Bayesian spatial modelling of disease vector data on Danish farmland Carsten Kirkeby Gerard Heuvelink Anders Stockmarr René Bødker
Biting midges Culicoides obsoletus group Bloodsucking females 1400 species ~ 40 in Denmark 1-2mm Parasites: protozoans, nematodes Virus: African Horse Sickness, Akabane Virus etc. Institute of Animal Health UK
Bluetongue virus Midge-borne Infects ruminants Northern Europe: Symptoms: Fever, diarrhoea, reduced milk production Institute of Animal Health UK
Schmallenberg virus Midge-borne Infects ruminants Northern Europe: ? Symptoms: Fever, stillbirths, malformations, reduced milk production Institute of Animal Health UK
Aim How are vectors distributed in farmland? Host animals Tree cover Temporal covariates High/low risk areas Optimization of vector surveillance Input for simulation models
Field study x
Data
Analysis Count data
Analysis Spatial component Your neighbours influence you, but you also influence your neighbours. Charles Manski
Analysis Temporal component t t-1
Analysis R: geoRglm package – GLGM kriging pois.krige.bayes() Bayesian kriging for the poisson spatial model Y ~ β + S(ρ) + ε β = day effect + lag 1
Analysis Spatial correlation: Matérn covariance function Φ
Analysis - separate
Analysis - simultaneous
Analysis - comparison Non-spatial Poisson regression
Analysis - prediction 1 km
Analysis – temporal covariates
Findings Quantify effects of cattle and pigs No effect of forests Quantify temporal covariates Weak positive correlation with previous catch More vectors at the pig farm than the cattle farm
Future Jackknife Validation on other dataset
Acknowledgements Thanks: Ole Fredslund Christensen Astrid Blok van Witteloostuijn
Thank you for your attention Carsten Kirkeby