Changes

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>

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%.<ref name="EPM4>Johnson, A.L (2008) Evidence-based clinical question: which is the most sensitive and specific commercial test to diagnose ''Sarcocystis neurona'' infection (equine protozoal myeloencephalitis) in horses?, ''Equine Vet Educ'', 20(3):166-168.</ref>  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.<ref>Furr, M (2002) Antigen-specific antibodies in cerebrospinal fluid after intramuscular injection of ovalbumin in horses, ''J Vet Intern Med'', 16:588-592.  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>  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.<ref name="EPM4>Johnson, A.L (2008) Evidence-based clinical question: which is the most sensitive and specific commercial test to diagnose ''Sarcocystis neurona'' infection (equine protozoal myeloencephalitis) in horses?, ''Equine Vet Educ'', 20(3):166-168.</ref>  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>  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>  

*'''Immunoblot analysis (Western blot) of serum and CSF''': senstivity around 90%, specificity 48-89%.<ref name="EPM4>Johnson, A.L (2008) Evidence-based clinical question: which is the most sensitive and specific commercial test to diagnose ''Sarcocystis neurona'' infection (equine protozoal myeloencephalitis) in horses?, ''Equine Vet Educ'', 20(3):166-168.</ref>  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.<ref>Furr, M (2002) Antigen-specific antibodies in cerebrospinal fluid after intramuscular injection of ovalbumin in horses, ''J Vet Intern Med'', 16:588-592.  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>  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.<ref name="EPM4>Johnson, A.L (2008) Evidence-based clinical question: which is the most sensitive and specific commercial test to diagnose ''Sarcocystis neurona'' infection (equine protozoal myeloencephalitis) in horses?, ''Equine Vet Educ'', 20(3):166-168.</ref>  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>  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>  

*'''Whole organism indirect fluorescent antibody test (IFAT)''': sensitivity around 90%, specificity 97-100%.<ref name="EPM4>Johnson, A.L (2008) Evidence-based clinical question: which is the most sensitive and specific commercial test to diagnose ''Sarcocystis neurona'' infection (equine protozoal myeloencephalitis) in horses?, ''Equine Vet Educ'', 20(3):166-168.</ref>  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<ref>Duarte, P.C, Daft, B.M, Conrad, P.A, Packham, A.E, Gardner, I.A (2003) Comparison of a serum indirect fluorescent antibody test with two Western blot tests for the diagnosis of equine protozoal myeloencephalitis, ''J Vet Diagn Invest'', 15:8-13.  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> 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>

*'''Whole organism indirect fluorescent antibody test (IFAT)''': sensitivity around 90%, specificity 97-100%.<ref name="EPM4>Johnson, A.L (2008) Evidence-based clinical question: which is the most sensitive and specific commercial test to diagnose ''Sarcocystis neurona'' infection (equine protozoal myeloencephalitis) in horses?, ''Equine Vet Educ'', 20(3):166-168.</ref>  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<ref>Duarte, P.C, Daft, B.M, Conrad, P.A, Packham, A.E, Gardner, I.A (2003) Comparison of a serum indirect fluorescent antibody test with two Western blot tests for the diagnosis of equine protozoal myeloencephalitis, ''J Vet Diagn Invest'', 15:8-13.  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> but is unable to distinguish between ''S.neurona'' and other related nonpathogenic organsims such as ''S.fayeri''.<ref>Granstrom, D.E (1995) Equine protozoal myeloencephalitis testing: review of 1993 and 1994.  ''Proc Annu Conv Am Assoc Equine Prac, 41:218-219.  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> This can lead to false positive results.  Compared with the immunblot test, CSF blood contamination has an insignificant effect on the IFAT.<ref>Finno, C.J, Packham, A.E, Wilson, W.D, ''et al''. (2007) Effects of blood contamination of cerebrospinal fluid on results of indirect fluorescent antibody tests for detection of antibodies against ''Sarcocystis neurona'' and ''Neospora hughesi''. ''J Vet Diag Invest'', 19:286–289.  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>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.<ref>Howe, D, Gaji, R, Marsh, A (2008) Strains of ''S.neurona'' exhibit differences in their surface antigens, including the absence of the major surface antigen SnSAG1.  ''Int J Parasitol'', 38:623-631.  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>  SAG-5 is an alternative surface antigen of ''S.neurona'' strains, which is mutually exclusive to SAG-1.<ref>Crowdus, C.A, Marsh, A.E, Saville, W.J, ''et al''. (2008) SnSAG5 is an

*'''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.<ref>Howe, D, Gaji, R, Marsh, A (2008) Strains of ''S.neurona'' exhibit differences in their surface antigens, including the absence of the major surface antigen SnSAG1.  ''Int J Parasitol'', 38:623-631.  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>  SAG-5 is an alternative surface antigen of ''S.neurona'' strains, which is mutually exclusive to SAG-1.<ref>Crowdus, C.A, Marsh, A.E, Saville, W.J, ''et al''. (2008) SnSAG5 is an

alternative surface antigen of ''Sarcocystis neurona'' strains that is mutually exclusive to SnSAG1. ''Vet Parasitol'', 158:36–43.</ref>  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>

alternative surface antigen of ''Sarcocystis neurona'' strains that is mutually exclusive to SnSAG1. ''Vet Parasitol'', 158:36–43.  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>  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===