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==Introduction==

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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 equids that have travelled in the Americas.<ref name="EPM3">Vatistas, N, Mayhew, J (1995) Differential diagnosis of polyneuritis equi.  ''In Practice'', Jan, 26-29.</ref>  Equine protozoal myeloencephalitis (EPM) is one of the most frequently diagnosed neurological conditions in 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>  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>

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 equids that have travelled in the Americas.<ref name="EPM3">Vatistas, N, Mayhew, J (1995) Differential diagnosis of polyneuritis equi.  ''In Practice'', Jan, 26-29.</ref>  Equine protozoal myeloencephalitis (EPM) is one of the most frequently diagnosed neurological conditions in 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>  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>

==Aetiology==

==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>

EPM results from infection of the CNS by the apicomplexan parasite [[Sarcocystis|''Sarcocystis neurona'']] or, less frequently, its close relative [[Neospora|''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>

==Epidemiology==

==Epidemiology==

[[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.'' ''']]

[[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.'' ''']]

Infective sporocysts are passed in the faeces of the definitive host and must be ingested by the horse for infection to occur.  See [[Sarcocystis|here]] for further details of the life cycle of ''Sarcocystis neurona''.

Infective sporocysts are passed in the faeces of the definitive host and must be ingested by the horse for infection to occur.  See [[Sarcocystis|the ''Sarcocystis'' page]] for further details of the life cycle of ''S.neurona''.

==Pathogenesis==

==Pathogenesis==

It is difficult to obtain a definitive antemortem diagnosis of EPM.  Certain criteria must be met before such a diagnosis is assigned<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>:

It is difficult to obtain a definitive antemortem diagnosis of EPM.  Certain criteria must be met before such a diagnosis is assigned<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 relevant clinical signs must be attributable to one or more lesions of the CNS<ref name="Johnson">Johnson, A.L (2009) Evidence-based review of diagnosis and treatment of ''Sarcocystis neurona'' infection (Equine Protozoal Myeloencephalitis).  ''Proceedings of the Annual Convention of the AAEP'' - Las Vegas, NV, USA, 55:172-176.</ref>

*The relevant clinical signs must be attributable to one or more lesions of the CNS<ref name="Johnson">Johnson, A.L (2009) Evidence-based review of diagnosis and treatment of ''Sarcocystis neurona'' infection (Equine Protozoal Myeloencephalitis).  ''Proceedings of the Annual Convention of the AAEP'' - Las Vegas, NV, USA, 55:172-176.</ref>

*Immunodiognostic tests must confirm exposure to the parasite

*Immunodiagnostic tests must confirm exposure to the parasite

*Other differentials with similar presentations should be ruled out wherever possible

*Other differentials with similar presentations should be ruled out wherever possible

*The horse should be resident in or have travelled within the Americas<ref name="EPM3">Vatistas, N, Mayhew, J (1995) Differential diagnosis of polyneuritis equi.  ''In Practice'', Jan, 26-29.</ref>

*The horse should be resident in or have travelled within the Americas<ref name="EPM3">Vatistas, N, Mayhew, J (1995) Differential diagnosis of polyneuritis equi.  ''In Practice'', Jan, 26-29.</ref>

The primary step in the diagnostic procedure should be to carry out thorough clinical and neurological examinations. <ref name="Johnson">Johnson, A.L (2009) Evidence-based review of diagnosis and treatment of ''Sarcocystis neurona'' infection (Equine Protozoal Myeloencephalitis).  ''Proceedings of the Annual Convention of the AAEP'' - Las Vegas, NV, USA, 55:172-176.</ref>  

The primary step in the diagnostic procedure should be to carry out thorough clinical and [[:Category:Neurological Examination - Horse|neurological examinations]]. <ref name="Johnson">Johnson, A.L (2009) Evidence-based review of diagnosis and treatment of ''Sarcocystis neurona'' infection (Equine Protozoal Myeloencephalitis).  ''Proceedings of the Annual Convention of the AAEP'' - Las Vegas, NV, USA, 55:172-176.</ref>  

===Immunodiagnostic  tests===

===Immunodiagnostic  tests===

|Plain lateral radiography of C1 to T1<ref name="Hahn">Hahn, C.N (2010) ''Cervical Vertebral Malformation'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>, myelography. <ref name="Seino">Seino, K.K (2010) ''Spinal Ataxia'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 3.</ref>

|Plain lateral radiography of C1 to T1<ref name="Hahn">Hahn, C.N (2010) ''Cervical Vertebral Malformation'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>, myelography. <ref name="Seino">Seino, K.K (2010) ''Spinal Ataxia'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 3.</ref>

|-

|-

|West Nile encephalitis

|[[West Nile Virus|West Nile encephalitis]]

|Systemically ill, pyrexia.  Difficult to differentiate if horse is afebrile and has no excessive muscle fasciculations.<ref name="Long">Long, M.T (2010) ''Flavivirus Encephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>  

|Systemically ill, pyrexia.  Difficult to differentiate if horse is afebrile and has no excessive muscle fasciculations.<ref name="Long">Long, M.T (2010) ''Flavivirus Encephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>  

|Leukogram, CSF analysis, IgM capture ELISA, plaque reduction neutralization test (PRNT),<ref name="Seino">Seino, K.K (2010) ''Spinal Ataxia'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 3.</ref>absence of mosquito vectors.<ref name="Johnson">Johnson, A.L (2009) Evidence-based review of diagnosis and treatment of ''Sarcocystis neurona'' infection (Equine Protozoal Myeloencephalitis).  ''Proceedings of the Annual Convention of the AAEP'' - Las Vegas, NV, USA, 55:172-176.</ref>

|Leukogram, CSF analysis, IgM capture ELISA, plaque reduction neutralization test (PRNT),<ref name="Seino">Seino, K.K (2010) ''Spinal Ataxia'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 3.</ref>absence of mosquito vectors.<ref name="Johnson">Johnson, A.L (2009) Evidence-based review of diagnosis and treatment of ''Sarcocystis neurona'' infection (Equine Protozoal Myeloencephalitis).  ''Proceedings of the Annual Convention of the AAEP'' - Las Vegas, NV, USA, 55:172-176.</ref>

|Leukogram, IgM ELISA<ref>Bertone, J.J (2010) ''Viral Encephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>

|Leukogram, IgM ELISA<ref>Bertone, J.J (2010) ''Viral Encephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>

|-

|-

|Equine herpesvirus-1 myeloencephalopathy  

|[[Equine Herpesvirus 1|Equine herpesvirus-1 myeloencephalopathy]]

|Sudden onset and early stabilization of neurological signs, multiple horses affected, recent fever, respiratory disease, abortion.<ref>Wilson, W.D, Pusterla, N (2010) ''Equine Herpesvirus-1 Myeloencephalopathy'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>  Dysuria not often seen in 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>

|Sudden onset and early stabilization of neurological signs, multiple horses affected, recent fever, respiratory disease, abortion.<ref>Wilson, W.D, Pusterla, N (2010) ''Equine Herpesvirus-1 Myeloencephalopathy'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>  Dysuria not often seen in 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>

|CSF analysis, buffy coat, nasal swab PCR.<ref name="Johnson">Johnson, A.L (2009) Evidence-based review of diagnosis and treatment of ''Sarcocystis neurona'' infection (Equine Protozoal Myeloencephalitis).  ''Proceedings of the Annual Convention of the AAEP'' - Las Vegas, NV, USA, 55:172-176.</ref><ref name="Seino">Seino, K.K (2010) ''Spinal Ataxia'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 3.</ref>

|CSF analysis, buffy coat, nasal swab PCR.<ref name="Johnson">Johnson, A.L (2009) Evidence-based review of diagnosis and treatment of ''Sarcocystis neurona'' infection (Equine Protozoal Myeloencephalitis).  ''Proceedings of the Annual Convention of the AAEP'' - Las Vegas, NV, USA, 55:172-176.</ref><ref name="Seino">Seino, K.K (2010) ''Spinal Ataxia'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 3.</ref>

|-

|-

|Rabies

|[[Rabies]]

|Rapid progression<ref name="Sommardahl">Sommardahl, C.S (2010) ''Rabies'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>, behavioural alterations, depression, seizure, coma.<ref name="Long">Long, M.T (2010) ''Flavivirus Encephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>  

|Rapid progression<ref name="Sommardahl">Sommardahl, C.S (2010) ''Rabies'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>, behavioural alterations, depression, seizure, coma.<ref name="Long">Long, M.T (2010) ''Flavivirus Encephalitis'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>  

|Post-mortem fluorescent antibody testing of brain required for definitive diagnosis.<ref name="Sommardahl">Sommardahl, C.S (2010) ''Rabies'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>  

|Post-mortem fluorescent antibody testing of brain required for definitive diagnosis.<ref name="Sommardahl">Sommardahl, C.S (2010) ''Rabies'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>  

|CSF analysis and culture.  '''NB: CSF collection contraindicated if clinical signs suggest high intracranial pressure'''  

|CSF analysis and culture.  '''NB: CSF collection contraindicated if clinical signs suggest high intracranial pressure'''  

|-

|-

|CNS abscessation due to 'bastard strangles'<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>

|CNS abscessation due to [[Streptococcus equi subsp. equi|'bastard strangles]]'<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>

|History of ''Streptococcus equi subsp. equi'' infection.<ref name="Byrne">Byrne, B. A (2010) ''Diseases of the Cerebellum'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>

|History of [[Streptococcus equi subsp. equi|''Streptococcus equi subsp. equi'']] infection.<ref name="Byrne">Byrne, B. A (2010) ''Diseases of the Cerebellum'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>

|CSF analysis (severe, suppurative inflammation), culture of CSF.<ref name="Byrne">Byrne, B. A (2010) ''Diseases of the Cerebellum'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>

|CSF analysis (severe, suppurative inflammation), culture of CSF.<ref name="Byrne">Byrne, B. A (2010) ''Diseases of the Cerebellum'' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12.</ref>

|-

|-

NB: EPM has been seen concurrently with equine motor neuron disease in a mule<ref>Finno, C.J, Eaton, J.S, Aleman, M, Hollingsworth, S.R (2010) Equine protozoal myeloencephalitis due to ''Neospora hughesi'' and equine motor neuron disease in a mule.  ''Vet Ophthalmol'', 13(4):259-65.</ref>

NB: EPM has been seen concurrently with equine motor neuron disease in a mule<ref>Finno, C.J, Eaton, J.S, Aleman, M, Hollingsworth, S.R (2010) Equine protozoal myeloencephalitis due to ''Neospora hughesi'' and equine motor neuron disease in a mule.  ''Vet Ophthalmol'', 13(4):259-65.</ref>

[[Image:Equine_Protozoal_Myeloencephalitis.jpg|600px|thumb|left|''' Sarcocystis neurona stages and lesions.  

[[Image:Equine_Protozoal_Myeloencephalitis.jpg|600px|thumb|right|''' Sarcocystis neurona stages and lesions.  

(A). Cross section of spinal cord of horse with focal areas of discoloration (arrows) indicative of necrosis. Unstained.  

(A). Cross section of spinal cord of horse with focal areas of discoloration (arrows) indicative of necrosis. Unstained.  

==Prognosis==

==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 name="MacKay">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).

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, there is a recovery rate of around 25% and an improvement in 60-75% of cases.<ref name="MacKay">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 a response to treatment within two weeks.  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.

==Prevention==

==Prevention==

===Prophylaxis===

===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>Protocols involving intermittent administration of ponazuril may also show promise in the prevention of EPM.<ref>Mackay, R.J, Tanhauser, S.T, Gillis, K.D, Mayhew, I.G, Kennedy, T.J (2008) Effect of intermittent oral administration of ponazuril on experimental ''Sarcocystis neurona'' infection of horses.  ''Am J Vet Res'', 69(3):396-402.</ref>

A killed vaccine, developed using ''S.neurona'' merozoites, was conditionally licensed for use in horses.<ref name="Saville1">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>Protocols involving intermittent administration of ponazuril may also show promise in the prevention of EPM.<ref>Mackay, R.J, Tanhauser, S.T, Gillis, K.D, Mayhew, I.G, Kennedy, T.J (2008) Effect of intermittent oral administration of ponazuril on experimental ''Sarcocystis neurona'' infection of horses.  ''Am J Vet Res'', 69(3):396-402.</ref>

 

 

 

 

 

==References==

==References==

[[Category:Tissue_Cyst_Forming_Coccidia]][[Category:Horse]]

[[Category:Expert_Review]]

[[Category:To_Do_-_Nina]]

[[Category:Neurological Diseases - Horse]]