Virulence and pathogenesis of Newcastle disease virus isolates for domestic chickens
Kommers, Glaucia Denise
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Newcastle disease virus (NDV) isolates vary greatly in virulence and pathogenicity depending on several factors including the host species and the infecting virus strain. This research was performed in order to investigate the effect of serial passages of several NDV isolates in domestic chickens. Six isolates were recovered from pigeons and six isolates had heterogeneous origin (recovered from chickens, wild, and exotic birds). A monoclonal antibody (MAb) panel revealed that four of the pigeon-origin isolates were the variant pigeon paramyxovirus-1 (PPMV-1) and two of them were avian paramyxovirus-1 (APMV-1) isolates. Pathotyping tests performed before and after passage in chickens demonstrated increased virulence of the passaged PPMV-1 isolates and high virulence of the original isolates of APMV-1. However, the PPMV-1 were still of moderate virulence for chickens after passages. The fusion protein cleavage site amino acid sequence of all six pigeon-origin (PPMV-1 and APMV-1) isolates was typical of virulent NDVs. Although the results of the pathotyping tests indicated a virulence increase of all passaged PPMV-1 isolates, clinical disease was limited to depression and nervous signs in some of the chickens inoculated intraconjunctivally. However, severe lesions were observed mostly affecting the heart and brain after intraconjunctival inoculation with passaged PPMV-1 isolates. Pigeons must be considered seriously as a potential source of NDV infection and disease for commercial poultry flocks. All six heterogeneous-origin isolates were characterized by reactivity to MAbs as members of the APMV-1 serotype. Three isolates showed low virulence for chickens before and after passage and had the F protein cleavage site typical of low virulence viruses. The other three heterogeneous-origin isolates were classified by the pathotyping tests and sequence analysis of the F protein cleavage site as moderate to highly virulent for chickens. An isolate recovered from an exotic dove had marked virulence increase after passage. The exact mechanism for the virulence increase observed with this isolate remains undefined. A pathogenesis study with the chicken-passaged isolates revealed that two of them were highly virulent for chickens, with marked tropism for lymphoid tissues. The results reported here demonstrate the high risk for domestic chickens represented by some NDV-infected non-poultry species.