title: Prior infection of pigs with a recent human H3N2 influenza virus confers minimal cross-protection against a European swine H3N2 virus.
abstract: BACKGROUND
  H3N2 influenza viruses circulating in humans and European pigs originate from the pandemic A/Hong Kong/68 virus. Because of slower antigenic drift in swine, the antigenic divergence between swine and human viruses has been increasing. It remains unknown to what extent this results in a reduced cross-protection between recent human and swine H3N2 influenza viruses.
  
  
  OBJECTIVE
  We examined whether prior infection of pigs with an old [A/Victoria/3/75 (A/Vic/75)] or a more recent [A/Wisconsin/67/05 (A/Wis/05)] human H3N2 virus protected against a European swine H3N2 virus [sw/Gent/172/08 (sw/Gent/08)]. Genetic and antigenic relationships between sw/Gent/08 and a selection of human H3N2 viruses were also assessed.
  
  
  RESULTS
  After challenge with sw/Gent/08, all challenge controls had high virus titers in the entire respiratory tract at 3 days post-challenge and nasal virus excretion for 5-6 days. Prior infection with sw/Gent/08 or A/Vic/75 offered complete virological protection against challenge. Pigs previously inoculated with A/Wis/05 showed similar virus titers in the respiratory tract as challenge controls, but the mean duration of nasal shedding was 1·3 days shorter. Unlike sw/Gent/08- and A/Vic/75-inoculated pigs, A/Wis/05-inoculated pigs lacked cross-reactive neutralizing antibodies against sw/Gent/08 before challenge, but they showed a more rapid antibody response to sw/Gent/08 than challenge controls after challenge. Cross-protection and serological responses correlated with genetic and antigenic differences.
  
  
  CONCLUSIONS
  Infection immunity to a recent human H3N2 virus confers minimal cross-protection against a European swine H3N2 virus. We discuss our findings with regard to the recent zoonotic infections of humans in the United States with a swine-origin H3N2 variant virus.
authors.affiliation: Laboratory of Virology, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium.
authors.forename: Yu
authors.initials: Y
authors.lastname: Qiu
authors.forename: Karen
authors.initials: K
authors.lastname: van der Meulen
authors.forename: Kristien
authors.initials: K
authors.lastname: Van Reeth
mesh_terms: D000818:Animals; D056738:Cross Protection; D053122:Influenza A Virus, H3N2 Subtype / Q000276:immunology* / Q000302:isolation & purification*; D009976:Orthomyxoviridae Infections / Q000276:immunology / Q000662:veterinary* / Q000821:virology; D012137:Respiratory System / Q000821:virology; D013552:Swine; D013553:Swine Diseases / Q000276:immunology* / Q000821:virology*; D017201:Virus Shedding
keywords: Cross-protection; Europe; H3N2 swine influenza virus; human H3N2 virus; zoonosis
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