Changes

===Seasonal Incidence===

===Seasonal Incidence===

The disease is not directly contagious between horses and humans but occurs sporadically in both species from mid-summer to late autumn - during the height of the vector season.  Case numbers peak in June to November in temperate climates.<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 vector season is longer in warmer climates, where the disease period is prolonged.  Global warming may promote more outbreaks in historically colder climates.<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 disease is not directly contagious between horses and humans but occurs sporadically in both species from mid-summer to late autumn - during the height of the vector season.<ref name="same">Pasquini, C, Pasquini S, Woods, P (2005)'''Volume 1: Guide to Equine Clinics''', third edition, p266, SUDZ publishing.</ref> Case numbers peak in June to November in temperate climates.<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 vector season is longer in warmer climates, where the disease period is prolonged.  Global warming may promote more outbreaks in historically colder climates.<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>

===Epidemics===

===Epidemics===

====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 OR decrease in Ab titre in paired serum samples taken 10-14 days apart.  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.  Colostral-derived Ab has a serum half-life of around 20days and may interfere with diagnosis in foals.

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.  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.  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. CF Ab against both Eastern and Western EEV is less useful for serological diagnosis because it appears relatively late and does not persist.

*Complement fixation (CF): to avoid anti-complementary effects, serum should be separated from blood as soon as possible. CF Ab against both Eastern and Western EEV is less useful for serological diagnosis because it appears relatively late and does not persist.

==Control==

==Control==

=== Vaccination===

=== Vaccination===

Most vaccines are killed (produced in cell culture and inactivated with formalin) and elicit significant increases in Ab titre after 3 days.  Protective titres last for 6-8 months.  Some cross-protection is seen between the serotypes but not between Western and Eastern EEV.  Monovalent, divalent and trivalent vaccines are available but the response to monovalent VEE vaccination is decreased in horses previously vaccinated against WEE and EEE.  The current recommendation is to vaccinate susceptible horses annually in late spring or several months before the high risk season.  Biannual or triannual vaccination should be employed in regions where the vector season is prolonged. Susceptible horses should also be vaccinated in the face of an outbreak.  Mares should be vaccinated one month prior to foaling to boost colostral-derived Ab<ref name="again">Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition), Merial found at http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/100900.htm&word=Equine%2cencephalitis, accessed July 2010</ref>, which persists for 6-7 months.<ref> 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>  Although foals can be vaccinated at any time, early vaccination should be followed by boosters at 6 months and at one year.  Vaccination does not interfere with the ELISA assay for VEE.<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>'''''PRECAUTION'': human vaccination is recommended for vets in endemic areas'''.

Most vaccines are killed (produced in cell culture and inactivated with formalin) and elicit significant increases in Ab titre after 3 days.  Protective titres last for 6-8 months.<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> Some cross-protection is seen between the serotypes but not between Western and Eastern EEV.  Monovalent, divalent and trivalent vaccines are available but the response to monovalent VEE vaccination is decreased in horses previously vaccinated against WEE and EEE.  The current recommendation is to vaccinate susceptible horses annually in late spring or several months before the high risk season.  Biannual or triannual vaccination should be employed in regions where the vector season is prolonged. Susceptible horses should also be vaccinated in the face of an outbreak.  Mares should be vaccinated one month prior to foaling to boost colostral-derived Ab<ref name="again">Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition), Merial found at http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/100900.htm&word=Equine%2cencephalitis, accessed July 2010</ref>, which persists for 6-7 months.<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>  Although foals can be vaccinated at any time, early vaccination should be followed by boosters at 6 months and at one year.  Vaccination does not interfere with the ELISA assay for VEE.<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>'''''PRECAUTION'': human vaccination is recommended for vets in endemic areas'''.

===Vector control===

===Vector control===