title: Cross-protection between antigenically distinct H1N1 swine influenza viruses from Europe and North America.
abstract: BACKGROUND
  An avian-like H1N1 swine influenza virus (SIV) is enzootic in swine populations of Western Europe. The virus is antigenically distinct from H1N1 SIVs in North America that have a classical swine virus-lineage H1 hemagglutinin, as does the pandemic (H1N1) 2009 virus. However, the significance of this antigenic difference for cross-protection among pigs remains unknown.
  
  
  OBJECTIVE
  We examined protection against infection with a North American triple reassortant H1N1 SIV [A/swine/Iowa/H04YS2/04 (sw/IA/04)] in pigs infected with a European avian-like SIV [A/swine/Belgium/1/98 (sw/B/98)] 4 weeks earlier. We also examined the genetic relationships and serologic cross-reactivity between both SIVs and with a pandemic (H1N1) 2009 virus [A/California/04/09 (Calif/09)].
  
  
  RESULTS
  After intranasal inoculation with sw/IA/04, all previously uninfected control pigs showed nasal virus excretion, high virus titers in the entire respiratory tract at 4 days post-challenge (DPCh) and macroscopic lung lesions. Most pigs previously infected with sw/B/98 tested negative for sw/IA/04 in nasal swabs and respiratory tissues, and none had lung lesions. At challenge, these pigs had low levels of cross-reactive virus neutralizing and neuraminidase inhibiting (NI) antibodies to sw/IA/04, but no hemagglutination-inhibiting antibodies. They showed similar antibody profiles when tested against Calif/09, but NI antibody titers were higher against Calif/09 than sw/IA/04, reflecting the higher genetic homology of the sw/B/98 neuraminidase with Calif/09.
  
  
  CONCLUSIONS
  Our data indicate that immunity induced by infection with European avian-like H1N1 SIV affords protection for pigs against North American H1N1 SIVs with a classical H1, and they suggest cross-protection against the pandemic (H1N1) 2009 virus.
authors.affiliation: Laboratory of Virology, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium.
authors.forename: Annebel R
authors.initials: AR
authors.lastname: De Vleeschauwer
authors.forename: Sjouke G
authors.initials: SG
authors.lastname: Van Poucke
authors.forename: Alexander I
authors.initials: AI
authors.lastname: Karasin
authors.forename: Christopher W
authors.initials: CW
authors.lastname: Olsen
authors.forename: Kristien
authors.initials: K
authors.lastname: Van Reeth
mesh_terms: D000818:Animals; D000956:Antigens, Viral / Q000276:immunology*; D003429:Cross Reactions; D005060:Europe; D053118:Influenza A Virus, H1N1 Subtype / Q000145:classification / Q000276:immunology*; D009656:North America; D058873:Pandemics; D016865:Reassortant Viruses / Q000276:immunology; D013552:Swine / Q000821:virology*
chemical_list: D000956:Antigens, Viral