title: Influenza A(H1N1)pdm09 virus infection in Norwegian swine herds 2009/10: the risk of human to swine transmission.
abstract: Influenza A viruses cause respiratory infection in humans and pigs, and some serotypes can be transmitted between these species. The emergence of influenza A(H1N1)pdm09 virus infections in the spring of 2009 quickly led to a worldwide pandemic in humans, with subsequent introduction of the virus to pig populations. Following a widespread infection in the human population in Norway, influenza A(H1N1)pdm09 virus was introduced to the influenza A naïve Norwegian pig population, and within a few months pigs in more than one third of Norwegian swine herds had antibodies against the virus. A cross-sectional study was performed on all swine nucleus and multiplier herds in Norway to analyze risk factors for introduction of infection, and the preventive effects of recommended biosecurity practices. A surveillance program provided information on infection status of the study herds, and a questionnaire was administered to all 118 nucleus and multiplier herds to collect information on herd variables. The surveillance program revealed that pigs in 42% of the herds had antibodies against influenza A(H1N1)pdm09 virus. The incidence of serologically positive pigs was similar in both multiplier herds (41%) and closed nucleus herds (43%). Multivariable logistic regression showed that presence of farm staff with influenza-like illness (ILI) (OR=4.15, CI 1.5-11.4, p=0.005) and herd size (OR=1.01, CI 1-1.02, p=0.009) were risk factors for infection. The rapid and widespread seroconversion for antibodies against influenza A(H1N1)pdm09 virus in the Norwegian pig population can be explained by the emergence of a novel virus that is readily transmitted between people and swine in a largely susceptible population of humans, and an entirely naïve population of pigs.
authors.affiliation: Norwegian School of Veterinary Science, Department of Production Animal Clinical Sciences, P.O. Box 8146, 0033 Oslo, Norway. carl.grontvedt@nvh.no
authors.forename: Carl Andreas
authors.initials: CA
authors.lastname: Grøntvedt
authors.forename: Chiek
authors.initials: C
authors.lastname: Er
authors.forename: Britt
authors.initials: B
authors.lastname: Gjerset
authors.forename: Anna Germundsson
authors.initials: AG
authors.lastname: Hauge
authors.forename: Edgar
authors.initials: E
authors.lastname: Brun
authors.forename: Anne
authors.initials: A
authors.lastname: Jørgensen
authors.forename: Bjørn
authors.initials: B
authors.lastname: Lium
authors.forename: Tore
authors.initials: T
authors.lastname: Framstad
mesh_terms: D000818:Animals; D000914:Antibodies, Viral / Q000097:blood; D003430:Cross-Sectional Studies; D006801:Humans; D015994:Incidence; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification*; D007251:Influenza, Human / Q000453:epidemiology / Q000517:prevention & control / Q000635:transmission* / Q000821:virology; D016015:Logistic Models; D008954:Models, Biological; D009664:Norway / Q000453:epidemiology; D009976:Orthomyxoviridae Infections / Q000453:epidemiology / Q000209:etiology* / Q000517:prevention & control / Q000662:veterinary*; D012307:Risk Factors; D011795:Surveys and Questionnaires; D013552:Swine; D013553:Swine Diseases / Q000453:epidemiology / Q000517:prevention & control / Q000635:transmission* / Q000821:virology; D015047:Zoonoses / Q000453:epidemiology / Q000517:prevention & control / Q000635:transmission / Q000821:virology
chemical_list: D000914:Antibodies, Viral