Efficacy of a live Pasteurella multocida vaccine for the prevention of experimentally induced bovine pneumonic pasteurellosis.

Seventeen Holstein-Friesian calves weighing an average of 139.8 +/- 13.5 (mean +/- standard deviation) kg were used in a study to determine the efficacy of a live vaccine containing of Pasteurella multocida A:3 and Pasteurella haemolytica A:1. Eleven calves received the vaccine by intramuscular injection in the right shoulder, whereas six calves received vaccine diluent and served as non-vaccinated controls. Fourteen days following vaccination (Day 15) all calves were inoculated deep intranasally with 3.6 X 10(7) TCID50 bovine herpes virus-1. On Day 16, calves were stressed by transports, and on Day 17 calves were challenged intratracheally with P. multocida A:3. On Day 22 calves were euthanized and necropsied, and tissues were collected for pathological and microbiological evaluations. Scores were assigned to each calf based on the severity of observed clinical signs. Macroscopic lung lesions were expressed as percentage of tissue involved relative to the total lung tissue of a calf. Plasma fibrinogen concentration, rectal temperature, serum antibody level, microscopic appearance of lung, and microbiologic results were also recorded for analyses. The control calves had significantly higher clinical-sign scores (P less than 0.05) and more severe gross lesions (P less than 0.05) than the vaccinated calves. Although the vaccinated calves had a slight increase of immunoglobulins M and G classes, the differences were not statistically significant (P greater than 0.05, P greater than 0.05). The results of the study indicate that the live Pasteurella vaccine is effective against experimental P. multocida infection in calves.