Background of the Liver fluke Risk Tool

The prediction models used in the Liver Fluke Risk Tool are developed through a research collaboration between Zoetis and Avia-GIS.

The prediction models were built in 2 phases. First a theoretical risk map for the intermediate host of liver fluke was developed. The theoretical map was then validated using recent and historical prevalence data at farm level, from a wide range of geographical areas.

The theoretical risk map is based on a spatial modelling approach called Multi-Criteria Decision Analysis  with fuzzy thresholds. Three groups of variables were retrieved from the systematic literature review: temperature, dryness and soil variables. More specifically the following variables were used:

• Days with temperature mean T >10°C;
• Start season defined as first day of the first period with four consecutive days with mean T >10°C;
• End season defined as the last day of the last period of five consecutive days with mean T >10°C;
• Duration of season in days;
• Cumulative growing degree days during season;
• Number of freezing days important to highlight harsh winters;
• Total yearly precipitation;
• Aridity index;
• Water capacity;
• Acid soil mask.