AN INVESTIGATION INTO THE RISK FACTORS CONTRIBUTING TO STREPTOCOCCUS SUIS OUTBREAKS IN NURSERY PIGLETS
Danielle HopkinsMasters StudentPopulation MedicineUniversity of Guelph
What is Streptococcus suis? • Considered to be one of the most important post weaning
pathogens• 35 serotypes identified currently• Opportunistic in nature• Causes sporadic outbreaks in the nursery (0-5%)
• Typically following clinical signs associated with acute meningitis• Occasionally causes severe outbreaks (>10%)
The Data: • 300 sow farrow-to-finish • All cause mortality recorded from
October 2011 to March 2012
Outbreak data set
Full Data Set• 2779 Observations• (TAR) Time at risk= 63 days
Sow Data• 297 sows• 15 removed
(missing data)
Pig Data• 483 pigs died• 107 removed
(died past TAR)
Figure 1: Farm experiencing outbreak of. S. suis
Photo by: Danielle Hopkins
Merged + Expanded Data
Objective Outbreak DataI) Determine sow- and litter- level factors that were
associated with the hazard of dying due to S. suis within the nursery
Figure 1: Outbreak data set demonstrating overall cause of mortality within the nursery
Factors of interest
S. suis mortality within the nursery
Nursery mortality within the same litter
Previous litter
mortality
Parity
Number of piglets
weaned Age of weaning
Pre-weaning mortality
Seasonal effects
Factors of interest
S. suis mortality within the nursery
Nursery mortality within the same litter
Previous litter
mortality
Parity
Number of piglets
weaned Age of weaning
Pre-weaning mortality
Seasonal effects
Final model based on Cox’s regressionCovariate HR P-value
Age of weaning 1.077 0.001
Age*TVC 0.996 0.001
Nursery mortality in the same litter
9.21 0.001
Previous litter mortality
0.337 0.024
Seasonal effects** (October to referent)
0.349 0.001
Number of piglets weaned
0.913 0.001
*TVC- time vary coefficient**January is referent category
Final model based on Cox’s regressionCovariate HR P-value
Age of weaning 1.077 0.001
Age*TVC 0.996 0.001
Nursery mortality in the same litter
9.21 0.001
Previous litter mortality
0.337 0.024
Seasonal effects** (October to referent)
0.349 0.001
Number of piglets weaned
0.913 0.001
*TVC- time vary coefficient**January is referent category
1
2
3
4
Age of weaning
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 640
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
Figure 1: Hazard ratio estimate if a hypothetical piglet's weaning age was increased by 7 days controlling for the time varying af-
fects of age
Haza
rd R
atio
s (lo
g_t)
Time in the nursery (days)
Age of weaning
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 640
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
Figure 1: Hazard ratio estimate if a hypothetical piglet's weaning age was increased by 7 days controlling for the time varying af-
fects of age
Haza
rd R
atio
s (lo
g_t)
Time in the nursery (days)
Figure 2: Graphical representation of overall mortality within litters organized by the week of death upon entering the nursery--- prior to vaccination trial
Figure 2: Graphical representation of overall mortality within litters organized by the week of death upon entering the nursery--- prior to vaccination trial
>70% mortality occurrences in 1st 4 weeks
Nursery mortality within the same litter
Legend
Blue line: No other pig within that litter died
Red Line: At least one additional pig died within a litter
Recall:HR=9.21P=0.001
Initial thoughts-within pen transmission?-similar passive immunity?-similar pathogen exposure?
Previous litter mortality Legend
Blue line: Sow with previous litter having 0% mortality
Red Line: Sow with previous litter having>0% mortality
Recall:HR=0.337P=0.024
Initial thoughts-Build up of immunity?
Seasonal effects
Conclusions1. In this farm, nursery pigs experiencing increasing
levels of mortality until week 4 when the mortality rates dramatically drop
• Similar pattern of mortality with S. suis? Serotype specific?
2. Pigs are more likely to have mortality if at least one other pig from the litter died
• Similar exposure characteristics, within litter spread of S. suis?
3. Pigs are less likely to have mortality if a sow had mortality associated with S. suis in their previous litter
• Build up of immunity?
Limitations• 483 mortalities were experienced during the 6-month
duration of the trial• 13 of those were submitted for post-mortem analysis and
confirmation of S. suis infection• Confirmation via clinical signs may not have been 100% accurate?
• 5% of sows didn’t have information on parity or pre-weaning mortality• Beneficial to explored these risk factors further
Future Steps• Steps to reduce clinical cases of S. suis• Isolate and treat sick pigs/
remove dead pigs from pen • All-in-all-out to reduce
pathogen load • Decrease stress within the
nursery• Reduce overcrowding• Maintain constant temperature
• **Vaccinate sows or piglets ***Vaccine efficacy against S. suis still under debate
Figure 2: “Future Steps” pigletRetrieved from: https://www.culturecraze.com
Acknowledgements
Advisory CommitteeDr. Robert FriendshipDr. Zvonimir Poljak Dr. Vahab Farzan
The farm and farmers that participated in the study
Funding via Swine Improvement Porc, and the University of Guelph/OMAFRA Research Partnership
Photo credit and fellow Streptococcus suis masters student: Emily Arndt