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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 2 Decades

Claudio L Afonso
Journal of Clinical Microbiology 2013 v.51 no.2 pp. 508-517
chickens, sequence analysis, Newcastle disease, viral fusion proteins, lymphatic system, lesions (animal), monitoring, morbidity, genome, phylogeny, disease outbreaks, Avian orthoavulavirus 1, viruses, genotype, wild birds, phenylalanine, virulence, mortality, Dominican Republic
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.