Changes

The Food and Drug Administration (FDA) has approved four treatments for use in horses with EPM, but not all of these are commercially available:<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 Food and Drug Administration (FDA) has approved four treatments for use in horses with EPM, but not all of these are commercially available:<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>

*'''Sulfadiazine and pyrimethamine combination, ('Rebalance™', Antiprotozoal Oral Suspension, IVX Animal Health)''': administered PO daily for a minimum of 90 days. Due to availability and ease of administration, some use an off-label regimen of trimethoprimsulfa tablets with pyrimethamine tablets.  ''Mode of action'': trimethoprim, sulfadiazine, and pyrimethamine all inhibit enzymes of folic acid synthesis.  ''Efficacy'': 61.5% improvement by one clinical grade.(98 in furr)''Potential adverse effects'': bone marrow suppression (mild anaemia, leucopenia, neutropenia, thrombocytopenia), fever, anorexia, depression, acute worsening of ataxiam altered reproductive performance in stallions<ref>Bedford, S.J, McDonnell, S.M (1999) Measurements of reproductive function in stallions treated with trimethoprim-sulfamethoxazole and pyrimethamine. ''J Am Vet Med Assoc'', 215:1317–1319.  In: 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>, congenital defects<ref>Toribio, R.E, Bain, F.T, Mrad, D.R, Messer, N.T, Sellers, R.S, Hinchcliff, K.W (1998) Congenital defects in newborn foals of mares treated for equine protozoal myeloencephalitis during pregnancy. ''J Am Vet Med Assoc'', 212:697–701.  In: 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>and abortion.  Folic acid deficiency may also cause gastrointestinal disturbances such as glossitis.<ref>Piercy, R.J, Hinchcliff, K.W, Reed, S.M (2002) Folate deficiency during treatment with orally administered folic acid, sulphadiazine and pyrimethamine in a horse with suspected equine protozoal myeloencephalitis (EPM). ''Equine Vet J'', 34:311–316.  In: 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>Blood dyscrazias are typically self-limiting and resolve on withdrawal of treatment.<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>   

*'''Sulfadiazine and pyrimethamine combination, ('Rebalance™', Antiprotozoal Oral Suspension, IVX Animal Health)''': administered PO daily for a minimum of 90 days. Due to availability and ease of administration, some use an off-label regimen of trimethoprimsulfa tablets with pyrimethamine tablets.  ''Mode of action'': trimethoprim, sulfadiazine, and pyrimethamine all inhibit enzymes of folic acid synthesis.  ''Efficacy'': 61.5% improvement by one clinical grade.<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>''Potential adverse effects'': bone marrow suppression (mild anaemia, leucopenia, neutropenia, thrombocytopenia), fever, anorexia, depression, acute worsening of ataxiam altered reproductive performance in stallions<ref>Bedford, S.J, McDonnell, S.M (1999) Measurements of reproductive function in stallions treated with trimethoprim-sulfamethoxazole and pyrimethamine. ''J Am Vet Med Assoc'', 215:1317–1319.  In: 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>, congenital defects<ref>Toribio, R.E, Bain, F.T, Mrad, D.R, Messer, N.T, Sellers, R.S, Hinchcliff, K.W (1998) Congenital defects in newborn foals of mares treated for equine protozoal myeloencephalitis during pregnancy. ''J Am Vet Med Assoc'', 212:697–701.  In: 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>and abortion.  Folic acid deficiency may also cause gastrointestinal disturbances such as glossitis.<ref>Piercy, R.J, Hinchcliff, K.W, Reed, S.M (2002) Folate deficiency during treatment with orally administered folic acid, sulphadiazine and pyrimethamine in a horse with suspected equine protozoal myeloencephalitis (EPM). ''Equine Vet J'', 34:311–316.  In: 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>Blood dyscrazias are typically self-limiting and resolve on withdrawal of treatment.<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>   

*'''Ponazuril (Marquis®, Bayer Animal Health)''': PO daily for 28 days, use in pregnant animals is off-label.  ''Mode of action'': ponazuril is a triazinetrione that targets the “apicoplast” organelle and inhibits the respiratory chain.  ''Efficacy'': well absorbed PO, achieves steady state therapeutic concentration in CSF within 3 days(100 in Furr), clinical response within 10 days, 60% improvement by at least one clinical grade, 8% relapse within 90 days of stopping treatment(91 in Furr).  ''Potential adverse effects'': none in a multi-centre field study<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>, no systemic toxicity even at high doses.(101 in Furr)However, the manufacturer reports signs that may have been related to treatment including blisters on nose and mouth, skin rash or hives, loose stools, mild colic, and a seizure.<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>

*'''Ponazuril (Marquis®, Bayer Animal Health)''': PO daily for 28 days, use in pregnant animals is off-label.  ''Mode of action'': ponazuril is a triazinetrione that targets the “apicoplast” organelle and inhibits the respiratory chain.  ''Efficacy'': well absorbed PO, achieves steady state therapeutic concentration in CSF within 3 days<ref>Furr, M, Kennedy, T (2001) Cerebrospinal fluid and serum concentrations of ponazuril in horses.  ''Vet Ther'', 2:232-237.  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>clinical response within 10 days, 60% improvement by at least one clinical grade, 8% relapse within 90 days of stopping treatment.<ref>Furr, M, Kennedy, T, MacKay, R, Reed, S, Andrews, F, Bernard, B, Bain, F, Byars, D (2001) Efficacy of ponazuril 15% oral paste as a treatment for equine protozoal myeloencephalitis. ''J Vet Ther'', 2:215-222.  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> ''Potential adverse effects'': none in a multi-centre field study<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>, no systemic toxicity even at high doses.<ref>Kennedy, T, Campbell, J, Selzer, V (2001) Safety of ponazuril 15% oral paste in horses.  ''Vet Ther'', 2:223-231.  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>However, the manufacturer reports signs that may have been related to treatment including blisters on nose and mouth, skin rash or hives, loose stools, mild colic, and a seizure.<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>

*'''Diclazuril''': PO, daily for 28 days, approved by FDA for use as top-dress tablet but not commercially available ''Mode of action'': chemically similar to ponazuril but mechanism of action unknown.  ''Efficacy'': one study reported clinical improvement in 58% of cases.(98 in Furr)  ''Potential adverse effects'': none found in one efficacy study.<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>  Reported problems in a multi-centre field study included worsening neurologic status and laminitis but these were not proven to be related to treatment.<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>

*'''Diclazuril''': PO, daily for 28 days, approved by FDA for use as top-dress tablet but not commercially available ''Mode of action'': chemically similar to ponazuril but mechanism of action unknown.  ''Efficacy'': one study reported clinical improvement in 58% of cases.(98 in Furr)  ''Potential adverse effects'': none found in one efficacy study.<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>  Reported problems in a multi-centre field study included worsening neurologic status and laminitis but these were not proven to be related to treatment.<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>

*'''Nitazoxanide, NTZ ('Navigator®', Idexx Pharmaceuticals)''': no longer commercially available in the US.  ''Mode of action'': a member of the 5-nitrothiazole class of antiparasitics that inhibits the pyruvate:ferredoxin oxidoreductase (PFOR) enzyme dependent electron transfer reaction essential for anaerobic energy metabolism.<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>  ''Efficacy'': 60% success rate in an FDA-regulated study.(98 in Furr) ''Potential adverse effects'': adverse effects and death at high doses(98), fever, anorexia, diarrhoea, lethargy, depression and laminitis recorded at lower doses.  Toxic signs usally resolve upon cessation of treatment.<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>  '''''Caution: 'administration of nitazoxanide can disrupt the normal microbial flora of the gastrointestinal tract leading to enterocolitis.  Deaths due to enterocolitis have been observed while administering the recommended dose in field studies.'''''<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>

*'''Nitazoxanide, NTZ ('Navigator®', Idexx Pharmaceuticals)''': no longer commercially available in the US.  ''Mode of action'': a member of the 5-nitrothiazole class of antiparasitics that inhibits the pyruvate:ferredoxin oxidoreductase (PFOR) enzyme dependent electron transfer reaction essential for anaerobic energy metabolism.<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>  ''Efficacy'': 60% success rate in an FDA-regulated study.<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> ''Potential adverse effects'': adverse effects and death at high doses(98), fever, anorexia, diarrhoea, lethargy, depression and laminitis recorded at lower doses.  Toxic signs usally resolve upon cessation of treatment.<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>  '''''Caution: 'administration of nitazoxanide can disrupt the normal microbial flora of the gastrointestinal tract leading to enterocolitis.  Deaths due to enterocolitis have been observed while administering the recommended dose in field studies.'''''<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>

==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>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, 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).

==Prevention==

==Prevention==