Risk categorisation of fish farms

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Risk categorisation of fish farms
Risk categorisation of fish farms
Birgit Oidtmann1, Fiona Pearce1, Mark Thrush1, Edmund
Peeler1, Chiara Cheolin2, Katharina DC Stärk 3, Manuela
Dalla Pozza2, Allan R. Reese1, Angus Cameron4
1Centre
for Environment, Fisheries and Aquaculture Science; 2Istituto
Zooprofilattico Sperimentale delle Venezie; 3Royal Veterinary College;
4AusVet
Outline
•
•
•
•
What is risk-based surveillance (RBS)?
Why do RBS?
EC directive requirement for RBS
RBS to support surveillance to
demonstrate disease freedom
• Viral haemorrhagic septicaemia case
study
• Future developments
Risk-based surveillance
Resources for surveillance are focused on
animal, farms, areas
– Where the likelihood of infection is highest
– Requires information on risk factors
The sensitivity of the system (ie capacity to
identify disease) increases for the same
resource input
Additional
operational costs
of RBS
Efficiency
savings from
RBS
Surveillance: exotic disease
Risk ranking farms or farming
areas is fundamental to
risk based surveillance
EC directive 2006/88 –
article 10
• Member States should ensure that a riskbased animal health surveillance scheme
is applied in all farms and mollusc farming
areas........
• Aimed at the ‘detection of
– Increased mortality
– Notifiable diseases
Annex V EC 2006/88
EU guidance
• Farming areas categorised as low,
medium or high
• Use simple matrix to combine likelihood of
introduction and spread
Likelihood of becoming
infected
Likelihood of spread
L
M
H
H
M
H
H
M
L
M
H
L
L
L
M
Risk ranking farms
RBS to demonstrate freedom
• Surveillance to demonstrate freedom need
only rank farms based on likelihood of
introduction
• Sampling focused on farms at highest risk
of disease introduction
Input vs output based surveillance
to demonstrate freedom
Input
– Sample all farms
– Take 150 fish two
times a year for
two years
Output
– Define minimum
prevalence(s)
– e.g. 2% of farms &
5% within farms
– Specify test
characteristics
– Define level of
confidence (e.g. 95%)
OIE guidance
• The OIE aquatic animal health code
provides guidance on output based
surveillance to demonstrate freedom from
disease
The model
• Calculate a likelihood score for individual
farms for disease introduction
• Calculated for a specific fish disease
• To be used for
– risk ranking of sites
– to support surveillance for demonstration of
disease freedom
Likelihood [Disease,
intro]
P [Disease,
freedom]
Routes of disease introduction
Grouped into themes:
A. Live fish and egg movements
B. Exposure via water
C. On-site processing
D. Short-distance mechanical transmission
E. Distance-independent mechanical
transmission
Multiple routes within some
themes.....
B. Exposure via water
D. Short-distance mechanical
transmission
E. Distance-independent mechanical
transmission
Weighting
Relative importance of
• Themes
• Routes within themes
Expert opinion
• Weights
– Themes
– Routes within
themes
• Pathogen specific
estimates
– Likelihood of spread
by water
– Likelihood of spread
by live fish
– etc.
Farm level data
• Live fish movement
• Distance from other
farms
• On farm processing
• Biosecurity
• etc.
Materials and Methods
• Stochastic model
– MS Excel (with PopToolsadd-in)
• Calculate weighted score for
each theme
• Sum weighted scheme scores
Calcuating disease spread via
live fish / eggs movements
Probability estimated using
• Species
• Estimate of source site disease status
• Number of consignments
a little probability theory.....
Source riskLFI= 1 – (1 - species risk × source
status) number of consignments
Total riskLFI = 1 – Π(1- source riskLFI)
Upstream sources of exposure
wild fish
farms
processing
fisheries
Probability decreases with
distance
• P[intro] = 1/ e distance (km)
• Decay term determined by expert
opinion
score
1
0
0 Distance
(km)
5
On farm processing
Likelihood assessed taking account of
• Introductions from external sources
• Methods to disinfect waste
• Species susceptibility
• Source infection status
• Number of movements
Short-distance mechanical
transmission
• Nearby susceptible
populations (sources)
– Farm, fishery, wild
– Species
– Distance to farm
Distance-independent
mechanical transmission
• Personnel or equipment shared with
other farms
• Unauthorised people
• Unauthorised vehicle
• Fish delivery vehicles
• Other vehicles
• Receiving waste from other farms
• Fishery on site
The maths.....
• Factors coded as 1 (present) and 0 (absent)
• Risk score = factor (1 or 0) * weighting
• Site riskdist indep = Σ (factor status × weight)
Final farm risk score
Sum of (weight × theme score)
Viral haemorrhagic septicaemia
– case study
Scenarios
1
2
3
4
Low prevalence (2%), endemic zone
Medium prevalence (5%), endemic zone
Free zone surrounded by an endemic zone
with low prevalence (2%)
Free zone surrounded by an endemic zone
with medium prevalence (5%)
Data
• 3 farm catchments in England (farms)
– Itchen (6)
– Test (17)
– Ouse (19)
• Italy
– Friuli Venezia Giulia (12)
– Trentino Alto Adige (10)
– Veneto (10)
65% freshwater
salmonid
production
Data
• 10 (of 32) Italian farms selected because
of known VHSV history
• UK is free of VHSV
Theme weighting
0.06
0.14
Live fish
movements
Water
0.04
0.14
0.62
Processing
Short
Distanceindependent
Number Receive Receive Upstream Process Nearby
of farms live fish eggs
sources
fish
sources
Italy
England
32
17
15
30
5
32
42
36
2
42
1
42
Source weights
SOURCE
Farms
Processors
Wild / fishery
Other
Water
50
25
20
5
Short-distance
transmission
60
30
10
Distance independent routes weights
Staff
Equipment
Fish vehicles
General vehicles
Fishery
Unauth people
20
35
22.5
5
10
7.5
English data
Italian data
Summary
• Risk ranking of farms requires
– data on risk factors for disease entry and
spread
• Costs of data collection and analysis must
not outweigh benefits
– Estimates of relative importance of risk factors
for disease are needed
– On-line farming reporting
Acknowledgements
• Defra (FC1201) & Efsa funding
– Project ‘Risk categorisation for Aquatic
Animal Health Surveillance’
(CFP/EFSA/AHAW/2011/03)
• Experts who are participated in the
consultations
Model and project reports will be available
on the Efsa website

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