A novel approach to mapping and calculating the rate of spread of endemic bovine tuberculosis in England and Wales

A mathematical method for estimating the endemic status of bovine tuberculosis (bTB) in cattle in England and Wales has been developed.6.25 km2 hexagonal cells were used as the base resolution. Maps were produced for overlapping two-year periods spanning 2001/03 to 2009/11. Distance from a farm to the ten nearest ‘Officially Tuberculosis Free status – Withdrawn’ incidents within the same time period was measured. Endemic areas were defined as those hexagons containing farms where the 3rd nearest incident occurred within 7 km. Temporal spread of endemic bTB was estimated by creating a contour map displaying the spread of endemic bTB over the two-year periods, and using boundary displacement to calculate the rate of spread across each hexagon. A rate was obtained for ∼2300 cells and varied between 0.04 km and 15.9 km per year (median = 3.3 km per year). This work will enable further analysis of the factors associated with this expansion.