Avian encephalomyelitis (AE) infection is seen as two distinct syndromes depending on the age when the susceptible chicken is infected.

In young chickens the disease affects the nervous system. Chickens may show ataxia, sitting on hocks, tremor of the head, neck and wings and an elevated mortality.  Layers experience a temporary drop in egg production and breeders a drop in hatchability, with neither showing any nervous signs.

Both vertical and horizontal transmission occurs and the virus can survive for four weeks or more in faeces. Fowl pox disease is slow spreading.  It is recognised by the characteristic pox lesions on the comb, wattles and non-feathered parts of the body and/or in the upper respiratory and digestive tract. The affected chickens show poor weight gain and a drop in egg production.

Fowl pox is spread by biting insects as well as direct transmission. The virus can survive for years in pox scabs.