Environmental risk factors for Fasciola hepatica infections in Dutch dairy cattle herds

Fasciola hepatica infections in cattle often lead to significant production losses. Infection rates are expected to increase due to environmental changes at regional and global level which favour the life cycle of F. hepatica. This study aimed to identify environmental and herd factors associated with F. hepatica antibody positivity in bulk tank milk (BTM) of Dutch dairy cattle herds. In total, 10403 BTM samples were collected yearly in October, from 2018 till 2023. For each farm, monthly averages of weather factors and soil moisture level were obtained for the twelve months preceding October, along with soil type and number and grazing of dairy cows. Logistic regression analyses were performed retrospectively using generalized estimating equations, with continuous variables analysed as quartiles. The odds of F. hepatica antibody positivity in BTM are higher for farms on peat (OR 1.69, 95% CI [1.27, 2.24]) and heavy clay soils (OR 1.75, 95% CI [1.30, 2.35]) compared to those on sand soil. In addition, the odds of antibody positivity increased with higher monthly temperatures (December: ORQ1-Q4 2.94, 95% CI [1.94, 4.46]) and rainfall (November: ORQ1-Q4 2.33, 95% CI [1.62, 3.34]) at the end of the previous grazing season. Stratified analyses by soil type yielded results consistent with those across soil types. Weather patterns that favour the number of overwintering snails infected with F. hepatica seem to increase the infection risk for dairy cattle in the next grazing season, which highlights the potential of prediction tools that facilitate early detection of new F. hepatica infections.