Histopathological diagnosis and genetic diversity of avian encephalomyelitis virus circulating in broiler farms in Egypt

Background: Avian encephalomyelitis (AE) is an imperative viral disease of avian species worldwide caused by the AE virus (AEV). Aim: This retrospective study aimed to genetically characterize field AEV strains circulating in the local governorates of Egypt and assess their genetic divergence in comparison with commercially available vaccines. To the best of our knowledge, this is the first described study of AEV-VP1 gene sequencing and phylogeny in broilers in Egypt. Methods: A total of 150 tissue specimens from broilers of four Egyptian governorates were used for isolation and genetic characterization. The samples were tested for other pathogens, including egg drop syndrome virus, Newcastle disease virus, avian reovirus, avian reticuloendotheliosis virus, infectious bronchitis virus, Chicken anemia virus, and Marek’s disease virus. Results: Young chicks showed neurological symptoms and a mortality rate of 4%–8%. Only crop impaction and distended proventriculus were observed in sick chicks. Histopathological findings revealed typical lesions of lymphocytic encephalomyelitis in the cerebrum with mononuclear cuffing of perivascular spaces in the cortex and medulla. The proventriculus revealed mild lymphocytic infiltration within the submucosa. Typical pathological changes in leg rigidity and encephalomalacia were observed in specific pathogen-free embryonated chicken eggs (SPF-ECE). Regarding reverse transcriptase quantitative polymerase chain reaction (RT-qPCR), 8 (8/150) samples were positive with a prevalence rate of 5.3%, and the screening results were negative for other viral infections. The 4 selected positive samples were amplified using a one-step conventional RT-PCR assay for partial sequencing of the AEV-VP1 gene. Interestingly, the phylogenetic analysis exhibited that AEV isolates belong to cluster II within the same clade of Chinese strains and have a genetic similarity to Chinese, Iranian, American vaccinal, and British isolates, with 94%–98%a nucleotide similarity, and 96%–99% amino acid identity. Conclusion: Continuous monitoring and potentially updating the vaccination strategies in a timely manner are necessary to ensure vaccine effectiveness as an efficient control strategy in poultry flocks.