The Western equine encephalomyelitis virus is the causative agent of relatively uncommon viral disease Western equine encephalomyelitis (WEE). An Alphavirus of the family Togaviridae, the WEE virus is an arbovirus (arthropod-borne virus) transmitted by mosquitoes of the genera Culexand Culiseta. WEE is a recombinant virus between two other alphaviruses, an ancestral Sindbis virus-like virus, and an ancestral Eastern equine encephalitis virus-like virus.