Location: Virus and Prion Research2012 Annual Report
1a. Objectives (from AD-416):
1) Pathogenesis of avian inluenza virus isolates in swine; 2) Role of avian polymerases in adaptation of swine influenza viruses to swine; 3) Genetic characterization of swine and avian influenza viruses to swine; and 4) Preparation of reagents.
1b. Approach (from AD-416):
1) Pathogenesis of avian influenza virus isolates in swine will be evaluated after inoculation into a group of four week old pigs. Microscopic and macroscopic lung lesions and viral replication in lungs and nasal cavities will be determined. 2) Various reassortant viruses containing avian and/or swine polymerase genes will be established using reverse genetics approaches. These reassortant viruses will be tested for their pathogenic potential in swine. 3) Swine and avian influenza isolates will be genetically characterized using conventional sequencing approaches. 4) Hyperimmune sera and various viruses will be made available as reagents.
3. Progress Report:
In the 1980s swine were proposed to be the "mixing vessel" for novel influenza viruses that could infect humans. This hypothesis was based on the identification of human-like and avian-like influenza virus receptors in the respiratory tract of swine. The presence of both receptors could allow pigs to be simultaneously infected with a human and avian influenza virus leading to the formation of a new virus that reflected the combination of the avian and human viruses. This novel virus would be transmitted to people and could lead to a pandemic. In the late 1990s an H5N1 influenza virus emerged in birds that sporadically jumped species to people often resulting in severe disease and death. The lethality of this virus for humans was of great concern and led to the formation of a long-term multi-institutional NIH-funded grant to study various aspects of the ecology and biology of influenza viruses. The National Animal Disease Center's initial role in this grant was to study molecular mechanisms by which influenza viruses acquire increased disease causing capacity or pathogenicity for humans and animals, and determination of the molecular mechanisms responsible for the transmission of influenza viruses between animals, between humans, and from animals to humans. Animal models used to study the molecular pathogenesis of human influenza virus infections have revealed a number of putative mechanisms that relate to how the virus can infect humans and cause disease. Based on a mouse model, a specific sequence in the influenza virus PB2 gene contributes to its pathogenicity. This same effect was not detected in swine indicating the complexity of using animal models. These differences are attributed to differences among species, and to the fact that influenza virus-swine is a natural virus-host interaction compared to the adaptation of human influenza viruses to mice for experimental purposes. Following changes in personnel and funding, the objectives of the grant were modified to conduct animal inoculation studies testing the susceptibility of swine to infection with low pathogenic avian and human influenza A viruses. To test the first part of the mixing vessel hypothesis, swine studies were initiated to inoculate pigs with an avian influenza virus (low pathogenic H5 and H7 viruses, and H9 isolates) or with human H1N1 influenza viruses. Pigs were shown to be susceptible to single experimental infection with avian or human influenza A virus isolates. Depending on isolate, minimal to mild clinical disease was produced suggesting swine could act as a reservoir for various influenza viruses and might serve as a mixing vessel. Studies designed to evaluate dual infections with avian and human viruses were put on hold with the emergence of the 2009 H1N1 pandemic virus of swine origin that contained avian and human genes, the product of a perfect mixing vessel experiment that proved the hypothesis. As part of a nationwide response to the pandemic, swine studies were re-designed to investigate the pathogenesis of the pandemic virus. In addition, plans were made to conduct collaborative studies evaluating the consequences highly pathogenic avian influenza viruses infections in swine and the potential for formation of unique viruses. However, a change in regulations delayed this proposed work and will require modification of research plans to investigate interspecies transmission of a new group of swine influenza viruses. The new lineage of viruses is of concern based on the growing number of swine to human transmission events that have occurred during the last year. This summary report covers the first 5 years of the 7-year-long grant, and the research under the multi-institutional grant that continues into 2014 will be documented in a new ARS subordinate project number.