Submitted to: International Congress of Virology
Publication Type: Abstract Only
Publication Acceptance Date: 7/27/2002
Publication Date: 7/27/2002
Technical Abstract: Swine influenza (SI) is an acute respiratory disease of swine caused by type A influenza viruses. Prior to 1998, mainly "classical" H1N1 SI viruses (SIV) were isolated from swine in the U.S. Since then, distinct reassortant H3N2 SIVs have been identified as causative agents of respiratory disease in pigs on U.S. farms. The H3N2 SIVs are triple reassortant viruses containing avian-, swine- and human-like gene segments. These triple reassortant SIVs acquired at least 3 distinct H3 molecules from human influenza viruses allowing a differentiation into 3 distinct antigenic clusters (I-III). In vitro studies using hyperimmune pig sera revealed that H3N2 clusters I and III share common epitopes, whereas only limited cross-reactivity was observed with a cluster II H3N2 virus. Infection of pigs with selected SIVs from all three H3N2 clusters resulted in clinical signs and associated lesions in the respiratory tract. However, differences sin severity of clinical signs and lesions between individual strains even within one antigenic cluster were observed. In addition, studies were conducted using plasmid-derived double and triple reassortant H3N2 viruses obtained using a DNA transfection system for the generation of influenza A viruses from eight plasmids. Parental and plasmid-derived H3N2 viruses showed similar in vitro growth characteristics and in vivo pathogenicity. These studies provide the basis for future cross protection experiments in order to assess the efficacy of vaccines against circulating H3N2 SIV strains. The SIV reverse genetics system will allow us to generate and manipulate any swine influenza virus and study the molecular basis of their pathogenicity in pigs.