Submitted to: Journal of Clinical Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2010
Publication Date: 1/27/2010
Publication URL: http://handle.nal.usda.gov/10113/61385
Citation: Rue, C.A., Susta, L., Brown, C.C., Pasick, J.M., Swafford, S.R., Wolf, P.C., Killian, M.L., Pedersen, J.C., Miller, P.J., Afonso, C.L. 2010. Evolutionary changes affecting rapid identification of 2008 Newcastle disease viruses isolated from double-crested cormorants. Journal of Clinical Microbiology. 48(7):2440-2448. DOI: 10.1128/JCM.02213-09. Interpretive Summary: Newcastle disease virus (NDV) causes substantial cost to the poultry industry worldwide. Continued vaccination programs are generally effective but the virus continues to evolve. In addition to being found in poultry, NDV is ubiquitious in certain wild bird populations such as cormorants. NDV circulating in wild cormorant populations pose a serious risk for transmission of virulent NDV to poultry. Ten isolates from a 2008 outbreak of cormorant NDV in North America were detected by the validated USDA test specific for all NDV (matrix gene) but the test specific for virulent viruses (fusion gene) only detected one of the ten isolates. A new test for the fusion gene was developed and successfully detected all ten isolates. Phylogenetic and pathological analyses showed that these 2008, cormorant isolates belong to the genotype V and are virulent. This analysis of the 2008 cormorant outbreak isolates reported here shows how continued monitoring of NDV in wild bird populations is needed to be able to reliably detect this evolving virus.
Technical Abstract: An outbreak of virulent Newcastle Disease Virus (NDV) in wild double-breasted cormorants (Phalacrocorax auritus) occurred in North America in the summer of 2008. All ten viruses isolated from cormorants were positively identified by the USDA validated real-time reverse transcriptase polymerase chain reaction (RT-PCR) assay targeting the matrix gene. However, the USDA validated real-time RT-PCR assay targeting the fusion gene that is specific for virulent isolates only identified one of these ten isolates. Additionally, several isolates from this outbreak have been sequenced and this information used to identify genomic changes that caused the failure of the test and to revisit the evolution of NDV in cormorants. The forward primer and fusion probe were redesigned from the 2008 cormorant isolate sequence and the revised fusion gene test successfully identified all ten isolates. Phylogenetic analyses using both full fusion sequence and the partial 374 nucleotide sequence identified these isolates as genotype V with their nearest ancestor being an earlier isolate from Nevada in 2005. Histopathological analysis of this ancestral strain showed disease in the spleen and cecal tonsil consistent with that of traditional mesogenic pathotype. Intracerebral pathogenicity assays indicated that each of these isolates are velogenic with values > 0.7 but are not more virulent than reported from earlier outbreak isolates in Canada.