Abstract
Background:
A neurological infectious viral disease, avian encephalomyelitis (AE) was initially discovered in two-week-old commercial chicks in 1930 and classified as a neurotropic viral disease.
Aim:
A neurological outbreak caused by avian encephalomyelitis virus (AEV) in young chicks was first reported in Al-Ahsa in Kingdom of Saudi Arabia (KSA) in 2010. The aim of this article is to examine the AEV in KSA, Al-Ahsa Province.
Methods:
Gizzard, proventriculus, cerebrum, cerebellum and medulla oblongata tissue samples were collected from infected chicks for histopathology test and molecular identification.
Results:
Infected chicks showed neurological signs particularly incoordination, mild head and neck tremors, stretching of legs and lameness. The average morbidity and mortality rates were 35% and 10% respectively. At necropsy, no obvious identifiable macroscopic lesions were found in the infected chicks. Non-suppurative encephalomyelitis was found histopathologically in the central nervous system (CNS), mainly in the cerebral molecular layer. Microscopic lesions in the proventriculus showed masses of heavy numbers of small lymphocytes within the muscular layer. RT-PCR followed by sequence analysis revealed that The Kingdom of Saudi Arabia (KSA) strain (KJ939252) is intimately related to chicken European strains from Poland (KC912695) and the United Kingdom (AJ225173) with identity 99.6% than Chinese strains (AY225319, AY517471 and AY275539) with identity ranged between 94.6% to 95%. The phylogenetic tree analysis showed that the KSA strain is grouped in the similar clade with chicken European strains.
Conclusion:
The pattern of disease findings was typical of vertically transmitted AEV. The spread of AEV in Saudi Arabia is most likely due to the trade of birds and bird’s products with European countries.

Key words: Avian Encephalomyelitis, Broiler chicks, Molecular identifications, Saudi Arabia