Mathematical modelling of epidemics among fish farms in the UK ISVEE X1 (2006) Cairns, Australia Kieran Sharkey The University of Liverpool
Funded by Defra (Department for Environment, Food and Rural Affairs) Investigate epidemiology of three fish diseases IHN (Infectious Haematopoietic Necrosis) VHS (Viral Haemorrhagic Septicaemia) GS (Gyrodactylus Salaris) Liverpool University Applied Maths Dept Liverpool University Veterinary Epidemiology Group Lancaster University Statistics Dept Stirling University Institute for Aquaculture CEFAS – Defra funded Laboratory
Pair-level equations and Foot&Mouth disease Application to fish farms Overview of modified model Results from new model applied to fish farm networks Outline
The Foot & Mouth Model Total animal movement ban Remaining transmission is symmetric
A D B C A B C D ABCDABCD Contact Network
S I R Infection Removal
S
S I SI Pair
S I
S I Insoluble
S I Mean Field
S I
SS I
d[SS]/dt = -2 [SSI] d[SI]/dt = ([SSI]-[ISI]-[SI])-g[SI] d[SR]/dt = - [RSI]+g[SI] d[II]/dt = 2 ([ISI]+[SI])-2g[II] d[IR]/dt = [RSI]+g([II]-[IR]) d[RR]/dt = 2g[IR] Pair-wise Equations
Triples Approximation A B C A B C A B C A B C +
Transmission routes between fish farms
Nodes Fish farms
Nodes Fish farms Fisheries
Nodes Fish farms Fisheries Wild fish (EA sampling sites)
Avon Test Thames Itchen Stour
Avon Test Thames Itchen Stour Route 1: Live Fish Movement
Route 2: Water flow (down stream)
Transmission routes for disease Transportation Non-symmetric Transmission Waterways Non-symmetric Transmission Fish disease Local Symmetric Transmission Foot&Mouth Transmission Mechanisms Local Symmetric Transmission
General pair-wise model
A D B C A B C D ABCDABCD Asymmetric Contact Network
SI SI SI S→I S←I S↔I
ISS -τ[I→S→S]
SSI -τ[S→S←I]-τ[I→S→S]
A B C A B C A B C +
Some results from the model
Nodes Fish farms Transport network (Live fish movement Database)
Infectious Time Series
Susceptible Time Series
Summary Symmetric pair-wise equations generalise to include asymmetric transmission Asymmetric equations perform better on asymmetric networks.
Pair-level approximations to the spatio-temporal dynamics of epidemics on asymmetric contact networks Journal of Mathematical Biology, Volume 53, Issue 1, Jul 2006, Pages , DOI /s , URL