Location: Virus and Prion Research
Project Number: 5030-32000-108-36-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 1, 2014
End Date: Feb 25, 2015
The objectives of this study are to: 1) Test by site-directed mutagenesis the amino acid substitutions responsible for the antigenic evolution observed in recent swine H3 subtype influenza A viruses identified in the U.S. swine population; 2) Generate reverse genetics (rg) derived H3N1 viruses with gene segments from the wild type swine strain and segments representing the putative human and swine donor viruses to define the genetic basis for fitness in pigs and ferrets; 3) Evaluate the pathogenesis and transmission of the wild type and rg-derived H3N1 viruses in pigs and ferrets; and 4) Compare the antigenic evolution of the novel H3N1 to human and swine strains to make inferences about the immunity to this virus in each population.
Since the introduction of the 2009 H1N1 pandemic virus into pigs, the H1N1 reassorted with H3N2. The resulting H3N2 subsequently underwent a period of expanded genetic and antigenic evolution. Six amino acid sites were recently identified by characterization of 33 contemporary swine H3N2 viruses as being associated with antigenic drift. Test amino acid substitutions at these sites for their contribution to antigenic variation using site-directed mutagenesis of the gene segment encoding a swine HA protein as single and combinations of mutations. Evaluate the effect of these substitutions in serologic assays combined with antigenic cartography. Explore the limits of antigenic variability and fitness on these sites and an additional site in the context of the swine host by introducing alternate substitutions observed in different host species at the same amino acid positions. These results will inform vaccine strain selection for swine as well as provide critical information on the amino acids sites important for population immunity for potentially all influenza host populations. Additionally, a novel H3N1 reassortant virus was identified in a swine herd in 2014. The genetic make up of the H3N1 contains a unique composition that has not been seen in the United States, including a hemagglutinin (HA) gene most closely related to contemporary H3N2 circulating in the human population and genes from the 2009 pandemic H1N1 virus (H1N1pdm09). The goal of this project is to elucidate the genetic components that confer fitness to swine and/or ferrets through reverse engineering of viruses with genes from the H3N1 reassortant swine strain and putative human and swine donor viruses. The wild type and reverse genetics derived viruses will be assessed for pathogenicity and transmission properties in swine at the ARS, and in ferrets as a risk assessment model for human public health by the cooperator.