FUNDED BY UNDERWRITERS AT LLOYD'S, LONDON JULY 2018 Volume 27, Number 3

COMMENTARY

IN THIS ISSUE on the Horizon for Insect Bite Hypersensitivity? Commentary he season is upon us when approximately 10 (AIT) involves inoculation with International Tpercent of horses worldwide are faced with gradually increasing doses of an to which First Quarter one of the most frustrating skin diseases in the the individual is allergic. The incremental increases 2018 ...... 2 equine industry, insect bite hypersensitivity (IBH), in exposure to the allergen cause the immune Insect Bite ...... 3 more commonly known as “sweet itch” or “summer system to become less sensitive to the substance, eczema.” IBH is an allergic, recurrent, seasonal der- which reduces the signs when the substance Theiler’s Disease . . . 3 matitis caused when the overacts is encountered in the future. Data are conflicting National or becomes ”hypersensitive” to in the as to whether or not traditional AIT therapies are Protecting your saliva primarily of biting midges (Culicoides) and successful in treating IBH. Research is now explor- Horse ...... 4 other biting insects. ing whether IBH can be prevented by vaccination Dr. Susan White in her article provides an with recombinant Culicoides antigens versus whole Kentucky overview of current diagnostic and management antigen preparations to more successfully modulate Rabies ...... 5 practices to combat signs of IBH. Although there the immune response, in particular, IgE response. is no cure for IBH, there is ongoing research to as- Another interesting area under current investiga- sess immunotherapies as future treatment options tion is oral immunotherapy, whereby transgenic for horses suffering with IBH. barely expressing allergens are administered orally While IBH has a multifactorial cause, it is ac- to prevent hypersensitivity to Culicoides. knowledged that the immune system plays a role Finally, given the important role of eosinophils in its development. Hypersensitivity reactions are in the pathology of IBH and the fact that IL-5 classified into four types, and IBH is a combina- drives eosinophil activity, a novel and allergen- tion of Type I and Type IV. independent vaccine has been evaluated that reactions develop when antigen specific allergens targets IL-5 and limits eosinophil recruitment to bind to IgE and cross-link receptors on mast cells, the affected skin. This is one of the few equine basophils and also involve eosinophils. These cells studies to investigate whether a vaccine can induce release vasoactive amines, such as , that autoantibodies to IL-5 and result in affect blood vessel size and leakage and produce clinical efficacy for IBH. This immunotherapeutic inflammatory and other mediators, approach may be the new generation for treating which result in inflammation and pruritus. Type chronic immune diseases, and may signal that new College of Agriculture, IV reactions, often referred to as delayed-type therapies are on the horizon for horses suffering Food and Environment hypersensitivity reactions, involve cell-mediated re- from IBH. Department of sponses particularly of activated Th-2 lymphocytes Veterinary Science CONTACT: which produce IL-5 cytokine and large numbers Amanda A . Adams, PhD of eosinophils, both contribute to the clinical Amanda .adams@uky .edu manifestations of IBH. Immunotherapy treatment (859) 218-1097 Maxwell H . Gluck Equine Research Center is based on a century-old concept that the immune University of Kentucky system can be desensitized to specific allergens Lexington, KY that trigger hypersensitivity reactions. Allergen 2 INTERNATIONAL First Quarter, 2018

he International Collating Centre, New- EHV-4 was recorded by France (four Tmarket, United Kingdom, and other sources outbreaks) and Switzerland (two cases). France reported the following equine disease outbreaks. (10 outbreaks) and Germany (four cases) reported The Republic of South Africa (RSA) reported occurrences of EHV-4 related respiratory disease. an expected seasonal increase in cases of African Also, France confirmed one case of EHV-4 abor- Horse Sickness. A total of 88 cases were recorded tion. in eight of the nine provinces. No cases occurred in The USA recorded multiple cases of EHV-2/5 the Western Cape Province, including the Disease infection in several states, some associated with Controlled Area. clinical evidence of respiratory disease. The UK and the USA reported outbreaks of Equine infectious anemia was confirmed by equine influenza. Two cases in recently imported Canada (three cases, one of which was clinical non-vaccinated horses were recorded in the UK. and died), France (one clinical case), and the USA The disease can be considered endemic in the USA (one case). in which it was confirmed in three states, with France reported equine piroplasmosis was en- multiple outbreaks in one of the states. demic in the country. The RSA recorded several France, Germany, Ireland, and the USA report- cases of the disease in four provinces. ed multiple outbreaks of strangles. The number of Taylorella equigenitalis, the causal agent of con- Equine Disease Quarterly outbreaks included 21 in France, two in Germany, tagious equine metritis was detected in an aged numerous cases in Ireland, and 65 outbreaks in stallion in France, and in six stallions and one mare Editors Peter Timoney 22 states in the USA, 10 involving multiple cases on a total of six premises in Germany. Alan Loynachan of the disease. A single case of equine coital exanthema caused Cynthia Gaskill Equine herpesvirus 1 (EHV-1) infection was by EHV-3 was diagnosed in a mare in Kentucky. Staff recorded in France, Germany, Ireland, Japan, A number of cases of nocardioform placentitis Diane Furry RSA, Switzerland, the UK, and the USA. Infec- were reported by the USA, several involving in- Tawana Brown Dennis Duross tion associated with fever was reported by France fection with Amycolatopsis spp and an additional Anita Fleming (two outbreaks), Ireland (seven outbreaks), and group associated with Crossiella equi infection, all Switzerland (one outbreak of combined EHV-1 but one in Kentucky. Correspondence should be and equine herpesvirus 4 infection). Respiratory The USA confirmed 11 cases of salmonellosis addressed to the editors, Department of Veterinary disease was diagnosed in Germany (25 cases), the during the review period, all isolates belonging to Science, Maxwell H . Gluck UK (eight outbreaks, majority in non-vaccinated, serogroup B. Equine Research Center, University of Kentucky, non-Thoroughbred horses), and the USA (wide- Three cases ofClostridium perfringens Type A Lexington, Kentucky USA, spread in various states). Cases of EHV-1 abortion toxin genotype were diagnosed in foals in Ken- 40546-0099 were recorded in France (eight outbreaks, three tucky. Telephone (859) 257-4757 Fax (859) 257-8542 involving multiple cases), Germany (four cases), Germany confirmed rotavirus infection in two Japan (single cases on 13 premises, all but four in foals on the same premises. Internet address: http://gluck .ca .uky edu/. vaccinated mares), the UK (five outbreaks involv- A case of Lawsonia intracellularis infection was equine-disease-quarterly ing vaccinated or non-vaccinated Thoroughbred diagnosed in a foal in Kentucky.

Material published in the and non-Thoroughbred mares), and the USA The USA recorded four cases of Eastern Equine Quarterly is not subject to (two cases). Encephalomyelitis (EEE) in the first quarter of copyright . Permission is EHV-1 associated neurologic disease was re- 2018, all in Florida. therefore granted to reproduce articles, although ported from France (one case), RSA (two cases on Equine encephalosis was reported by the RSA, acknowledgment of the same premises), Switzerland (one case), the UK with numerous cases in one province and isolated source and author is re- quested . (a single case on two premises), and the USA (23 cases in three other provinces. outbreaks involving 27 horses and multiple states). Rhodococcus equi infection is endemic in the The University of Kentucky is an Equal Opportunity USA, with many cases going unreported. Organization .

Printed on recycled paper Insect Bite Hypersensitivity in Horses 3 4 cases have been associated wit of tetanus antitoxin, although commer large percentage of horses affected with sea- sure to insects should be fully implemented. Farm Insect Bite Hypersensitivity in Horses (left): products also have been incriminated. The number sonal pruritic dermatitis are hypersensitive sanitation to compost manure properly, eliminate of horses that become ill following administration A Table 1. Breeding location and time of feeding for insects associated of a specific lot of incriminated blood product is (allergic) to the bites of insects. Culicoides spp wet areas with decomposing vegetation, and the with IBH . (gnats), black flies, stable flies, and horn flies are use of fly predators or feed through fly inhibitors estimated at 1 to 2 percent, although mor Insect Breeding Area Feeding Times the most commonly implicated insects although can greatly reduce fly populations. Heat, humidity, might have sub-clinical disease. An infectious any biting insect may contribute to insect bite- and solar radiation exacerbate pruritus, thus the Stable flies Manure and rotting Daytime agent, such as a virus, has long been suspected to vegetation induced hypersensitivity (IBH). IBH is character- provision of shade and wind currents by fans pro- cause this condition, and a ne ized by intense pruritus (itching) that often leads vide relief. Stabling to avoid the most significant Horn flies Cattle manure Daytime was recently discover to excoriation (abrasive skin damage), extensive insects (Table 1) and the use of fly sheets and face Horse and deer flies Vegetation and water Daytime of serum hepatitis. The par hair loss, secondary , and chronically masks are helpful. Because some horses develop the diseased horse an Culicoides spp Standing water and Twilight to dawn it had received nine weeks earlier to hyperkeratosis and lichenification (thickened contact to topical products, judicious and manure experimental horses skin). Many horses develop IBH in middle age cautious use of fly repellants is advisable. Simple Simulium (black) flies Running water Morning and evening or later, although horses with atopy may exhibit feeds and whole grains are better than mixed, resulted in transmission of this ne clinical signs as early as 1 year of age. Clinical signs multiple-grain sweet feeds. Cool-water rinses virus and in liver disease. often progress in each subsequent year. and shampoos can rehydrate and sooth dry skin immune responses to low percentage of clinically affected horses. Diagnosis is made from the signalment, history, as well as reduce the amount of allergens on the Rabies in the Horse and Beyond in Kentucky (page 5): clinical signs, and ruling out of other possible di- skin. Colloidal oatmeal, pramoxine, and 1 percent An identical disease, both in terms of clinical Table 2. Rabies virus test results broken down by wildlife, domestic signs and pathologic findings, is sporadically agnoses. The distribution of lesions on an affected hydrocortisone shampoos or leave-on hydrocorti- species (excluding horses), and horses . horse with IBH is dependent on the biting char- sone rinses may reduce pruritus and minimize or in adult horses without recent administration of an acteristics of the insect(s) responsible. Since there reduce the amount of systemic antipruritic medica- Domestic equine origin biologic. These “non-biologic is still much to be learned about the identification tion needed. Systemic medications (steroids and Species tend to mostly occur between J (excluding and can occur in small outbr and feeding habits of many insects implicated ) may help interrupt the itch-scratch Results Wildlife horses) Horses TOTAL in allergic dermatoses, it may not be possible to cycle, however long term use, particularly of ste- weeks. Non-biologic Negative 12,378 16,733 1,034 30,145 identify the exact etiological agent(s). IBH typi- roids, should be avoided. A complete and detailed commonly on brood cally improves and exacerbates seasonally, whereas investigation into the etiology of the disease should Positive 680 28 25 733 incidence of the non-biologic cases suggests the clinical expression of allergies in atopic horses may occur simultaneously with general symptomatic Unsatisfactory 823 675 11 1,509 possibility of insect transmission of par occur at any time of the year. Urticaria (hives), care. Intradermal skin testing to determine anti- specimen these “non-biologic” cases. Clinically affected horses with Theiler’ commonly found in atopy, is not a diagnosis but gens for allergen specific immunotherapy may be TOTAL 13,881 17,436 1,070 32,387 a cutaneous reaction pattern that may be induced helpful, particularly in young animals with atopy. frequently have both neurologic signs (hepatic by a wide variety of causes, both immunologic and Clients should understand that hypersensitivities encephalopathy: head pressing, stumbling, blind Figure 1. Geographic location ness) and jaundice (y non-immunologic. Rule outs for urticaria include and atopy are lifelong. Affected horses will need of the 25 horses testing positive drug and vaccine reactions; stinging and biting continuous management and/or therapy. Often a for rabies virus in Kentucky from insects (such as wasps) and arachnids; infections; patient may be symptom-free with low exposure to 1989 to 2017 . contact irritation; vasculitis; and cold, stress, or inciting antigens and symptomatic as the antigen exercise-induced lesions. Other diseases that ex- load increases. Antigen exposure is additive, thus hibit pruritus are Oxyuris (pin worm) infestation, comprehensive management is needed to best onchocerciasis, and mite (Chorioptes) and tick in- control clinical disease. festations. Diseases that occasionally are associated Importance of Prot CONTACT: with pruritus include ringworm and pemphigus, Susan L . White, DVM, MS, DACVIM Encephalomy an autoimmune disease. slwhite@uga .edu In all cases of pruritic dermatitis, managerial (706) 296-8607 Department of Large Animal Medicine 0 2 4 6 he two most fr procedures to decrease exposure to exciting agents College of Veterinary Medicine Tof equine encephalitis or equine encepha as well as symptomatic therapy to reduce pruritus University of Georgia lomyelitis in North America are Eastern E Athens, GA Figure 2. Geographic location is warranted. In IBH procedures to decrease expo- of skunks in Kentucky testing Encephalomyelitis (EEE) and W positive for rabies virus in the last litis (WNE) viruses. Both are mosquito-borne 29 years . and neurotropic. The respectiv Theiler’s Disease restricted to equids in terms of their host range; each can be transmitted heiler’s disease, or equine serum hepatitis, is antiserum, which was used as part of a vaccination other mammalian and avian species. Both diseases Tan infrequent but sometimes life-threatening strategy for African Horse Sickness. Since then, are a source of concern for the equine industr liver disease of adult horses. Sir Arnold Theiler many additional cases of serum hepatitis have not only from the first described the disease in the early 1900s as been reported, and a variety of blood products consequences of either infection, but also from a form of highly fatal acute liver failure that oc- of equine origin have been associated with the the economic losses involv curred 4-12 weeks after administration of equine disease. In North America, the majority of recent 0 2 4 6 Insect Bite Hypersensitivity in Horses 3 4 cases have been associated with the administration the neurologic signs are noted, there is a rapid of tetanus antitoxin, although commercial plasma progression to death in approximately 70 per- large percentage of horses affected with sea- sure to insects should be fully implemented. Farm Insect Bite Hypersensitivity in Horses (left): products also have been incriminated. The number cent of the cases. Horses that receive supportive sonal pruritic dermatitis are hypersensitive sanitation to compost manure properly, eliminate of horses that become ill following administration therapy and survive for five days after the onset of A Table 1. Breeding location and time of feeding for insects associated of a specific lot of incriminated blood product is fulminant disease generally recover and have no (allergic) to the bites of insects. Culicoides spp wet areas with decomposing vegetation, and the with IBH . (gnats), black flies, stable flies, and horn flies are use of fly predators or feed through fly inhibitors estimated at 1 to 2 percent, although more horses long-term effects. Insect Breeding Area Feeding Times the most commonly implicated insects although can greatly reduce fly populations. Heat, humidity, might have sub-clinical disease. An infectious Another recently discovered virus that causes any biting insect may contribute to insect bite- and solar radiation exacerbate pruritus, thus the Stable flies Manure and rotting Daytime agent, such as a virus, has long been suspected to liver disease in horses is non-primate hepacivirus vegetation induced hypersensitivity (IBH). IBH is character- provision of shade and wind currents by fans pro- cause this condition, and a new equine parvovirus (NPHV). NPHV is genetically the closest homolog ized by intense pruritus (itching) that often leads vide relief. Stabling to avoid the most significant Horn flies Cattle manure Daytime was recently discovered in a horse with a fatal case of human hepatitis C virus (HCV) discovered to to excoriation (abrasive skin damage), extensive insects (Table 1) and the use of fly sheets and face Horse and deer flies Vegetation and water Daytime of serum hepatitis. The parvovirus was present in date. Experimental horse infections consistently re- hair loss, secondary infections, and chronically masks are helpful. Because some horses develop the diseased horse and in the biologic product that sult in biochemical and histopathologic evidence of Culicoides spp Standing water and Twilight to dawn it had received nine weeks earlier. Inoculation of hepatitis, but the disease is mild and clinical signs to hyperkeratosis and lichenification (thickened contact allergies to topical products, judicious and manure experimental horses with the commercial product are either absent or very mild in recently infected skin). Many horses develop IBH in middle age cautious use of fly repellants is advisable. Simple Simulium (black) flies Running water Morning and evening or later, although horses with atopy may exhibit feeds and whole grains are better than mixed, resulted in transmission of this newly discovered horses. NPHV and equine parvovirus are present clinical signs as early as 1 year of age. Clinical signs multiple-grain sweet feeds. Cool-water rinses virus and in liver disease. Variation in individual in some healthy horses, indicating that horses can often progress in each subsequent year. and shampoos can rehydrate and sooth dry skin immune responses to the virus could explain the become healthy carriers of these viruses. low percentage of clinically affected horses. The USDA Center for Veterinary Biologics Diagnosis is made from the signalment, history, as well as reduce the amount of allergens on the Rabies in the Horse and Beyond in Kentucky (page 5): clinical signs, and ruling out of other possible di- skin. Colloidal oatmeal, pramoxine, and 1 percent An identical disease, both in terms of clinical has issued a notice that all licensed equine blood Table 2. Rabies virus test results broken down by wildlife, domestic signs and pathologic findings, is sporadically seen products have to test free of equine parvovirus agnoses. The distribution of lesions on an affected hydrocortisone shampoos or leave-on hydrocorti- species (excluding horses), and horses . horse with IBH is dependent on the biting char- sone rinses may reduce pruritus and minimize or in adult horses without recent administration of an and NPHV. This should improve horse health by acteristics of the insect(s) responsible. Since there reduce the amount of systemic antipruritic medica- Domestic equine origin biologic. These “non-biologic” cases eliminating most of the blood product-associated is still much to be learned about the identification tion needed. Systemic medications (steroids and Species tend to mostly occur between June and November cases of hepatitis. Non-biologic associated cases (excluding and can occur in small outbreaks that span a few will likely continue to occur until natural means and feeding habits of many insects implicated antihistamines) may help interrupt the itch-scratch Results Wildlife horses) Horses TOTAL in allergic dermatoses, it may not be possible to cycle, however long term use, particularly of ste- weeks. Non-biologic cases seem to occur most of virus transmission are determined and necessary Negative 12,378 16,733 1,034 30,145 identify the exact etiological agent(s). IBH typi- roids, should be avoided. A complete and detailed commonly on broodmare farms. The seasonal control methods implemented. incidence of the non-biologic cases suggests the cally improves and exacerbates seasonally, whereas investigation into the etiology of the disease should Positive 680 28 25 733 CONTACT: clinical expression of allergies in atopic horses may occur simultaneously with general symptomatic Unsatisfactory 823 675 11 1,509 possibility of insect transmission of parvovirus in Thomas J . Divers, Joy E . Tomlinson and Gerlinde R . Van de Walle occur at any time of the year. Urticaria (hives), care. Intradermal skin testing to determine anti- specimen these “non-biologic” cases. Clinically affected horses with Theiler’s disease tjd1@cornell .edu commonly found in atopy, is not a diagnosis but gens for allergen specific immunotherapy may be TOTAL 13,881 17,436 1,070 32,387 (607) 253-3100 a cutaneous reaction pattern that may be induced helpful, particularly in young animals with atopy. frequently have both neurologic signs (hepatic College of Veterinary Medicine Cornell University by a wide variety of causes, both immunologic and Clients should understand that hypersensitivities encephalopathy: head pressing, stumbling, blind- Figure 1. Geographic location ness) and jaundice (yellow gums and eyes). Once Ithaca, NY non-immunologic. Rule outs for urticaria include and atopy are lifelong. Affected horses will need of the 25 horses testing positive drug and vaccine reactions; stinging and biting continuous management and/or therapy. Often a for rabies virus in Kentucky from insects (such as wasps) and arachnids; infections; patient may be symptom-free with low exposure to 1989 to 2017 . contact irritation; vasculitis; and cold, stress, or inciting antigens and symptomatic as the antigen exercise-induced lesions. Other diseases that ex- load increases. Antigen exposure is additive, thus NATIONAL hibit pruritus are Oxyuris (pin worm) infestation, comprehensive management is needed to best onchocerciasis, and mite (Chorioptes) and tick in- control clinical disease. festations. Diseases that occasionally are associated Importance of Protecting your Horse against Eastern Equine CONTACT: with pruritus include ringworm and pemphigus, Susan L . White, DVM, MS, DACVIM Encephalomyelitis and West Nile Encephalitis an autoimmune disease. slwhite@uga .edu In all cases of pruritic dermatitis, managerial (706) 296-8607 Department of Large Animal Medicine 0 2 4 6 he two most frequently encountered causes Eastern equine encephalomyelitis poses an procedures to decrease exposure to exciting agents College of Veterinary Medicine Tof equine encephalitis or equine encepha- annual threat to equids in the Gulf and Atlantic as well as symptomatic therapy to reduce pruritus University of Georgia lomyelitis in North America are Eastern Equine coastal states and the Great Lakes region, extending Athens, GA Figure 2. Geographic location is warranted. In IBH procedures to decrease expo- of skunks in Kentucky testing Encephalomyelitis (EEE) and West Nile Encepha- in certain years as far north as eastern Canada. It positive for rabies virus in the last litis (WNE) viruses. Both are mosquito-borne is occasionally recorded in some inland states such 29 years . and neurotropic. The respective viruses are not as Arkansas, Oklahoma, Tennessee, Kentucky, Theiler’s Disease restricted to equids in terms of their host range; and Iowa. Evidence of EEE activity is most often each can be transmitted to humans and certain reported in Florida, in which it has been confirmed heiler’s disease, or equine serum hepatitis, is antiserum, which was used as part of a vaccination other mammalian and avian species. Both diseases as early as January, as recorded in 2018. Over the Tan infrequent but sometimes life-threatening strategy for African Horse Sickness. Since then, are a source of concern for the equine industry past 15 years, the yearly incidence of EEE cases in liver disease of adult horses. Sir Arnold Theiler many additional cases of serum hepatitis have not only from the potentially life-threatening equids has ranged from 60 (2011) to 712 (2003), first described the disease in the early 1900s as been reported, and a variety of blood products consequences of either infection, but also from with an annual average of 206 cases. In 2017, 86 a form of highly fatal acute liver failure that oc- of equine origin have been associated with the the economic losses involved. cases of the disease were reported in 13 states. curred 4-12 weeks after administration of equine disease. In North America, the majority of recent 0 2 4 6 3 4 cases have been associated with the administration the neurologic signs are noted, there is a rapid of tetanus antitoxin, although commercial plasma progression to death in approximately 70 per- arm Insect Bite Hypersensitivity in Horses (left): products also have been incriminated. The number cent of the cases. Horses that receive supportive e properly, eliminate of horses that become ill following administration therapy and survive for five days after the onset of Table 1. Breeding location and time of feeding for insects associated of a specific lot of incriminated blood product is fulminant disease generally recover and have no eas with decomposing vegetation, and the with IBH . ough fly inhibitors estimated at 1 to 2 percent, although more horses long-term effects. Insect Breeding Area Feeding Times educe fly populations. Heat, humidity, might have sub-clinical disease. An infectious Another recently discovered virus that causes and solar radiation exacerbate pruritus, thus the Stable flies Manure and rotting Daytime agent, such as a virus, has long been suspected to liver disease in horses is non-primate hepacivirus vegetation shade and wind currents by fans pro- cause this condition, and a new equine parvovirus (NPHV). NPHV is genetically the closest homolog oid the most significant Horn flies Cattle manure Daytime was recently discovered in a horse with a fatal case of human hepatitis C virus (HCV) discovered to Horse and deer flies Vegetation and water Daytime of serum hepatitis. The parvovirus was present in date. Experimental horse infections consistently re- ecause some horses develop the diseased horse and in the biologic product that sult in biochemical and histopathologic evidence of Culicoides spp Standing water and Twilight to dawn it had received nine weeks earlier. Inoculation of hepatitis, but the disease is mild and clinical signs contact allergies to topical products, judicious and manure experimental horses with the commercial product are either absent or very mild in recently infected imple Simulium (black) flies Running water Morning and evening feeds and whole grains are better than mixed, resulted in transmission of this newly discovered horses. NPHV and equine parvovirus are present virus and in liver disease. Variation in individual in some healthy horses, indicating that horses can drate and sooth dry skin immune responses to the virus could explain the become healthy carriers of these viruses. low percentage of clinically affected horses. The USDA Center for Veterinary Biologics educe the amount of allergens on the Rabies in the Horse and Beyond in Kentucky (page 5): skin. Colloidal oatmeal, pramoxine, and 1 percent An identical disease, both in terms of clinical has issued a notice that all licensed equine blood Table 2. Rabies virus test results broken down by wildlife, domestic signs and pathologic findings, is sporadically seen products have to test free of equine parvovirus tisone shampoos or leave-on hydrocorti- species (excluding horses), and horses . uritus and minimize or in adult horses without recent administration of an and NPHV. This should improve horse health by uritic medica- Domestic equine origin biologic. These “non-biologic” cases eliminating most of the blood product-associated oids and Species tend to mostly occur between June and November cases of hepatitis. Non-biologic associated cases (excluding and can occur in small outbreaks that span a few will likely continue to occur until natural means antihistamines) may help interrupt the itch-scratch Results Wildlife horses) Horses TOTAL er long term use, particularly of ste- weeks. Non-biologic cases seem to occur most of virus transmission are determined and necessary Negative 12,378 16,733 1,034 30,145 oided. A complete and detailed commonly on broodmare farms. The seasonal control methods implemented. incidence of the non-biologic cases suggests the Positive 680 28 25 733 CONTACT: occur simultaneously with general symptomatic Unsatisfactory 823 675 11 1,509 possibility of insect transmission of parvovirus in Thomas J . Divers, Joy E . Tomlinson and Gerlinde R . Van de Walle to determine anti- specimen these “non-biologic” cases. Clinically affected horses with Theiler’s disease tjd1@cornell .edu gens for allergen specific immunotherapy may be TOTAL 13,881 17,436 1,070 32,387 (607) 253-3100 ticularly in young animals with atopy. frequently have both neurologic signs (hepatic College of Veterinary Medicine Cornell University Clients should understand that hypersensitivities encephalopathy: head pressing, stumbling, blind- Figure 1. Geographic location ness) and jaundice (yellow gums and eyes). Once Ithaca, NY of the 25 horses testing positive continuous management and/or therapy. Often a for rabies virus in Kentucky from ee with low exposure to 1989 to 2017 . inciting antigens and symptomatic as the antigen e is additive, thus NATIONAL ment is needed to best Importance of Protecting your Horse against Eastern Equine ACVIM Encephalomyelitis and West Nile Encephalitis

edicine 0 2 4 6 he two most frequently encountered causes Eastern equine encephalomyelitis poses an edicine Tof equine encephalitis or equine encepha- annual threat to equids in the Gulf and Atlantic Figure 2. Geographic location lomyelitis in North America are Eastern Equine coastal states and the Great Lakes region, extending of skunks in Kentucky testing Encephalomyelitis (EEE) and West Nile Encepha- in certain years as far north as eastern Canada. It positive for rabies virus in the last litis (WNE) viruses. Both are mosquito-borne is occasionally recorded in some inland states such 29 years . and neurotropic. The respective viruses are not as Arkansas, Oklahoma, Tennessee, Kentucky, restricted to equids in terms of their host range; and Iowa. Evidence of EEE activity is most often each can be transmitted to humans and certain reported in Florida, in which it has been confirmed sed as part of a vaccination other mammalian and avian species. Both diseases as early as January, as recorded in 2018. Over the ickness. Since then, are a source of concern for the equine industry past 15 years, the yearly incidence of EEE cases in of serum hepatitis have not only from the potentially life-threatening equids has ranged from 60 (2011) to 712 (2003), ted, and a variety of blood products consequences of either infection, but also from with an annual average of 206 cases. In 2017, 86 been associated with the the economic losses involved. cases of the disease were reported in 13 states. th America, the majority of recent 0 2 4 6 5 In temperate regions, transmission of EEE virus by the American Veterinary Medical Association is seasonal, occurring in the summer and the fall. with respect to “core vaccines”–namely those that In sub-tropical regions such as Florida, there is a protect against diseases that are endemic, of poten- year-round risk of EEE, with virus transmission tial public health significance, and represent a risk peaking in the summer months. of causing severe disease—strongly recommends Equids and humans are tangential or dead-end that horses be immunized against EEE and WNE. hosts of EEE virus and neither plays a role in the Available inactivated whole-virus vaccines against natural life-cycle of the virus. Infections in horses, EEE (including Western Equine Encephalomy- mules, and donkeys are frequently life-threatening; elitis) have been shown to be safe and effective in case fatality rates can be as high as 90 percent. protecting against this disease. Two inactivated West Nile encephalitis (WNE) is also a cause of whole-virus vaccines, a live canary pox vector vac- significant concern to veterinary practitioners and cine and an inactivated flavivirus chimera vaccine members of the equine industry. Within four years are available against WNE. All have been con- following initial introduction of the causal virus in firmed safe and effective in preventing the disease. New York State in 1999, the virus had spread to Despite the AAEP recommendations to horse 48 states and several provinces in Canada. Since owners to vaccinate their horses against EEE 1999, the yearly incidence of WNE cases in equids and WNE, regrettably many fail to do so. The has ranged from 60 (2000) to 15,257 (2002). The vast majority of equine cases of EEE and WNE annual average number of cases over the past 10 either have no history of vaccination against the years was 272. In 2017, 307 equine cases were particular virus or else the vaccination history is reported in 39 states. incomplete. There is need for an ongoing concerted Similar to EEE, transmission of WNE virus is effort, utilizing all avenues of communication in- seasonal, occurring in the summer and extending cluding social media, to alert horse owners of the well into the fall. Neither equids nor humans serve dangers of these two vector-borne diseases and of as amplifying hosts for WNE virus insofar as vire- the importance of vaccination as an effective means mias are insufficient in magnitude and duration to of prevention and averting the losses that continue infect mosquitoes. Unlike EEE, only about 10% to occur every year in unprotected horses. of WNE virus-exposed horses will develop clinical CONTACT: infections. Reported case-fatality rates in affected Peter J . Timoney, MVB, MS, PhD, FRCVS horses can reach 30-40 percent, less than half that ptimoney@uky .edu encountered in cases of EEE. (859) 218-1094 Maxwell H . Gluck Equine Research Center The American Association of Equine Practitio- University of Kentucky ners (AAEP), in accordance with criteria defined Lexington, KY

KENTUCKY Rabies in the Horse and Beyond in Kentucky: A Look at the Last 29 Years

abies virus exposure typically occurs following uted nearly worldwide. Attention to the disease Rthe bite of an infected animal. Depending is primarily focused on preventive and control on the anatomic site of exposure, an incubation strategies. Many countries are considered rabies- period of variable duration follows as the virus free for the purposes of importing dogs into the evades the immune response by hiding in the United States (https://www.cdc.gov/importation/ central nervous system. Amplification of the virus rabies-free-countries.html). occurs in the dorsal root ganglion after which it Rabies can be prevented by pre-exposure vac- travels towards the brain via the spinal cord. At cination of humans and animals. A human diploid this point, clinical signs of rabies become manifest cell vaccine and a purified chick embryo vaccine and therapy is almost invariably futile. Without are available for humans (the latter is mainly used early treatment, rabies is nearly 100 percent fatal. outside of the USA) for pre- and post-exposure to Rabies is a zoonotic (capable of being transmitted rabies, with rabies immune globulin available only from animals to humans) disease that is distrib- for post-exposure treatment in exposed humans. Equine Disease Quarterly Newsletter

Department of Veterinary Science Maxwell H. Gluck Equine Research Center University of Kentucky Lexington, Kentucky 40546-0099

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Pre-exposure vaccination involves administration domestic animals were horses (Table 2), which of three doses of vaccine given over a one month means that horses accounted for less than 1 per- period. In unvaccinated humans, post-exposure cent of the total positive rabies cases in Kentucky treatment consists of the administration of five over the last 29 years. Rabies-positive horses were doses of vaccine. Vaccines for multiple species of primarily located in Central Kentucky (Figure 1). domestic animals are available to licensed veterinar- The terrestrial reservoir for rabies in the state is the ians. Wildlife vaccines may be available from veteri- striped skunk, and skunks positive for rabies virus narians, but are typically used in targeted locations have been located in all counties where infected by the Kentucky Department of Fish and Wildlife horses have resided (Figure 2). and the United States Department of Agriculture. As a closing comment, a robust surveillance From January 1989 through December 2017, program involving the UK Veterinary Diagnostic Kentucky tested 32,387 animals for rabies virus. Lab, Breathitt Veterinary Center, the Kentucky Of this total, 2.3 percent (733 animals) tested posi- Cabinet for Health, Kentucky Fish and Wildlife, tive, 93.1 percent (30,145 animals) tested negative, and USDA is in place to thoroughly monitor rabies and 4.6 percent (1509 animals) were unsatisfactory in Kentucky. The vast majority of animals testing for testing (i.e. the sample was untestable due to positive for rabies are wildlife, with little or no maceration, degradation, or insufficient mate- exposure to humans, pets and domestic animals. rial). Of note: Animals suspected of having rabies More importantly for horse enthusiasts within should not be euthanized by traumatic insult (e.g. the state, the number of horses testing positive for gunshot) to the brain, because trauma frequently rabies is extremely low. renders the sample unsatisfactory for testing. Of CONTACT: the 733 positive animals, only 7.2 percent (53 Jacqueline Smith, PhD animals) were from domestic species (i.e. pets and jsmit8@uky .edu farm animals), and the other 92.8 percent (680 (859) 257-7559 University of Kentucky Veterinary Diagnostic Laboratory animals) were wildlife. Twenty-five of the positive Lexington , KY