Severe systemic disease associated with a cytopathogenic bovine viral diarrhoea virus strain in suckling calves

Bovine viral diarrhoea virus (BVDV) is a major cattle pathogen causing substantial economic losses. This study describes the isolation and characterisation of a cytopathogenic BVDV isolate, strain 11227, recovered during a fatal outbreak in a high‐health‐status herd. Forty‐five suckling calves aged 2–3 months died within 4 days after the onset of acute systemic and respiratory disease. Necropsy revealed erosive‒ulcerative lesions and bronchopneumonia, while histopathology demonstrated widespread vasculitis. Virus isolation in Madin–Darby bovine kidney cells showed cytopathic effects, and RT‐PCR targeting the non‐coding region (5′UTR) confirmed the isolate as BVDV. Phylogenetic analysis classified it within the BVDV‐1a subgenotype. Although cytopathogenic BVDV is classically associated with mucosal disease in persistently infected animals, the outbreak pattern may be explained by horizontal spread of a cytopathogenic BVDV strain within a susceptible calf cohort that potentially included a substantial proportion of persistently infected animals. These findings underscore the need for BVDV‐specific surveillance beyond general disease‐free certification.