Vaccine associated mucosal disease case study

Abstract

Mucosal disease (MD) affected a single-source group of 461 recently purchased yearling steers shortly after vaccination with a multivalent vaccine containing 2 strains of modified-live bovine viral diarrhea virus (BVDV). Terminal disease affected 21 steers at 18 to 66 days post-vaccination, and was confirmed as mucosal disease in 3 carcasses examined postmortem. An additional 17 animals identified as persistently infected remained asymptomatic during the study A laboratory study was undertaken to determine whether mucosal disease was triggered by a BVDV in the multivalent vaccine. Purified cytopathic BVDV isolates from 2 animals that died early in the outbreak were genetically identical (>99%) to the vaccine type 2 BVDV strain 125a in 3 genomic regions: 5′-untranslated region to the Npro, E2, and NS2/3. This genetic identity combined with the presence of a single peak outbreak occurring soon after vaccination suggests that the vaccine BVDV was the cause of mucosal disease in these steers. The investigation underscores laboratory challenges in determining the role of vaccinal BVDV when mucosal disease affects multiple animals within 2 months of vaccination, and the need for laboratory testing to identify all persistently infected animals.