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       This is one of the less common Alphavirus spp. viral diseases that occur in North and South America.  It is primarily an arboviral infection of birds, which are the amplifying and maintenance hosts (Service 2008).  The virus is of the recombinant type of two other alphaviruses.  The incidence of infection is quite low as there have been only about 690 confirmed cases in the United States over the  1964-2016 period.  These occurred mostly west of the Mississippi River.  The disease was discovered in 1930 affecting horses in the San Joaquin Valley of California.  There was considerable difficulty in diagnosing the disease because horse owners did not trust the public health investigators.


       Symptoms include serious sequelae among young children.  Compared to the eastern form of the virus, mortality is below 4.2 percent confined mostly to elderly patients. 


       Transmission is by the Culex tarsalis and other Culex spp., Culiseta spp. and Aedes spp. mosquitoes.  The Aedes spp. &  #2. also vector the virus to other mammals, humans and horses.


       Although no vaccine for western equine encephalitis has been developed, there are some therapeutic drugs available for the infection.



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Key References:     <medvet.ref.htm>    <Hexapoda>


     Matheson, R. 1950.  Medical Entomology.  Comstock Publ. Co, Inc.  610 p.

      Service, M.  2008.  Medical Entomology For Students.  Cambridge Univ. Press.  289 p

      Legner, E. F.  1995.  Biological control of Diptera of medical and veterinary importance.  J. Vector Ecology 20(1): 59_120.

      Legner, E. F.  2000.  Biological control of aquatic Diptera.  p. 847_870.  Contributions to a Manual of Palaearctic Diptera,

            Vol. 1, Science  Herald, Budapest.  978 p.