Dr. Chamba Pardo and colleagues from the University of Minnesota share results of the implementation of sow vaccination to control influenza infections in pigs at weaning through a special issue article published in Transboundary and Emerging Diseases.
Sow vaccination against IAV was effective at reducing the number of infected groups of pigs at weaning, and the number of positive nasal swab pools within a group.
Both prefarrow or whole herd vaccination protocols, and use of commercial or autogenous inactivated vaccines, yielded significant and similar reduction of IAV infections in pigs at weaning.
Sow vaccination can help control IAV infections in pigs at weaning and, thus, minimize transmission to growing pigs and other farms.
Sow vaccination decreased influenza infections in piglets at weaning.
Influenza positive gilts at entry were associated with positive piglets at weaning.
More work is needed to assess herd closure, gilt isolation and gilt vaccination.
83 farms from 2 different pig production companies and located in Iowa, Minnesota and South Dakota were enrolled in this study. Samples were collected at weaning on a monthly basic for a little less than 6 years as part of routine surveillance programs. The majority of farms submitted 4 oral fluid samples per month but some collected nasal swabs or oro-pharyngeal swabs.
23% of the samples tested positive for influenza allowing the collection of 173 hemagglutinin sequences. In the H1 hemagglutinin subtype, isolates were 93.8% to 99% similar between each other and 94.3% to 97.4% similar to the vaccine strains. The largest discrepancy was found in the delta 1 clade. In the H3 hemagglutinin subtype, isolates were 95.9 to 99.7% similar among each other and 997.3% to 97.5% similar to the vaccine strains.
The influenza status of the piglets at weaning was influenced by several factors.
Seasons and vaccination status of the sows against influenza influenced piglet infection status at weaning. Indeed, sow influenza vaccination was significantly associated with a decreased probability of piglets testing influenza positive at weaning. Both whole-herd and pre-farrow vaccination protocols were better compared to no vaccination and there were no differences between both protocols. Additionally, having influenza positive gilts at entry increased the probability of detecting positive piglets at weaning.
Among all the factors evaluated, sow influenza vaccination and gilt influenza status at entry were the only factors associated with influenza in piglets at weaning in Midwestern breed-to-wean farms.
Breed-to-wean pig farms play an important role in spreading influenza A virus (IAV) because suckling piglets maintain, diversify and transmit IAV at weaning to other farms. Understanding the nature and extent of which farm factors drive IAV infection in piglets is a prerequisite to reduce the burden of influenza in swine. We evaluated the association between IAV infection in piglets at weaning and farm factors including farm features, herd management practices and gilt- and piglet-specific management procedures performed at the farm. Voluntarily enrolled breed-to-wean farms (n = 83) agreed to share IAV diagnostic testing and farm data from July 2011 through March 2017 including data obtained via the administration of a survey. There were 23% IAV RT-PCR positive samples of the 12,814 samples submitted for IAV testing within 2989 diagnostic submissions with 30% positive submissions. Among all the factors evaluated (n = 24), and considering the season-adjusted multivariable analysis, only sow IAV vaccination and gilt IAV status at entry significantly reduced (p-value<0.05) IAV infections in piglets at weaning. Results from this study indicate that veterinarians and producers could manage these identified factors to reduce the burden of influenza in piglets prior to wean and perhaps, reduce the spread of IAV to other farms and people.