title: Quantifying the roles of host movement and vector dispersal in the transmission of vector-borne diseases of livestock.
abstract: The role of host movement in the spread of vector-borne diseases of livestock has been little studied. Here we develop a mathematical framework that allows us to disentangle and quantify the roles of vector dispersal and livestock movement in transmission between farms. We apply this framework to outbreaks of bluetongue virus (BTV) and Schmallenberg virus (SBV) in Great Britain, both of which are spread by Culicoides biting midges and have recently emerged in northern Europe. For BTV we estimate parameters by fitting the model to outbreak data using approximate Bayesian computation, while for SBV we use previously derived estimates. We find that around 90% of transmission of BTV between farms is a result of vector dispersal, while for SBV this proportion is 98%. This difference is a consequence of higher vector competence and shorter duration of viraemia for SBV compared with BTV. For both viruses we estimate that the mean number of secondary infections per infected farm is greater than one for vector dispersal, but below one for livestock movements. Although livestock movements account for a small proportion of transmission and cannot sustain an outbreak on their own, they play an important role in establishing new foci of infection. However, the impact of restricting livestock movements on the spread of both viruses depends critically on assumptions made about the distances over which vector dispersal occurs. If vector dispersal occurs primarily at a local scale (99% of transmission occurs <25 km), movement restrictions are predicted to be effective at reducing spread, but if dispersal occurs frequently over longer distances (99% of transmission occurs <50 km) they are not.
authors.affiliation: The Pirbright Institute, Pirbright, Surrey, United Kingdom.
authors.forename: Tom
authors.initials: T
authors.lastname: Sumner
authors.affiliation: Boyd Orr Centre for Population and Ecosystem Health, Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Orton
authors.affiliation: Institute of Aquaculture, University of Stirling, Stirling, Stirlingshire, United Kingdom.
authors.forename: Darren M
authors.initials: DM
authors.lastname: Green
authors.affiliation: Boyd Orr Centre for Population and Ecosystem Health, Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom.
authors.forename: Rowland R
authors.initials: RR
authors.lastname: Kao
authors.affiliation: The Pirbright Institute, Pirbright, Surrey, United Kingdom.
authors.forename: Simon
authors.identifier: 0000-0003-0538-4173
authors.initials: S
authors.lastname: Gubbins
mesh_terms: D000818:Animals; D001499:Bayes Theorem; D001820:Bluetongue virus / Q000472:pathogenicity*; D002417:Cattle; D002418:Cattle Diseases / Q000635:transmission* / Q000821:virology; D004196:Disease Outbreaks; D054884:Host-Pathogen Interactions; D007303:Insect Vectors; D058751:Livestock; D008962:Models, Theoretical; D012328:RNA Viruses / Q000472:pathogenicity*; D012756:Sheep; D012757:Sheep Diseases / Q000635:transmission* / Q000821:virology