Changes

===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 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)

*'''Immunoblot analysis (Western blot) of serum and CSF''': 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 the high number of seropositive horses. 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 are rare but possible.  Horse may fail to respond to the specific proteins recognised by the immunoblot.  Cases that originally test negative should be re-tesed 14-21 days later.  In most cases, detectable levels of IgG are present prior to the emergence of clinical signs due to a substantial incubation period.(Furr)  

*'''Immunoblot analysis (Western blot) of serum and CSF''': 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)  

*'''Whole organism indirect fluorescent antibody test (IFAT)''': 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)

*'''Whole organism indirect fluorescent antibody test (IFAT)''': 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)

*'''ELISA for antibodies to the snSAG-1 protein''': based on an immunodominant surfae 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)

*ELISA fr antibodies to the snSAG-1 protein : serum titres more than 1:100 indicate active infection. False negatives are pssoble as not all S.neurona isolates oproduce the SAG-1 protein (58 in Furr).  A stall-side version of the test exitss. based on an immunodominant surface antigen of S. neurona (SAG-1).  Later work supported S. neurona surface antigen diversity and showed that SAG-5 is an alternative surface antigen of S. neurona strains, which is mutually exclusive to SAG-1.15 Therefore,the SAG-1 ELISA is only likely to be useful in areas where SAG-1 expressing strains of S. neurona predominate; in areas where SAG-5 expressing strains predominate, the test will fail to identify infected horses. (IVIS 4)

The and the IFAT appear to have similar sensitivities, approaching 90%. Estimates of WB specificity vary from 44–89%, while estimates of IFAT specificity range from 97–100%. Results vary depending on the sample set and whether serum or CSF is used. Therefore, available evidence suggests that either test is appropriate if high sensitivity (and therefore high negative predictive value) is desired. If high specificity (and therefore high positive predictive value) is desired, the IFAT may be the better choice.(EPM 4)

 

Both the WB and the IFAT appear to have similar sensitivities, approaching 90%. Estimates of WB specificity vary from 44–89%, while estimates of IFAT specificity range from 97–100%. Results vary depending on the sample set and whether serum or CSF is used. Therefore, available evidence suggests that either test is appropriate if high sensitivity (and therefore high negative predictive value) is desired. If high specificity (and therefore high positive predictive value) is desired, the IFAT may be the better choice.(EPM 4)

Available evidence indicates that both the WB and IFAT have similar sensitivities (_90%). The estimated IFAT specificity is higher than the estimated WB specificity, and the IFAT CSF results are much less affected by blood contamination than WB CSF results. The

Available evidence indicates that both the WB and IFAT have similar sensitivities (_90%). The estimated IFAT specificity is higher than the estimated WB specificity, and the IFAT CSF results are much less affected by blood contamination than WB CSF results. The

SAG-1 ELISA has the least amount of evidence to support its use, and preliminary data yield a low sensitivity that will likely limit its use in some or most geographic regions.(IVIS 4)

SAG-1 ELISA has the least amount of evidence to support its use, and preliminary data yield a low sensitivity that will likely limit its use in some or most geographic regions.(IVIS 4)