Intranasal vaccination of New Zealand white rabbits against pasteurellosis, using alginate-encapsulated Pasteurella multocida toxin and potassium thiocyanate extract

Objective: We evaluated the efficacy of intranasal administration of Pasteurella multocida toxin (PMT) and a potassium thiocyanate extract of P. multocida (CN) encapsulated in alginate microspheres, compared with unencapsulated PMT and CN antigens, in protection of rabbits against pasteurellosis. Methods: New Zealand male rabbits (n=24) were allotted randomly into four intranasally administered vaccine groups: 1, PMT/CN; 2, microencapsulated PMT/CN with or; 3, without subcutaneous priming; and 4, empty microspheres (control). Blood samples and nasal wash specimens were collected before vaccination and one week after each vaccination (days 7, 21, 35, and 49). Rabbits were primed subcutaneously with either unencapsulated PMT/CN or aluminum hydroxide (control) (day 0), vaccinated intranasally (days 14, 28, and 42), challenged intranasally with live P. multocida (day 56), and necropsied (day 60). Results: Compared with controls, PMT/CN-immunized rabbits had significantly higher concentrations of serum IgG and IgM, nasal IgG, and bronchoalveolar lavage fluid IgA and IgG against CN. Immunized rabbits had 100% survival rate and low numbers of bacteria in liver and lungs; the control group had 50% survival rate and higher numbers of bacteria (> 4x) per gram of tissue in liver and lungs. Conclusion: The PMT/CN microspheres stimulated systemic and mucosal immune responses similar in effectiveness (protection) to those in response to unencapsulated PMT/CN administration.