A geographic information system (GIS) is being developed to study the spread of pseudorabies virus (PRV) among swine herds in the state of Minnesota. This GIS features an interface with a database management system that stores and manages pertinent data. These data include herd size, type of production system, degree of confinement, topographical features surrounding the farm, density of swine herds and distance to the closest quarantined herd. A pilot study was conducted in one Minnesota county with 280 swine herds, of which the PRV status was known in 115. Cox regression analysis was used to determine factors associated with herd PRV status. Relative risks (RR) and 95% confidence intervals (CI) were calculated. No association was detected between the PRV status of the herd and distance to the nearest county road, highway or quarantined herd. However, the following factors were significant: located within 1 km of a river or lake (RR, 0.524; CI, 0.328-0.828); farrow to finish (RR, 2.120; CI, 1.194-3.791); complete confinement (RR, 3.423; CI, 1.639-7.139); density of swine herds within a 5 km radius (RR, 1.036 per herd; CI, 0.996-1.064).
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The authors acknowledge the cooperation and assistance of Drs. W.J. Mackey and P.L. Anderson, and support staff at the Minnesota Board of Animal Health in providing data for this study. We are grateful to the Minnesota Pork Producers' Association and the Minnesota Pollution Agency for providing access to mailing lists. Thanks are due to Ms. J. Bearman for the many hours of entering data and to the staff of the Land Management Information Center of the Minnesota State Planning Land Agency for support of the EPPL7 package. This work was supported in part by grants from the Academic Computing Services and the Agricultural Experiment Station (No. 0302-4862 ) at the University of Minnesota.