1.
PREDICTED IMPROVED CONTROL OF FOOT-AND-MOUTH
DISEASE TRANSMISSION BETWEEN FARMS BY USING
PRECLINICAL DETECTION
Nelson N., Paton D.J., Gubbins S., Colenutt C.,Brown E., Hodgson S., Gonzales J.L.

2.
Preclinical transmission
2
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
-24 -12 0 12 24
Proportion
Time (hours) relative to clinical onset
Charleston et al., Science (2011)
Frequency of transmission before onset of clinical signs

3.
“Only few secondary infections are to be expected from infected calves when they
are not clinically affected” Orsel et al. PVM (2009)
R = 0.30 [0.03; 3.43]
3

4.
Lower shedding during incubation period
4
Will detection during the incubation period “stop” transmission?

5.
Objective
Evaluate the potential of preclinical detection during reactive surveillance to reduce the
risk of between farm transmission
5

6.
Methods
1. Sensitivity of sampling methods used for preclinical detection.
2. Are any of these methods likely to result in more effective control compared with
clinical surveillance?
– Use a transmission model to simulate dynamics of infection and impact of surveillance
6

7.
Modelling early detection
Susceptible
S
Latent
E
Infectious
I
Recovered
R
preclinical clinical recovery
Select a random sample of animals from the herd at certain time interval
do any samples test positive (sensitivity)?
Herd detected and removed
Reproduction Ratio (R) < 1

8.
Test sensitivity
8

9.
OS16
Animal-level air samples Room air samples
(preclinical)
Test sensitivity
Pacheco et al. 2016, TED

10.
• No surveillance
• Reporting (as in 2001)
• Clinical surveillance (20 animals, twice per week)
• Nasal swab (10 animals, once per week)
• Probang (10 animals, once per week)
• Oral swab (10 animals, once per week)
• Serum (10 animals, once per week)
• Air sample (herd) (twice per day)
Surveillance scenarios

11.
Rherd
Assessing surveillance efficacy
Herd infectiousness vs time
– area under the curve is reproduction number (Rherd)

12.
“late” detection
Rh > 1
“early” detection
Rh < 1
Reducing infectiousness by implementing surveillance

13.
Efficacy of surveillance of stopping transmission using different sampling approaches
(sample size) and weekly sampling frequency
0
0.5
1
1.5
2
2.5
3
3.5
No control Reporting
cases
Nasal swab
(10)
Probang
(10)
Saliva swab
(10)
Serum
(10)
Air sample
(1 daily)
0
0.5
1
1.5
2
2.5
3
3.5
No control Reporting
cases
Nasal swab
(15)
Probang
(15)
Saliva swab
(15)
Serum
(15)
Air sample
(2 daily)
Incubation period = 4.3 days
Latent period = 4.5 days
Infectious period = 2.6 days.
Incubation period = 4.3 days
Latent period = 2.2 days
Infectious period = 4.9 days.

14.
Conclusions
• Preclinical detection can be expected to reduce or stop transmission between herds
during epidemics
• Simple and fast methods of sampling and diagnosis can be used. Use of pen-side
testing can improve the efficiency of the system
• Oral (saliva) swabs can be easily taken.
• less frequent sampling needed; non-invasive
• Could be given to farmers (farmers sampling improves biosecurity – Veterinarians not
entering farms)
• Air samples
• more frequent sampling, herd level samples - improves biosecurity
• Further evaluations on use of these samples at the herd level needed.
14

15.
Acknowledgements
15
Jose.gonzales@wur.nl