An Australian Newcastle Disease Virus With a Virulent Fusion Protein Cleavage Site Produces Minimal Pathogenicity in Chickens

Abstract

Newcastle disease is an important disease of poultry caused by virulent strains of Newcastle disease virus (NDV). During the 1998 to 2002 outbreaks of Newcastle disease in Australia, it was observed that the mild clinical signs seen in some chickens infected with NDV did not correlate with the viruses' virulent fusion protein cleavage site motifs or standard pathogenicity indices. The pathogenicity of 2 Australian NDV isolates was evaluated in experimentally challenged chickens based on clinical evaluation, histopathology, immunohistochemistry, and molecular techniques. One of these virus isolates, Meredith/02, was shown to induce only very mild clinical signs with no mortalities in an experimental setting, in contrast to the velogenic Herts 33/56 and Texas GB isolates. This minimal pathogenicity was associated with decreased virus replication and antigen distribution in tissues. This demonstrates that the Australian Meredith/02 NDV, despite possessing a virulent fusion protein cleavage site, did not display a velogenic phenotype.

Molecular and pathological characterisation of genotype VII Newcastle disease virus on Egyptian chicken farms during 2016–2018

“…The severe lymphocytic depletion in the lymphoid tissues found in this study might reflect some degree of immune depression leading to other infections as previously reported by Bergfeld et al (2017). Immunohistochemical detection of NDV in the lymphocytes and macrophages may indicate that infected macrophages play a role in inducing the apoptosis of non-infected cells, through immune signalling as suggested by Harrison et al (2011).…”

Pathogenesis of Velogenic Genotype VII.1.1 Newcastle Disease Virus Isolated from Chicken in Egypt via Different Inoculation Routes: Molecular, Histopathological, and Immunohistochemical Study

“…These findings may be due to the quick clearance and shedding of virus through diarrhea, as well as due to the protective role of the digestive tract associated with lymphoid aggregation, which may have led to the atrophied cecal tonsils in the choanal inoculated group. Another previous study reported similar symptoms including hemorrhagic cecal tonsils in the oculo-nasal, intraocular, and intranasal inoculated groups [ 61 ]. Furthermore, similar multiple white foci on the spleen were observed in all experimental groups [ 62 ], whereas, in the choanal challenged groups, the splenic foci were smaller in size than other groups.…”

Phylogeny, pathogenicity and transmissibility of a genotype XII Newcastle disease virus in chicken and goose

“…However, although the E115 strain induced obvious clinical signs and exhibited systemic replication in chickens, none of the infected chicken died during the experimental period. Notably, the NDV strain, Meredith/02, isolated from 1998 to 2002 from outbreaks of ND in Australia, containing a virulent F protein cleavage site ( 112 RRQRRF 117 ) and an ICPI of 1.61, induced only very mild clinical signs without mortality via the natural route of infection in an experimental setting (Bergfeld et al, ). Similar results were observed in a study by Susta, Miller, Afonso, and Brown (), which revealed some NDVs with virulent‐type cleavage site motifs and high ICPI values responsible for ND outbreaks in Australia in 1998–2002 were also less pathogenic to chickens under laboratory conditions.…”