Intranasal immunization of mice against Pasteurella multocida.

A potassium thiocyanate (KSCN) extract of Pasteurella multocida serotype III:A was shown to protect mice from an intranasal challenge with up to 300 50% lethal doses of P. multocida. In addition to preventing death, bacteria were rapidly cleared from the lungs of immunized mice so that by 72 to 96 h postchallenge no bacteria were present in the lungs of immunized mice, whereas up to 10(9) bacteria were present in lungs of nonimmunized mice. Immunization by the intranasal route was slightly better than that by the intramuscular route. Protection was considered specific, since immunization with P. multocida protected only against P. multocida and not against Salmonella agona. Furthermore, a similar KSCN extract from P. haemolytica did not protect against P. multocida challenge. A comparison of the KSCN extract with a Formalin-killed bacterin suggested that the KSCN extract may be superior to the bacterin.