Results of intradermal testing for the investigation of atopic dermatitis and recurrent urticaria in 50 horses in the south of England

Atopic dermatitis (AD) and recurrent urticaria (RU) are common immune‐mediated conditions of horses and ponies associated with high morbidity. Effective pharmacological treatment options are limited but identification of the causal allergens allows avoidance strategies and immunotherapy regimens to be employed. Intradermal testing (IDT) is the most widely accepted means of identifying the relevant allergens but there are no published reports of this technique being used in the UK for the investigation of dermatological disease. This study presents the results of testing with a varied panel of allergens in 50 horses with dermatological disease living in the south of England. Intradermal testing was performed in horses presented to The Liphook Equine Hospital for further investigation of AD or RU between June 2002 and March 2009. Allergen selection was based upon availability, results of previous studies, pollen charts and the likelihood of allergens being prevalent in the stable or pasture environment in the south of England. Injection sites were evaluated at 1 h (immediate phase), 4 h (late phase) and 24 h (delayed phase) and skin responses compared to the response generated by the positive control (histamine) at 1 h. Total numbers of positive reactions and numbers of positive reactions to specific allergens were similar in horses with atopic dermatitis and those with urticaria (P = 0.39). There was a statistically significant difference in the number of reactions observed at different time points, with more positive reactions occurring at 1 h than 24 h (P<0.001), and at 4 h than 24 h (P<0.001). Reading the test at 24 h rarely provides additional information. Reaction patterns were similar to those of previous studies performed in other countries with large numbers of positive reactions reported to mites, dusts and insects. Positive reactions were also common to allergens not previously identified as irritants or common allergens in equids; nettle, daisy, dandelion, horse chestnut, cat, cattle, sheep and pigeon. These allergens may be important causes of allergic dermatitis in equids in the UK; however, further studies should be performed in both normal horses and horses with allergic dermatitis to investigate irritant thresholds and validate these findings. Intradermal testing may be shortened from the conventional 24 h to 4 h without significantly affecting the results of the test.     

A Retrospective Study of Hyposensitization in Canine Atopy Based on a Polyclonal ELISA test

Compliance with the treatment protocol and the most significant reasons encountered in general practice for the discontinuation of treatment in hyposensitized dogs are examined. The data are based on (1) a review of order forms for the hyposenzitization mixture and information sheets for an ELISA test and (2) telephone interviews with dog owners. Most of the owners (81%) gave their dogs allergen injections at home. Non-compliance was defined as discontinuation of treatment in the induction period; 33.9% of the owners became non-compliant. A large proportion of non-compliant owners (51.2%) claimed to be unaware of the length of the induction period. Furthermore, 70.2% of the owners were not aware that treatment would most likely need to be lifelong if it was to remain effective. Although 67.5% of the owners perceived that their dogs had beneficial effects from hyposensitization, only 36.3% of the dogs were receiving maintenance injections at the time of the telephone interview, considerably reducing the long-term benefit from treatment. Canine atopy is a chronic disease characterized by remission and relapses. Since no control group was available in this study, the beneficial outcome of treatment reported by the owners could be partly due to the natural course of the disease. Nevertheless, the results indicated that the long-term effect of hyposensitization in canine atopy will be reduced by premature discontinuation of treatment in the maintenance period. The discontinuation of treatment could be a reflection of the treatment becoming less effective, owing to the development of new hypersensitivities or to a reduction in the placebo effect that may occur in `new' treatments. However, poor client education and follow-up seem to be important reasons for both non-compliance and discontinuation of the treatment in the maintenance period.     

The suitability of medetomidine sedation for intradermal skin testing in dogs

The objective of this study was to determine the suitability of medetomidine sedation for facilitating intradermal skin testing in dogs. Quality of sedation and immobilization, and effects of sedation on responses to intradermally injected histamine were evaluated. Ten clinically normal dogs were injected intradermally before and after medetomidine sedation (10 μg kg^?1 intravenously) with diminishing concentrations of histamine (100–10^?5μg mL^?1) and a negative control. Mean wheal responses at injection sites were compared before and during sedation, and no significant suppression of responses occurred during sedation. Medetomidine produced sedation that notably increased the ease of performing multiple intradermal injections in all dogs and sedative effects were rapidly reversed by the antagonist atipamezole. It was concluded that medetomidine may be an excellent sedative for facilitating intradermal skin testing in dogs provided further studies similarly reveal no inhibition of responses to intradermally injected allergens in atopic dogs.     

The use of compound 48/80 and codeine phosphate as positive controls for intradermal skin testing in dogs

The mast cell secretagogues compound 48/80 and codeine phosphate were evaluated as potential positive controls for intradermal skin testing in dogs. Wheal responses to both agents were compared with responses to histamine and saline in 11 normal dogs, and were strong and not significantly different from histamine responses in nine dogs ( P < 0.01), and significantly weaker than histamine in two dogs ( P < 0.05). Wheal responses to compound 48/80 (1 mg mL⁻¹) were evaluated in 82 suspected atopic dogs and were similar to histamine in 79 dogs and markedly weaker than histamine in three dogs. Of nine confirmed atopic dogs with weak responses to injected allergens, seven had strong responses to compound 48/80, and eight had strong responses to histamine. Compound 48/80 and codeine phosphate appear unreliable positive controls for skin testing in normal dogs. Compound 48/80 (1 mg mL⁻¹) may be a reliable positive control in atopic dogs but is a poor indicator of skin reactivity to allergens.     

Comparison of intradermal testing and serum testing for allergen-specific IgE using monoclonal IgE antibodies in 84 atopic dogs

OBJECTIVE: To compare an ELISA measuring serum allergen-specific IgE with intradermal skin testing in canine atopic dermatitis. PROCEDURE: Eighty-four dogs with the clinical diagnosis of atopic dermatitis underwent intradermal skin testing and serum testing for allergen-specific IgE. Tests were performed in a blinded fashion. Positive reactions were compared and the sensitivity and specificity of the serum test (using intradermal skin test as the standard) were determined overall and for individual allergen groups (grass pollens, weed pollens, tree pollens, house dust mites and fleas). RESULTS: The sensitivity of the ELISA overall was 90.4%. Evaluating the individual allergen groups, the sensitivity for dust mite hypersensitivity was 95.1%, for fleas 85.4%, for tree pollens 84.3%, for grass pollens 95.1% and for weed pollens 96.4%. The specificity was 91.6% overall, for dust mites 96.3%, for fleas 92.7%, for tree pollens 95.2%, for grass pollens 94% and for weed pollens 80.7%. CONCLUSION: The evaluated ELISA seemed reliable for the diagnosis of atopy in practice and can be recommended as a screening test prior to intradermal skin testing or for use in dogs when immunotherapy is not a therapeutic option.     

Inhibition of histamine release from dispersed canine skin mast cells by cyclosporin A, rolipram and salbutamol, but not by dexamethasone or sodium cromoglycate

Despite the important role that canine skin mast cells play in IgE-mediated allergic inflammation, clinically useful compounds for modulating mediator release from these cells or for suppressing cell response are lacking in the dog. The ability of five compounds to inhibit histamine release induced by non immunological (calcium ionophore A23187 and substance P) and IgE-dependent (concanavalin A) stimuli were compared. Sodium cromoglycate, a mast cell stabilizer, and dexamethasone, a glucocorticoid, failed to inhibit histamine release from isolated skin mast cells following any kind of stimulation. Salbutamol, a β-adrenergic agonist, exhibited inhibitory activity (46.0%) only after concanavalin A activation. In contrast, rolipram, a selective phosphodiesterase IV inhibitor and cyclosporin A, an immunosuppressor, showed potent anti allergic actions, inhibiting both IgE-dependent and -independent stimuli. Rolipram inhibited 42.8%, 44.7% and 19.2% of the mediator release induced by ionophore A23187, substance P and concanavalin A, respectively. Similarly cyclosporin A induced 85.9%, 14.9% and 67.3% inhibition after ionophore A23187, substance P and concanavalin A stimulation, respectively. These results suggest that rolipram and cyclosporin A merit to be clinically tested as agents for the treatment of chronic allergic diseases in the dog.