Submitted to: Journal of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/21/2007
Publication Date: 11/13/2007
Citation: Kim, L.M., King, D.J., Curry, P., Suarez, D.L., Swayne, D.E., Stallknecht, D., Slemons, R.D., Pedersen, J.C., Senne, D.S., Winker, K., Afonso, C.L. 2007. Phylogenetic diversity among low-virulence Newcastle disease viruses from waterfowl and shorebirds and comparison of genotype distributions to those of poultry-origin isolates. Journal of Virology. 81(22):12641-12653. Interpretive Summary: Newcastle disease virus (NDV) is of significant concern to poultry producers worldwide. While the virulent NDV viruses which are typically known to cause disease in poultry are considered exotic to the United States (U.S.), there are viruses which circulate in wild bird populations that are referred to as endemic NDV. There is a paucity of information about the distribution and genetic diversity of these particular viruses which is partly because they are not known to cause disease in wild bird species. To further our understanding of the these endemic viruses, genetic and biologic characterization of 249 waterfowl and shorebird (WS) NDV viruses and 19 NDV viruses isolated from U.S. live bird markets (LBM) was performed. All viruses were determined to be of low virulence and of low potential to cause disease in poultry. The analysis of the genetic sequence of these viruses revealed that most of the WS viruses and all of the LBM viruses were significantly divergent from virulent viruses. Additionally, viruses isolated from LBM were found to be closely related to a subset of WS viruses. Another finding was that a matrix-gene targeted real time RT-PCR assay, which has commonly been used to detect NVD, failed to identify most of the LBM and WS viruses. The evident similarity between viruses found in LBMs and those recovered from WS and the concern that many of these viruses may circulate undetected suggest that endemic NDV viruses from WS could potentially infect birds in LBMs.
Technical Abstract: Low virulence Newcastle disease viruses (loNDV) are frequently recovered from wild bird species, but little is known about their distribution, genetic diversity, or potential to cause disease in poultry. NDV isolates recovered from cloacal samples of apparently healthy waterfowl and shorebirds (WS) in the U.S. during 1986 to 2005 were examined for genomic diversity and their potential for virulence (n = 249). In addition 19 loNDV isolates from U.S. live bird markets (LBMs) were analyzed and found to be genetically distinct from NDV used in live vaccines, but related to WS-origin NDV. Phylogenetic analysis of the fusion protein identified nine novel genotypes among the class I NDV and new genomic subgroups were identified among genotypes I and II of the class II viruses. The WS-origin viruses exhibited broad genetic and antigenic diversity and some WS genotypes displayed a closer phylogenetic relationship to LBM-origin NDV. All NDV were predicted to be lentogenic based upon sequencing of the fusion cleavage site, intracerebral pathogenicity index, or mean death time in embryo assays. The USDA real-time RT-PCR (RRT-PCR) assay that targets the matrix gene identified nearly all of the class II NDV viruses tested, but failed to detect class I viruses from both LBM and WS. The close phylogenetic proximity of some WS and LBM loNDV suggests that viral transmission may occur among wild birds and poultry; however, these events may occur unnoticed due to the broad genetic diversity of loNDV, the lentogenic presentation in birds, and the limitations of current rapid diagnostic tools.