Neurological lesions in chickens experimentally infected with virulent Newcastle disease virus isolates.

Distribution, character, and severity of lesions were evaluated in tissues from the central nervous system of chickens inoculated with 10 different Newcastle disease virus (NDV) isolates: CA 1083, Korea 97-147, Australia (all velogenic viscerotropic), Texas GB and Turkey North Dakota (both velogenic neurotropic), Nevada cormorant, Anhinga and Roakin (all mesogenic), and B1 and QV4 (lentogenic). Tissues for the present study included archived formalin-fixed, paraffin-embedded brain (all strains) plus spinal cord (two strains). Encephalitis was observed in all velogenic viscerotropic and velogenic neurotropic strains, and in some mesogenic strains. In general, the encephalitic lesions began at 5 days post infection, with more severe lesions occurring around 10 days post infection. At this time point, especially in the grey matter of the brain, cerebellum and spinal cord, there were neuronal necrosis, neuronal phagocytosis, and clusters of cells with microglial morphology. Axonal degeneration and demyelination was also observed. Immunohistochemistry (IHC) for viral nucleoprotein confirmed the presence of virus. In the areas of encephalomyelitis, IHC for CD3 revealed that many of the inflammatory cells were T lymphocytes. IHC using an antibody for glial fibrillar acid protein showed reactive astrogliosis, which was most pronounced at the later time points.