Kristien Van Reeth, Ghent University, Belgium, presented ‘Pigs and Pandemic Influenza: Myths versus Facts’ at the 2009 Al Leman Swine Conference. The presentation examined the role of pigs in influenza pandemics.
Her presentation casts doubt on the theory of the pig as a mixing vessel for influenza viruses and questions the significance of the pig's role in the emergence or future transmission of the novel 2009 H1N1 pandemic influenza virus.
Van Reeth offers a thorough explanation of the mechanisms and implications of antigenic shift and drift common to influenza viruses and how this genetic reassortment can lead to the emergence of novel subtypes with the potential for epidemic or pandemic consequences. She emphasized that the consensus is that all novel influenza viruses arise from wild aquatic birds but that interspecies transmission is actually fairly uncommon.
Interestingly, although they have evolved along different pathways, the classical swine H1N1 (cH1N1) and the early human H1N1 viruses both derived from the 1918 pandemic influenza outbreak when clinical signs were observed simultaneously in swine and humans. This was the first report of influenza-like disease in swine although symptoms of human influenza had been recognized for centuries. It is unclear whether the 1918 virus arose in humans and was transmitted to pigs or vice versa.
The evolution of the human and swine H1N1 viruses, however, has resulted in antigenic differences between the recent swine and recent human seasonal H1N1 subtypes. The cH1N1 has further combined with avian and human viruses to produce an internal triple reassortant gene cassette.