Newcastle disease (ND) in juvenile double-crested cormorants (Phalacrocorax auritus) occurred several times since 1975, but there are relatively few studies on its pathology and diagnosis. In order to describe the distribution of Newcastle disease virus (NDV) and associated lesions in cormorants with ND and to compare diagnostic methods, 25 cormorants with nervous signs from a ND epizootic in Saskatchewan in 1995 (NDE cormorants) were compared with 18 negative control cormorants. Tissues of these birds were examined by necropsy, histology, virus isolation, immunohistochemistry, serology, and reverse transcriptase-polymerase chain reaction (RT-PCR) methods. The NDE cormorants had a characteristic non-suppurative encephalomyelitis, with a significantly higher prevalence of neuronal necrosis, gliosis, perivascular infiltration with mononuclear cells, and endothelial hypertrophy than control cormorants. These lesions were found more frequently in the cerebellum and brain stem than in other parts of the central nervous system. Immunohistochemically, NDV antigen was limited to neurons, glial and endothelial cells in the central nervous system, and to tubular epithelial cells in the kidney. Newcastle disease virus was isolated with the highest prevalence (4/5) and the highest concentration (104.8 ELD50/g) from the kidney. The virus isolates often did not agglutinate erythrocytes in the standard hemagglutination test; the presence of NDV was confirmed by use of an indirect immunoperoxidase assay. By RT-PCR, NDV was detected in kidney and jejunum of a NDE cormorant. There was no significant difference between sensitivity of histology, virus isolation, and serology for detecting ND in NDE cormorants.

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