Identification of avian encephalomyelitis virus in outbreaks among broilers in Morocco between 2020 and 2024

Avian encephalomyelitis (AE) is a viral disease of poultry caused by avian encephalomyelitis virus (AEV; family Picornaviridae) that affects multiple avian species and continues to pose economic concerns for the poultry industry. Clinical expression differs with age, with neurological manifestations predominating in young birds, while adult layers mainly exhibit a transient reduction in egg production.

This study describes the clinical, pathological, and molecular findings associated with AE outbreaks in six Moroccan broiler flocks aged 6-17 days. Histopathological examination was performed on brain tissues, while AEV was detected by RT-PCR and confirmed by Sanger sequencing. Phylogenetic analysis based on partial 5'-UTR sequences was conducted to determine the genetic relationships among the detected isolates.

Affected flocks showed severe neurological signs, including tremors, drowsiness, ataxia, locomotor incoordination, and paresis, leading to reduced feed and water intake. Morbidity reached up to 90%, with cumulative mortality exceeding 25%. Histopathological examination revealed multifocal gliosis, neuronal degeneration and chromatolysis, axonal degeneration, demyelination, and perivascular cuffing, with the cerebellum particularly affected, showing marked Purkinje cell degeneration and glial proliferation. Phylogenetic analysis classified four Moroccan isolates within genotype B, closely related to the Hungarian strain pf-HK1, and two isolates within genotype A, indicating the circulation of two distinct evolutionary lineages in Moroccan broiler flocks.

This study provides the first pathological and molecular characterization of avian encephalomyelitis in Moroccan poultry flocks. These findings highlight the need for continued surveillance and further epidemiological investigations, including assessment of breeder immunity and maternal antibody transfer, to improve understanding of AEV circulation and its impact on poultry production in Morocco.