Changes

====Serology====

====Serology====

Ab titre increases sharply within 24 hours of the initial viraemia, before clinical signs are apparent.  It then deteriorates over 6 months.  Samples taken when clinical signs appear are likely to miss the Ab peak and will demonstrate a decreasing titre.  Thus, serological confirmation of Eastern or Western EEV infection requires a four-fold or greater increase<ref name="same">Pasquini, C, Pasquini S, Woods, P (2005)'''Volume 1: Guide to Equine Clinics''', third edition, p266, SUDZ publishing.</ref> OR decrease in Ab titre in paired serum samples taken 10-14 days apart.<ref name="manual">''Manual of Diagnostic Tests and Vaccines for Terrestrial Animals'' found at http://www.oie.int/eng/normes/mmanual/A_00081.htm, accessed July 2010.</ref>  A presumptive diagnosis can be made on a single sample if an unvaccinated horse with suggestive clinical signs has Ab against only Eastern or Western EEV.<ref name="manual">''Manual of Diagnostic Tests and Vaccines for Terrestrial Animals'' found at http://www.oie.int/eng/normes/mmanual/A_00081.htm, accessed July 2010.</ref>  Colostral-derived Ab has a serum half-life of around 20days and may interfere with diagnosis in foals.<ref name="repeat"> Ferguson, J.A, Reeves, W.C, Hardy, J.L (1979) Studies on immunity to alphaviruses in foals, ''Am J Vet Res'', 40:5-10.  In: 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>

Ab titre increases sharply within 24 hours of the initial viraemia, before clinical signs are apparent.  It then deteriorates over 6 months.  Samples taken when clinical signs appear are likely to miss the Ab peak and will demonstrate a decreasing titre.<ref name="multiple">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> Thus, serological confirmation of Eastern or Western EEV infection requires a four-fold or greater increase<ref name="same">Pasquini, C, Pasquini S, Woods, P (2005)'''Volume 1: Guide to Equine Clinics''', third edition, p266, SUDZ publishing.</ref> OR decrease in Ab titre in paired serum samples taken 10-14 days apart.<ref name="manual">''Manual of Diagnostic Tests and Vaccines for Terrestrial Animals'' found at http://www.oie.int/eng/normes/mmanual/A_00081.htm, accessed July 2010.</ref>  A presumptive diagnosis can be made on a single sample if an unvaccinated horse with suggestive clinical signs has Ab against only Eastern or Western EEV.<ref name="manual">''Manual of Diagnostic Tests and Vaccines for Terrestrial Animals'' found at http://www.oie.int/eng/normes/mmanual/A_00081.htm, accessed July 2010.</ref>  Colostral-derived Ab has a serum half-life of around 20days and may interfere with diagnosis in foals.<ref name="repeat"> Ferguson, J.A, Reeves, W.C, Hardy, J.L (1979) Studies on immunity to alphaviruses in foals, ''Am J Vet Res'', 40:5-10.  In: 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>

   

   

*Complement fixation (CF): to avoid anti-complementary effects, serum should be separated from blood as soon as possible.<ref name="manual">''Manual of Diagnostic Tests and Vaccines for Terrestrial Animals'' found at http://www.oie.int/eng/normes/mmanual/A_00081.htm, accessed July 2010.</ref> CF Ab against both Eastern and Western EEV is less useful for serological diagnosis because it appears relatively late and does not persist.<ref name="manual">''Manual of Diagnostic Tests and Vaccines for Terrestrial Animals'' found at http://www.oie.int/eng/normes/mmanual/A_00081.htm, accessed July 2010.</ref>

*Complement fixation (CF): to avoid anti-complementary effects, serum should be separated from blood as soon as possible.<ref name="manual">''Manual of Diagnostic Tests and Vaccines for Terrestrial Animals'' found at http://www.oie.int/eng/normes/mmanual/A_00081.htm, accessed July 2010.</ref> CF Ab against both Eastern and Western EEV is less useful for serological diagnosis because it appears relatively late and does not persist.<ref name="manual">''Manual of Diagnostic Tests and Vaccines for Terrestrial Animals'' found at http://www.oie.int/eng/normes/mmanual/A_00081.htm, accessed July 2010.</ref>

*Haemagglutination inhibition (HAI): titres of 1/10 and 1/20 are indicative, titres of 1/40 and above are positive.<ref name="manual">''Manual of Diagnostic Tests and Vaccines for Terrestrial Animals'' found at http://www.oie.int/eng/normes/mmanual/A_00081.htm, accessed July 2010.</ref>

*Haemagglutination inhibition (HAI): titres of 1/10 and 1/20 are indicative, titres of 1/40 and above are positive.<ref name="manual">''Manual of Diagnostic Tests and Vaccines for Terrestrial Animals'' found at http://www.oie.int/eng/normes/mmanual/A_00081.htm, accessed July 2010.</ref>

*ELISA may be used to detect viral-specific IgM to the surface glycoprotein of Venezuelan EEV, from 3 days post-onset of clinical signs up to 21 days post-infection.  This is useful in acute infections where convalescent serum samples are unobtainable.

*ELISA may be used to detect viral-specific IgM to the surface glycoprotein of Venezuelan EEV, from 3 days post-onset of clinical signs up to 21 days post-infection.  This is useful in acute infections where convalescent serum samples are unobtainable.<ref name="multiple">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>

*The plaque reduction neutralization (PRN) test is very specific and can differentiate EEE and WEE infections.  It is performed in duck embryo fibroblast, Vero, or BHK-21 cell cultures.  Serum is tested against 100 plaque-forming units of virus.  Endpoints are based on a 90% reduction in the number of plaques compared with the virus control.<ref name="manual">''Manual of Diagnostic Tests and Vaccines for Terrestrial Animals'' found at http://www.oie.int/eng/normes/mmanual/A_00081.htm, accessed July 2010.</ref>

*The plaque reduction neutralization (PRN) test is very specific and can differentiate EEE and WEE infections.  It is performed in duck embryo fibroblast, Vero, or BHK-21 cell cultures.  Serum is tested against 100 plaque-forming units of virus.  Endpoints are based on a 90% reduction in the number of plaques compared with the virus control.<ref name="manual">''Manual of Diagnostic Tests and Vaccines for Terrestrial Animals'' found at http://www.oie.int/eng/normes/mmanual/A_00081.htm, accessed July 2010.</ref>