218


EQUINE VETERINARY EDUCATION / AE / APRIL 2018


provided, due to the complexity of this condition, and the high variability in responses, dosing frequency and duration often have to be adjusted.


Integumentary system


Insect bite hypersensitivity Insect bite hypersensitivity (IBH) is the most common cause of pruritus in horses, and reaction to bites by various Culicoides spp. gnats is the most well documented cause (Petersen 2009; Stepnik et al. 2012). IgE-mediated, type I hypersensitivity with release of histamine and other inflammatory mediators are often involved in IBH. However, in some horses, cell-mediated, type IV hypersensitivity may also contribute to the pathogenesis (Jonsdottir et al. 2015). Common signs include pruritus and papules, usually observed along the dorsum, mane, rump and tail base. Histologically, the lesions are characterised by mixed perivascular to diffuse cellular infiltrates consisting of mononuclear cells and eosinophils in acute lesions (Schaffartzik et al. 2012). Intradermal testing (IDT) has been used in horses as a diagnostic tool for conditions such as IBH, urticaria, or RAO. It is known that horses with clinical signs of Culicoides hypersensitivity have stronger IDT reactions than healthy horses do, which is an advantage when immunotherapy is considered to prevent flare-ups of the condition (Jose-Cunilleras et al. 2001). Decreasing exposure to insects is the most important


management practice; however, severely affected horses, particularly those with marked pruritus, may need anti- inflammatory treatment with systemic glucocorticoids (Rees 2005; Petersen 2009; Schaffartzik et al. 2012). Prednisolone at 1 mg/kg bwt orally every 24 h or dexamethasone at 0.05– 0.1 mg/kg bwt orally once daily can be used until pruritus and self-trauma are controlled, at which point the dose is tapered to the lowest dosage that controls pruritus (Pilsworth and Knottenbelt 2004; Petersen 2009). In severe cases, prednisolone can be administered at 2 mg/kg bwt orally once daily for 3–10 days until the pruritus is controlled, followed by tapering to 0.5 mg/kg bwt every other day (Marsella 2013). Glucocorticoid therapy should be discontinued as soon as the biting season has passed (Pilsworth and Knottenbelt 2004). It is important to mention that despite medical therapy or environmental management, equine insect hypersensitivity is a seasonal and recurrent condition, with no long-term cure. Based on results of IDT, hyposensitisation injections are useful in preventing this condition or any other atopic dermatitis. Injections are usually recommended for at least one year, and continue thereafter based on the clinical response of the patient (White 2015). The aim of the therapy is to control and prevent acute exacerbations (Pilsworth and Knottenbelt 2004; Ferroglio et al. 2006).


Atopic dermatitis Atopic dermatitis is an IgE mediated type I hypersensitivity response to environmental allergens. The condition may be seasonal or nonseasonal, depending on the allergens involved (White 2015). Clinical signs of atopic dermatitis in horses may include urticaria and/or pruritus; usually affecting the face, distal legs or trunk (White 2005). The most effective way to prevent and control this condition is by identifying the triggering allergens and reducing exposure.


© 2016 EVJ Ltd


In clinical cases, the response to glucocorticoids is usually


prompt and administration of dexamethasone at a dose of 0.05 mg/kg bwt may result in complete resolution (White 2015). For cases requiring ongoing therapy, once daily administration of 1 mg/kg bwt of prednisolone orally, followed by gradual reduction of the dose, proved to be effective with a low likelihood for adverse effects (Littlewood 2011). Resolution of the pruritus or urticaria has been achieved by the use of prednisolone at 200–400 mg/500 kg administered orally once daily, or dexamethasone at 0.05– 0.1 mg/kg bwt, either by the enteral or parenteral route, once daily (White 2005).


Vasculitis Vasculitis is a histopathological term that implies the presence of inflammatory changes in the walls of blood vessels, and it is associated with a broad spectrum of disorders. In horses, vasculitis is most often seen as a feature of drug reactions, urticaria, photosensitisation or purpura haemorrhagica (White et al. 2009). Glucocorticoids have been recommended in the treatment


of equine cutaneous vasculitis due to both their anti- inflammatory and immune-suppressive effects (White 2014). The use of prednisolone at 1 mg/kg bwt given orally twice daily or dexamethasone at 0.08–0.2 mg/kg bwt once daily have been described in a retrospective study (White 2009). The previously mentioned glucocorticoid treatment was administered for 2 weeks, and then tapered over the next 4–6weeks. In this study, the clinical response was variable, and recurrence of the condition was observed in approximately 25% of the cases (White 2009). Purpura haemorrhagica is characterised by leucocytoclastic


vasculitis leading to extensive oedema and haemorrhage of the mucosa and subcutaneous tissue (Fig 3). The disease has been recognised as a sequela to infection or exposure to Streptococcus equi ssp. equi, Streptococcus zooepidemicus, Rhodococcus equi and Corynebacterium pseudotuberculosis (Knottenbelt 2002). Immune complexes primarily composed of IgM or IgA and streptococcal M protein may be present in capillaries, leading to a type III hypersensitivity reaction. Prolonged treatment with glucocorticoids (2–4weeks) has resulted in a favourable outcome and low relapse rate (Kaese et al. 2005). Depending on the severity of clinical signs, the proposed dosage is 0.04–0.2 mg/kg bwt of dexamethasone once or twice daily or 0.5–1.0 mg/kg bwt of prednisolone orally once or twice daily, with a gradual reduction of the dosage (Aleman and Watson 2015a). Doses of prednisolone as high as 2 mg/kg bwt twice daily have been used for prolonged periods (Kaese et al. 2005).


Pemphigus foliaceus Pemphigus foliaceus is an autoimmune disorder characterised by the production of autoantibodies and histologically by intraepidermal acantholysis. The clinical lesions recognised in horses are primarily scaling and crusting (Vandenabeele et al. 2004). The recommended treatment is glucocorticoids, such as prednisolone at 1 mg/kg bwt orally every 12–24 h or dexamethasone at 0.08–0.1 mg/kg bwt orally once daily, then tapering (White 2009). In a retrospective study, horses with pemphigus foliaceus were reported to have been in remission for 1–3 years, some of them receiving medications for up to 12 months (prednisolone 0.5–1 mg/kg bwt orally every other day)


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80