NEW INSIGHTS ON NEUROPATHOLOGICAL LESIONS PROGRESSION WITH SPECIAL EMPHASIS ON RESIDENCE OF VELOGENIC NEWCASTLE DISEASE VIRAL ANTIGEN IN THE NERVOUS SYSTEM OF EXPERIMENTALLY INFECTED BROILER CHICKENS

New castle disease virus affecting poultry industry resulting in extensive chicken mortalities and economic losses. Evaluation of distribution and severity of neuropathological lesions progressed in different areas of central nervous system was performed in chickens experimentally infected by velogenic Newcastle virus (vNDV). Chickens were inoculated by genotype VII strain (NDV-B7-RLQP-CH-EG-12) via intraocular route at different ages (10, 20 and 30 days old). Serum samples for antibody titer estimation and tissue sections from nervous system were collected for histopathological examination at 1, 3, 5 and 7-days post inoculation (dpi) from all groups. Results indicated that there was variation in antibody titers among different age groups. Encephalitis, myelitis with marked demyelination and axonal spheroids formation were the main neuropathological alterations. Lesions were detected in different areas of central nervous system which vary in distribution and severity among age and duration of infection with complete tract degeneration which was responsible for the developed nervous signs. The experimental infection of broilers by vNDV via intraocular inoculation induced virus dissemination into the central nervous system with progression of neuropathological lesions that were varied in severity, distribution and the onset according to the age of birds with subsequent development of nervous clinical signs and mortalities, in addition the distribution of virus along the CNS clarify the possible pathways of virus dissemination and progression in the neuroparenchyma denoting the neuropathogenesis of the vNDV. The age of bird at the time of infection is a crucial factor in determining the viral replication in neuroparenchyma with subsequently developed neuropathology.