Avian encephalomyelitis virus (AEV)
Avian encephalomyelitis virus (AEV) is a type of picornavirus and member of the Picornaviridae family of viruses. It occurs worldwide and predominately affects young chicks (between 1-2 weeks of age), although it has been known to occur in chicks upon hatching.
Initial signs that chicks are infected with AEV include a dull expression of the eye which eventually leads to a weakened cry. Chicks also display a sudden onset of progressive ataxia, leading to chicks seen sit on their hocks, which, when disturbed, may randomly exhibit locomotion, exhibiting little control over their speed and gait. Soon after, chicks will suddenly rest or fall on their sides or some may refuse to move or may walk on their hocks and shanks. Fine tremors of the head and neck may be observed, varying in the frequency and magnitude and is usually brought on by exciting or disturbing the chicks. Chicks with ataxia and prostration are frequently trampled to death by other flock members. Some chicks with definite signs of AE may survive and grow to maturity, and in some instances signs may disappear completely. Survivors may later develop blindness from an opacity giving a bluish discoloration to the lens of their eyes.