PRRS Factors Related to Time-to-Stability and Summer Breaks - Dr. Juan Sanhueza, from the 2018 Allen D. Leman Swine Conference, September 15-18, 2018, St. Paul, Minnesota, USA. More presentations at http://www.swinecast.com/2018-leman-swine-conference-material

1. PRRS Factors Related to
Time-to-Stability and Summer
Breaks
Juan Sanhueza, Carles Vilalta, Paulo Fioravante, Emily Geary, Andreia Arruda, Cesar Corzo

2. Outline
• Investigating PRRS summer
outbreaks
• The effect of PRRS outbreak season
on time-to-stability

3. PRRS summer outbreaks
• A number of MSHMP participants
concerned about summer outbreaks
• Was there a higher number of summer
outbreaks in 2017 than in previous
years?
• Where do summer outbreaks occur
geographically (or do not occur)?

4. Data description
• Use MSHMP database (2009-2017)
• 1509 PRRS outbreaks in ~9 years

5. Data description
• 196 (13%) PRRS
outbreaks occurred
during summer
• 309 (20.5%) PRRS
outbreaks occurred
during spring

6. Temporal description
~3.5% of sow farms had summer outbreaks each year

7. Temporal description

8. Summary (a)
• No obvious increase in the percentage of
summer outbreaks
• Overall 3.5% of farms had a PRRS
outbreak during summer

9. Geographical description
PRRS outbreaks 2009-2017

10. Summer outbreaks
(Cases)
Non-summer outbreaks
(Controls)

12. Summary (b)
• There are areas that have a
higher risk of PRRS
summer outbreaks
• Southern Minnesota –
Northern Iowa

13. Outline
• Investigating PRRS summer
outbreaks
• The effect of PRRS outbreak season
on time-to-stability

14. PRRS time-to-stability
• Anecdotal reports: harder to achieve
stability when the outbreak occurred during
summer
• Does time to stability differ according to the
season when the PRRS outbreak occurred?

15. PRRS time-to-stability
• Time from PRRS outbreak/intervention to
negative piglets at weaning (category II)
• PRRS status classification (Holtkamp et al. 2011)
– No clinical signs in breeding herd
– Minimum of 4 negative PCR tests in piglets at
weaning sampled every 30 days

16. Methods
• Data
–Data from 6 MSHMP participants
–March 2011 to March 2017
–Similar in the way the test and classify
PRRSv status and are guided by
Holtkamp et al., 2011 terminology

17. Methods
–Outcome:
• time from outbreak to reported stability
–Predictors: • Outbreak season
• RFLP
• Intervention
• Outbreak status
• Herd size
• System
• Outbreak year
• Filtered (yes/no)
• PED outbreak
• Previous outbreak
within a year

18. Methods
• Analysis
–Survival analysis to model PRRS
time-to-stability
–Cox proportional hazards model
–Farm id and System as random
effects to account for clustering in the
data

19. Results
• 161 PRRS outbreak events in 82 farms
• Median: 2 outbreaks per farm

20. PRRS time-to-stability
Kaplan-Meier curve
41 weeks

21. Time-to-stability by system
• Varied significantly across
systems

22. How different is time-to-
stability in the same farm?
Mean raw difference: 20 weeks
ICC: 1.2%

23. Season

24. Time-to-stability and PRRS season
• Winter: 36 weeks Autumn: 38 weeks
• Spring: 53 weeks Summer: 54 weeks
p=0.001

25. Variable Levels n HR (95% CI) p-value
Season Winter 44 2.18 (1.28 - 3.7) 0.004
Autumn 58 1.91 (1.16 - 3.13) 0.011
Spring 30 1.09 (0.62 - 1.91) 0.76
Summer 29 Reference
RFLP 1-18-2 19 2.71 (1.41 - 5.21) 0.003
1-26-2 28 1.94 (1.07 - 3.54) 0.03
1-3-4 6 2.59 (0.98 - 6.83) 0.055
1-4-3 6 1.46 (0.52 - 4.10) 0.47
1-4-4 31 2.34 (1.28 - 4.25) 0.006
1-8-4 5 1.44 (0.51 - 4.06) 0.49
Other 29 2.55 (1.41 - 4.64) 0.002
Unknown 11 4.14 (1.82 - 9.40) 0.001
1-7-4 26 Reference
Previous PRRS outbreak within a year Yes 18 2.18 (1.23 - 3.86) 0.008
No 143 Reference
Multivariable mixed Cox model results

26. Summary
• Farms that had outbreaks in summer
took significantly longer to achieve
stability than farms that had outbreaks
during Winter or Autumn
• 1-7-4 longer time-to-stability than other
specific RFLPs

27. Acknowledgements
MSHMP participants

28. …

29. p=0.001

33. Time-to-stability and Parity
• Is PRRSv maintained in the sow herds
by young parity litters?
• Nine herds enrolled ~18 weeks after
the PRRS outbreak
• Processing fluids collected weekly
– 15 parity 1
– 15 parity 2 PCR test
– 15 parity 3+