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Also known as: '''''Alphaviral encephalitis — Alphaviral encephalitides —  Eastern equine encephalitis — Eastern equine encephalomyelitis — EEE — Western equine encephalitis — Western equine encephalomyelitis — WEE — Venezuelan equine encephalitis — Venezuelan equine encephalomyelitis — VEE

| Also known as:

|'''Alphaviral encephalitis, Alphaviral encephalitides<br>

'''Eastern equine encephalitis, Eastern equine encephalomyelitis, EEE<br>

'''Western equine encephalitis, Western equine encephalomyelitis, WEE<br>

'''Venezuelan equine encephalitis, Venezuelan equine encephalomyelitis, VEE'''

 

==Description==

==Introduction==

'''NOTIFIABLE''' and '''ZOONOTIC''' OIE List B, infectious, mosquito-borne diseases of equidae affecting the central nervous system (CNS).  They include:

'''NOTIFIABLE''' and '''ZOONOTIC''' OIE List B, infectious, mosquito-borne diseases of equidae affecting the central nervous system (CNS).  They include:

*Eastern Equine Encephalitis (EEE)

*Eastern Equine Encephalitis (EEE)

*Western Equine Encephalitis (WEE)

*Western Equine Encephalitis (WEE)

*Venezuelan Equine Encephalitis (VEE) - '''reportable''' in the USA<ref name="same">Pasquini, C, Pasquini S, Woods, P (2005)'''Volume 1: Guide to Equine Clinics''', third edition, p266, SUDZ publishing.</ref>

*Venezuelan Equine Encephalitis (VEE) - '''reportable''' in the USA<ref name="same">Pasquini, C, Pasquini S, Woods, P (2005) '''Guide to Equine Clinics Volume 1: Equine Medicine''', third edition, p266, SUDZ publishing.</ref>

==Aetiology==

==Aetiology==

[[Equine Encephalitis Virus|See this page for details of the causal pathogens]].  Some of the virus strains can infect swine<ref>Karsted, L, Hansen, R.P (1959) Natural and experimental infections in swine with the virus of eastern equine encephalomyelitis, ''J Infect Dis'' 105:293-296.  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>, poultry and other farmed birds including quail and ratites.<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>  Isolated cases have also been noted in cattle<ref>Pursell, A.R, Mitchell, F.E, Seibold, H.R (1976) Naturally occurring and experimentally induced eastern encephalomyelitis in calves, ''J Am Vet Med Assoc'', 169:1101-1103.  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>, sheep and non-domestic ungulates.<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 strains are potential agents of biowarfare or bioterrorism<ref>Steele, K.E, Twenhafel, N.A (2010) Review Paper: Pathology of Animal Models of Alphavirus Encephalitis. ''Vet Pathol.'' Jun 15. [Epub ahead of print].</ref>.

See this page for details of the [[Equine Encephalitis Virus|equine encephalitis causal pathogens]].  Some of the virus strains can infect swine<ref>Karsted, L, Hansen, R.P (1959) Natural and experimental infections in swine with the virus of eastern equine encephalomyelitis, ''J Infect Dis'' 105:293-296.  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>, poultry and other farmed birds including quail and ratites.<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>  Isolated cases have also been noted in cattle<ref>Pursell, A.R, Mitchell, F.E, Seibold, H.R (1976) Naturally occurring and experimentally induced eastern encephalomyelitis in calves, ''J Am Vet Med Assoc'', 169:1101-1103.  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>, sheep and non-domestic ungulates.<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 strains are potential agents of biowarfare or bioterrorism<ref>Steele, K.E, Twenhafel, N.A (2010) Review Paper: Pathology of Animal Models of Alphavirus Encephalitis. ''Vet Pathol.'' Jun 15. [Epub ahead of print].</ref>.

==Epidemiology==

==Epidemiology==

===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.<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>

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) '''Guide to Equine Clinics Volume 1: Equine Medicine''', 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===

==Signalment==

==Signalment==

Unvaccinated adult horses and other equids (for '''VEE in donkeys''' [[Venezuelan Equine Encephalomyelitis (VEE) - Donkey|'''see here''']]) are at risk in areas with suitable vectors.  Vaccinated horses can still develop the disease, particularly if they are young or old.

Unvaccinated adult horses and other equids ([[Venezuelan Equine Encephalomyelitis (VEE) - Donkey|'''VEE in donkeys''']]) are at risk in areas with suitable vectors.  Vaccinated horses can still develop the disease, particularly if they are young or old.

==Clinical Signs==

==Clinical Signs==

===EEE and WEE===

===EEE and WEE===

Following an incubation period of up to 21days<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>, an initial pyrexia and mild depression are short-lived and often missed.  The acute phase of the disease presents with mild to severe pyrexia, anorexia and stiffness, lasting up to 5 days.  During this time, the horse is viraemic and capable of amplifying the disease.  The fever may then fluctuate with neurological derangements appearing a few days post-infection.<ref name="same">Pasquini, C, Pasquini S, Woods, P (2005)'''Volume 1: Guide to Equine Clinics''', third edition, p266, SUDZ publishing.</ref>  These changes indicate disease progression, which occurs more frequently with EEE (the most virulent of the three serotypes).  Any of the following may be observed<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>:

Following an incubation period of up to 21days<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>, an initial pyrexia and mild depression are short-lived and often missed.  The acute phase of the disease presents with mild to severe pyrexia, anorexia and stiffness, lasting up to 5 days.  During this time, the horse is viraemic and capable of amplifying the disease.  The fever may then fluctuate with neurological derangements appearing a few days post-infection.<ref name="same">Pasquini, C, Pasquini S, Woods, P (2005) '''Guide to Equine Clinics Volume 1: Equine Medicine''', third edition, p266, SUDZ publishing.</ref>  These changes indicate disease progression, which occurs more frequently with EEE (the most virulent of the three serotypes).  Any of the following may be observed<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>:

*conscious proprioceptive deficits

*conscious proprioceptive deficits

*propulsive walking

*propulsive walking

*apparent blindness

*apparent blindness

*facial and appendicular muscle fasciculations

*facial and appendicular muscle fasciculations

*pendulous lower lip<ref name="same">Pasquini, C, Pasquini S, Woods, P (2005)'''Volume 1: Guide to Equine Clinics''', third edition, p266, SUDZ publishing.</ref>

*pendulous lower lip<ref name="same">Pasquini, C, Pasquini S, Woods, P (2005) '''Guide to Equine Clinics Volume 1: Equine Medicine''', third edition, p266, SUDZ publishing.</ref>

*pharynx, larynx and tongue paralysis

*pharynx, larynx and tongue paralysis

*seizures<ref name="same">Pasquini, C, Pasquini S, Woods, P (2005)'''Volume 1: Guide to Equine Clinics''', third edition, p266, SUDZ publishing.</ref>

*seizures<ref name="same">Pasquini, C, Pasquini S, Woods, P (2005) '''Guide to Equine Clinics Volume 1: Equine Medicine''', third edition, p266, SUDZ publishing.</ref>

*recumbency for 1-7 days followed by death<ref name="same">Pasquini, C, Pasquini S, Woods, P (2005)'''Volume 1: Guide to Equine Clinics''', third edition, p266, SUDZ publishing.</ref>

*recumbency for 1-7 days followed by death<ref name="same">Pasquini, C, Pasquini S, Woods, P (2005) '''Guide to Equine Clinics Volume 1: Equine Medicine''', third edition, p266, SUDZ publishing.</ref>

===VEE===

===VEE===

==Diagnosis==

==Diagnosis==

Presumptive based on history, epidemiology and clinical signs.<ref name="same">Pasquini, C, Pasquini S, Woods, P (2005)'''Volume 1: Guide to Equine Clinics''', third edition, p266, SUDZ publishing.</ref>  Definitive diagnosis requires virus identification, serological tests and/or post-mortem examination.   

Presumptive based on history, epidemiology and clinical signs.<ref name="same">Pasquini, C, Pasquini S, Woods, P (2005) '''Guide to Equine Clinics Volume 1: Equine Medicine''', third edition, p266, SUDZ publishing.</ref>  Definitive diagnosis requires virus identification, serological tests and/or post-mortem examination.   

===Laboratory Tests===

===Laboratory Tests===

====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.<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>

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) '''Guide to Equine Clinics Volume 1: Equine Medicine''', 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>

==Treatment<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>==

==Treatment<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>==

No effective, specific treatment is available.<ref name="same">Pasquini, C, Pasquini S, Woods, P (2005)'''Volume 1: Guide to Equine Clinics''', third edition, p266, SUDZ publishing.</ref>  Supportive management includes:

No effective, specific treatment is available.<ref name="same">Pasquini, C, Pasquini S, Woods, P (2005) '''Guide to Equine Clinics Volume 1: Equine Medicine''', third edition, p266, SUDZ publishing.</ref>  Supportive management includes:

*NSAIDs (phenylbutazone, flunixin meglumine) to control pyrexia, inflammation and discomfort

*NSAIDs (phenylbutazone, flunixin meglumine) to control pyrexia, inflammation and discomfort

*DMSO IV in a 20% solution to control inflamation, provide some analgesia and mild sedation

*DMSO IV in a 20% solution to control inflamation, provide some analgesia and mild sedation

==Control==

==Control==

=== Vaccination===

=== Vaccination===

Most vaccines are killed (produced in cell culture and inactivated with formalin)<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> and elicit significant increases in Ab titre after 3 days.<ref name="attenuated">Ferguson, J.A, Reeves, W.C, Milby, M.M, Hardy, J.L (1978) Study of homologous and heterologous antibody responses in California horses vaccinated with attenuated Venezuelan equine encephalomyelitis vaccine (strain TC-83), ''Am J Vet Res'', 39:371-376.  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>  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.<ref>Jochim, M.M, Barber, T.L (1974) Immune response of horses after simultaneous or sequential vaccination against eastern, Western and Venezuelan equine encephlaomyelitis, ''J Am Vet Med Assoc'', 165:621-625.  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>  Monovalent, divalent and trivalent vaccines are available but the response to monovalent VEE vaccination is decreased in horses previously vaccinated against WEE and EEE.<ref>Calisher, C.H, Sasso, D.R, Sather, G.E (1973) Possible evidence for interference with Venezuelan equine encephalitis virus vaccination of equines by pre-existing antibody to eastern or western equine encephalitis virus, or both, ''Appl Microbiol'', 26:485-488.  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>  The current recommendation is to vaccinate susceptible horses annually in late spring or several months before the high risk season.<ref name="same">Pasquini, C, Pasquini S, Woods, P (2005)'''Volume 1: Guide to Equine Clinics''', third edition, p266, SUDZ publishing.</ref>  Biannual or triannual vaccination should be employed in regions where the vector season is prolonged.<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> Susceptible horses should also be vaccinated in the face of an outbreak.<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>  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> '''NOTE''': Formalin-treated preparations of virulent epizootic VEE virus should never be used in equids as residual virulent virus can result in severe illness.  Instead, the attenuated vaccine, strain TC-83<ref name="attenuated">Ferguson, J.A, Reeves, W.C, Milby, M.M, Hardy, J.L (1978) Study of homologous and heterologous antibody responses in California horses vaccinated with attenuated Venezuelan equine encephalomyelitis vaccine (strain TC-83), ''Am J Vet Res'', 39:371-376.  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>, or an inactivated preparation created from that strain should be used. <ref>Walton, T.E, Grayson, M.A (1989)Chapter 46, Venezuelan equine encephalomyelitis. In: ''The Arboviruses: Epidemiology and Ecology'', Vol. 4, Monath T.P., ed. CRC Press, Boca Raton, Florida, USA, 203-231.  In:''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> '''''PRECAUTION'': human vaccination is recommended for vets in endemic areas'''.

Most vaccines are killed (produced in cell culture and inactivated with formalin)<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> and elicit significant increases in Ab titre after 3 days.<ref name="attenuated">Ferguson, J.A, Reeves, W.C, Milby, M.M, Hardy, J.L (1978) Study of homologous and heterologous antibody responses in California horses vaccinated with attenuated Venezuelan equine encephalomyelitis vaccine (strain TC-83), ''Am J Vet Res'', 39:371-376.  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>  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.<ref>Jochim, M.M, Barber, T.L (1974) Immune response of horses after simultaneous or sequential vaccination against eastern, Western and Venezuelan equine encephlaomyelitis, ''J Am Vet Med Assoc'', 165:621-625.  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>  Monovalent, divalent and trivalent vaccines are available but the response to monovalent VEE vaccination is decreased in horses previously vaccinated against WEE and EEE.<ref>Calisher, C.H, Sasso, D.R, Sather, G.E (1973) Possible evidence for interference with Venezuelan equine encephalitis virus vaccination of equines by pre-existing antibody to eastern or western equine encephalitis virus, or both, ''Appl Microbiol'', 26:485-488.  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>  The current recommendation is to vaccinate susceptible horses annually in late spring or several months before the high risk season.<ref name="same">Pasquini, C, Pasquini S, Woods, P (2005) '''Guide to Equine Clinics Volume 1: Equine Medicine''', third edition, p266, SUDZ publishing.</ref>  Biannual or triannual vaccination should be employed in regions where the vector season is prolonged.<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> Susceptible horses should also be vaccinated in the face of an outbreak.<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>  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> '''NOTE''': Formalin-treated preparations of virulent epizootic VEE virus should never be used in equids as residual virulent virus can result in severe illness.  Instead, the attenuated vaccine, strain TC-83<ref name="attenuated">Ferguson, J.A, Reeves, W.C, Milby, M.M, Hardy, J.L (1978) Study of homologous and heterologous antibody responses in California horses vaccinated with attenuated Venezuelan equine encephalomyelitis vaccine (strain TC-83), ''Am J Vet Res'', 39:371-376.  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>, or an inactivated preparation created from that strain should be used. <ref>Walton, T.E, Grayson, M.A (1989)Chapter 46, Venezuelan equine encephalomyelitis. In: ''The Arboviruses: Epidemiology and Ecology'', Vol. 4, Monath T.P., ed. CRC Press, Boca Raton, Florida, USA, 203-231.  In:''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> '''''PRECAUTION'': human vaccination is recommended for vets in endemic areas'''.

===Vector control===

===Vector control===

Responsible use of insecticides and repellents<ref name="same">Pasquini, C, Pasquini S, Woods, P (2005)'''Volume 1: Guide to Equine Clinics''', third edition, p266, SUDZ publishing.</ref>, elimination of standing water, and stable screening will all help to reduce viral transmission.  Environmental application of insecticides may be useful in endemic areas or during an outbreak.<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>  Horses infected with Venezuelan EEV should be isolated for 3 weeks after complete recovery.<ref name="same">Pasquini, C, Pasquini S, Woods, P (2005)'''Volume 1: Guide to Equine Clinics''', third edition, p266, SUDZ publishing.</ref>

Responsible use of insecticides and repellents<ref name="same">Pasquini, C, Pasquini S, Woods, P (2005) '''Guide to Equine Clinics Volume 1: Equine Medicine''', third edition, p266, SUDZ publishing.</ref>, elimination of standing water, and stable screening will all help to reduce viral transmission.  Environmental application of insecticides may be useful in endemic areas or during an outbreak.<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>  Horses infected with Venezuelan EEV should be isolated for 3 weeks after complete recovery.<ref name="same">Pasquini, C, Pasquini S, Woods, P (2005) '''Guide to Equine Clinics Volume 1: Equine Medicine''', third edition, p266, SUDZ publishing.</ref>

 

 

 

 

 

==References==

==References==

 

 

 

[[Category:Expert_Review]]

[[Category:Expert_Review]]

[[Category:Zoonoses]]

[[Category:Zoonoses]]