Sulphido-leukotriene production from peripheral leukocytes and skin in clinically normal dogs and house dust mite positive atopic dogs

Pathogenesis of canine atopy has not been completely elucidated. In humans, sulphido-leukotrienes (s-LT) play a role in atopy, and increased production of s-LT occurs in the skin and peripheral leukocytes after allergen challenge. The study population included 16 clinically normal and 13 atopic dogs. All atopic dogs had in common a positive reaction (4+) to the intradermal injection of house dust mite (allergen of reference). Blood samples and skin biopsies were collected. Sulphido-LT synthesis by peripheral leukocytes after stimulation was measured, and no statistically significant difference was found between clinically normal and atopic dogs. Sulphido-LT concentrations in skin samples from stimulated and unstimulated sites were measured, and no statistically significant difference was detected between clinically normal and atopic dogs or between lesional and nonlesional skin within the atopic group. Clinical signs of atopic dogs were graded by owners and no correlation was found between their severity and cutaneous concentrations of s-LT. In this study there was no increase in s-LT synthesis in atopic dogs.     

Patch test reactions to house dust mites in dogs with atopic dermatitis

The purpose of this study was to determine the percentage of dogs with spontaneous atopic dermatitis that show a positive patch test reaction to a commercially available 20% house dust mites mixture containing equal parts of Dermatophagoides farinae and Dermatophagoides pteronyssinus in white petrolatum. In addition, we evaluated whether skin reactions induced after the epicutaneous application of house dust mites were clinically and histologically similar to naturally developed skin lesions of dogs with atopic dermatitis. Furthermore, we investigated if the reactions induced by house dust mites were true allergic reactions by comparing them to atopic lesional skin and to patch test reactions induced by an irritant substance (sodium lauryl sulphate). White petrolatum alone and nonlesional skin sites were used as negative controls. Macroscopic and microscopic evaluations of the patch test and control sites were performed in a blinded fashion at 48 and 72 h after patch test application. Microscopic results were evaluated in a qualitative and quantitative manner. A chi‐square test for homogenicity was used for the quantitative analysis to compare the proportion of each dermal inflammatory cell type among positive histopathological tested sites. P values ≤ 0.05 were considered significant. The study included 12 healthy nonatopic dogs and 13 dogs with nonseasonal atopic dermatitis. None of the nonatopic dogs reacted to house dust mites and white petrolatum. Ten (77%) of the 13 atopic dogs reacted macroscopically and histopathologically to house dust mites. Macroscopic reactions induced by house dust mites were characterized by erythema, oedema and papules. The macroscopic reactions induced by house dust mites were identical to lesional skin in 20% of the dogs and identical to reactions induced by sodium lauryl sulphate in 40% of the dogs. Qualitative histopathological findings showed that the reactions induced by house dust mites were similar to atopic lesional skin in 80% of the dogs and were similar to sodium lauryl sulphate in 20% of the dogs. Quantitative analyses showed that the proportion of neutrophils in reactions induced by sodium lauryl sulphate was significantly higher (P < 0.05) compared to house dust mites reactions, which could be a differentiator factor between an allergic and an irritant reaction. These results showed that the epicutaneous application of house dust mites in dogs with atopic dermatitis induced histopathological lesions similar to spontaneous atopic lesions in dogs. Therefore, this study demonstrated that house dust mites penetrated the skin of dogs with atopic dermatitis and induced an inflammatory response that resembled a true allergic reaction. Funding: Small Companion Animal Grant, University of Minnesota.     

Tolerability and clinical efficacy of oral immunotherapy with house dust mites in a model of canine atopic dermatitis: a pilot study

Atopic dermatitis (AD) is a chronic, life‐long disease. In humans, immunotherapy (IT) is the only treatment that can alter the course of AD. Oral IT is appealing owing to the ease of administration and the potential for increased compliance. The purposes of this study were to investigate the tolerability, clinical efficacy and effects on allergen‐specific IgE of oral IT using a canine AD model. Thirteen atopic beagles sensitized to house dust mites (HDMs) were randomly divided into two groups. One group received daily oral doses of HDMs while the other group received vehicle only for 7 months. The investigator evaluating the dogs was blinded to the allocation of treatments. Prior to and after 2 and 7 months of IT, dogs were challenged daily with HDMs for 3 days concurrently, and clinical signs were scored using a modified Canine Atopic Dermatitis Extent and Severity Index (CADESI). Prior to and at completion of oral IT, serum was collected for measurement of allergen‐specific IgE. Oral IT was well tolerated, and no adverse effects were noted. Analysis of variance showed no significant effect of time, group and group × time interaction for CADESI scores. In addition, there were no significant differences in allergen‐specific IgE levels. In conclusion, it appears that oral administration of HDMs is well tolerated in these atopic beagles but that this protocol was not sufficient to induce clinical improvement. Further, longer‐term studies will be necessary to explore the potential of oral IT in veterinary medicine.     

House dust and forage mite allergens and their role in human and canine atopic dermatitis

This article reviews the literature regarding the role of house dust and forage mite allergens in canine atopic dermatitis. The presence of immunoglobulin E (IgE) to these mites, especially to Dermatophagoides farinae, is common in both normal and atopic dogs. Exposure of dogs to the different mites is described both in the direct environment and in the coat of animals for house dust mites and in the food for forage mites. Allergens causing allergic disease in dogs seem to be different from those in humans. Dogs seem to react to high molecular weight allergens, compared to the low molecular weight group 1 and group 2 proteases that are commonly implicated in humans with atopic diseases. Despite numerous published studies dealing with this subject, a number of questions still need to be addressed to better understand the exact role of these mites in the pathogenesis of canine atopic dermatitis and to improve the quality of the allergens used in practice.     

Intradermal testing with the storage mite Tyrophagus putrescentiae in normal dogs and dogs with atopic dermatitis in Colorado

The purpose of this study was to evaluate reactions to intradermal injections of Tyrophagus putrescentiae extract in healthy dogs and dogs with atopic dermatitis and to compare the prevalence of positive reactions in the two groups. Twenty-one healthy dogs and 26 atopic dogs were tested intradermally with T. putrescentiae extract at 1000, 500, 250, 125, 63, 32 and 16 PNU/mL. Reactions were evaluated objectively and subjectively. A Mann-Whitney test was used to determine differences in grade of reaction to storage mites between healthy dogs and dogs with atopic dermatitis. Positive reactions to storage mite extract were most common at 1000 PNU/mL with approximately one third of normal and atopic dogs showing a positive reaction to T. putrescentiae. There was no significant difference in the incidence of positive reactions between normal and atopic dogs for any of the Tyrophagus extract concentrations.     

Late-phase reactions to intradermal testing with Dermatophagoides farinae in healthy dogs and dogs with house dust mite-induced atopic dermatitis

OBJECTIVE: To determine the prevalence of late-phase reactions to intradermal testing with Dermatophagoides farinae in healthy dogs and dogs with atopic dermatitis and an immediate reaction to D farinae. ANIMALS: 6 healthy dogs and 20 dogs with atopic dermatitis and immediate reactions to D farinae. PROCEDURE: ntradermal tests were performed with D farinae at 1:1,000 wt/vol and 1:50,000 wt/vol concentrations, and skin reactivity was evaluated after 0.25, 6, and 24 hours. Serum D farinae-specific IgE antibodies were assayed. Extent of lesions (atopy index) and pruritus (visual analogue scale) were evaluated in dogs with atopic dermatitis. RESULTS: Late-phase reactions were observed in healthy dogs at 6 hours (n = 2 dogs) and 24 hours (1) with the 1:1,000 wt/vol concentration, and at 6 hours (1) and 24 hours (1) with the 1:50,000 wt/vol concentration of allergen. Late-phase reactions in healthy dogs were only observed in dogs with an immediate reaction to D farinae. Late-phase reactions were observed in 11 of 20 dogs with atopic dermatitis at 6 and 24 hours with the 1:1,000 wt/vol concentration and in 10 of 20 at 6 and 24 hours with the 1:50,000 wt/vol concentration of allergen. There was no difference in mean atopy index, mean visual analogue scale of pruritus, or mean serum D farinae-specific IgE concentration of dogs with a late-phase reaction, compared to dogs without a late-phase reaction. CONCLUSIONS AND CLINICAL RELEVANCE: Late-phase reactions may be observed after an immediate reaction to intradermal skin testing in healthy and allergic dogs but are more commonly observed in dogs with atopic dermatitis.     

Reactivity to intradermal injection of extracts of Dermatophagoides farinae, Dermatophagoides pteronyssinus, house dust mite mix, and house dust in dogs suspected to have atopic dermatitis: 115 cases (1996-1998)

OBJECTIVE: To compare reactivities to intradermal injection of extracts of Dermatophagoides farinae, Dermatophagoides pteronyssinus, house dust mite mix, and house dust in dogs suspected to have atopic dermatitis. DESIGN: Retrospective study. ANIMALS: 115 dogs. PROCEDURES: Records of all dogs suspected to have atopic dermatitis that underwent intradermal testing between October 1996 and July 1998 were reviewed. Reactivities to intradermal injection of crude mixed house dust mite (1:25,000 wt/vol) and crude house dust (25 PNU/ml) extracts were compared with reactivities to intradermal injection of individual extracts of D farinae and D pteronyssinus (1:50,000 wt/vol). RESULTS: Ninety dogs were confirmed to have atopic dermatitis including 61 of the 69 dogs with positive reactions to either or both of the individual house dust mite extracts. Intradermal testing with the mixed house dust mite extract had sensitivity of 75%, specificity of 96%, and accuracy of 83%. Intradermal testing with the house dust extract had sensitivity of 30%, specificity of 93%, and accuracy of 56%. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that use of crude mixed house dust mite and crude house dust extracts for intradermal testing in dogs is not as accurate a method of determining house dust mite hypersensitivity as is the use of individual D farinae and D pteronyssinus extracts mainly because of the high percentage of false-negative results. Extracts of individual house dust mites are recommended for intradermal testing of dogs suspected to have atopic dermatitis.     

Quantitation of house dust mites and house dust mite allergens in the microenvironment of dogs

OBJECTIVE: To quantitate the density of Dermatophagoides farinae and D pteronyssinus and concentrations of house dust mite (HDM) allergens (Der f 1, Der p 1, and Group 2 allergens) in the indoor microenvironment of dogs. SAMPLE POPULATION: 50 homes in Columbus, Ohio. PROCEDURES: In each home, samples of dust were collected from 3 locations in which dogs spent most time. Whenever possible, the species of mites collected was identified. Mite density (mites/g of dust) was assessed, and allergen concentrations were assayed by standardized ELISAs. Relative humidity and temperature in each home were monitored during a 5-day period. Characteristics of homes and sample sources were evaluated. RESULTS: Dust samples from all 50 homes contained > or = 1 HDM allergen; Der f 1 and Der p 1 were detected in 100 and 74% of homes, respectively. Fifteen homes had HDMs; compared with D pteronyssinus, D farinae was found more commonly (14/15 homes) and at a higher density. Basements, homes without central air-conditioning, and dog beds that were > or = 1 year old had high HDM allergen concentrations. Homes with > or = 2 microg of Der f 1 or Group 2 allergens/g of dust or > or = 100 mites/g of dust were significantly more likely to have a maximum relative humidity > or = 75%. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated the presence of HDMs and HDM allergens in the specific microenvironment of dogs in homes. Factors associated with high levels of exposure were identified, which may be associated with increased risk for sensitization and development of atopic diseases.     

Quantitation of house dust mites and house dust mite allergens in the microenvironment of dogs

OBJECTIVE: To quantitate the density of Dermatophagoides farinae and D pteronyssinus and concentrations of house dust mite (HDM) allergens (Der f 1, Der p 1, and Group 2 allergens) in the indoor microenvironment of dogs. Sample Population-50 homes in Columbus, Ohio. PROCEDURES: n each home, samples of dust were collected from 3 locations in which dogs spent most time. Whenever possible, the species of mites collected was identified. Mite density (mites/g of dust) was assessed, and allergen concentrations were assayed by standardized ELISAs. Relative humidity and temperature in each home were monitored during a 5-day period. Characteristics of homes and sample sources were evaluated. RESULTS: Dust samples from all 50 homes contained > or = 1 HDM allergen; Der f 1 and Der p 1 were detected in 100 and 74% of homes, respectively. Fifteen homes had HDMs; compared with D pteronyssinus, D farinae was found more commonly (14/15 homes) and at a higher density. Basements, homes without central air-conditioning, and dog beds that were > or = 1 year old had high HDM allergen concentrations. Homes with > or = 2 microg of Der f 1 or Group 2 allergens/g of dust or > or = 100 mites/g of dust were significantly more likely to have a maximum relative humidity > or = 75%. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate the presence of HDMs and HDM allergens in the specific microenvironment of dogs in homes. Factors associated with high levels of exposure were identified, which may be associated with increased risk for sensitization and development of atopic diseases.     

Dermatophagoides farinae house dust mite allergen challenges reduce stratum corneum ceramides in an experimental dog model of acute atopic dermatitis

Background – Ceramides are essential stratum corneum (SC) lipids and they play a pivotal role in maintaining effective cutaneous barrier function. Objectives – The present study aimed at determining the effect of a Dermatophagoides farinae house dust mite (Df‐HDM) allergen challenge on SC ceramides of atopic dogs experimentally sensitized to these allergens. Animals – Six Df‐HDM‐sensitized atopic Maltese–beagle dogs were used. Methods – Prechallenge SC was obtained by cyanoacrylate stripping. One week later, the dogs were challenged topically with Df‐HDM allergens, which resulted in mild to moderate inflammation 24 h later. Two weeks after challenge, SC of lesional and nonlesional skin was obtained. Finally, SC was collected from challenge sites 2 months after lesion resolution. The different SC lipids were quantified blindly by thin‐layer chromatography. Results – Significantly lower amounts of ceramides [AH], [AP], [AS], [NP], [EOP], [NS] and [EOS] were observed in lesional SC compared with prechallenge samples, while no significant effect was found on the amount of other lipids, including cholesterol and free fatty acids. The ceramide profile of nonlesional skin generally showed the same postchallenge reduction pattern. Ceramide amounts returned to normal within 2 months after lesion remission. Conclusion and clinical importance – These findings suggest that the allergic reactions caused by Df‐HDM allergens lead to a selective reduction of SC ceramides, not only at sites of inflammation but also at sites away from those of allergen application. There is normalization of ceramide amounts after inflammation subsides. These observations suggest that the deficiency of ceramides observed in canine atopic skin occurs, at least in part, secondary to inflammation.     

Importance of house dust and storage mites in canine atopic dermatitis in the geographic region of Galicia, Spain

Sensitisation to mites is frequent in atopic dogs. The main mite genus involved in canine atopic dermatitis is Dermatophagoides. The importance of storage mite allergens in dogs has been controversial. The aim of this study was to evaluate the sensitisation rates against storage mites (Lepidoglyphus destructor and Tyrophagus putrescentiae) and house dust mites (Dermatophagoides farinae and D. pteronyssinus) in atopic dogs from Galicia, a highly humid and temperate region of Spain, using a FcepsilonRIalpha-based immunoglobulin E (IgE) in vitro test. The study was performed on 95 dogs suffering from atopic dermatitis and presenting detectable specific serum IgE levels: 91.6% of the dogs tested positive for storage mites, whereas sensitisation to house dust mites was detected in 87.4%. These results indicate the importance of storage mites in this specific geographic area.     

Determination of skin threshold concentration of an aqueous house dust mite allergen in normal dogs

Fifty-six healthy dogs with no known history of atopic disease to indoor allergens were skin tested with 6 different dilutions of an aqueous house dust mite extract. A concentration of 31.25 PNU/ml was found to be the maximum, nonirritating concentration. Thirty-two percent of the research dogs used had to be excluded because they failed to show reactions to any test dilution.     

Dust mite species in the households of mite-sensitive dogs with atopic dermatitis

Background – The presence of important house dust and storage mite species in the microenvironment of atopic dogs has not been thoroughly investigated. Objectives – To compare the presence and population of five dust mite species (Dermatophagoides farinae, Dermatophagoides pteronyssinus, Acarus siro, Tyrophagus putrescentiae and Lepidoglyphus destructor) among households with mite‐sensitive atopic dogs (Group A), households with clinically healthy dogs (Group B) and households without pets (Group C, n = 25) in Greece. Animals – Twenty mite‐sensitive atopic dogs and 20 clinically healthy dogs. Methods – Dust samples were collected with a vacuum cleaner from owners’ mattresses (all groups) and from dogs’ sleeping areas (Groups A and B) or living room couch (Group C), once every season of the year. Following dust flotation, mites were counted and identified. Results – Dermatophagoides farinae was the most prevalent (60, 40 and 64% in Groups A, B and C, respectively), followed by D. pteronyssinus (45, 35 and 48%, respectively), whereas the three storage mites were found in fewer households. No major differences could be found between Groups A and B or between households with (Groups A and B) and without dogs (Group C) regarding the presence or numbers of the five dust mite species. Conclusions and clinical importance – The presence and population of five common house dust and storage mite species does not differ among Greek households with mite‐sensitive atopic dogs, households with healthy dogs and households without pets.     

Characterization of house dust mite and scabies mite allergens by use of canine serum antibodies

OBJECTIVE: To identify the major allergenic proteins from the 3 main species of dust mites to which dogs react (Dermatophagoides farinae, D. pteronyssinus, and Euroglyphus maynei) and evaluate the potential cross-reactivity of dust mite allergens with antigens from the ectoparasitic mite Sarcoptes scabiei var canis. SAMPLE POPULATION: Sera from 83 dogs with atopic dermatitis. PROCEDURE: Sodium dodecylsulfate-polyacrylamide gel electrophoresis and immunoblotting using serum from atopic dogs was used to identify IgE-binding proteins in extracts of the 4 mite species. RESULTS: Sera of atopic dogs contained IgE against 23, 17, 25, and 17 allergens from D. farinae, D. pteronyssinus, E. maynei, and S. scabiei, respectively. Unlike the situation for humans, the major allergens for dogs are mostly proteins that are larger than 90 kd molecular weight. Dermatophagoides farinae and E. maynei appear to be more allergenic for dogs than is D. pteronyssinus. Some dogs with serum IgE against dust mites also had IgE against antigens of S. scabiei var canis. CONCLUSIONS AND CLINICAL RELEVANCE: Multiple dust mite allergens induce an IgE response in dogs. These allergens are mostly greater than 90 kd molecular weight.     

Sensitization rates of causative allergens for dogs with atopic dermatitis: detection of canine allergen-specific IgE

Allergen-specific IgE serology tests became commercially available in the 1980s. Since then these tests have been widely used to diagnose and treat allergic skin diseases. However, the relationship between a positive reaction and disease occurrence has been controversial. The purpose of this study was to evaluate allergens using a serologic allergy test in dogs with atopic dermatitis (AD). Dogs clinically diagnosed with AD (n=101) were tested using an allergen-specific IgE immunoassay. Among the total 92 environmental and food allergens, house dust and house dust mites were the most common. Several allergens including airborne pollens and molds produced positive reactions, and which was considered increasing allergens relating to the climate changes. The presence of antibodies against staphylococci and Malassezia in cases of canine AD was warranted in this study. Additionally, strong (chicken, turkey, brown rice, brewer''s yeast, and soybean) and weakly (rabbit, vension, duck, and tuna) positive reactions to food allergens could be used for avoidance and limited-allergen trials.     

Effects of age and allergen exposure on transepidermal water loss in a house dust mite-sensitized beagle model of atopic dermatitis

Transepidermal water loss (TEWL) was measured as assessment of barrier function in house dust mite-sensitized atopic ( n  = 24) and normal ( n  = 21) beagle dogs before and after allergen challenge. Dogs of the two groups were matched for age and housed in the same environment. Ten sites were evaluated including both areas of high and low predisposition to atopic lesion formation. On day 0 (before allergen exposure) and day 3 (3 days after allergen exposure), TEWL measurements were taken using an open-chamber evaporimeter. On day 0, significant differences (one-way ANOVA) were found between normal and atopic dogs in the chin, pinna, periocular region, axilla, antebrachium and thorax. Within the atopic group, a significant increase (one-way ANOVA) in TEWL was found in the axilla on day 3. Such a difference was particularly marked in young dogs (chin, pinna, axilla, antebrachium and groin). Within the normal group, allergen challenge did not change TEWL except for the chin. When atopic and nonatopic sites were compared within the atopic group, a significant difference in TEWL was found on day 0. A two-way ANOVA showed a significant effect of site, a significant effect of time but no site × time (i.e. allergen exposure) interaction. It is concluded that the house dust mite-sensitized atopic beagle dogs used in this study have altered barrier function in 'atopic' areas and that such differences are more evident in young individuals and are aggravated by allergen exposure.     

Validation of a novel epicutaneous delivery system for patch testing of house dust mite‐hypersensitive dogs

Background – Patch tests with allergens are used for the evaluation of cellular hypersensitivity to food and environmental allergens in dogs and humans with atopic dermatitis. Viaskin is a novel allergen epicutaneous delivery system that enhances epidermal allergen capture by immune cells. Objectives – To compare the use of Viaskin and Finn chamber patch tests in dogs hypersensitive to mite allergens. Methods – Empty control or Dermatophagoides farinae house dust mite‐containing Viaskin or Finn chamber patches were applied to the thoracic skin of six mite‐hypersensitive Maltese‐beagle crossbred atopic dogs. Lesions were graded 49 and 72 h after patch test application, and skin biopsies were collected after 72 h. Overall microscopic inflammation, eosinophil and T‐lymphocyte infiltrations were scored. Results – Positive macroscopic patch test reactions developed at five of six Viaskin application sites and four of six Finn chamber application sites. Median microscopic epidermal and dermal inflammation, as well as eosinophil and CD3 T‐lymphocyte dermal scores were always higher in biopsies collected at Viaskin than at Finn chamber sites. Microscopic inflammation scores were significantly higher after mite allergen‐containing Viaskin compared with empty patches, but this was not the case for mite‐containing Finn chambers compared with control chambers. Scores obtained using Viaskin were not significantly different from those obtained using Finn chambers. Macroscopic and microscopic scores were significantly correlated. Conclusions and clinical importance – In mite‐allergic dogs, Viaskin epicutaneous delivery systems appear to induce stronger allergen‐specific inflammation than currently used Finn chamber patch tests. Consequently, Viaskin patches might offer a better alternative for screening cellular hypersensitivity to food and environmental allergens.     

The ACVD task force on canine atopic dermatitis (IX): the controversy surrounding the route of allergen challenge in canine atopic dermatitis.

For decades, the dogma that environmental allergens trigger cutaneous inflammation led to the denomination of canine atopic dermatitis as "allergic inhalant dermatitis". Definitive proof for a respiratory route of allergen challenge is lacking, however. Recent observations suggest, in fact, that skin inflammation could occur because of epidermal allergenic contact. The aim of this paper is to review the evidence published in favor and against the two suspected routes of allergen provocation.