Texas Equine Veterinary Association

www.texasequineva.com • 16 ons and/or hand-pump insect sprays since automated systems do not spray horses' underside or limbs. • Solitude (Zoetis) is an oral daily insect growth regulator (IGR) fed in the feed. It prevents the maturation of immature stages of stable and house flies in horse manure. To maximize the effectiveness of the IGR, it should be given to each individual horse on the premises. • Cattle on the premises can receive medicated ear tags to reduce the horn fly population. Medicated cattle ear tags can also be attached to horse halters. Lastly, cattle can be fed an IGR (many products contain the active ingredient S-methoprene) often mixed with protein/mineral supplements to prevent the emergence of horn flies from their manure. Control of Secondary Infections Pruritic crusting papules are not specific to "insect bites," and their presence should prompt the clinician to exclude bacterial folliculitis, namely staphylococcal pyoderma and dermatophilosis. Although, typically not very pruritic, dermatophytosis is another folliculitide to consider. Impression cytology and/or skin culture can help navigate what therapy to prescribe. Overall, all forms of folliculitis are best treated topically with antimicrobial shampoos/ rinses (e.g., chlorhexidine 3–4%, benzoyl peroxide, sodium hypochlorite, selenium sulfide, accelerated hydrogen peroxide, ethyl lactate, ketoconazole, miconazole, and lime sulfur) and/ or ointments and creams (mupirocin 2%, silver sulfadiazine, miconazole, and terbinafine) depending on the organism of interest. Frequency of application with these products is reduced based on clinical response. Systemic antibacterial therapy should be given for one week beyond clinical resolution (Table 2). Failure to respond suggests an incorrect diagnosis or a "resistant" organism. Skin biopsy for histopathology and culture would be the "next step" in this scenario. Symptomatic Control of Short-term Pruritus and/or Urticaria Initially, some form of glucocorticoid is required to halt pruritus and reduce self-trauma. Topical steroids are preferred to reduce the risk of laminitis, but usually a 5–10 day course of systemic Table 1. Characteristics of Insects that Cause Irritation, Pruritus, and/or Hypersensitivity in the Horse Insect Lesion/pruritic distribution Feeding times Breeding habitat Culicoides (gnats) Species dependent Dorsum: face, mane, withers, rump, tail Ventrum: intermandibular space, ventral midline Twilight to dawn Standing water, manure, vegetation Mosquitoes Ventral midline, lower limbs; may be generalized Dusk to early twilight Water Black flies (Simulium) Face, intermandibular space, ears, neck, ventrum, limbs Morning and evening Running water Stable flies (Stomoxys) Dorsum, neck, chest, abdomen, limbs Daytime Rotting vegetation, manure Horse flies (Tabanus) Neck, lateral body wall, ventrum, limbs Daytime Vegetation, water Deer flies (Chrysops) Neck, lateral body wall, ventrum, limbs Daytime Vegetation, water Horn flies (Haematobia) Ventral midline Daytime Cattle pastures, manure

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