here - Australian College of Veterinary Scientists

More documents

Recommendations

Info

90 How I treat: equine insect bite hypersensitivity ACVSC Proceedings Dermatology Chapter Science Week 2005 Mandy Burrows Insect bite hypersensitivity is the most common allergic skin disease of the horse. It has a worldwide distribution. Cause and Pathogenesis This disorder represents type I (immediate and late phase) and type IV (delayed) hypersensitivity to antigens (presumably salivary) from numerous Culicoides (gnats) and Simulium (black flies) species, Stomoxys calcitrans (stable fly) and possibly Haematobia irritans (horn fly). Some horses have hypersensitivities to multiple insects. Culicoides gnats (biting midges, sandflies) are the most important cause of equine insect hypersensitivity. Results of gnat collection techniques, intradermal testing with gnat antigens and passive cutaneous anaphylaxis trials have incriminated numerous Culicoides species in various parts of the world. C.brevitarus (C.robertsi) appears to be most important in Australia. In general Culicoides gnats are most active when the ambient temperature is above 28C, when humidity is high and when there is no breeze. Culicoides gnats breed in standing water and generally fly short distances. Clinical evidence strongly suggests that this disorder has familial and genetic predispositions. Intradermal injections of Culicoides (and occasionally Simulium, Stomoxys and Haematobia) extracts produce immediate (30 mins) and delayed (24 to 48 hours) reactions in over 80% and about 50% respectively of affected horses. Some affected horses also develop late phase immediate (4 to 6 hours) reactions. Affected horses typically react to all Culicoides spp injected suggesting shared common allergens. Most horses react to two or more genera of insects. Clinical features No age or sex predilection; most horses first develop clinical signs at 3 to 4 years and the condition typically worsens with age. Coat colour is not a risk factor. It may be seen in any breed but certain breeds are reported to be at increased risk; Icelandic, German Shire, Welsh ponies, Arabians, Connemaras, and quarter horses. Clinical signs are distinctly seasonal (spring through to autumn) but in warmer subtropical to tropical climates the disease can be non seasonal with seasonal (summer) exacerbations. Clinical signs are often worse near dawn and dusk as this is the favourite feeding time for many Culicoides species.
Affected horses usually scratch and chew themselves and rub against environmental objects (stalls, fences, doorways, posts, trees etc) Reflex nibbling movements can often be elicited by manipulation of the skin of the mane. Horses usually show one of three patterns of skin disease i.e dorsal, ventral or some combination thereof and these differences in lesion distribution probably reflect the different preferential feeding sites of the various insect species. Dorsal insect hypersensitivity is characterised by pruritus with or without crusted papules, usually beginning at the mane, rump and base of tail. The condition then extends to involve the face, pinna, neck, shoulder and dorsal thorax. Self trauma and chronicity lead to excoriations, variable hypotrichosis and alopecia, lichenification and pigmentary disturbances especially melanoderma and melanotrichia. Ventral insect hypersensitivity is characterised by pruritus with or without crusted papules, beginning on the ventral thorax and abdomen, axillae and groin. The legs and intermandibular space are often involved. Secondary changes may occur as above. Horses with insect bite hypersensitivity rarely have involvement of the flanks. In addition, horses with insect hypersensitivity uncommonly develop urticaria and when they do it is typically papular. Secondary bacterial folliculitis is not uncommon. Affected horses may suffer behavioural changes (anxious, nervous, restless, aggressive) and be unfit for riding, showing or working. Some horses will lose weight due to the constant irritation. Some horses have concurrent atopic disease or adverse food reactions which can greatly complicate the diagnostic work-up and therapeutic management. Diagnosis The differential diagnosis will vary according to the distribution of lesions. The definitive diagnosis is based on history, physical examination, ruling out other conditions and response to insect control. Intradermal testing with insect extracts, especially Culicoides is usually positive with insect hypersensitivity. Reactions may be present at 30 minutes (immediate), 4-6 hrs (late phase) and 24-48hrs (delayed) or combinations of these. Normal horses can have positive reactions and the prevalence of positive reactions in normal horses increases with increasing age. Antibodies against Culicoides and Stomoxys have been detected in the serum of affected horses by ELISA. Other investigators have found no difference in ELISA scores using Culicoides extract between normal horses and horses with insect hypersensitivity. The diagnostic value of ELISA results is presently undocumented. ACVSC Proceedings Dermatology Chapter Science Week 2005 91
Page 1 and 2:
Australian College of Veterinary Sc
Page 3 and 4:
Australian College of Veterinary Sc
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
Page 15 and 16:
dusts, grain smuts, moulds, danders
Page 17 and 18:
References: Evans AG, Paradis MR, &
Page 19 and 20:
Comparatively simple, cheap and eff
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 and 38:
much higher and corresponded to the
Page 39 and 40: and this and other uncontrolled tri
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
Page 57 and 58: identify plants in a pasture that m
Page 59 and 60: Equine sarcoidosis Sonya Bettenay T
Page 61 and 62: described as a possible feature of
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
Page 85 and 86: indicated. Each sample for culture
Page 87 and 88: Proper dosage and proper duration a
Page 89: 2. Affect on the horse and 3. Affec
Page 93 and 94: • Cattle ear tags impregnated wit
Page 95 and 96: How I treat: equine pemphigus folia
Page 97 and 98: Treatment of pemphigus foliaceus in
Page 99 and 100: SCOTT, D.W., WALON, D.K., SLATER, M
Page 101 and 102: Diagnosis History of access of hors
Page 103 and 104: These vaccines are not manufactured
Page 105 and 106: References Alfaro AA & Mendoza L (1
Page 107 and 108: y a variety of fungal metabolites.
Page 109 and 110: Authors recommendations: 1. Both Im
Page 111 and 112: chorioptic mange by the author (Lit
Page 113 and 114: Clinical Disease The clinical resul
Page 115 and 116: treatment options have been used. P
Page 117 and 118: Notes ACVSC Proceedings Dermatology
show all

here - Australian College of Veterinary Scientists

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?