Submitted to: Journal of Clinical Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/16/2012
Publication Date: 2/2/2013
Publication URL: http://handle.nal.usda.gov/10113/57514
Citation: Courtney, S.C., Gomez, D., Hines, N.L., Pedersen, J.C., Miller, P.J., Afonso, C.L., Susta, L., Brown, C. 2013. Highly divergent virulent isolates of newcastle disease virus from the Dominican Republic are members of a new genotype that may have evolved unnoticed for over two decades. Journal of Clinical Microbiology. 51(2):508-517. Interpretive Summary: Newcastle disease virus (NDV) causes a serious disease in avian species and is especially important due to the economic damages it causes to the international poultry industry. The virus continues to evolve worldwide and it is important for U.S. veterinarians to be able to recognize and characterize the threat presented by highly virulent viruses present in countries with commercial or geographic links to the U.S. Here we present the presence of a highly virulent NDV strain isolated in the Dominican Republic that possessed a 100% fatality rate in chickens. This strain did not resemble any of the previously identified strains of NDV and possibly represents a new genotype. The full fusion protein of this new strain was compared to that of another strain that was stored at NVSL and was collected from the Dominican Republic in 1986 and was determined that the two are ancestors. However, this new strain was dramatically different from the LaSota vaccine strain and could therefore lead to problems with commercial vaccination programs in the Dominican Republic.
Technical Abstract: Newcastle disease (ND) is caused by Newcastle disease virus (NDV) and causes significant morbidity and mortality in most bird species. An ND outbreak was recently reported in the Dominican Republic in 2008 and was determined to be caused by NDV. The complete genome of one isolate and the fusion protein of three other related viruses were sequenced and phylogenetically analyzed to determine that these isolates, were genetically, highly distinct from all other currently known isolates of NDV. Together with a 1986 Dominican Republic isolate and a Mexican virus from 1946, all four isolates constitute a distinct genotype of virulent viruses that has evolved unnoticed for over 22 years. The fusion protein cleavage site was identified to contain multiple basic amino acids and a phenylalanine at position 117, along with an ICPI score of 1.88, indicating this strain to be velogenic. These results were further confirmed by clinicopathologically assessing NDV-DR/08 infections in chickens. Gross lesions were observed by 2 dpi and peaked at 4 dpi, mainly throughout the lymphoid tissues. Similarly, virus presence was observed in 20 out of the 25 tissues analyzed. The fact that NDV-DR/08 is a viscerotropic velogenic strain of NDV that is genetically distinct from all other known NDV isolates suggests the existence of unknown reservoirs and underline the importance of continued and improved epidemiological surveillance strategies to detect NDV in wild bird species and commercial poultry.