Spatial analysis of Neospora caninum distribution in dairy cattle from Sweden

The national herd prevalence and spatial distribution of Neospora caninum infected dairy herds in Sweden were investigated. The study was based on a bulk milk survey comprising samples from 2,978 herds. Test-positive herds were found in all parts of Sweden and the overall prevalence of test-positive herds was 8.3% (95% confidence interval = 7.3-9.3%). The presence of spatial autocorrelation was tested using the Moran's I test. Possible clusters of test-positive herds were identified by applying the local indicator of spatial association (LISA) test statistic and the spatial scan statistic. Analysis based on data aggregated by postal code areas as well as analysis based on exact coordinates identified significant clusters of high prevalence in the middle parts of Sweden and low prevalence in the south. This was not expected considering the results from other European studies of N. caninum in cattle. However, the findings are supported by the distribution of previously known case herds.