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Matt Allerson - Swine influenza virus prevalence and risk factors in weaning-age pigs

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Swine influenza virus prevalence and risk factors in weaning-age pigs - Matt Allerson, University of Minnesota, College of Veterinary Medicine, from the 2013 Allen D. Leman Swine Conference, September 14-17, 2013, St. Paul, Minnesota, USA.

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Matt Allerson - Swine influenza virus prevalence and risk factors in weaning-age pigs

  1. 1. Influenza virus prevalence and risk factors in weaning-age pigs Leman Swine Conference Tuesday, September 17 2013 Matt Allerson, DVM, PhD University of Minnesota College of Veterinary Medicine
  2. 2. Influenza A Virus • Orthomyxoviridae family – Type • A, B, and C – Subtype • HA and NA • H1N1, H1N2, H3N2 – Clusters • H1 = α, β, γ, δ, and pandemic • H3 = I, II, III, and IV Image: www.cdc.gov
  3. 3. Influenza A Virus • Cause of disease in many animal species – Pigs Humans Avian • pH1N1 • vH3N2 • Pigs – Respiratory disease – Transmission between species – Economic impact
  4. 4. Influenza A Virus • Economic impact – $3.23 difference from baseline in loss per head placed (Dykhuis Haden et al., 2012) – $10.41 difference from baseline in loss per head placed due to SIV/PRRSV combination (Dykhuis Haden et al., 2012)
  5. 5. Influenza A virus • Seroprevalence – – – – – 20-47% (Hinshaw et al., 1978) 51% (Chambers et al., 1991) 27% H1, 8% H3 (Olsen et al., 2000) 83% in sow herds in Ontario (Poljak et al., 2008) Over 90% in sow herds in Belgium, Germany, and Spain (Van Reeth et al., 2008) • Active surveillance (Corzo et al., 2013) – 91% of growing pig sites tested influenza virus positive at least once
  6. 6. Background Influenza A virus Duration Incidence
  7. 7. “What should we do about flu?” • M. Torremorell, 2011 Leman conference – Not ignore influenza – Take a “PRRS-like” approach • How much is it costing us • Address flu at the top of the production system with a focus on producing negative pigs at weaning • Understand where the viruses come from
  8. 8. Sow farms Day of sampling Sampling Sows event Gilts Pigs 3-10 days of age Pigs 11-26 days of age 0 1 0/60 0/59 1/60 6/60 27 2 0/60 0/60 0/60 4/58 56 3 NT NT NT 0/58 0/120 0/119 1/120 10/176 Overall
  9. 9. Sow farms Median ELISA S/N ratios Subpopulation Median Sows 0.17 Gilts 0.23 Pigs 3-10 days of age 0.15 Pigs 11-26 days of age 0.26
  10. 10. Vaccination estimates Source Year USDA:APHIS 2000 56% 20% USDA:APHIS 2006 70% 15-20% 71% 8% Beaudoin et al. 2007-09 Breeding Growing
  11. 11. Objectives • Assess the prevalence and temporal patterns of influenza virus infection in weaning age pigs • Characterize viruses obtained within selected sow farms • Evaluate the association between sow herd attributes (including influenza vaccination) and the prevalence of influenza virus positive weaning-age pigs
  12. 12. Methods • 52 sow farms – Farrow to wean sow herds – History of influenza virus infection at the sow herd within the previous year – Replacement gilts introduced to the sow herd from a source outside of the sow herd premises • 8 production systems • 6 different states
  13. 13. Methods • 30 weaning age pigs sampled monthly – Nasal swabs – 3 to 6 sampling events • RRT-PCR • Virus isolation • Subtyped and HA sequencing • HA gene sequences compared within farm
  14. 14. Results Sow farms n=52 44% + Sampling Events n=252 26% + Pools n=2,520 15% + (pools of 3 swabs)
  15. 15. Pool results
  16. 16. Sampling event Farm 1 2 3 1 H1 H1 4 Sampling event 5 H1 6 Farm 1 2 3 4 5 H1 H1 H1 6 H1 27 2 28 3 29 4 30 5 H3 H1 H1 31 6 32 7 33 8 34 H1 35 H3 H3 H3 H3 H3 H3 36 H3 H3 H3/H1 H3 H3 H3 37 H1 H1 H1 H1 H1 H1 38 H1 H1 H3 H3 H1 H1 H1 H3 H3 H3 9 H3 H3 H3 10 11 H1 H1 H1 12 13 H1 H1 H3 39 14 40 15 41 16 H3 H3 42 17 43 18 44 H1 45 H3 19 H1 H1 H1 20 46 21 47 22 48 23 49 24 50 H1 H1 51 H1 H1 52 H1 H1 25 26 H1 H1 H1
  17. 17. Results Farm ID 1 9 11 13 19 25 30 35 36 37 38 40 44 47 50 51 52 Count of HA gene sequences compared Subtype Lowest % identity between all sequences 3 3 2 2 3 2 2 6 6 6 2 2 4 2 2 2 3 H1 H3 H1 H1 H1 H1 H1 H3 H3 H1 H1 H3 H1 H3 H1 H1 H1 99.8 99.7 99.8 99.4 99.5 99.8 99.9 98.8 98.8 99.4 99.9 100 99.8 99.8 99.7 99.9 99.8 • HA gene sequences similar across (+) sampling events within farm • 3 sow herds tested (+) for 6 consecutive sampling events over durations of 156, 165, and 165 days • Different viruses across farms
  18. 18. Results • 88% of sow herds that tested IAV negative at the first sampling event continued to test negative throughout the study period • 84% of sow herds that tested influenza virus positive at the first sampling event tested positive for at least one additional sampling event • 3 sow herds tested positive for 6 consecutive sampling events over durations of 156, 165, and 165 days
  19. 19. Discussion • Weaning age pig as a target for influenza virus testing and surveillance • Maintenance within herds and transport to distant sites • Sampling event results repeatable over study period • HA gene sequences were also similar over positive sampling events within herds • Sow herds an important population for influenza virus epidemiology and diversity
  20. 20. Dissemination • Regional movement • Transport of influenza virus via weaning age pigs
  21. 21. Spatial dynamics (Nelson et al., 2011) • Spatial dissemination of human origin H1 viruses (δ cluster) in North America • Dissemination follows swine movement
  22. 22. Example – influenza positive 3 months 3,000 head sow farm Weaning 1,200 pigs per week 15,000 pigs 10 different sites?
  23. 23. Still to come…… • Association of influenza virus weaning age pig status: – Vaccination – Filtration – Gilt introductions – Pig density – Etc.
  24. 24. Limitations • Farm selection • Not able to assess seasonality • HA sequence comparison only
  25. 25. Acknowledgements • Funding and support – Merck Animal Health – Newport Laboratories – Novartis Animal Health – Zoetis • Producers and veterinarians
  26. 26. Thank you! Questions?

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