Location: Virus and Prion Research2010 Annual Report
1a. Objectives (from AD-416)
Evaluate swine influenza virus (SIV) isolates through in vivo challenge and transmission studies, antigenic characterization with in-house reference sera, and molecular analysis. Assess pathogenesis of selected reassortant swine and avian influenza viruses of mutual interest in pigs.
1b. Approach (from AD-416)
The ARS' National Animal Disease Center (NADC) will support the proposed USDA-APHIS swine influenza surveillance program by providing additional characterization of emerging swine influenza virus (SIV) isolates identified through the surveillance program. The SIV isolates will be evaluated through in vivo challenge and transmission studies, antigenic characterization with in-house reference sera, and molecular analysis. Molecular analysis may include follow-up sequencing, nucleic acid and amino acid sequence comparisons, as well as computation of evolutionary relationships with reference sequences to construct phylogenetic trees. The in vivo studies will aid in identifying viruses with increased virulence, increased transmissibility, or other phenotypic properties. The molecular analyses will aid in identifying viruses with novel genetic make-up and allow a better understanding of the evolution and epidemiology of whole virus genomes. In addition to the NALN submission criteria, the NADC criteria shall be 1) Novel subtype; 2) Novel gene introduction; 3) Novel antigenic properties; or 4) Unusual clinical presentation. Groups of pigs will be inoculated with the appropriate influenza virus strains and doses (to be determined) by the intratracheal or intranasal route. Subsets of animals at selected time points following challenge will be euthanized to determine virus load in the respiratory tract whereas the remaining animals will be further studied to determine the duration of virus shedding and transmission to naïve animals introduced a few days after challenge inoculation. Clinical, virologic and serologic monitoring will be used to assess the outcomes of infection with different viruses to ascertain their potential threat to animal and human health.
3. Progress Report
A series of in vivo challenge and transmission studies in the swine were conducted with 2 isolates of 2009 pandemic H1N1 as outlined in the agreement with the Centers for Disease Control (CDC). Pigs were shown to be susceptible to infection; however, the infection was demonstrated to be limited to the respiratory tract. Antigenic characterization was conducted between the pandemic H1N1 and the swine anti-H1 reference panel, with the results suggesting U.S. swine would be susceptible to outbreaks with the pandemic H1N1 although some may have partial immunity. Two manuscripts have been published and a third is in progress. The implementation of the USDA-APHIS surveillance program was delayed, and no SIV isolates have been identified for characterization at the National Animal Disease Center (NADC) through this mechanism. The two pandemic H1N1 isolates were shown to have differing phenotypes in shedding and transmission characteristics. To evaluate the genetic basis of the phenotypes, reverse genetics technology has been utilized to generate reassortant viruses and the first series of in vitro and in vivo experiments has just recently been completed. A modified amendment was made to the original CDC agreement to add additional studies to be conducted at the NADC with pandemic H1N1 and avian reassortant viruses prepared at the CDC to evaluate pathogenesis and transmission in pigs. A post doctoral research associate has been recruited to fulfill the objectives of the amendment.