The spatial distribution of non-clinical T. parva infection among indigenous cattle populations in Uganda: January 2011 to April 2012. The spatial distribution of non-clinical T. parva infection derived from apparently healthy indigenous cattle populations in Uganda (January 2011 to April 2012) was interpolated using 209 study herd prevalence values to create a nation-wide spatial effect. An inverse distance weighted interpolation (IDWI) on the spatial analyst extension of ArcMap 10 was used to generate the continuous non-clinical T. parva infection distribution map on a red colour for higher and green for lower parasite occurrence. Parameters were set so that for each pixel in the continuous raster an average prevalence was calculated based on all non-clinical T. parva prevalence values at herd level. Being a weighted average, the weights was higher for herds near the pixel (red) and lower for more distant herds (green). An appropriate exponent value of 20 km was chosen to generate a continuous non-clinical T. parva prevalence map over the 209 individual herd prevalence values.