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
Jul 07, 2015
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
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
Influenza A Virus
• Cause of disease in many animal species
– Pigs Humans Avian
• pH1N1
• vH3N2
• Pigs
– Respiratory disease
– Transmission between species
– Economic impact
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)
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
Background
Influenza A virus
IncidenceDuration
“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
Sow farms
Day
of sampling
Sampling
event
Sows 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
Overall 0/120 0/119 1/120 10/176
Sow farms
Subpopulation Median
Sows 0.17
Gilts 0.23
Pigs 3-10 days of age 0.15
Pigs 11-26 days of age 0.26
Median ELISA S/N ratios
Vaccination estimates
Source Year Breeding Growing
USDA:APHIS 2000 56% 20%
USDA:APHIS 2006 70% 15-20%
Beaudoin et al. 2007-09 71% 8%
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
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
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
Sow farms
Sampling
Events
Pools(pools of 3 swabs)
n=52
n=252
n=2,520
44% +
26% +
15% +
Results
Pool results
Sampling event Sampling event
Farm 1 2 3 4 5 6 Farm 1 2 3 4 5 6 1 H1 H1 H1 27
2 28
3 29 H1 H1
4 30 H1 H1 H1 H1
5 H3 31
6 32 H3
7 33
8 34 H1
9 H3 H3 H3 35 H3 H3 H3 H3 H3 H3
10 36 H3 H3 H3/H1 H3 H3 H3
11 H1 H1 H1 37 H1 H1 H1 H1 H1 H1
12 38 H1 H1
13 H1 H1 39
14 40 H3 H3
15 41
16 H3 H3 42
17 43
18 44 H1 H1 H1 H1
19 H1 H1 H1 45 H3
20 46
21 47 H3 H3 H3
22 48
23 49
24 50 H1 H1
25 H1 H1 51 H1 H1
26 52 H1 H1 H1
ResultsFarm
ID
Count of HA
gene sequences
compared
Subtype Lowest % identity
between all
sequences
1 3 H1 99.8
9 3 H3 99.7
11 2 H1 99.8
13 2 H1 99.4
19 3 H1 99.5
25 2 H1 99.8
30 2 H1 99.9
35 6 H3 98.8
36 6 H3 98.8
37 6 H1 99.4
38 2 H1 99.9
40 2 H3 100
44 4 H1 99.8
47 2 H3 99.8
50 2 H1 99.7
51 2 H1 99.9
52 3 H1 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
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
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
Dissemination
• Regional movement
• Transport of influenza virus via weaning age
pigs
Spatial dynamics (Nelson et al., 2011)
• Spatial dissemination of human origin H1
viruses (δ cluster) in North America
• Dissemination follows swine movement
Example – influenza positive 3 months
3,000 head sow farm
Weaning 1,200 pigs per week
15,000 pigs
10 different sites?
Still to come……
• Association of influenza virus weaning age
pig status:
– Vaccination
– Filtration
– Gilt introductions
– Pig density
– Etc.
Limitations
• Farm selection
• Not able to assess seasonality
• HA sequence comparison only
Acknowledgements
• Funding and support
– Merck Animal Health
– Newport Laboratories
– Novartis Animal Health
– Zoetis
• Producers and veterinarians
Thank you!
Questions?