LanguageAvian Encephalomyelitis (AE) is a viral infection of the central nervous system and visceral organs, which can attack chickens, turkeys, pheasants and quail. This highly contagious disease, caused by a very tenacious picornavirus (a non-enveloped small RNA-virus), has worldwide distribution. The AE virus is serologically uniform. Embryo-adapted vaccine strains tend to lose their enterotropic properties, while retaining their neurotropic properties.
During the acute phase of an AE infection, which may take up to one month, there is an intermittent shedding of virus in the eggs. This vertically transmitted AEV may affect hatchability, but most infected chicks hatch and start to show symptoms from their first day of life. The infected progeny will subsequently excrete virus via faeces, contributing to a horizontal spreading of the AEV. The disease is prevalent in multiple age farms.
The clinical signs of AE appear after hatch, mostly between weeks 1 and 3 of life: diarrhoea, ataxia, paralysis and especially the typical, neurological signs (epidemic tremor), which aggravate when the birds are agitated. Morbidity may reach up to 40-60% of the flock and mortality may claim up to 25 to 50 % of birds. Few birds recover completely (mostly will suffer growth retardation, with consequent reduced egg production).
AE infections in rearing pullets (6-16 weeks) usually pass without symptoms. AE in adult laying hens may cause considerable drop in egg productions. If the infection occurs in breeding hens during lay, apart from the drop in egg production, the hens will produce infected eggs, causing embryo mortality and infected day-old chicks. Due to the immune response of the chicken, this period of active virus replication stops within 4 weeks.
Vaccination is the recommended method of control. It protects against drop in egg production, prevents vertical transmission and protects offspring against horizontal infection.