Birds infected with avian encephalomyelitis, through vertical transmission within the egg, may develop neurologic signs 1-2 weeks after hatch. Signs may include progressive ataxia, incoordination, paralysis, and prostration (seen here). Young birds are more susceptible to this disease than older birds. Humoral immunity, or antibody response, constitutes the basis of this age resistance. Birds exposed after 2-3 weeks of age may not develop neurologic signs and adults may only experience a slight drop in egg production.