title: Dynamics of influenza A virus infections in permanently infected pig farms: evidence of recurrent infections, circulation of several swine influenza viruses and reassortment events.
abstract: Concomitant infections by different influenza A virus subtypes within pig farms increase the risk of new reassortant virus emergence. The aims of this study were to characterize the epidemiology of recurrent swine influenza virus infections and identify their main determinants. A follow-up study was carried out in 3 selected farms known to be affected by repeated influenza infections. Three batches of pigs were followed within each farm from birth to slaughter through a representative sample of 40 piglets per batch. Piglets were monitored individually on a monthly basis for serology and clinical parameters. When a flu outbreak occurred, daily virological and clinical investigations were carried out for two weeks. Influenza outbreaks, confirmed by influenza A virus detection, were reported at least once in each batch. These outbreaks occurred at a constant age within farms and were correlated with an increased frequency of sneezing and coughing fits. H1N1 and H1N2 viruses from European enzootic subtypes and reassortants between viruses from these lineages were consecutively and sometimes simultaneously identified depending on the batch, suggesting virus co-circulations at the farm, batch and sometimes individual levels. The estimated reproduction ratio R of influenza outbreaks ranged between 2.5 [1.9-2.9] and 6.9 [4.1-10.5] according to the age at infection-time and serological status of infected piglets. Duration of shedding was influenced by the age at infection time, the serological status of the dam and mingling practices. An impaired humoral response was identified in piglets infected at a time when they still presented maternally-derived antibodies.
authors.affiliation: Anses, Laboratoire de Ploufragan/Plouzané, Unité Epidémiologie et Bien-Être du Porc, BP 53, 22440 Ploufragan, France. nicolas.rose@anses.fr.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Rose
authors.forename: Séverine
authors.initials: S
authors.lastname: Hervé
authors.forename: Eric
authors.initials: E
authors.lastname: Eveno
authors.forename: Nicolas
authors.initials: N
authors.lastname: Barbier
authors.forename: Florent
authors.initials: F
authors.lastname: Eono
authors.forename: Virginie
authors.initials: V
authors.lastname: Dorenlor
authors.forename: Mathieu
authors.initials: M
authors.lastname: Andraud
authors.forename: Claire
authors.initials: C
authors.lastname: Camsusou
authors.forename: François
authors.initials: F
authors.lastname: Madec
authors.forename: Gaëlle
authors.initials: G
authors.lastname: Simon
mesh_terms: D000818:Animals; D004196:Disease Outbreaks / Q000662:veterinary*; D004797:Enzyme-Linked Immunosorbent Assay / Q000662:veterinary; D005260:Female; D005500:Follow-Up Studies; D005602:France / Q000453:epidemiology; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification*; D057221:Influenza A Virus, H1N2 Subtype / Q000302:isolation & purification*; D009976:Orthomyxoviridae Infections / Q000453:epidemiology / Q000662:veterinary* / Q000821:virology; D060888:Real-Time Polymerase Chain Reaction / Q000662:veterinary; D016865:Reassortant Viruses / Q000302:isolation & purification*; D013552:Swine; D013553:Swine Diseases / Q000453:epidemiology* / Q000821:virology