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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

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)

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

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