New Occurance of Avian Encephalomyelitis in Broiler – Is this an Emerging Disease?

Avian encephalomyelitis is caused by an Hepatovirus and primarily affects chickens. Chickens of all ages are susceptible to the virus, but the nervous symptoms are manifested only in young chicks, between one to five weeks of age. During the last thirty years, avian encephalomyelitis appeared to be well controlled by breeder vaccination. However, the increase of the number of cases is causing concern in the poultry industry. In the present study, we performed a retrospective analysis of the cases presenting histological lesions compatible with avian encephalomyelitis in broilers. The evaluated cases affected broilers from one to 35 days old from the southern region of Brazil. Only cases with compatible microscopic lesions and associated with clinical symptoms in the field were considered. In addition the histopathological diagnosis, sera were tested by ELISA (Enzyme-Linked Immunosorbent Assay). Considering the clinical, histopathological, and serological evidences, the disease was confirmed, showing an increase in outbreaks from the last quarter of 2012, extending through 2013. The cause of this increase is not clear, although we suspect vaccine or vaccination error. Enhancing vaccinated breeders flocks monitoring before the beginning of egg production and/or using a protocol with two vaccinations is recommended.