Influenza2010: Zoonotic Influenza and Human Health: Part-B

Abstract

The epidemiology of influenza virus in pig populations is unique, with different lineages of viruses identified based on spatio-temporal characteristics. Co-circulation of viruses leads to the generation of new strains through genetic reassortment and the consequences of independent evolution of influenza viruses in pigs gives rise to considerable genetic diversity at continental level. Whilst the pig has been postulated as a mixing vessel for the generation of new influenza viruses, more recent work would indicate that this is a complex dynamic. However, the emergence of pandemic (H1N1) 2009 virus (pH1N1) in humans is postulated to have derived from pigs. Limited surveillance studies in pigs have revealed changes in virus diversity through the occurrence of novel reassortant viruses containing genes from both avian, human and swine sources. The correlates for successful cross-species transmission are multi-factoral and include host, virus and the impact of prior immunity to endemic swine influenza viruses. The pH1N1 virus has spread from humans to pigs in numerous countries. The future dynamics of infection with this virus in pig populations will be complex and impacted by the immune status and characteristics of viruses circulating in pig populations in different regions. Detailed studies of the transmission, infection dynamics and immunopathology of pH1N1 virus in pigs and it’s comparability to human infection will be reported. These studies have also been extended to understanding the epidemiological and evolutionary characteristics of pH1N1 virus in pigs and the associated occupational risks. Preliminary data indicates that the virus has a high capability to transmit within and between pigs and has become established in UK pig populations. The impact of prior immunity to endemic swine strains will, we predict, impact the future epidemiology of influenza virus in pig populations around the globe. Furthermore, clusters of infection within farm networks have been detected through detailed epidemiological investigations, which have also revealed potentially higher seroprevalence to pandemic virus amongst pig veterinarians compared to cohorts of ‘non-exposed’ humans. The implications of these results will be discussed. Events subsequent to the emergence of the pandemic virus have provided further focus and interest in pigs relating to the evolution and ecology of influenza viruses relevant to veterinary public health.