Pair-level approximations to the spatio-temporal dynamics of epidemics on asymmetric contact networks Roger G Bowers Kieran Sharkey The University of Liverpool
Outline Networks Pair approximation on symmetric networks Pair approximation on asymmetric networks Application Comparison with simulation Conclusion
Networks and Incidence Matrices Symmetric Asymmetric ●4 transposed → open
Dynamics of Singletons ( Symmetric Networks ) Closure – mean field approximation N nodes nN = ║G ║ links τ transmission; g recovery S susceptible; I infected; R recovered […] the number of …
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] Dynamics of Pairs ( Symmetric Networks )
the ratio of the number of triples with no open links to the total number of triples Closure – Pair Approximation ( Symmetric Networks )
Dynamics of Singletons ( Asymmetric Networks ) Closure – mean field approximation
Dynamics of Pairs ( Asymmetric Networks )
Closure – Pair Approximation ( Asymmetric Networks ) ratios of the number of triples closed by given links to the total number of triples of given type
Application - Disease transmission between fish farms Nodes Fish Farms Fisheries Wild populations Routes of transmission Live fish movement Water flow Wild fish migration Fish farm personnel & equipment ? Epidemiology of three fish diseases IHN (Infectious Haematopoietic Necrosis) VHS (Viral Haemorrhagic Septicaemia) GS (Gyrodactylus Salaris)
Nodes Fish farms Fisheries Wild fish (EA sampling sites) Slides in this section provided by Mark Thrush at CEFAS
Avon Test Thames Itchen Stour
Avon Test Thames Itchen Stour Route 1: Live Fish Movement
Route 2: Water flow (down stream)
Route 1: Live Fish Movement
Infectious Time Series
Results obtained by applying symmetric results directly … naïve use of G
Infectious Time Series
Susceptible Time Series
Conclusion Pleasing extension of the theory of pair approximation to asymmetric networks. Illustration of its efficacy in dealing with applied situations
Closure – Pair Approximation ( Asymmetric Networks )