The role of spatial mixing in the spread of foot-and-mouth disease G. Chowell a,b, , A.L. Rivas a , N.W. Hengartner c , J.M. Hyman b , C. Castillo-Chavez d a Department of Biological Statistics and Computational Biology, Cornell University, 432 Warren Hall, Ithaca, NY 14853, USA b Theoretical Division (MS B284), Los Alamos National Laboratory, Los Alamos, NM 87545, USA c Statistical Science (MS F600), Los Alamos National Laboratory, Los Alamos, NM 87545, USA d Department of Mathematics and Statistics, Arizona State University, P.O. Box 871804, Tempe, AZ 85287-1804, USA Received 18 September 2004; received in revised form 31 August 2005; accepted 4 October 2005 Abstract A model of epidemic dispersal (based on the assumption that susceptible cattle were homo- geneously mixed over space, or non-spatial model) was compared to a partially spatially explicit and discrete model (the spatial model), which was composed of differential equations and used geo-coded data (Euclidean distances between county centroids). While the spatial model accounted for intra- and inter-county epidemic spread, the non-spatial model did not assess regional differences. A geo- coded dataset that resembled conditions favouring homogeneous mixing assumptions (based on the 2001 Uruguayan foot-and-mouth disease epidemic), was used for testing. Significant differences between models were observed in the average transmission rate between farms, both before and after a control policy (animal movement ban) was imposed. They also differed in terms of daily number of infected farms: the non-spatial model revealed a single epidemic peak (at, approximately, 25 epidemic days); while the spatial model revealed two epidemic peaks (at, approximately, 12 and 28 days, respectively). While the spatial model fitted well with the observed cumulative number of infected farms, the non-spatial model did not (P < 0:01). In addition, the spatial model: (a) indicated an early intra-county reproductive number R of  87 (falling to < 1 within 25 days), and an inter-county R < 1; (b) predicted that, if animal movement restrictions had www.elsevier.com/locate/prevetmed Preventive Veterinary Medicine 73 (2006) 297–314 PREVET-2125; No of Pages 18  Corresponding author. Fax: +1 505 665 5757. E-mail address: gchowell@t7.lanl.gov (G. Chowell). 0167-5877/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.prevetmed.2005.10.002