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38 Immunotherapy for Equine Atopic Dermatitis ACVSC Proceedings Dermatology Chapter Science Week 2005 Janet Littlewood Allergen-specific immunotherapy (ASIT) is widely used in small animal dermatology in the management of atopic dermatitis and in some countries for atopic humans. ASIT is indicated in in animals in which avoidance of allergens is not possible or is ineffective, where signs are pesent for more than 4-6 months of the year, and drugs for symptomatic control are ineffective, or required at excessively high doses, or are contraindicated (Scott & Miller 2003). Since the author has had very few cases that fall into the above category, she has only limited personal experience with immunotherapy in the horse and this presentation will draw on published information. The mechanisms of action of immunotherapy are complex and the details of their action still poorly characterised. Various hypotheses put forward historically include humoral desensitisation (reduced IgE production), immunisation (blocking IgG antibodies), cellular desensitisation (reduced reactivity of mast cells and basophils, induction of tolerance (generation of allergen-specific suppressor cells) and combinations of the above. However, in patients with good clinical responses to immunotherapy vaccine, there may be no decrease and even increases in IgE concentrations. Increased numbers of CD25+ T-suppressor lymphocytes has been shown to correlate with a favourable response, indicating that the major beneficial effect is cellular rather than humoral. There is a scarcity of published studies demonstrating the efficacy of ASIT in horses in prospective, randomised, controlled trials, although a number of publications report the clinical benefits in retrospective case studies. Overall success rates that are reported are remarkably similar to those reported for ASIT in dogs and cats, with 60-71% of cases having a good to excellent response, when therapy is based on intradermal testing. Most published reports have used aqueous allergens, with a variety of protocols used. Although there are some theoretical objections raised to the use of alum-precipitated vaccines (potential to further stimulate Th 2 type of response and enhanced IgE production) experience with small animals would suggest that these are not clinically relevant, with the only randomised, blinded, placebo-controlled trial of ASIT in atopic dogs using an alum-precipitated vaccine,
and this and other uncontrolled trials using alum-precipitated vaccine having very similar rates of success compared with aqueous vaccines (~60-70% of cases showing good to excellent/greater than 50% improvement). There is controversy regarding the benefits of ASIT using insect extracts. A randomised, double-blinded, placebo-controlled clinical trial of ASIT for Culicoides hypersensitive horses involving 14 horses over a 6-month period demonstrated no difference between verum and placebo treated groups (Barbet 1990). However, a later Canadian open study conducted over 1-2 years with a crude Culicoides extract injected into 10 horses severely affected by disease resulted in a reduction of clinical signs in 9/10 (90%) in the first year. Of the eight horses treated during the second year, three were free of clinical signs at the end of the year(37.5%), three showed much less severe signs(37.5%), and two (25%) showed moderate reduction in clinical signs (Anderson et al 1996). In a retrospective study of 43 horses with allergic skin disease, of which 33 had been on immunotherapy for a minimum of 4 months the following data were reported (Rosenkrantz 1992): 10 horses showed pruritus only, 14 were urticarial and 9 had pruritus and urticaria. Good-to-excellent responses to ASIT were reported in 60% of the pruritic horses, 71% of the urticaria cases and 66% of the horses with both urticaria and pruritus. Another study (Fadok 1996) showed that in horses that were purely atopic 5/7 (71.4%) were greater than 50% improved and 7/13 (53.8%) atopic and insect-allergic horses were greater than 50% improved, whereas 3 of 4 (75%) insect-only allergic horses had no response to immunotherapy. A subsequent study of symptomatic horses with positive intradermal responses to insect and environmental allergens evaluated the efficacy of insect hyposensitisation compared to insect and environmental hyposensitisation in a double-blinded, placebo-controlled study (Rosenkrantz et al 1998). Clinical scores were ascribed for pruritus, excoriations, scale-crust and alopecia) ranging from 1-10 for affected regions of the body and mean scores ascribed. Cases were re-evaluated after 3 months and those that had received placebo were allowed to receive verum treatment, and subsequently horses in the insect-only treatment group were permitted to convert to insect + environmental ASIT. Analysis of clinical scores after the initial 3 months treatment showed no statistically significant difference between the placebo and verum treated groups with either formulation of immunotherapy. However, when the pre-treatment and post-treatment scores for individual horses were analysed, there was a significant difference in verum treated animals compared to the placebo groups. Similarly, when the placebo groups were changed to verum treatments, statistically significant changes in scores were achieved. There was no significance in changing from insect only to insect + environmental ASIT. Minor reactions characterised by swelling at the injection site was observed in six of 27 horses receiving ASIT, but all reactions subsided in 24-72 hours. ACVSC Proceedings Dermatology Chapter Science Week 2005 39
Page 1 and 2: Australian College of Veterinary Sc
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Page 5 and 6: 3.00 Afternoon tea 3.30 How I treat
Page 7 and 8: Dr Jennifer A. Charles BVSc MVS Dip
Page 9 and 10: Scientists in Feline Medicine in 19
Page 11 and 12: IgE-bearing cells have been demonst
Page 13 and 14: years, median age 6.5 years, with a
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Page 17 and 18: References: Evans AG, Paradis MR, &
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Page 21 and 22: TABLE 1: CURRENT ALLERGENS SELECTED
Page 23 and 24: AmericanCockroach Cockroach mix
Page 25 and 26: Patient Preparation Drug Withdrawal
Page 27 and 28: Each injection site is visually exa
Page 29 and 30: References 1. Scott DW, Miller WH:
Page 31 and 32: Intradermal Testing (IDT) in Horses
Page 33 and 34: TABLE 2 Additional allergens used i
Page 35 and 36: Allergen Positive reactions Mosquit
Page 37: much higher and corresponded to the
Page 41 and 42: Introduction Diagnostic Approach to
Page 43 and 44: Wheals vary in size and shape and q
Page 45 and 46: References Evans AG, Paradis MR & O
Page 47 and 48: Introduction: Equine Chronic Urtica
Page 49 and 50: Acute treatment - Epinephrine 1:100
Page 51 and 52: anecdotal success with use of human
Page 53 and 54: an 80:20 mixture of evening primros
Page 55 and 56: Clinical approach to the horse with
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Page 59 and 60: Equine sarcoidosis Sonya Bettenay T
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Page 63 and 64: others 2001), isotretinoin(Waldinge
Page 65 and 66: 12. LeGall, F., Loeuillet, L., Dela
Page 67 and 68: Introduction The equine sarcoid: an
Page 69 and 70: Clinical Presentation Small fibrous
Page 71 and 72: Assessment should be made on the fo
Page 73 and 74: (ix)Bone becomes devitalized if inc
Page 75 and 76: and mitomycin C have been used. All
Page 77 and 78: Owen LN & Barnett KC (1983) - Treat
Page 79 and 80: any anatomic location but commonly
Page 81 and 82: epidermis may be histologically nor
Page 83 and 84: References D.C. Knottenbelt, S. Edw
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2. Affect on the horse and 3. Affec
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Affected horses usually scratch and
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• Cattle ear tags impregnated wit
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How I treat: equine pemphigus folia
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Treatment of pemphigus foliaceus in
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SCOTT, D.W., WALON, D.K., SLATER, M
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Diagnosis History of access of hors
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These vaccines are not manufactured
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References Alfaro AA & Mendoza L (1
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y a variety of fungal metabolites.
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Authors recommendations: 1. Both Im
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chorioptic mange by the author (Lit
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Clinical Disease The clinical resul
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treatment options have been used. P
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Notes ACVSC Proceedings Dermatology
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