Avian Encephalomyelitis (AEV): Epidemic Tremor & Egg Drops
Scientific manual covering Picornaviridae etiology, ataxia, head/neck tremors, cataract blindness, and breeder vaccination.
Scientific Overview
Avian Encephalomyelitis (AE / Epidemic Tremor) is a viral disease of young chicks, turkey poults, and laying hens caused by Avian Encephalomyelitis Virus (AEV). In chicks, AEV causes central nervous system signs (ataxia, head/neck tremors). In adult layers, it causes sudden 10% to 50% drops in egg production without respiratory signs.
Etiology & Neurotropism
Avian Encephalomyelitis Virus (AEV) is defined as a non-enveloped single-stranded RNA virus of the family Picornaviridae, genus Tremovirus.
Transmission occurs vertically through infected eggs laid during active hen infection, or horizontally via fecal-oral contamination in brooder houses.
Clinical Signs: Nervous Tremors vs Layer Egg Drops
Manifestations depend on host age:
- Young Chicks (1 to 3 weeks): Progressive ataxia, dullness, falling on sides, and fine rapid tremors of the head and neck ('Epidemic Tremor'). Surviving birds often develop bilateral eye cataracts (lens opacity) and blindness.
- Laying Hens: Sudden drop in egg production (10% to 50%) lasting 2 to 3 weeks, accompanied by dropped hatchability in breeder flocks.
Breeder Vaccination Protocol
AEV is prevented by vaccinating breeder pullets and commercial layers between 10 and 14 weeks of age (via drinking water or wing-web, often combined with Fowl Pox). Vaccination during egg production must be avoided as it triggers vaccine-induced egg drops.