SYSTEMIC PASTEURELLA-HAEMOLYTICA INFECTION AS A RARE SEQUEL TO AVIRULENT LIVE PASTEURELLA-HAEMOLYTICA VACCINATION IN CATTLE

Eleven cases of systemic Pasteurella haemolytica infection in cattle w ere identified from routine diagnostic laboratory submissions during t he falls of 1988, 1989, and 1991. All cases came with a history of rec ent vaccination with an avirulent live culture P. haemolytica product. Nine of 11 cases involved cattle vaccinated between 2 and 18 days pre viously with this product. Ten of 11 cases involved 182-227-kg beef ca lves that were vaccinated between September and November during routin e processing for entry into feedlots. The morbidity and mortality was generally low. The major pathologic findings included meningitis, inje ction site abscessation and/or cellulitis, and polyarthritis. Systemic infection was indicated in all cases by the isolation of P. haemolyti ca from 2 or more organs or distinct anatomical sites. In 6 cases, the vaccine injection site was cultured, and in all 6 cases, P. haemolyti ca was isolated. Three separate P. haemolytica isolates from 2 cases w ere further studied by restriction enzyme analysis (REA). These isolat es were from tissues with suppurative inflammation, including the brai n, joint, and injection site. The REA patterns of each of these 3 isol ates were identical to the REA pattern of the vaccine masterseed, whic h strongly suggested that the organisms causing systemic infection wer e the same as the organism used to produce the vaccine. Because the ov erall incidence was quite low, other factors, such as stress, probably played a major role in the expression of this syndrome.