Submitted to: Veterinary Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/13/2001
Publication Date: 5/10/2002
Citation: Interpretive Summary: Clinical Newcastle disease (ND) periodically occurs in free-living pigeons and cormorants as well as racing lofts of pigeons. To simulate the consequences of virus entry and bird to bird spread of these isolates in a chicken flock, selected ND virus (NDV) isolates from pigeons were passaged serially in chickens and the virulence of the isolates before and after passage in chickens was evaluated. Two of the isolates caused severe disease and mortality in the first chickens passage and their hazard to poultry was readily evident. Four of the chicken passaged pigeon isolates produced mild clinical disease in only some of the inoculated birds. However severe microscopic brain lesions were a consistent finding even in some birds that showed no nervous signs. Microscopic lesions were also found in heart and immune system of birds infected with the passaged isolates that produced only mild if any clinical disease. All of the tested isolates are clearly more virulent than the isolates routinely isolated from chickens and turkeys in the U. S. Viruses similar in origin and virulence to the tested isolates pose an increased risk to commercial poultry flocks and management techniques should be implemented to exclude these viruses from production units.
Technical Abstract: The pathogenesis of pigeon isolates of Newcastle disease virus (NDV) was investigated in chickens. Four were characterized as pigeon paramyxovirus-1 (PPMV-1) and two were classified as avian paramyxovirus-1 (APMV-1). Birds inoculated with PPMV-1 isolates were euthanized and sampled at 2, 5, and 10 days post-inoculation (DPI). Birds inoculated with hAPMV-1 isolates died or were euthanized and sampled at 2, 4 and 5 DPI. Tissues were examined by histopathology, immunohistochemistry (IHC) to detect NDV nucleoprotein, and in situ hybridization (ISH) for presence of viral matrix gene mRNA. Two different procedures were used to detect apoptotic cells. Apoptosis was more prominent at 2 DPI by IHC-Casp and at 5 DPI by the TUNEL assay. Brain sections of PPMV-1-infected birds were examined by IHC to detect T- and B-lymphocytes, as well as glial fibrillary acidic protein (GFAP). Histologically, birds inoculated with PPMV-1 isolates had marked lesions in the heart and brain. Presence of viral nucleoprotein and viral mRNA in the affected tissues was confirmed by IHC and by ISH, respectively. Numerous reactive astrocytes were observed in brain sections stained for GFAP. The APMV-1-infected birds developed a disease characteristic of highly virulent NDV with an extensive viral infection evident by IHC.