Thierry Olivry

Treatment of canine atopic dermatitis: 2010 clinical practice guidelines from the International Task Force on Canine Atopic Dermatitis

Atopic dermatitis (AD) is a common chronic relapsing pruritic skin disease of dogs for which treatment has varied over time and geographical location. Recent high quality randomized controlled trials and systematic reviews have established which drugs are likely to offer consistent benefit. The International Task Force for Canine AD currently recommends a multi-faceted approach to treat dogs with AD. Acute flares should be treated with a combination of nonirritating baths and topical glucocorticoids, once an attempt has been made to identify and remove the suspected causes of the flare. Oral glucocorticoids and antimicrobial therapy must be added when needed. In dogs with chronic AD, a combination of interventions should be considered. Again, factors that trigger flares of AD must be identified and, if possible, avoided. Currently recognized flare factors include food, flea and environmental allergens, Staphylococcus bacteria and Malassezia yeast. Skin and coat hygiene and care must be improved by bathing with nonirritating shampoos and dietary supplementation with essential fatty acids. The severity of pruritus and skin lesions can be reduced with a combination of anti-inflammatory drugs. Currently, medications with good evidence of high efficacy include topical and oral glucocorticoids, and calcineurin inhibitors such as oral ciclosporin and topical tacrolimus. The dose and frequency of administration of these drugs should be tailored to each patient considering each drugs efficacy, adverse effects and cost. Allergen-specific immunotherapy should be offered, whenever feasible, in an attempt to prevent recurrence of clinical signs upon further exposure to environmental allergens to which the patient is hypersensitive.

Langerhans cell hyperplasia and IgE expression in canine atopic dermatitis.

Langerhans cells appear to be critical for IgE-mediated allergen capture and presentation in human atopic dermatitis. The present study sought to determine whether epidermal (i.e Langerhans cells) and dermal dendritic cells in the skin of dogs with atopic dermatitis are hyperplastic and expressed surface IgE. Frozen sections of lesional or nonlesional atopic and normal control canine skin were immunostained with CD1a-, CD1c-, and IgE-specific monoclonal antibodies. The enumeration of cells was performed by morphometry in both the epidermis and the dermis. Cell counts were compared with each individual’s total serum IgE levels. Higher numbers of epidermal and dermal dendritic cells were present in atopic dogs than in normal control animals. Epidermal Langerhans cell counts were significantly higher in lesional than in nonlesional atopic specimens. IgE+ dendritic cells were observed in lesional atopic epidermis and dermis, and nonlesional atopic dermis, but not in normal control skin specimens. The percentages of IgE+ dendritic cells were correlated with each patient’s total serum IgE levels. These results demonstrate dendritic cell hyperplasia and IgE expression in canine atopic dermatitis. Increased epidermal Langerhans cell counts in lesional specimens suggest an epidermal allergen contact in canine atopic dermatitis.

CHARACTERIZATION AND CLONING OF A MAJOR HIGH MOLECULAR WEIGHT HOUSE DUST MITE ALLERGEN (DER F 15) FOR DOGS

Although house dust mites (HDM(s)) are important elicitors of canine allergy, the low molecular weight molecules defined as major allergens for humans do not appear to be major allergens for dogs. Western blotting of Dermatophagoides farinae (D. farinae) extracts with sera from sensitized dogs showed that the majority of animals had IgE antibodies specific for two proteins of apparent molecular weights of 98 and 109kDa (98/109kDa). The N-terminal sequences of these two proteins were identical, suggesting they were very closely related, and sequencing of internal peptides showed the protein(s) to have homology with insect chitinases. A purified preparation of 98/109kDa proteins elicited positive intradermal skin tests (IDST(s)) in a group of well-characterized atopic dogs sensitized to D. farinae, but not in normal dogs. A rabbit polyclonal antiserum raised against the purified proteins was used to immunoscreen a D. farinae cDNA library. The mature coding region of the isolated chitinase cDNA predicts a protein of 63.2kDa; sequence analysis and glycan detection blotting suggest that the molecule is extensively O-glycosylated. Monoclonal antibodies made against the purified native protein were used to localize the chitinase in sections of whole D. farinae mites. The protein displayed an intracellular distribution in the proventriculus and intestine of the mite, suggesting that it has a digestive, rather than a moulting-related, function. The high prevalence of IgE antibodies to this antigen in canine atopic dermatitis makes it a major HDM allergen for dogs, and the protein has been formally designated Der f 15.

Interventions for atopic dermatitis in dogs: a systematic review of randomized controlled trials

The objective of this systematic review, which was performed following the guidelines of the Cochrane collaboration, was to assess the effects of interventions for treatment of atopic dermatitis (AD) in dogs. Citations identified from three databases (MEDLINE, Thomsons Science Citation Index Expanded and CAB Abstracts) and trials published by December 2007 were selected. Proceedings books from the major veterinary dermatology international congresses were hand searched for relevant citations. The authors selected randomized controlled trials (RCTs), published from January 1980 to December 2007, which reported the efficacy of topical or systemic interventions for treatment or prevention of canine AD. Studies had to report assessments of either pruritus or skin lesions, or both. Studies were selected and data extracted by two reviewers, with discrepancies resolved by a third arbitrator. Missing data were requested from study authors of recently published trials. Pooling of results and meta-analyses were performed for studies reporting similar interventions and outcome measures. A total of 49 RCTs were selected, which had enrolled 2126 dogs. This review found some evidence of efficacy of topical tacrolimus (3 RCTs), topical triamcinolone (1), oral glucocorticoids (5), oral ciclosporin (6), subcutaneous recombinant gamma-interferon (1) and subcutaneous allergen-specific immunotherapy (3) to decrease pruritus and/or skin lesions of AD in dogs. One high-quality RCT showed that an oral essential fatty acid supplement could reduce prednisolone consumption by approximately half. Additional RCTs of high design quality must be performed to remedy previous flaws and to test interventions for prevention of flares of this disease.

Toward a canine model of atopic dermatitis: amplification of cytokine-gene transcripts in the skin of atopic dogs

Abstract: The objectives of the present study were to characterize and compare the repertoire of cytokine‐genes transcribed in skin homogenates obtained from normal dogs and dogs with atopic dermatitis (AD) using a reverse‐transcriptase polymerase chain reaction and canine‐specific cytokine‐gene primers. Whereas IL‐4 and IL‐5 cytokine‐gene transcripts were detected more commonly in atopic skin biopsy homogenates, IL‐2 mRNA was amplified more often from normal control specimens. IFN‐γ mRNA was detected in 5/29 atopic specimens, 4 of them obtained from the only dog with chronic skin lesions. One‐fourth of atopic samples exhibited clear type‐2 cytokine profiles; the remainder did not demonstrate polarized repertoires. Conversely, type‐1 cytokine profiles were characterized in one‐fourth of normal control specimens. The present study establishes, for the first time, the transcription of type‐2 cytokine‐genes in the skin of dogs with AD. Future experiments investigating the cellular origin and dynamics of allergic cytokine‐gene transcription are needed to confirm whether or not canine AD could be considered an immunological model for a human disease.

Current evidence of skin barrier dysfunction in human and canine atopic dermatitis

Atopic dermatitis (AD) is a multifaceted disease resulting from a complex interaction between environmental and genetic factors. Both of these factors can shape skin barrier function and the immunological response of predisposed patients. There is increasing evidence that an impaired skin barrier plays a role in both human and canine AD. Although many primary skin barrier defects had already been documented in the past in humans, the recent identification of the filaggrin mutations and the fact that such mutations are now considered the most important risk factor for development of AD have further emphasized the relevance of epidermal dysfunction in human AD. Much less is known in veterinary medicine, but evidence is rapidly building to support a role for skin barrier dysfunction in canine AD. Canine AD shares many clinical and immunological similarities with its human counterpart. The similar distribution of clinical lesions and the importance of the epicutaneous route of allergen exposure provided the incentive to investigate the role of skin barrier impairments in canine AD. The purpose of this comparative review is to present the current evidence of barrier dysfunction in both human and canine AD.

Electron Microscopic Observations of Stratum Corneum Intercellular Lipids in Normal and Atopic Dogs

The barrier function of mammalian skin is maintained by intercellular stratum corneum lipids. In human patients with atopic dermatitis, an abnormal lipid barrier results in dry skin and increased transepidermal water loss. At this time, it is not known if a defective lipid barrier is present in atopic dogs. Normal and atopic canine skin were postfixed in ruthenium tetroxide and studied using transmission electron microscopy to determine structural differences within stratum corneum lipids. Intercellular lipid lamellae were graded on a semiquantitative scale. The deposition of stratum corneum lipid lamellae in atopic canine skin appeared markedly heterogeneous compared with that seen in normal canine skin. When present, the lamellae often exhibited an abnormal structure. The continuity and thickness of the intercellular lipid lamellae were significantly less in nonlesional atopic than in normal canine skin. These preliminary observations suggest that the epidermal lipid barrier is defective in atopic canine skin. Additional studies are needed to further characterize the biochemical defect and to possibly correct it with nutritional and/or pharmacologic intervention.

The Skin Microbiome in Healthy and Allergic Dogs

Background Changes in the microbial populations on the skin of animals have traditionally been evaluated using conventional microbiology techniques. The sequencing of bacterial 16S rRNA genes has revealed that the human skin is inhabited by a highly diverse and variable microbiome that had previously not been demonstrated by culture-based methods. The goals of this study were to describe the microbiome inhabiting different areas of the canine skin, and to compare the skin microbiome of healthy and allergic dogs. Methodology/Principal Findings DNA extracted from superficial skin swabs from healthy (n = 12) and allergic dogs (n = 6) from different regions of haired skin and mucosal surfaces were used for 454-pyrosequencing of the 16S rRNA gene. Principal coordinates analysis revealed clustering for the different skin sites across all dogs, with some mucosal sites and the perianal regions clustering separately from the haired skin sites. The rarefaction analysis revealed high individual variability between samples collected from healthy dogs and between the different skin sites. Higher species richness and microbial diversity were observed in the samples from haired skin when compared to mucosal surfaces or mucocutaneous junctions. In all examined regions, the most abundant phylum and family identified in the different regions of skin and mucosal surfaces were Proteobacteria and Oxalobacteriaceae. The skin of allergic dogs had lower species richness when compared to the healthy dogs. The allergic dogs had lower proportions of the Betaproteobacteria Ralstonia spp. when compared to the healthy dogs. Conclusions/Significance The study demonstrates that the skin of dogs is inhabited by much more rich and diverse microbial communities than previously thought using culture-based methods. Our sequence data reveal high individual variability between samples collected from different patients. Differences in species richness was also seen between healthy and allergic dogs, with allergic dogs having lower species richness when compared to healthy dogs.

Comparison of Alopecia areata in Human and Nonhuman Mammalian Species

Alopecia areata (AA) is a nonscarring form of inflammatory hair loss in humans. AA-like hair loss has also been observed in other species. In recent years the Dundee experimental bald rat and the C3H/HeJ mouse have been put forward as models for human AA. AA in all species presents with a wide range of clinical features from focal, locally extensive, diffuse hair loss, to near universal alopecia. Histologically, all species have dystrophic anagen stage hair follicles associated with a peri- and intrafollicular inflammatory cell infiltrate. Autoantibodies directed against anagen stage hair follicle structures are a consistent finding. Observations on AA pathogenesis suggest nonhuman species can provide excellent models for the human disease. Ultimately, animal models will be used to determine the genetic basis of AA, potential endogenous and/or environmental trigger(s), mechanism(s) of disease initiation and progression, and allow rapid evaluation of new and improved disease treatments.

The ACVD task force on canine atopic dermatitis (XIX): general principles of therapy

The treatment of canine atopic dermatitis is multifaceted and consists of a combination of actions that include the use of allergen avoidance, anti-inflammatory agents, allergen-specific immunotherapy and antimicrobial drugs. The importance and order of these treatment steps vary from patient to patient. General recommendations for each of the therapeutic steps are highlighted in this paper. Specific details are covered in other papers of this issue.