Changes

==Diagnosis==

==Diagnosis==

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

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 (IVIS 4)

*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

*Immunodiognostic 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 (EPM3)

*The horse should be resident in or have travelled within the Americas (EPM3)

The primary step in the diagnostic procedure should be to carry out thorough clinical and neurological examinations (IVIS 4).   

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>

===Immunodiagnostic  tests===

===Immunodiagnostic  tests===

All of these tests aim to confirm exposure to the pathogens of EPM by detecting the presence of antibodies to these agents(FUrr). None of these tests is considered a gold standard and they are only supportive. Currently, a definitive diagnosis can only be obtained at postmortem.(IVIS 4)

All of these tests aim to confirm exposure to the pathogens of EPM by detecting the presence of antibodies to these parasites.<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> None of these tests is considered a gold standard and they are only supportive. Currently, a definitive diagnosis can only be obtained at postmortem.<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>

*'''Immunoblot analysis (Western blot) of serum and CSF''': senstivity around 90%, specificity 48-89%.(EPM4)  Cultured merozoites are used to detect antibodies versus ''S.neurona''-specific proteins.  The CSF test has over 90% specificity and sensitivity(86 in Furr).  The blood brain barrier is not prevent the passage of antibodies, thus the CSF concentration of a specific antibody will be directly related to its serum concnetration (87 in Furr).  This permeability is likely responsible for many of the weakly false-positive CSF immunoblot tests.  Blood contamination during CSF collection or bleeding within the CNS due to trauma or infection might also cause false positives.  The CSF titre will be greatly increased during CNS infection as there will be local production of the antibody.  One of the difficulties in interpreting immunoblot results is that many horses develop antibodies against ''S.neurona'' in the absence of neurological disease.(EPM4)  For this reason, testing CSF may be preferable to serum despite the impact that minor blood contamination may have on CSF results.(IVIS 4)False negative results may arise if horses fail to respond to the specific proteins recognised by the immunoblot.  Such cases are rare, so a negative immunoblot result tends to exclude the diagnosis of EPM.(Merck) Cases that originally test negative should be re-tesed 14-21 days later.  In most instances, owing to a substantial incubation period, detectable levels of IgG are present prior to the emergence of clinical signs.(Furr)  

*'''Immunoblot analysis (Western blot) of serum and CSF''': senstivity around 90%, specificity 48-89%.(EPM4)  Cultured merozoites are used to detect antibodies versus ''S.neurona''-specific proteins.  The blood brain barrier does not prevent the passage of antibodies, thus the CSF concentration of a specific antibody will be directly related to its serum concentration(87 in Furr).  This permeability is likely responsible for many of the weakly false-positive CSF immunoblot tests.  Blood contamination during CSF collection or bleeding within the CNS due to trauma or infection might also cause false positives.  The CSF titre will be greatly increased during CNS infection as there will be local production of the antibody.  One of the difficulties in interpreting immunoblot results is that many horses develop antibodies against ''S.neurona'' in the absence of neurological disease.(EPM4)  For this reason, testing CSF may be preferable to serum despite the impact that minor blood contamination may have on CSF results.<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>  False negative results may arise if horses fail to respond to the specific proteins recognised by the immunoblot.  Such cases are rare, so a negative immunoblot result tends to exclude the diagnosis of EPM.<ref name="Merck">Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition), Merial</ref>

*'''Whole organism indirect fluorescent antibody test (IFAT)''': sensitivity around 90%, specificity 97-100%.(EPM4)  Serum titres of more than 1:100 and CSF titres of more than 1:5 indicate an active infection. The IFAT is considered to have slightly improved diagnostic efficiency than the immunoblot test(92 in furr) but is unable to distinguish between ''S.neurona'' and other related nonpathogenic organsims such as ''S.fayeri''(94 in Furr).  This can lead to false positive results.  Compared with the immunblot test, CSF blood contamination has an insignificant effect on the IFAT.(11 in IVIS 4)  An IFAT for ''N.hughesi'' is also available from the Universty of California.(Furr)

  Cases that originally test negative should be re-tesed 14-21 days later.  In most instances, owing to a substantial incubation period, detectable levels of IgG are present prior to the emergence of clinical signs.<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>

*'''ELISA for antibodies to the snSAG-1 protein''': based on an immunodominant surface antigen of ''S.neurona'' (SAG-1).(IVIS 4)  Serum titres more than 1:100 suggest an active infection.  False negatives are possible as not all ''S.neurona'' isolates produce the specific protein.(58 in Furr).  SAG-5 is an alternative surface antigen of ''S.neurona'' strains, which is mutually exclusive to SAG-1.(15 in IVIS 4) Therefore, the ELISA may only be of use where strains of ''S.neurona'' expressing SAG-1 predominate.(IVIS 4)

*'''Whole organism indirect fluorescent antibody test (IFAT)''': sensitivity around 90%, specificity 97-100%.(EPM4)  Serum titres of more than 1:100 and CSF titres of more than 1:5 indicate an active infection. The IFAT is considered to have slightly improved diagnostic efficiency than the immunoblot test(92 in furr) but is unable to distinguish between ''S.neurona'' and other related nonpathogenic organsims such as ''S.fayeri''(94 in Furr).  This can lead to false positive results.  Compared with the immunblot test, CSF blood contamination has an insignificant effect on the IFAT.(11 in IVIS 4)  An IFAT for ''N.hughesi'' is also available from the Universty of California.<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>

*'''ELISA for antibodies to the snSAG-1 protein''': based on an immunodominant surface antigen of ''S.neurona'' (SAG-1).<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> Serum titres more than 1:100 suggest an active infection.  False negatives are possible as not all ''S.neurona'' isolates produce the specific protein.(58 in Furr).  SAG-5 is an alternative surface antigen of ''S.neurona'' strains, which is mutually exclusive to SAG-1.(15 in IVIS 4) Therefore, the ELISA may only be of use where strains of ''S.neurona'' expressing SAG-1 predominate.<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>

===Other tests===

===Other tests===

*'''CSF analysis''': to rule out other conditions as stated below.  Most horses with EPM have normal CSF (Furr). Rarely, increased totoal protein or white blood cell count is seen in severe cases(Furr). PCR can be used to detect ''S.neurona'' DNA in CSF. (EPM8)

*'''CSF analysis''': to rule out other conditions as stated below.  Most horses with EPM have normal CSF.<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> Rarely, an increased total protein or white blood cell count is seen in severe cases(Furr). PCR can be used to detect ''S.neurona'' DNA in CSF.<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>

*'''Diclazuril''': a positive response to treatment with diclazuril would firmly support a diagnosis of EPM, since the drug has no antimicrobial activity.(EPM 1)

*'''Diclazuril''': a positive response to treatment with diclazuril would firmly support a diagnosis of EPM, since the drug has no antimicrobial activity.(EPM 1)

*'''Blood gene expression biomarkers''': may be sensitive and specific indicators of early and active disease<ref>Eastman, E, Furr, M, McKenzie, H, Saville, W.J, Dubey, J.P (2005) Early diagnosis of Sarcocystis neurona infection  using bloodgene expression biomarkers.  In:  ''51st Annual Convention of the American Association of Equine Practitioners - AAEP'', Seattle, WA, USA.</ref>

*'''Blood gene expression biomarkers''': may be sensitive and specific indicators of early and active disease<ref>Eastman, E, Furr, M, McKenzie, H, Saville, W.J, Dubey, J.P (2005) Early diagnosis of Sarcocystis neurona infection  using bloodgene expression biomarkers.  In:  ''51st Annual Convention of the American Association of Equine Practitioners - AAEP'', Seattle, WA, USA.</ref>