Occurrence of blackleg and current preventive measures against outbreaks in the Canton of Bern.

Blackleg is an acute, lethal, infectious disease caused by Clostridium chauvoei. It affects mainly cattle and is characterized by severe necrohemorrhagic myositis and myocarditis. While the disease has caused substantial economic losses in the past, the number of diseased cattle has been decreasing in the last 30 years. Subsequently, the status of blackleg has been officially changed in Switzerland and the disease is no longer reportable since 2022. Considering the potential persistence of C. chauvoei spores in the environment, blackleg may however still be prevalent in certain areas of the Canton of Bern, an important and large agricultural region of Switzerland. In this study, we evaluated both the spatio-temporal distribution of blackleg from 1992-2023 and the currently implemented prophylactic measurements used by veterinarians in the risk areas of the Canton of Bern. Our results show that most of the cases occurred in areas still defined as risk areas by the Cantonal Veterinary Office, however some occurred in areas no longer listed as risk areas since 2020. In parallel, veterinarians reported suspected cases in recent years as well as a decreased acceptance of vaccination by farmers in risk areas. The combination of lack of blackleg monitoring, reduced disease awareness, decreasing willingness of farmers to vaccinate and the long environmental persistence of C. chauvoei spores represent a risk for reoccurrence of the disease. Veterinarians practicing in once affected areas, in the Canton of Bern and elsewhere in Switzerland, should be aware of this and act accordingly once blackleg outbreaks are suspected.