Equine Health Update EHU Vol 20 Issue 03 - Page 27

Equine Disease Quarterly | EQUINE autoimmune disease. management is needed to best control clinical disease. In all cases of pruritic dermatitis, managerial procedures to decrease exposure to exciting agents as well as symptomatic therapy to reduce pruritus is warranted. In IBH procedures to decrease exposure to insects should be fully implemented. Farm sanitation to compost manure properly, eliminate wet areas with decomposing vegetation, and the use of fly predators or feed through fly inhibitors can greatly reduce fly populations. Heat, humidity, and solar radiation exacerbate pruritus, thus the provision of shade and wind currents by fans provide relief. Stabling to avoid the most significant insects (Table 1) and the use of fly sheets and face masks are helpful. Because some horses develop contact allergies to topical products, judicious and cautious use of fly repellants is advisable. Simple feeds and whole grains are better than mixed, multiple-grain sweet feeds. Cool-water rinses and shampoos can rehydrate and sooth dry skin as well as reduce the amount of allergens on the skin. Colloidal oatmeal, pramoxine, and 1 percent hydrocortisone shampoos or leave-on hydrocortisone rinses may reduce pruritus and minimize or reduce the amount of systemic antipruritic medication needed. Systemic medications (steroids and antihistamines) may help interrupt the itch-scratch cycle, however long term use, particularly of steroids, should be avoided. A complete and detailed investigation into the etiology of the disease should occur simultaneously with general symptomatic care. Intradermal skin testing to determine antigens for allergen specific immunotherapy may be helpful, particularly in young animals with atopy. Clients should understand that hypersensitivities and atopy are lifelong. Affected horses will need continuous management and/or therapy. Often a patient may be symptom-free with low exposure to inciting antigens and symptomatic as the antigen load increases. Antigen exposure is additive, thus comprehensive CONTACT: Susan L. White, DVM, MS, DACVIM, slwhite@uga.edu, (706) 296-8607, Department of Large Animal Medicine, College of Veterinary Medicine, University of Georgia Athens, GA Theiler’s Disease Theiler’s disease, or equine serum hepatitis, is an infrequent but sometimes life-threatening liver disease of adult horses. Sir Arnold Theiler first described the disease in the early 1900s as a form of highly fatal acute liver failure that occurred 4-12 weeks after administration of equine antiserum, which was used as part of a vaccination strategy for African Horse Sickness. Since then, many additional cases of serum hepatitis have been reported, and a variety of blood products of equine origin have been associated with the disease. In North America, the majority of recent cases have been associated with the administration of tetanus antitoxin, although commercial plasma products also have been incriminated. The number of horses that become ill following administration of a specific lot of incriminated blood product is estimated at 1 to 2 percent, although more horses might have sub-clinical disease. An infectious agent, such as a virus, has long been suspected to cause this condition, and a new equine parvovirus was recently discovered in a horse with a fatal case of serum hepatitis. The parvovirus was present in the diseased horse and in the biologic product that it had received nine weeks earlier. Inoculation of experimental horses with the commercial product resulted in transmission of this newly discovered virus and in liver disease. Variation in individual immune responses to the virus could explain the low percentage of clinically affected horses. An identical disease, both in terms of clinical signs • Volume 20 Issue 3 | October 2018 • 27