|Dimitrov, K - National Diagnostic And Research Veterinary Medicine Institute|
|Lee, Dong-hun - Orise Fellow|
|Williams Coplin, Tina|
Submitted to: Journal of Clinical Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2015
Publication Date: 5/1/2016
Publication URL: http://handle.nal.usda.gov/10113/62694
Citation: Dimitrov, K.M., Lee, D., Williams Coplin, T.D., Olivier, T.L., Miller, P.J., Afonso, C.L. 2016. Newcastle disease viruses causing recent outbreaks worldwide show unexpectedly high genetic similarity with historical virulent isolates from the 1940s. Journal of Clinical Microbiology. 54(5)1228-1235 doi: 10.1128/JCM.03044-15.
Interpretive Summary: Virulent Newcastle disease viruses cause significant disease in non-vaccinated and poorly vaccinated poultry worldwide and represent a significant threat to U.S. poultry industries. Because of the large mobility of the virus and of current interconnected economies, the agent can be easily transported across the globe. Therefore, there is strong interest in identifying the different strains circulating worldwide as there is a need for understanding the causes of outbreaks. Epidemiological and evolutionary studies can be very powerful in identifying the source of outbreaks. Together these studies provide a large capacity to predict and prevent outbreaks. Here 43 viruses from China, Egypt, India, and Hungary were studied and found to be nearly identical to historical viruses from the ‘40s. Based on phylogenetic analysis, nucleotide distances, and rates of change, these isolates do not appear to have evolved significantly from ancestral viruses. Low mutational rates and minimal genetic distances suggest that these more recent isolates are evolutionarily nearly static. Furthermore, these viruses are most closely related to old strains used in experimental studies than to vaccine isolates (isolated in the 1940s), therefore, suggesting that they did not originate by a change in virulence from current vaccine viruses, but rather they may represent cases of releases from human activity.
Technical Abstract: Virulent strains of Newcastle disease virus (NDV) cause Newcastle disease (ND), a devastating disease of poultry and wild birds. Phylogenetic analyses clearly distinguish historical isolates (obtained prior to 1960) from currently circulating viruses of class II genotypes V, VI, VII, and XII through XVIII. Here, partial and complete genomic sequences of recent virulent isolates from China, Egypt, India, and Hungary were found to be nearly identical to historical viruses isolated in the 1940s. Phylogenetic analysis, nucleotide distances, and rates of change, demonstrate that these recent isolates have not evolved significantly from the most related ancestors from the 1940s. As with any other ribonucleic acid (RNA) virus, Newcastle disease virus is expected to naturally evolve. Low rates of change for virulent viruses of genotype II and IX (10-5 to 10-6 per year), and the minimal genetic distances existing between recent virulent viruses of genotypes II, III, IV, and IX with historical viruses (0.3 to 1.3%), indicate an unnatural origin and that some recent field isolates should be excluded from evolutionary studies. Furthermore, phylogenetic analyses show that these recent virulent isolates are more closely related to challenge strains used in experimental studies. Since the preservation of viable viruses in the environment for over six decades is highly unlikely, these findings indicate that some of the recent outbreaks may be the result of lax biosecurity.