Pathology of Newcastle disease in double-crested cormorants from Saskatchewan, with comparison of diagnostic methods

Newcastle disease (ND) in juvenile double-crested cormorants (Phalacrocorax auritus) occurred several times since 1975, but there are relatively few s tudies on its pathology and diagnosis. In order to describe the distributio n of Newcastle disease virus (NDV) and associated lesions in cormorants wit h ND and to compare diagnostic methods, 25 cormorants with nervous signs fr om a ND epizootic in Saskatchewan in 1995 (NDE cormorants) were compared wi th 18 negative control cormorants. Tissues of these birds were examined by necropsy, histology, virus isolation, immunohistochemistry, serology, and r everse transcriptase-polymerase chain reaction (RT-PCR) methods. The NDE co rmorants had a characteristic non-suppurative encephalomyelitis, with a sig nificantly higher prevalence of neuronal necrosis, gliosis, perivascular in filtration 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. Immunohistoc hemically, NDV antigen was limited to neurons, glial and endothelial cells in the central nervous system, and to tubular epithelial cells in the kidne y. Newcastle disease virus was isolated with the highest prevalence (4/5) a nd the highest concentration (10(4.8) ELD50/g) from the kidney. The virus i solates often did not agglutinate erythrocytes in the standard hemagglutina tion test; the presence of NDV was confirmed by use of an indirect immunope roxidase assay. By RT-PCR, NDV was detected in kidney and jejunum of a NDE cormorant. There was no significant difference between sensitivity of histo logy, virus isolation, and serology for detecting ND in NDE cormorants.