Streptococcus bovis/S. equinus complex septicemia in a group of calves following intramuscular vaccination.

Organisms previously classified as Streptococcus bovis (i.e., the S. bovis/S. equinus complex) are common in cattle feces, but may also act as opportunistic pathogens. In the current work, Streptococcus infantarius subsp. coli, a member of this complex, was associated of a cluster of calves that died within hours of injection with a modified live viral vaccine. Within 12 h of vaccination of 46 calves at a cow/calf operation, 4 calves had died, 3 calves were ill, and 1 unvaccinated cow was dead. Autopsies were performed on the cow, 2 dead calves, and 1 affected surviving calf, which was euthanized ~24 h after vaccine administration. The animals had similar gross anatomic and microscopic lesions, including subcutaneous and intramuscular dark hemorrhage on the caudal neck, multiorgan ecchymosis and petechiation, and alveolitis to interstitial pneumonia. Gram-positive cocci were in the vasculature of the lung and skeletal muscle, and S. infantarius subsp. coli was cultured from tissues and from the vaccines used on affected animals, but not in vials used on unaffected animals. Together, these findings suggest death caused by streptococcal septicemia and toxemia as a result of contamination.