NEWCASTLE DISEASE EPIDEMIOLOGY, PATHOGENESIS, AND CONTROL
Location: Exotic and Emerging Avian Viral Diseases Research Unit
Title: Pathogenicity evaluation of different Newcastle disease virus chimeras in 4-week-old chickens
Submitted to: Tropical Animal Health and Production
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 1, 2010
Publication Date: December 1, 2010
Citation: Susta, L., Miller, P.J., Afonso, C.L., Estevez, C., Yu, Q., Zhang, J., Brown, C.C. 2010. Pathogenicity evaluation of different Newcastle disease virus chimeras in 4-week-old chickens. Tropical Animal Health and Production. 42(8):1785-1795.
Interpretive Summary: Recombinant Newcastle disease virus chimeras, some of which have previously been tested as NDV vaccines, were put into chickens to evaluate their virulence and the lesions cause by these viruses. These chimeras had four or five of their six genes from a NDV of moderate virulence with the replacement of one or two genes from more virulent NDV. There was not a significant increase in the virulence or lesions seen in 4 week old SPF white Leghorns when they were infected with the chimeras containing genes of more virlent viruses versus results from previous experiments performed with the wild-type viruses of moderate virulence. While all of the chimeras replicated, the viruses that had the two glycoproteins from the virulent virus (both F and HN) replicated better and cause a higher antibody response than the chimera with only the HN from the virulent virus. All of the chimeras produced histopathological lesions of inflammation of the brain tissue, but again, the viruses with both the F and HN produced more significant lesions. The results suggest that virulence is due to more than one or two genes. They also suggest that genes act in combination to produce disease.
Infection with a virulent strain of Newcastle disease virus is considered one of the most important threats to the poultry industry worldwide. The causative virus, Newcastle disease virus, belongs to the Paramyxoviridae family, genus Avulavirus, and its genome encodes for 6 structural proteins: nucleoprotein (NP), phosphoprotein (P), matrix (M), fusion (F), hemagglutinin-neuraminidase (HN), and large protein (L). Although all strains are classified in a single serotype, avian paramyxovirus type 1 (APMV-1), the different isolates vary greatly in virulence and pathogenic potential. Several studies provide evidence that the F and HN genes may be most important for virulence. In this study, chimeras consisting of a recombinant mesogenic virus backbone (Anhinga) containing F and/or HN genes from two virulent viruses (Turkey North Dakota and California 2002) were inoculated into 4-week-old chickens to assess capacity for inducing natural disease. All viruses replicated successfully in the natural host based on virus recovery from oral or cloacal swabs and seroconversion evident at 10 and 14dpi. Viral recovery and seroconversion were most frequent and higher in those viruses containing both F and HN genes from the same virulent virus rather than the virus with a heterologous HN. There was minimal to no increase in clinicopathologic disease due to infection with any the chimeras compared to an infection with the recombinant backbone. However, all birds developed histological evidence of encephalitis, which was most severe in those birds receiving the chimeras with both genes from the same virulent virus. The results suggest that virulence is due to more than one or two genes. They also suggest that genes act in combination to produce disease.