APPLICATION OF BIOLOGICAL AND MOLECULAR TECHNIQUES TO THE DIAGNOSIS AND CONTROL OF AVIAN INFLUENZA AND OTHER EMERGING POULTRY PATHOGENS
Location: Exotic and Emerging Avian Viral Diseases Research Unit
Title: NP, PB1 and PB2 viral genes contribute to altered replication of H5N1 avian influenza viruses in chickens
Submitted to: Journal of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 15, 2005
Publication Date: February 27, 2008
Citation: Wasilenko, J.L., Lee, C., Sarmento, L., Spackman, E., Kapczynski, D.R., Suarez, D.L., Pantin Jackwood, M.J. 2008. NP, PB1 and PB2 viral genes contribute to altered replication of H5N1 avian influenza viruses in chickens. Journal of Virology. 82(9):4544-4553.
Interpretive Summary: Avian influenza viruses (AIV's) cause a wide range of disease in avian species. These viruses have a genome composed of 8 genes segments. These gene segments can mix when a bird is infected with two different AIV's at the same time and new virus with a different set of genes that may cause different types of disease or infect different type of animals. However, the factors that determine the virulence of AIV are not clearly defined. We used system to generate viruses with mixed genes in order to better understand the role of the different AIV genes in causing disease in chickens. Three genes: PB1, PB2, and NP were shown to greatly affect the virulence of the virus and also affect the immune response in the chicken. The disease caused by AIV in chickens is clearly dependent on the interaction of several genes.
The virulence determinant for highly pathogenic avian influenza viruses is considered multigenic, although the best characterized virulence factor is the hemagglutinin cleavage site. The capability of influenza viruses to reassort gene segments is one potential way for new viruses to emerge with different virulence characteristics. To evaluate the role of other gene segments in virulence, we used reverse genetics to generate two H5N1 recombinant viruses with differing pathogenicity in chickens. Single-gene reassortants were used to determine which viral genes contribute to the altered virulence. Exchange of the PB1, PB2, and NP genes impacted replication of the reassortant viruses while also altering host gene expression levels. Disruption of the parental virus’ functional polymerase complexes by exchanging, PB1 or PB2 genes, decreased viral replication in tissues and consequently the pathogenicity of the viruses. In contrast, exchanging the NP gene greatly increased viral replication and expanded tissue tropism, thus resulting in decreased mean death times. Infection with the NP reassortant virus also resulted in the up-regulation of interferon and inducible Nitric Oxide Synthase gene expression. In addition to the impact of PB1, PB2, and NP on viral replication, the HA, NS, and M genes also contributed to the pathogenesis of the reassortant viruses. While pathogenesis of AIVs in chickens is clearly dependent on the interaction of multiple gene products, we have shown that single gene reassortment events are sufficient to increase virulence of AIVs in chickens.