Signs : biphasic fever (38-41°C, 2 and 6 days), then general depression, dullness, anorexia, stiffness, ataxia, hyperesthesia, aggression, excitability, continuous chewing
[vetstream.com]
Thus, horses with WNV may present with signs of spinal cord ataxia, hyperesthesia, and muscle fasiculations without cortical signs.
[vetbook.org]
Within another day, the horse will experience generalized stiffness throughout his body as well as hyperesthesia---a hypersensitivity to sensory stimuli---which causes him
[equusmagazine.com]