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==Description==

==Description==

'''NOTIFIABLE''' and '''ZOONOTIC''' 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)

==Aetiology==

==Aetiology==

[[Equine Encephalitis Virus|See this page for details of the causal pathogens]].  Some of the virus strains can infect swine, poultry and other farmed birds including quail and ratites.  Isolated cases have also been noted in cattle, sheep and non-domestic ungulates.  Some strains are potential agents of biowarfare or bioterrorism (Steele and Twenhafel, 2010).

[[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>.

==Epidemiology==

==Epidemiology==

===Distribution===

===Distribution===

Togaviral encephalitis in equids is largely confined to the Western Hemisphere.  Venezuelan EEV can cause large outbreaks of disease over extensive geographical areas in both humans and horses.  Spread of this virus into Central America has had disasterous consequences with epidemics as far north as Texas. Climatic conditions and interventions that support vector populations, such as irrigation, greatly influence the geographical spread of the disease.  EEE has been recorded across the United States, but mostly in the Southeastern States. As its names suggests, WEE has a predilection for the Western states which have been subject to significant outbreaks in the past.  A regional alteration in virulence has been proposed for the steep decline in clinical case numbers observed in this area.  A lag phase of 2-5weeks is commonly observed between horse and human cases of WEE in a given locus.  Both are dead-end hosts for the virus.    A subtype of Western EEV, Highlands J virus, was isolated from the brain of a horse with encephalitis in Florida (Karabatsos ''et al''., 1988).

Togaviral encephalitis in equids is largely confined to the Western Hemisphere.<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> Venezuelan EEV can cause large outbreaks of disease over extensive geographical areas in both humans and horses.  Spread of this virus into Central America has had disasterous consequences with epidemics as far north as Texas. Climatic conditions and interventions that support vector populations, such as irrigation, greatly influence the geographical spread of the disease.  EEE has been recorded across the United States, but mostly in the Southeastern States. As its names suggests, WEE has a predilection for the Western states which have been subject to significant outbreaks in the past.  A regional alteration in virulence has been proposed for the steep decline in clinical case numbers observed in this area.  A lag phase of 2-5weeks is commonly observed between horse and human cases of WEE in a given locus.  Both are dead-end hosts for the virus.    A subtype of Western EEV, Highlands J virus, was isolated from the brain of a horse with encephalitis in Florida (Karabatsos ''et al''., 1988).

===Transmission===

===Transmission===

==References==

==References==

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.

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.

Walton T.E. (1981). Venezuelan, eastern, and western encephalomyelitis. In: ''Virus Diseases of Food Animals. A World Geography of Epidemiology and Control''. Disease Monographs, Vol. 2, Gibbs E.P.J, ed. Academic Press, New York, USA, 587-625.

Walton T.E. (1981). Venezuelan, eastern, and western encephalomyelitis. In: ''Virus Diseases of Food Animals. A World Geography of Epidemiology and Control''. Disease Monographs, Vol. 2, Gibbs E.P.J, ed. Academic Press, New York, USA, 587-625.

 

The Merck Veterinary Manual, 50th Anniversary Edition, Copyright © 2008; Merck & Co., Inc. found at http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/100900.htm&word=Equine%2cencephalitis, accessed July 2010.

The Merck Veterinary Manual, 50th Anniversary Edition, Copyright © 2008; Merck & Co., Inc. found at http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/100900.htm&word=Equine%2cencephalitis, accessed July 2010.