Atypical Prolonged Clinical Course of Blackleg in Nelore Cattle

Blackleg, caused by Clostridium chauvoei, is a severe infectious disease of cattle typically characterized by an acute or peracute course with rapid progression to death within 48 h after the onset of clinical signs. However, well-described reports of chronic or prolonged clinical evolution are rare. This study aimed to describe an outbreak with an atypical, prolonged course and to report the therapeutic management of affected animals. In March 2023, an outbreak occurred in an unvaccinated Nelore herd, with seven cattle showing clinical signs and one dying before veterinary intervention. Due to disease severity, four animals were referred to the Veterinary Hospital (HOVET) of the School of Veterinary Medicine and Animal Science, University of São Paulo (FZEA-USP), while others were managed on-farm. Clinical management included fluid therapy, systemic antimicrobial treatment, surgical debridement of necrotic tissues, drainage, and intensive wound care. Despite treatment, three animals died during hospitalization. One severely affected animal underwent partial amputation of a hind limb and survived, and it was discharged after 116 days of treatment. Diagnosis was confirmed by PCR, clinical examination, and necropsy findings. Overall, the clinical course observed differed from the typical acute presentation, with two animals surviving, suggesting that intensive medical and surgical management may improve outcomes in selected cases. Cardiac lesions were identified in necropsied animals, with exclusive involvement of the left ventricle, a finding that may warrant further investigation. This report highlights atypical manifestations of blackleg and contributes to the limited literature on prolonged cases.