#15-026

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Date Full Report Received

Date Abstract Report Received

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Influenza is a major respiratory disease of pigs. Influenza causes reduction in pig’s performance and is a public health concern given that strains with pandemic potential can emerge in pigs. The main strategy to control influenza in pigs is sow vaccination, which enhances the transfer of maternally-derived antibodies to the offspring. Sow vaccination can reduce the level of influenza in piglets at weaning and we hypothesize that reduction of prevalence at weaning impacts influenza circulation after weaning. In this project, we aimed to assess the impact of influenza prevalence at weaning on transmission, clinical signs and performance in nursery pigs.

We studied 10 cohorts of pigs, and we identified 4 different patterns of influenza transmission in nursery pigs. The patterns differed in terms of number of pigs weaned influenza positive, duration of the infectious period, recovery rates and transmission parameters. In two of the patterns almost all pigs were influenza positive at weaning which resulted in rapid recovery from infection. In one of these patterns, however there was a recurrence of infection at 4 weeks post weaning. Of interest was the persistence of influenza throughout the nursery stage in pigs weaned when prevalence rates ranged between 10 and 60% (medium prevalence group) which points towards these groups being responsible for maintaining and disseminating influenza. Lastly, lack of influenza detection at weaning resulted in limited infection throughout the nursery which suggests that there are benefits of weaning low prevalence groups.  However, in this study we did not find an association between prevalence at weaning and percentage of sneezing and coughing pigs, or with average daily gain during the 6 week study in the nursery stage. This is the first study that addresses the impact of prevalence at weaning on transmission dynamics and points at the benefits of having strategies in place to reduce influenza at weaning.