Dynamics of swine influenza in a wean-finish population - Andres Diaz, University of Minnesota, College of Veterinary Medicine, from the 2013 Allen D. Leman Swine Conference, September 14-17, 2013, St. Paul, Minnesota, USA. More presentations at http://www.swinecast.com/2013-leman-swine-conference-material

1. Dynamics of influenza A infection
in a wean to finish population
Andres Diaz, Cesar Corzo,
Marie Culhane, Montserrat Torremorell
Allen D. Leman Swine Conference 2013
Saint Paul, September 17th 2013

2. Outline
• Introduction
– Influenza A virus (IAV) and swine populations
•
•
•
•
•
Objectives
Materials and methods
Results
Work in progress
Conclusions

3. Introduction
•
•
•
•
•
•
Enveloped virus
ss -sense RNA Virus
8 Gene segments
12 different proteins
Hemagglutinin (HA) - 17 subtypes
Neuraminidase (NA) - 9 subtypes
Cell Host & Microbe 2012;7(6):440-451

4. IAV Diversity – Antigenic drift
Plos Pathogens 2011;7(6):e1002077

5. IAV Diversity – Antigenic shift
Advances in virus research 2008;72:127-154

6. IAV and swine population
• Worldwide distributed
• Endemic or epidemic?
• Primary cause of disease in pigs
– Respiratory disease complex
– Reduced feed conversion and ADG
– Increased number of days to market
• Public health threat
Veterinary research 2007;38(2):243-260
Cell Host & Microbe 2012;7(6):440-451

7. IAV diversity in growing pigs
Emerging infectious diseases 2013;19(6):954-960

8. IAV Transmission in pigs
•
•
•
•
Direct contact
Airborne transmitted
Fomites
Transmission rate (R0)
– Active immunity
• Immune pigs (homologous virus)
• Immune pigs (heterologous virus)
• Naïve pigs
0
1
10.66
(95% CI 0.39, 2.09)
(95% CI 6.57, 16.46)
0.8
7.1
10.4
(95% CI 0.1, 3.7)
(95% CI 4.2, 11.3)
(95% CI 6.6, 15.8)
– Passive immunity
• Immune pigs (homologous virus):
• Immune pigs (heterologous virus)
• Naïve pigs
Veterinary research 2011;42(1):120
Vaccine 2013;31(3):500-505
Transboundry and emrging diseases 2012;59(SI:1):68-84

9. Research questions
• How is IAV maintained in swine populations and
what is the role of weaned pigs in this process?
• What is the transmission and infection pattern of
IAV in weaned populations?
• How does IAV change over time in endemically
infected populations?

10. Objectives
• To characterize the evolution of IAV infection
and transmission in weaned pigs
– To explore IAV transmission pattern in weaned
pigs
– To understand the association between IAV
exposure, immunity and infection after weaning

11. Materials and methods
•
Cohort study: Prospective over time
•
1 endemically infected wean to finishing farm
–
–
–
•
MN
8 barns
≈ 2000 pigs per barn
Single source of pigs
– Sow herd positive
•
132 pigs randomly selected from 2000 pigs weaned
– 95% confident to detect at least 1 when the prevalence is higher than 2.5%
•
Ear tagged and identified at arrival

12. 0 1 2 3
4 5 6 7 8 9 10 11 12 13 14 15
Nasal swab
X X X X
X X X X X X X
X
X
X
X
X
Oral fluid
X X X X
X X X X X X X
X
X
X
X
X
Serum sample
X
X
X
X

13. Laboratory tests
• RT-PCR (M gene): Nasal swabs and oral
fluids
– Positive CT < 34
– Suspect > 34 < 40
– Negative > 40
• ELISA S/N (NP protein): Serum samples
– Positive SN < 0.6
– Suspect SN > 0.6 < 0.9
– Negative > 0.9

14. Analysis and hypothesis testing
• Seroprevalence
– Mean change of the S/N value over time (paired t-test,
p<0.05 between weeks)
– Effect of being seropositive at weaning on the
seroprevalence after weaning (paired t-test, p<0.05)
• Weekly prevalence
– Number of positive cases by week
– Comparison of the number of positives over time (chi square
test, p<0.05)
• Weekly incidence
– Number of NEW cases by week
• Assessing re-infection with IAV

15. Results
Serology

16. 0 vs 4
0 vs 8
0 vs 12
4 vs 8
4 vs 12
8 vs 12
p<0.05
p<0.05
p<0.05
p<0.05
p<0.05
p<0.05

18. PW4 vs SW4
PW4 vs NW4
PW8 vs SW8
PW8 vs NW8
PW12 vs SW12
PW12 vs NW12
p<0.05
p>0.05
p>0.05
p>0.05
p>0.05
p>0.05
SW4 vs NW4
SW8 vs NW8
SW12 vs NW12
p<0.05
p>0.05
p>0.05

19. Results
RT-PCR

20. Positives
Re infected
99 (75%)
29 (29%)
Positives
Re infected
124 (98%)
102 (82%)

21. Epidemiological findings
Week
Prevalence rate%
Incidence rate %
Cumulative Incidence rate
R
0
19
NA
1
50
45
45
1.6
2
64
52
97
1.2
3
10
5
102
4
4
3
105
5
4
3
108
6
15
5
113
7
55
50
163
8
29
6
169
9
5
3
172
10
3
3
175
11
2
1
176
12
4
4
180
13
4
4
184
14
4
4
188
15
6
6
194
-

22. Work in progress....
• 96 samples selected for whole genome
amplification and sequencing (Antigenic drift and
shift)
• Selection of samples for VI
– Reference virus by week
• Estimate real exposure by HI reactivity of serum
samples to references viruses and explore
antigenic differences by antigenic cartography

23. Conclusions
• Wean pigs can be a source of IAV to other
swine populations
• The presence of maternal immunity in
weaned pigs is highly variable
• The maternal immunity did not protect
weaned pigs from IAV infection but it did
reduce transmission (lower R0).

24. Conclusions
• Maternal immunity at weaning was correlated with antibody
levels at 4 weeks post weaning but not at 8 and 12 weeks
post weaning.
• The interaction between IAV transmission, infection, and
maternal immunity allowed for two epidemic waves of IAV in
less than 8 weeks post-weaning
• Our results indicate that pigs can be re-infected over a short
period of time and as a result IAV can remain in the
population.
• At the end of the study, all pigs tested positive to IAV by
ELISA, indicating that all pigs were infected to the IAV.

25. Acknowledgments
•
•
•
•
•
•
•
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Dr. Montse Torremorell
Dr. Srinand Sreevatsan
Dr. Marie Gramer
Dr. Cesar Corzo
Dr. HanSoo Joo
Dr. Meggan Craft
Pipestone Veterinary clinic
– Dr. Spencer Wayne
Swine producers and farm
staff
•
Graduate students and
research assistants
– Victor Neira
– Macarena Cortez
– My Yang
– Mathew Allerson
– Steve Tousignant
– Carmen Alonso
– Nubia Macedo
– Maria Jose Clavijo
– Jonathan Ertl
– Jennifer Reynolds
– Douglas Marthaler