Leptospira Hardjo introduction in certified‐free dairy herds in the Netherlands

The Dutch Leptospira Hardjo control programme was established to prevent human and veterinary cases of leptospirosis. All dairy farms and 33% of non‐dairy farms participate in the programme. It is based on antibody testing of bulk milk and serum. In 2013, the herd prevalence in non‐dairy herds was very low, at 0.8%, while all dairy herds were free. If an infection is suspected, farms lose their free status, which impedes the trading of animals. Therefore, national trade is considered to be a limited risk for the spread of L. Hardjo. In 2019, the numbers of imported cattle, and also of L. Hardjo seropositive imported cattle, increased. This case study describes the spread of leptospirosis in dairy herds after the importation of L. Hardjo seropositive cattle and measures that were undertaken to stop the spread of infections and to monitor infected farms to prevent further spread.