Avian encephalomyelitis virus (AEV) is an important pathogen of poultry and is classified as a member of picornaviridae. Nearly all chicken flocks eventually become infected with the virus, but the incidence of clinical disease is very low unless a breeder flock is not vaccinated and becomes infected after the commencement of egg production. This report describes an outbreak of avian encephalomyelitis (AE) in broiler chicken farms around Shiraz, Iran. This survey included 60,000 birds (18-23 days of age), with 5% mortality. Characteristic clinical symptoms including ataxia, tremor of the head, and stretching of the legs were seen. Pathologically, lesions in the central nervous system (CNS) consisted of gliosis, lymphocytic perivascular infiltration, and neuronal degeneration. Lesions in other tissues involved foci of infiltrating leukocytes in the muscle layer of the gizzard, and lymphoid aggregations in the submucosal muscle layer of the proventriculus. There was an increase in serum encephalomyelitis virus antibody titer in affected flocks. These findings showed an AE infection in broiler flocks around Shiraz, Iran
