect of a wide range of environmental factors still need more clarification. Genome-wide association studies and investigations on genetic biomarkers, such as microRNAs, have provided some new information. Environmental factors appear to play a major role. Lifestyle, especially during puppyhood, appears to have an important impact on the developing immune system. Factors such as growing up in a rural environment, large size of family, contact with other animals, and a nonprocessed meat-based diet may reduce the risk for subsequent development of cAD. It appears that Toxocara canis infection may have a protective effect against Dermatophagoides farinae-induced cAD. House dust mites (D. farinae and D. pteronyssinus) remain the most common allergen group to which atopic dogs react. Currently, the major allergens related to D. farinae in dogs include Der f 2, Der f 15, Der f 18 and Zen 1. CONCLUSIONS AND CLINICAL RELEVANCE: Canine atopic dermatitis remains a complex, genetically heterogeneous disease that is influenced by multiple environmental factors. Further, well-designed studies are necessary to shed more light on the role of genetics, environmental factors and major allergens in the pathogenesis of cAD.

Update on the skin barrier, cutaneous microbiome and host defence peptides in canine atopic dermatitis.

BACKGROUND: Canine atopic dermatitis (AD) is a complex inflammatory skin disease associated with cutaneous microbiome, immunological and skin barrier alterations. This review summarises the current evidence on skin barrier defects and on cutaneous microbiome dysfunction in canine AD. OBJECTIVE: To this aim, online citation databases, abstracts and proceedings from international meetings on skin barrier and cutaneous microbiome published between 2015 and 2023 were reviewed. RESULTS: Since the last update on the pathogenesis of canine AD, published by the International Committee on Allergic Diseases of Animals in 2015, 49 articles have been published on skin barrier function, cutaneous/aural innate immunity and the cutaneous/aural microbiome in atopic dogs. Skin barrier dysfunction and cutaneous microbial dysbiosis are essential players in the pathogenesis of canine AD. It is still unclear if such alterations are primary or secondary to cutaneous inflammation, although some evidence supports their primary involvement in the pathogenesis of canine AD. CONCLUSION AND CLINICAL RELEVANCE: Although many studies have been published since 2015, the understanding of the cutaneous host-microbe interaction is still unclear, as is the role that cutaneous dysbiosis plays in the development and/or worsening of canine AD. More studies are needed aiming to design new therapeutic approaches to restore the skin barrier, to increase and optimise the cutaneous natural defences, and to rebalance the cutaneous microbiome.

Update on the role of cytokines and chemokines in canine atopic dermatitis.

BACKGROUND: Cytokines and chemokines play central roles in the pathogenesis of canine atopic dermatitis (cAD). Numerous studies have been published and provide new insights into their roles in cAD. OBJECTIVES: To summarise the research updates on the role of cytokines and chemokines in the pathogenesis of cAD since the last review by the International Committee on Allergic Diseases of Animals in 2015. MATERIAL AND METHODS: Online citation databases, abstracts and proceedings from international meetings on cytokines and chemokines relevant to cAD that had been published between 2015 and 2022 were reviewed. RESULTS: Advances in technologies have allowed the simultaneous analysis of a broader range of cytokines and chemokines, which revealed an upregulation of a multipolar immunological axis (Th1, Th2, Th17 and Th22) in cAD. Most studies focused on specific cytokines, which were proposed as potential novel biomarkers and/or therapeutic targets for cAD, such as interleukin-31. Most other cytokines and chemokines had inconsistent results, perhaps as a consequence of their varied involvement in the pathogenesis of different endotypes of cAD. CONCLUSIONS AND CLINICAL RELEVANCE: Inconsistent results for many cytokines and chemokines illustrate the difficulty of studying the complex cytokine and chemokine networks in cAD, and highlight the need for more comprehensive and structured studies in the future.

Evaluation of residual antibacterial effects on canine skin surface and hair following treatment with five commercial mousse products against Staphylococcus pseudintermedius.

BACKGROUND: Antibacterial effect studies of commercial antiseptics typically have evaluated hair and not the skin. OBJECTIVES: To evaluate the antibacterial effects of mousse products on both canine skin and hair. ANIMALS: Fifteen short-haired and eight long-haired dogs without skin disease. MATERIALS AND METHODS: Five mousses were applied once: (1) 2% chlorhexidine and 2% miconazole; (2) 0.05% phytosphingosine; (3) 2% salicylic acid and 10% ethyl lactate; (4) 3% chlorhexidine and 0.5% climbazole; and (5) 2% chlorhexidine and 1% ketoconazole. Skin swabs and hair were collected from application sites before treatment, and at 1 h and at Day (D)2, D4, D8, D10 and D14 post-treatment. Skin swabs and hair were placed on Mueller-Hinton plates inoculated with Staphylococcus pseudintermedius inoculum suspension. Inhibition zones were measured after incubation. RESULTS: Inhibition was not noted with mousses 2 and 3. In mousse 5, inhibition zone sizes produced by swabs from long- and short-haired dogs were not significantly different (p = 0.105), and all swabs and hair produced inhibition until D14, regardless of hair length. By contrast, in mousse 1, inhibition zones produced by swabs from long-haired dogs were smaller than those from short-haired dogs (p < 0.001), and swabs from long-haired dogs produced a shorter duration of bacterial inhibition than hair. CONCLUSIONS AND CLINICAL RELEVANCE: The antibacterial effects of mousse 5 were not affected by hair length. Hair may be acceptable for evaluating effects on the skin in short-haired dogs. However, long hair may interfere with product distribution and duration of bacterial inhibition. Therefore, the evaluation of hair alone may overestimate clinically relevant antibacterial effects.

Identification of major and minor chicken allergens in dogs.

BACKGROUND: Allergens targeted by serum-specific immunoglobulin E (sIgE) in dogs clinically allergic to chicken have not been reported. OBJECTIVES: To characterise the allergens targeted by sIgE in dogs sensitised and allergic to chicken. ANIMALS: Sera from three dogs not sensitised to chicken, from 10 chicken sensitised dogs and from 12 chicken allergic dogs. METHODS AND MATERIALS: Enzyme-linked immunosorbent assay (ELISA) and immunoblotting with a commercial chicken extract were utilized. The bands identified on immunoblotting were sequenced by mass spectrometry for allergen characterization. RESULTS: Using ELISA, we detected chicken-sIgE above the positive threshold in zero of three (0%) nonsensitised dogs, five of five (100%) chicken-sensitised dogs (a selection criterion), and in seven of 12 (58%) chicken-allergic dogs. Immunoblotting performed with the same extract revealed IgE-bound protein bands in 100% of all chicken-sensitised and -allergic dogs, respectively. To identify the allergens, we excised the corresponding bands on the electrophoretic gel, and submitted them for sequencing by mass spectrometry. We conclusively identified seven major allergens (serum albumin, pyruvate kinase M, enolase 3, creatine kinase M, lactate dehydrogenase A, glyceraldehyde-3-phosphate dehydrogenase and triose-phosphate isomerase) and one minor allergen (troponin C), which are relevant to dogs. CONCLUSIONS AND CLINICAL RELEVANCE: We identified herein seven major chicken allergens for dogs, several of which are known to be cross-reactive allergens for humans. Based on their degree of sequence identity, these allergens exhibit the theoretical potential to be cross-reactive between poultry and mammalian meats; six of these allergens already are known to be cross-reactive between chicken and fish species. Future studies should address the clinical relevance and cross-reactivity potential of these chicken allergens in dogs.

Clinical signs and diagnosis of feline atopic syndrome: detailed guidelines for a correct diagnosis.

BACKGROUND: Feline atopic syndrome (FAS) describes a spectrum of hypersensitivity disorders characterised by highly diverse clinical presentations including skin, gastrointestinal and respiratory systems. Among these disorders is feline atopic skin syndrome (FASS), in which hypersensitivity is typically associated with environmental allergens, although food allergy may coexist. Involvement of other organ systems (e.g. asthma) also may occur. Because of its highly heterogeneous clinical presentation, diagnosis of FASS can be challenging. OBJECTIVES: A subgroup of the International Committee on Allergic Diseases of Animals was tasked to summarise the most current information on the clinical presentations of FASS and to develop diagnostic guidelines. METHODS AND MATERIALS: Online citation databases and abstracts from international meetings were searched for publications related to feline allergic conditions. These were combined with expert opinion where necessary. RESULTS: A total of 107 publications relevant to this review were identified. Compilation of these data enabled development of a detailed description of the clinical features of FASS and development of guidelines focusing on systematic elimination of other skin conditions with similar clinical characteristics. As allergen tests are frequently used by dermatologists to support a clinical diagnosis of FASS, a brief review of these methodologies was also performed. CONCLUSIONS AND CLINICAL IMPORTANCE: In a similar way to atopic dermatitis in dogs, FASS is a clinical diagnosis based on the presence of compatible clinical signs and exclusion of other diseases with similar clinical features. Elimination or exclusion of fleas/flea allergy, other parasites, infections and food allergy is mandatory before reaching a diagnosis of FASS.

Feline allergic diseases: introduction and proposed nomenclature.

BACKGROUND: Feline allergic diseases present as challenging problems for clinicians, not least because of the number of reaction patterns of the feline skin, none of which are specific for allergy. Furthermore, there is some controversy over the nomenclature that should be used in their description. OBJECTIVES: To review the literature, assess the status of knowledge of the topic and the extent to which these diseases could be categorized as atopic in nature, and make recommendations concerning nomenclature. METHODS: Atopic diseases in humans and cats were researched. A comparison then was made of the essential features in the two species. RESULTS: There were sufficient similarities between human atopic diseases and the manifestations of feline diseases of presumed allergic aetiology to justify the use of "atopic" to describe some of the feline conditions affecting the skin, respiratory and gastrointestinal tract. However, none of the allergic skin diseases showed features consistent with atopic dermatitis as described in man and the dog. CONCLUSIONS AND CLINICAL IMPORTANCE: The term "Feline Atopic Syndrome" (FAS) is proposed to encompass allergic diseases of the skin, gastrointestinal tract and respiratory tract, and "Feline atopic skin syndrome" (FASS) proposed to describe allergic skin disease associated with environmental allergies. We are not aware of any adverse food reactions in cats that are attributable to causes other than immunological reactions against the food itself. We therefore propose an aetiological definition of "Food Allergy" (FA) to describe such cases.

Serum IgE and IgG responses to dietary antigens in dogs with and without cutaneous adverse food reactions.

BACKGROUND: It is suspected that many canine cutaneous adverse food reactions (CAFR) are true immunological hypersensitivities; however, few specific dietary allergens have been identified. OBJECTIVE: To compare serum immunoglobulin (Ig)E and IgG reactivity to specific food antigens in privately owned dogs with and without CAFR. ANIMALS: Eighteen adult dogs with nonseasonal pruritus recruited from a hospital population. METHODS AND MATERIALS: Dogs were fed an extensively hydrolysed poultry-based diet exclusively for 12 weeks. Serum was collected at the beginning of the trial. Canine atopic dermatitis extent and severity index and pruritus Visual Analog Scale scoring were performed at the beginning and end of the trial. Immunoblotting was performed to identify IgE and/or IgG binding to specific proteins in beef, egg, milk, chicken, pork, soy and wheat extracts. RESULTS: A CAFR (defined as an unequivocal relapse of pruritus after dietary challenge) was diagnosed in 10 dogs, with 60% relapsing when fed chicken-based diets. Binding of subjects' IgG to almost all proteins in all extracts was seen regardless of reported dietary history. Few proteins were exclusively or predominantly bound by IgE in CAFR dogs. Exceptions included a 42 kDa band (chicken), a 52 kDa band (beef), a 46 kDa band (beef and milk) and a poorly defined high molecular weight protein or proteins (beef and milk). CONCLUSION: This study demonstrated three protein bands and a poorly defined band predominantly recognized by sera from dogs with CAFR relative to non-CAFR dog sera. Almost all proteins were bound by IgG in all dogs, suggesting prior exposure to unreported foods.

Invasive histiocytoma in the ear canal of a dog.

BACKGROUND: Cutaneous histiocytomas (CH) are derived from epidermal Langerhans cells. Single CH are generally associated with a good prognosis in dogs because most undergo spontaneous remission. However, aggressive behaviour and lymph node metastasis have been reported in a small number of dogs with single CH. OBJECTIVE: To describe the clinical presentation, treatment and disease progression of an aggressive CH located in the ear canal of a dog. ANIMAL: An 8-year-old intact male Rottweiler dog. METHODS AND MATERIALS: A unilateral ear canal mass was identified as a CH on routine haematoxylin and eosin stained samples. The diagnosis was confirmed by the demonstration of markers associated with Langerhans cells (Iba-1, E-cadherin and CD18) and the absence of markers associated with B cells (CD79a, CD20, Pax5), T cells (CD3), plasma cells (Mum-1) and macrophages (CD11d, CD204). RESULTS: A total ear canal ablation was performed, but tumour cells extended throughout the horizontal canal and to the deep surgical margin. Due to the locally invasive nature of the mass and incomplete excision, adjunctive chemotherapy with CCNU was pursued. No measurable local disease was appreciable at the time of the last treatment. At 250 days post-surgery the dog was euthanized owing to the development of multiple abdominal masses. No evidence of local tumour recurrence was noted. CONCLUSIONS AND CLINICAL IMPORTANCE: Although single CH are typically associated with benign behaviour, the mass in this dog demonstrated locally invasive behaviour. Cutaneous histiocytomas in the ear canals of dogs may represent a particularly aggressive variant of the condition.

Residual antibacterial activity of canine hair treated with five mousse products against Staphylococcus pseudintermedius in vitro.

BACKGROUND: Topical therapy alone can be effective in the treatment of canine pyoderma. Topical products are commercially available as shampoos, sprays, wipes and mousses. To date, no studies have evaluated the efficacy of commercially available mousse products in the treatment of canine pyoderma. OBJECTIVE: To determine the residual antibacterial activity of canine hairs treated with mousse products containing different active ingredients. ANIMALS: Fifteen client-owned dogs with no history of dermatological disease. METHODS AND MATERIALS: Dogs were treated once with five mousse products [(i) 2% chlorhexidine and 1% ketoconazole, (ii) 2% chlorhexidine and 2% miconazole, (iii) 3% chlorhexidine and 0.5% climbazole, (iv) 2% salicylic acid 10% ethyl lactate and (v) phytosphingosine HCl 0.05%; control]. Hair samples were collected from each treatment area before application, one hour after application and on days 2, 4, 7, 10 and 14 post-treatment. Collected hairs were weighed and plated on Mueller-Hinton agar plates streaked with a Staphylococcus pseudintermedius isolate showing no antimicrobial resistance. Plates were incubated for 24 h and bacterial growth inhibition zones around the hairs were measured. RESULTS: Mousses 1, 2 and 3 created significant inhibition zones up to Day 10 when compared to pre-treatment samples. On Day 14, only mousse 3 produced a significant zone of inhibition when compared to the pre-treatment sample. Mousses 4 and 5 showed no statistical difference between any of the samples. CONCLUSIONS AND CLINICAL IMPORTANCE: These results suggest that three of the mousse products had residual activity in inhibiting S. pseudintermedius growth in vitro for at least 10 days.

Determination of irritant threshold concentrations of multiple tree, grass, weed and mould allergens for intradermal testing of horses residing in the southern USA.

BACKGROUND: Appropriate allergen threshold concentrations (TCs) for intradermal testing (IDT) have not been established in horses for many pollen and mould allergens. OBJECTIVES: To determine the TCs in non-allergic horses and describe the frequency of late phase reactions for 26 allergens, including trees, grasses, weeds and moulds in horses residing in the southern Unites States. ANIMALS: Twenty four clinically normal horses in the southern United States. METHODS: Threshold concentrations for different allergens were determined using IDT subjective measurements at 30 minutes. Delayed reactions were evaluated at 4 and 24 h. RESULTS: Threshold concentrations (all PNU/mL) were established for eight tree allergens (black willow 1,000, box elder 1,000, live oak 1,000, pecan 2,000, white ash 4,000, red oak 4,000, red mulberry 2,000 and green ash 2,000); two grass allergens (Johnson grass 250 PNU/mL and Kentucky blue grass 500 PNU/mL); two weeds (carelessweed 1,000 PNU/mL, great ragweed 500 PNU/mL) and one mould (Curvularia 8,000 PNU/mL). The TC was not determined due to excessive reactivity at the lowest concentration tested (1,000 PNU/mL) for bahia and perennial rye grass. Eleven other allergens did not meet the criteria to establish a TC when evaluated at 30 min due to lack of positive reactions. Multiple allergens caused positive reactions in ≥10% of horses at 4 h. Reactions at 24 h were rare with the exception of one horse. CONCLUSIONS AND CLINICAL IMPORTANCE: This study identified intradermal TC for multiple pollen and mould allergens in horses. These values may prove useful for optimizing allergen concentrations for IDT of allergic horses.

Sepsis and multi-organ dysfunction associated with postgrooming furunculosis in a dog.

BACKGROUND: Postgrooming furunculosis, as previously described in the dog, is a type of pyoderma that typically responds to routine antimicrobial therapy. Systemic clinical signs are common but are usually mild. ANIMAL: A 3-year-old spayed female great dane was presented with marked dorsal furunculosis of 24 h duration. The clinical signs and blood analyses were consistent with sepsis, systemic inflammatory response syndrome and disseminated intravascular coagulopathy (DIC). METHODS AND RESULTS: Skin culture revealed multi-drug resistant Pseudomonas aeruginosa infection. The dog did not respond to aggressive medical therapy including intravenous antibiotic therapy, fresh frozen plasma and haemodynamic support, and was humanely euthanized. Postmortem findings were consistent with postgrooming furunculosis with associated sepsis and DIC affecting multiple organs including the lungs and brain. CONCLUSIONS AND CLINICAL IMPORTANCE: Postgrooming furunculosis can progress to sepsis and multiple organ dysfunction in the dog and can lead to death.

Dorsal skin necrosis secondary to a solar-induced thermal burn in a brown-coated dachshund.

A 5-year-old neutered male brown dachshund dog was presented for a large dorsal cutaneous burn that occurred following direct sunlight exposure outdoors in high ambient temperatures. Although burns are quite common in dogs, full-thickness solar-induced radiation burns are less common and have not been previously reported in animals without a black hair coat.

Nécrose de la peau dorsale secondaire à une brûlure thermique induite par l'exposition au soleil chez un Dachsund à pelage brun. Un chien Dachsund brun stérilisé âgé de 5 ans a été présenté pour une grande brûlure cutanée dorsale qui s'était produite après une exposition directe au soleil à l'extérieur durant des températures élevées. Même si les brûlures sont assez courantes chez les chiens, les brûlures du troisième degré causées par l'exposition au soleil sont moins communes et n'ont pas déjà été signalées chez des animaux sans un pelage à poil noir.(Traduit par Isabelle Vallières).

Review: Lymphocytes, cytokines, chemokines and the T-helper 1-T-helper 2 balance in canine atopic dermatitis.

BACKGROUND: The development of atopic dermatitis (AD) and other cutaneous hypersensitivities involves the activation and differentiation of allergen-specific lymphocytes. Although hypersensitivity is often considered to be a 'T-helper 2-polarized' lymphocyte response, recent evidence suggests that clinical disease is associated with the development of multiple lymphocyte phenotypes. OBJECTIVES: The purpose of this paper is to review recent advances in the understanding of the roles of lymphocytes, cytokines and noncytokine factors in the pathogenesis of canine AD. METHODS: Citation databases, abstracts and proceedings from international meetings published between 2001 and 2013 were reviewed in this update. Where necessary, older articles were included for background information. RESULTS: The development of canine AD is associated with changes in both cutaneous and circulating lymphocyte populations. These lymphocyte responses are characterized by the production of a complex variety of cytokines, including not only T-helper 2 but also T-helper 1, T-helper 17 and regulatory T-cell responses. In addition, microarray gene expression analysis has enabled the identification of a number of noncytokine factors that appear to be associated with atopic inflammation. These include the calcium-binding protein S100A8, serum amyloid A and a number of protease inhibitors, as well as genes involved in epidermal barrier formation, innate immunity receptors, cell cycle proteins and apoptosis. CONCLUSIONS: The development of AD in dogs is characterized by the development of a delicate balance between a variety of T-cell phenotypes and inflammatory mediators, including cytokines, chemokines and noncytokine factors.

Review: Innate immunity, lipid metabolism and nutrition in canine atopic dermatitis.

BACKGROUND: The pathogenesis of canine atopic dermatitis (AD) involves dysfunction of the adaptive immune system. Recent evidence suggests that nonantigen-specific inflammatory elements may play a role in the development and perpetuation of canine AD. OBJECTIVES: The objective of this review is to provide an update on recent advances in the understanding of the role of innate immune cells, keratinocytes, lipid metabolism and nutrition in the pathogenesis of AD in dogs. METHODS: Citation databases, abstracts and proceedings from international meetings published between 2001 and 2013 are reviewed in this update. Where necessary, older articles are included for background information. RESULTS: Members of the innate immune system (including dendritic cells, Langerhans cells and mast cells) and keratinocytes interact with each other and with environmental antigens during both induction and effector phases of atopic inflammation. The responses of these cells and associated noncellular factors (such as complement and protease-activated receptors) to environmental stimuli influence the entire future course of the immune response to a given agent. Abnormalities in lipid metabolism may also influence the pathogenesis of canine AD via the production of inflammatory mediators and by alteration of epidermal barrier function and antigen presentation. However, a lack of fully controlled studies precludes definitive interpretation of these data. CONCLUSIONS AND CLINICAL IMPORTANCE: Evidence indicates that the cells and noncellular components of the innate immune system and the epidermis may play critical roles during both the sensitization and the effector phases of canine AD. Derangements in lipid metabolism may be involved in the pathogenesis of AD in dogs, but additional controlled studies are required in this area.

Review: The role of antibodies, autoantigens and food allergens in canine atopic dermatitis.

BACKGROUND: Canine atopic dermatitis (AD) is considered to be an immunoglobulin E (IgE)-mediated hypersensitivity response to environmental allergens. The role of other antibody isotypes and nonenvironmental allergens in disease pathogenesis remains unclear. OBJECTIVES: The objective of this review is to provide an update on advances in the understanding of the relevance of specific antibody isotypes, autoallergens and nonenvironmental allergens in the pathogenesis of canine AD. METHODS: Citation databases, abstracts and proceedings from international meetings published between 2001 and 2013 were reviewed. Where necessary, older articles were included for background information. RESULTS: Neither total nor allergen-specific IgE necessarily correlates with clinical disease in canine AD. Some dogs exhibit clinical signs that are indistinguishable from AD but have no demonstrable allergen-specific IgE (atopic-like dermatitis). Allergen-specific immunoglobulin G may be demonstrated in canine AD, but there is no evidence that this isotype plays a role in disease development. Although humans with AD may develop serum IgE against autoallergens, this finding has not been substantiated in the dog. In contrast, adverse food reactions are frequently co-associated with AD in the dog. Ingestion of food and environmental allergens may trigger exacerbations of AD. CONCLUSIONS AND CLINICAL IMPORTANCE: Determination of the role of IgE in the pathogenesis of canine AD still requires clarification. Clinical trials and research studies must distinguish atopic dogs with allergen-specific IgE or skin test reactivity from those without. There is no convincing evidence demonstrating a pathogenic role for either allergen-specific immunoglobulin G or autoallergens in canine AD, but food items may be triggers for disease flares in certain individuals.

Review: Role of genetics and the environment in the pathogenesis of canine atopic dermatitis.

BACKGROUND: Multiple levels of evidence support the role of genetics and the environment in the pathogenesis of canine atopic dermatitis (AD). OBJECTIVES: This review summarizes the current evidence in genetics and the effect of environmental factors on the development and perpetuation of canine AD. METHODS: Citation databases, abstracts and proceedings from international meetings published between 2001 and 2013 were reviewed in this update. Where necessary, older articles were included for background information. RESULTS: Canine AD is a heritable disease, in which interaction with environmental factors influences disease risk and phenotype. A study of British guide dogs indicated that nearly 50% of the risk of developing AD was determined by an individual's genotype. Genomic studies performed so far in canine AD have uncovered numerous gene candidates likely to be involved in pathogenesis through their role in immunity, skin barrier formation, apoptosis and inflammation. In addition to genetics, there is evidence to suggest that exposure to certain environmental factors influences the prevalence and course of canine AD. For example, living in rural areas or feeding noncommercial diets was negatively associated with the development of AD in dogs, while exposure to high levels of smoke was associated with increased prevalence of allergic skin disease. CONCLUSIONS: It is becoming clear that canine AD is genotypically complex and influenced by a variety of environmental factors. Well-designed studies with sufficient statistical power will be critical to identify the complex genetic and environmental factors involved in disease development and progression. Recognition of such factors may help to identify new targets for therapy and enable better disease prevention and management.

Review: Pathogenesis of canine atopic dermatitis: skin barrier and host-micro-organism interaction.

BACKGROUND: Canine atopic dermatitis (AD) is a common, genetically predisposed, inflammatory and pruritic skin disease. The pathogenesis of canine AD is incompletely understood. OBJECTIVES: The aim of this review is to provide an in-depth update on the involvement of skin barrier and host-microbiome interaction in the pathogenesis of canine AD. METHODS: Online citation databases and abstracts from international meetings were searched for publications related to skin barrier and host-microbiome interaction (e.g. bacteria, yeast, antimicrobial peptides). RESULTS: A total of 126 publications were identified. This review article focuses on epidermal barrier dysfunction and the interaction between cutaneous microbes (bacteria and yeasts) and the host (antimicrobial peptides). Epidemiological updates on the presence of pathogenic organisms and canine AD are also provided. CONCLUSIONS AND CLINICAL IMPORTANCE: Major advances have been made in the investigation of skin barrier dysfunction in canine AD, although many questions still remain. Skin barrier dysfunction and host-microbiome interactions are emerging as primary alterations in canine AD. Based on this review, it is clear that future studies focused on the development of drugs able to restore the skin barrier and increase the natural defences against pathogenic organisms are needed.

Review: Clinical and histological manifestations of canine atopic dermatitis.

BACKGROUND: Many studies focusing on clinical and histological signs of canine atopic dermatitis (AD) have been published since its early descriptions decades ago. Findings of these studies contributed to our current knowledge about the disease pathogenesis and allowed establishment of diagnostic criteria used by clinicians and researchers. OBJECTIVES: This review serves as an update on the clinical and histological features of canine AD published by the American College of Veterinary Dermatology Task Force on Canine Atopic Dermatitis in 2001 and summarizes the recent discoveries in these fields. RESULTS: The overall findings of studies focusing on clinical features mirrored those published by the Task Force in 2001. The novelty was the larger number of animals included in these studies, which allowed establishment of a new set of diagnostic criteria that exceeded the sensitivity and specificity of the previous criteria. The same study uncovered some clinical differences between dogs with food-induced and nonfood-induced AD; however, the authors concluded that these two entities cannot be distinguished based on clinical signs only. Another study demonstrated some major breed-specific phenotypes. Several publications addressed the histological features of canine AD skin lesions in experimental models of AD, but none of those addressed naturally occurring lesions. Nevertheless, the histopathological description of the skin reactions was generally similar to that published by the Task Force in 2001. CONCLUSIONS: Considerable work has been done in recent years to provide a better definition of the clinical appearance and histopathology of canine AD. New sets of diagnostic criteria have been developed, and additional breed-associated differences in phenotypes have been demonstrated.