1.
A RISK BASED MODEL TO GUIDE DECISIONS ON
ZONIFICATION TO STOP VACCINATION IN A FREE COUNTRY
WITH VACCINATION
O. Daza, N. Guzman, D. Gareca, J.L. Gonzales

2.
Bolivia
Geographical regions
Amazons
Chaco
Valleys
Highlands
Area: 1.098.581 Km2

3.
8 637 358 cattle 5 386 939 Sheep
2 572 226 camelids 1 722 606 goats

4.
FMD situation
2003 2006
2012 2013
2014
Free without vaccination
Free with vaccination
• Eradication programme (started 2000) based on surveillance, control of movements and
mass vaccination of the cattle population
• The goal is to gradually extend the free without vaccination zones in a risk based manner

5.
Objective
To develop a model to quantify the risk of FMD introduction into zones where
vaccination is discontinued and evaluate the efficacy of control measures to minimise
this risk.

6.
Methods: Scenario tree model

7.
OS16
Parameters Description Reference
Vaccination Province vaccination coverage -
Proportion
SENASAG
Herd level infection Prevalence = 0.015
Design prevalence used for surveillance
SENASAG
Risk of infection Adjusted relative risk for non-
vaccinated Vs vaccinated
Gonzales et al 2014. Vaccine
Anima level infection Within herd prevalence 0.29 (0.04-0.50) Gonzales et al 2014. Vaccine

8.
OS16
Cattle movements
Parameters Description Reference
Destination Proportion cattle going to area
of interest
SENASAG – Movement
records
Herd inspection (clinical) Sensitivity clinical inspection
0.35 (0.25 – 0.40)
Gonzales et al 2014. Vaccine

9.
OS16
Parameters Description Reference
Movement
inspections
Proportion of animals
inspected at road control
posts
0.10 (0.05-0.015)
SENASAG.
Clinical
inspection
Sensitivity clinical
inspection
0.35 (0.25 – 0.40)
Gonzales et al
2014. Vaccine
Purpose of
movement
Proportion of cattle
moved for breeding
SENASAG –
Movement
records

10.
Results
Zones
No vaccination
No Vaccination
Once per year
Twice per year
One Mass vaccination
+ One < 24 months

11.
Two zones as examples
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
Prevalence 3% Prevalence 1.5%
Probabiltyofintroduction
0
0.1
0.2
0.3
0.4
0.5
0.6
Inspection 10% Inspection 50% Inspection 80%
Probabilityofintroduction
Valleys Santa Cruz Punata
Yearly probability of introduction

12.
0
0.0005
0.001
0.0015
0.002
0.0025
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Probabilityofintroduction
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Probabilityofintroduction
Monthly probability of introduction
Valleys Santa Cruz
Punata

13.
Conclusions
• Clear differences in risk of introduction in different regions/zones can be observed
• This differences can be used to stop vaccination or target vaccination to specific
zones
• Cattle moved from areas free with vaccination are considered the main risk for
areas where vaccination is not applied
• Work is being done on improving data collection on inspection parameters from
control posts and fairs in the country
• Future work: Combine risk of introduction with risk of transmission

14.
Thank you
14
Jose.gonzales@wur.nl