Neutralizing Antibodies Against Pandemic, Seasonal And Avian-Like H1n1 Swine Influenza Virus In Swine Contacts And Swine, Western-Europe

Background: Serological studies for swine influenza viruses (SIVs) in humans with occupational exposure to pigs have only been reported from the Americas, but not from Europe. Human infections with SIV have been rare and mostly reported in contacts with swine, as serological studies suggest that swine workers are at increased risk of zoonotic infection with SIV. Methods: Antibodies against pandemic H1N1 2009 influenza virus, a 2007/2008 seasonal H1N1 virus and an avian-like, enzootic H1N1 SIV were analyzed by virus neutralization assay in 211 swine contacts in Luxembourg compared to a matched general population. In addition, neutralizing antibodies to SIV and H1N1 2009 in 203 swine were determined. Results: We showed that swine workers have more often and higher titers of antibodies against pandemic flu and SIV than the control population, and that these titers cannot be explained by cross-reactivity with antibodies at least from recent seasonal flu. Antibodies against SIV and pandemic H1N1 2009 correlated with each other but not with the 2007/2008 seasonal H1N1. The pigs showed a strong positive antibody response to avian like H1N1 and to a weaker extend to H1N1 2009. A correlation between the two virus subtypes was observed, but not to the same extend as for the human cohort. Conclusion: Higher antibody titers against the pandemic H1N1 2009 virus and the avian like SIVs were found in swine workers compared to the general population. As this cannot be explained by cross reactivity from recent seasonal viruses only, we assume that in SIV antibodies swine workers recognize an epitope that is also present in pandemic H1N1 2009 virus, but that is not widely recognized by antibodies found among the general population.