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Equine Protozoal Myeloencephalitis (view source)

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====Description====

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==Description==

A progressive, infectious,<ref name="Pasq">Pasquini, C, Pasquini, S, Woods, P (2005) '''Guide to Equine Clinics Volume 1: Equine Medicine''' (Third edition), ''SUDZ Publishing'', 245-250.</ref>neurological disease of horses, endemic in the USA<ref name="EPM8">Gray, L.C, Magdesian, K.G, Sturges, B.K, Madigan, J.E (2001) Suspected protozoal myeloencephalitis in a two-month-old colt. ''Vet Rec'', 149:269-273.</ref> and only encountered elsewhere in imported equids.<ref name="EPM3">Vatistas, N, Mayhew, J (1995) Differential diagnosis of polyneuritis equi. ''In Practice'', Jan, 26-29.</ref> EPM is one of the most frequently diagnosed neurological conditions of the Western Hemisphere<ref name="Furr">Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref> and the principal differential for multifocal, asymmetric progressive central nervous system (CNS) disease.<ref name="Pasq">Pasquini, C, Pasquini, S, Woods, P (2005) '''Guide to Equine Clinics Volume 1: Equine Medicine''' (Third edition), ''SUDZ Publishing'', 245-250.</ref> As it can resemble any neurological disorder, EPM must be considered in any horse with neurological signs if it resides in the Americas or if it has been imported from that area<ref name="EPM8">Gray, L.C, Magdesian, K.G, Sturges, B.K, Madigan, J.E (2001) Suspected protozoal myeloencephalitis in a two-month-old colt. ''Vet Rec'', 149:269-273.</ref><ref name="EPM9">DEFRA, The Animal Health Trust, The British Equine Veterinary Association (2009) Surveillance: Equine disease surveillance, April to June 2009, ''The Vet Rec'', Oct 24:489-492.</ref> The disease is not contagious.<ref name="Pasq">Pasquini, C, Pasquini, S, Woods, P (2005) '''Guide to Equine Clinics Volume 1: Equine Medicine''', (Third edition), ''SUDZ Publishing'', 245-250.</ref>

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====Aetiology====

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==Aetiology==

EPM results from infection of the CNS by the apicomplexan parasite ''Sarcocystis neurona'' or, less frequently, its close relative ''Neospora hughesi''.<ref>Dubey, J.P, Lindsay, D.S, Saville, W.J, Reed, S.M, Granstrom, D.E, Speer, C.A (2001)A review of ''Sarcocystis neurona'' and equine protozoal myeloencephalitis (EPM). ''Vet Parasitol'', 95:89-131. In: Pusterla, N, Wilson, W.D, Conrad, P.A, Barr, B.C, Ferraro, G.L, Daft, B.M, Leutenegger, C.M (2006) Cytokine gene signatures in neural tissue of horses with equine protozoal myeloencephalitis or equine herpes type 1 myeloencephalopathy. ''Vet Rec'', Sep 9:''Papers & Articles''.</ref><ref>Wobeser, B.K, Godson, D.L, Rejmanek, D, Dowling, P (2009) Equine protozoal myeloencephalitis caused by ''Neospora hughesi'' in an adult horse in Saskatchewan. ''Can Vet J'', 50(8):851-3.</ref> These protozoans develop within neurons<ref name="Furr">Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref> causing immediate or inflammatory-mediated neuronal damage. The organisms migrate randomly through the brain and spinal cord causing asymmetrical lesions of grey and white matter and thus multifocal lower and upper motor neuron deficits.<ref name="Pasq">Pasquini, C, Pasquini, S, Woods, P (2005) '''Guide to Equine Clinics Volume 1: Equine Medicine''' (Third edition), ''SUDZ Publishing'', 245-250.</ref>

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====Epidemiology====

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==Epidemiology==

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In endemic areas of the United States, around a quarter of referrals for equine neurological disease are attributed to EPM.<ref>Reed, S.M, Granstrom, D, Rivas, L.J, Saville, W.A, Moore, B.R, Mitten, L.A (1994) Results of cerebrospinal fluid analysis in 119 horses testing positive to the Western blot test on both serum and CSF to equine protozoal encephalomyelitis. In ''Proc Am Assoc Equine Pract'', Vancouver BC, AEEP, Lexington, KY, p199. In: Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref> According to the United States Department of Agriculture, the average incidence of the disease is 14 cases per 10,000 horses per year. However, the challenges of obtaining a definitive diagnosis may mean this figure is an underestimate.<ref name="Furr">Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref> The disease has been identified in parts of Central and South America, southern Canada and across most of the USA..<ref name="Furr">Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref> EPM is noted occasionally in other countries, in horses that have been imported from the Americas.<ref>Pitel, P.H, Pronost, S, Gargala, G, Anrioud, D, Toquet, M-P, Foucher, N, Collobert-Laugier, C, Fortier, G, Ballet, J-J (2002) Detection of ''Sarcocystis neurona'' antibodies in French horses with neurological signs, ''Int J Parasitol'', 32:481-485. In: Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref><ref>Goehring, L.S (2001) Sloet van Oldruitenborgh-Oosterbaan MM: Equine protozoal myeloencephalitis in the Netherlands? An overview, ''Tijdschr Diergeneeskd'', 126:346-351. In: Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref> It is likely that these animals underwent transportation carrying a silent but persistent infection. There have been reports of EPM in horses that have not travelled to or from endemic regions,<ref name="Furr">Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref> although cross-reacting antigens on the immunoblot test may explain this discrepancy. <ref name="Furr">Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>

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Increasing age and environmental temperature have been associated with an increased seroprevalence of ''S. neurona''.<ref>Tillotson, K, McCue, P.M, Granstrom, D.E, Dargatz, D.A, Smith, M.O, Traub-Dargatz, J.L (1999) Seroprevalence of antibodies to ''Sarcocystis neurona'' in horses residing in northern Colorado, ''J Equine Vet Sci'', 19:122-126. In: Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref> Seroprevalence for this species is typically higher than for ''N. hughesi''.<ref name="Furr">Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>Other risk factors for EPM include the presence of opossums, rats, mice and woodland, increased population density of humans and horses, bedding horses on shavings or wood chips and the use of purchased grain.<ref name="Furr">Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>Case clustering may operate where all the risk factors occur, but the majority of cases appear in isolation.<ref name="Furr">Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>

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====Life Cycle====

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==Life Cycle==

[[Image:Equine_Protozoal_Myeloencephalitis_life_cycle.jpg|600px|thumb|centre|''' Life cycle diagram of ''Sarcocystis neurona''. Created by the ''Agricultural Research Service, the research agency of the United States Department of Agriculture'', July 2005. ''Sourced from the USDA Agricultural Research Service page on EPM/Sarcocystis neurona, located via WikiMedia Commons.'' ''']]

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The causative pathogen(s) have been isolated from species other than the horse including zebra, domestic cat, Canadian lynx, sea otter, straw-necked ibis, mink, raccoon and sunk. (Furr)

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====Signalment====

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==Signalment==

Mostly Standardbreds and Thoroughbreds aged 1-6years.<ref name="Pasq">Pasquini, C, Pasquini, S, Woods, P (2005) '''Guide to Equine Clinics Volume 1: Equine Medicine''' (Third edition), ''SUDZ Publishing'', 245-250.</ref> Foal infection may be possible.<ref name="EPM8">Gray, L.C, Magdesian, K.G, Sturges, B.K, Madigan, J.E (2001) Suspected protozoal myeloencephalitis in a two-month-old colt. ''Vet Rec'', 149:269-273.</ref>

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====Clinical Signs====

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==Clinical Signs==

The disease onset may be acute, peracute or chronic. An insidious onset ataxia is most typical and with such cases, the clinical examination may reveal a bright, alert horse, perhaps with some focal muscle atrophy.<ref name="Furr">Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref> In all cases, the clinical signs are referable to diffuse focal and multifocal lesions of the white and grey matter of the spinal cord and brain.<ref name="EPM3">Vatistas, N, Mayhew, J (1995) Differential diagnosis of polyneuritis equi. ''In Practice'', Jan, 26-29.</ref> The three characteristic 'As' (ataxia, asymmetry, atrophy) suggest multifocal or diffuse disease, but are not pathognomonic for EPM.<ref name="Furr">Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>

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Lesions of the brainstem, cerebrum or cerebellum are less frequently recognized than those of the spinal cord. Horses with severe EPM may be unable to stand or swallow and, if left untreated, progress to recumbency within 14 days to 6 months.<ref name="Pasq">Pasquini, C, Pasquini, S, Woods, P (2005) '''Guide to Equine Clinics Volume 1: Equine Medicine''' (Third edition), ''SUDZ Publishing'', 245-250.</ref> This deterioration may occur smoothly or spasmodically,<ref name="Merck">Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition), Merial</ref> but is likely to result in death. It has been suggested that rapidly progressive presentations reflect brainstem lesions.<ref name="Furr">Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>

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====Diagnosis====

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==Diagnosis==

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====Differential Diagnoses====

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===Differential Diagnoses===

The protozoan can migrate to any region of the CNS<ref name="EPM8">Gray, L.C, Magdesian, K.G, Sturges, B.K, Madigan, J.E (2001) Suspected protozoal myeloencephalitis in a two-month-old colt. ''Vet Rec'', 149:269-273.</ref>, thus the differential list comprises almost all diseases of this system.

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(H). An oocyst with two sporocysts each with banana-shaped sporozoites. Unstained.

Created by the ''Agricultural Research Service, the research agency of the United States Department of Agriculture'', July 2005. ''Sourced from the USDA Agricultural Research Service page on EPM/Sarcocystis neurona, located via WikiMedia Commons.'' ''']]

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====Pathology====

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===Pathology===

Widespread lesions of the CNS are typically observed in horses.<ref name="Furr">Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>

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=====Gross exam=====

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====Gross exam====

Lesions may be up to several centimetres across.<ref name="Furr">Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref> They range from mild discolouration to multifocal areas of haemorrhage and/or malacia<ref name="Merck">Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition), Merial</ref> of the brain, spinal cord and less commonly, peripheral nerves.<ref name="Furr">Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>

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=====Histopathology=====

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====Histopathology====

Microscopically, both grey and white matter may be affected with focal to diffuse areas of nonsuppurative inflammation, necrosis and neuronal destruction. Perivascular infiltrates comprise lymphocytes, macrophages, plasma cells, giant cells, eosinophils and gitter cells.<ref name="Furr">Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref> In around 25% of cases, schizonts or merozoites may be found in the neuronal cytoplasm.<ref name="Merck">Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition), Merial</ref> Less frequently, protozoa parasitize intravascular and tissue neutrophils and eosinophils, capillary endothelial cells and myelinated axons<ref name="Furr">Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref><ref name="Merck">Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition), Merial</ref>. Free merozoites may be seen in necrotic regions. If organisms are absent, the diagnosis relies on recognition of the inflammatory changes described above.<ref name="Merck">Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition), Merial</ref>

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====Treatment====

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==Treatment==

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====Prognosis====

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==Prognosis==

Depends on duration and severity of neurological signs<ref name="EPM3">Vatistas, N, Mayhew, J (1995) Differential diagnosis of polyneuritis equi. ''In Practice'', Jan, 26-29.</ref> but clinical resolution is more likely if the condition is diagnosed and treated early.<ref name="EPM8">Gray, L.C, Magdesian, K.G, Sturges, B.K, Madigan, J.E (2001) Suspected protozoal myeloencephalitis in a two-month-old colt. ''Vet Record'', 149:269-273.</ref> With standard therapy, involving 6-8months of ponazuzril or pyrimethamine-sulfadiazine (V), there is a recovery rate of around 25% and an improvement in 60-75% of cases.<ref>MacKay, R.J (2006) Equine protozoa myeloencephalitis: treatment, prognosis and prevention. ''Clin Tech Equine Pract'', 5:9-16. In: Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref> A good prognosis might be expected if there is an improvement in clinical signs within two weeks of commencing anti-protozoal and anti-inflammatory treatment (V). The prognosis will be guarded to poor<ref name="Pasq">Pasquini, C, Pasquini, S, Woods, P (2005) '''Guide to Equine Clinics Volume 1: Equine Medicine''' (Third edition), ''SUDZ Publishing'', 245-250.</ref> for a horse with severe irreversible neuronal damage or one that has not been diagnosed or treated appropriately (V).

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====Prevention====

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==Prevention==

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=====Prophylaxis=====

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===Prophylaxis===

A killed vaccine, developed using ''S.neurona'' merozoites, was conditionally licensed for use in horses.<ref>Saville, W.J.A, Reed, S.M, Dubey, J.P (2002) Prevention of equine protozoal myeloencephalitis

(EPM). ''Proceedings of the Annual Convention of the AAEP'', 48:181-185.</ref> The vaccine proved to be ineffective in the prevention of EPM and has since been removed from the market.<ref name="Furr">Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref> There is evidence to suggest that the antiprotozoal, ponazuril, may be useful prophylactically to reduce the incidence and severity of clinical signs.<ref>Furr, M, MacKenzie, H, Dubey, J.P (2006) Pretreatment of horses with ponazuril limits infection and neurologic signs resulting from S.neurona. ''J Parasitol'', 92:637-643. In: Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref> Implementing such a regime prior to and during stressful events may be beneficial, although the cost is likely to be prohibitive.<ref name="Furr">Furr, M (2010) ''Equine protozoal myeloencephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>

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====References====

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==References==

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