Managing Complexity: Simplifying Assumptions of Foot-and-Mouth Disease Models for Swine - Dr. Amy Kinsley, College of Veterinary Medicine, University of Minnesota, from the 2017 Allen D. Leman Swine Conference, September 16-19, 2017, St. Paul, Minnesota, USA. More presentations at http://www.swinecast.com/2017-leman-swine-conference-material

1. Managing Complexity:
Simplifying Assumptions
for FMD models for swine
Amy Kinsley, DVM
Kimberly VanderWaal, PhD
Meggan Craft, PhD
Robert Morrison, DVM, PhD
Andres Perez, DVM, PhD

2. Vesicular lesions on feet of pigs
experimentally infected with
Senecavirus A.
Vesicular lesions on feet and snout of experimentally
infected with Senecavirus A.
Recent outbreaks of vesicular disease

3. FMD: Timing of clinical signs and transmission
• Affected animals develop lameness,
decreased appetite, vesicles in and
around the mouth and on the feet-varies
by species
• Mortality in adults is low but can reach up
to 100% in young
• Transmission occurs through direct
contact, indirect contact, and aerosol
spread

4. Distribution of Livestock in the United States
0 100
Miles
2012CensusofAgriculture
1 Dot = 20,000 Hogs and Pigs
1 Dot = 10,000 Cattle and Calves
1 Dot = 1,000 Sheep and Lambs

5. Individual Herd
Production
system
Why use models?
To predict the outcome of a particular action on a system
To test, verify, and improve our understanding of a system
To explore the effects of population scales
To characterize transmission dynamics of infectious diseases to guide policy
decisions on disease outbreak management.

6. Each farm has an
equal chance of
mixing with every
other farm in study.
Homogenous
mixing within a
defined
geographical area.
(Pomeroy et al., 2015)
Transmission is
scaled inversely
with distance from
infected farm.
All means of contact
that can cause FMDV
transmission that is
spatially independent.
Current models: Methods used to represent contact

7. Each farm has an
equal chance of
mixing with every
other farm in study.
Homogenous
mixing within a
defined
geographical area.
(Pomeroy et al., 2015)
Transmission is
scaled inversely
with distance from
infected farm.
All means of contact
that can cause FMDV
transmission that is
spatially independent.
Current models: Methods used to represent contact

8. Objective: To develop a within-herd simulation model
to estimate the spread of FMD on a swine farm.
• Because FMD control strategies are
implemented at the herd-level
(Pomeroy, 2015).
• FMDV is highly transmissible,
therefore immediate or rapid spread
through the population (Keeling,
2001).
• Within-herd dynamics may vary
depending on farm structure which
can have rippling effects on down the
transmission chain, which is
particularly important in swine.

9. Demographic
and structural
model
representing
the number of
animals in each
room on a
swine farm on a
daily basis

10. Conceptual transmission model
A stochastic, state-transition, frequency-dependent,
transmission model (within- and between-room transmission)
Two strains: O/TAW/97 and O/NET/01.
Accounted for piglet death in the O/TAW/97 model (farrow to
finish and farrow to wean only)
LS Is RIc

11. Methods and Approach
• We ran 1,000 simulations to account for the
stochastic nature of an outbreak and account
for biological uncertainty.
• Integrated the models using R to simulate the
spread of FMDV within a herd.

12. Data Analysis
• The mean time to detection was calculated based on
the proportion of animals displaying clinical signs in
each of the stages of production.

13. Data Analysis
• The mean time to detection was calculated based on
the proportion of animals displaying clinical signs in
each of the stages of production.
• The mean duration of the epidemic was calculated at
the time from the introduction of the index case to the
time when the number of infected pigs reached zero.
• The mean time to the peak of the epidemic and the
mean number of infected pigs was calculated for the
duration of the epidemic.

18. Within-herd model conclusions
Most practitioners feel confident that FMD will be
detected in a herd when less than 15% is demonstrating
clinical signs, which is at about 11-12 days after
introduction into the herd.
Sow farms may experience FMD persistence or a longer
period of infectiousness to other farms.
However, the time to detection will likely we influenced
by the mortality rate in piglets which may vary by FMD
strain. Identifying the cause of piglet mortality is
important.

19. Dr. Andres Perez and Dr. Meggan Craft
Dr. Kim VanderWaal
Dr. Bob Morrison
Experts and veterinarians involved in the development of parameter
values
Acknowledgements

20. Questions?