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 Pasteu rella multocida toxin (PMT) and a potassium thiocyanate extract of P. multo cida (CN) encapsulated in alginate microspheres, compared with unencapsulat ed PMT and CN antigens, in protection of rabbits against pasteurellosis. Methods: New Zealand male rabbits (n=24) were allotted randomly into four i ntranasally administered vaccine groups: 1, PMT/CN; 2, microencapsulated PM T/CN with or; 3, without subcutaneous priming; and 4, empty microspheres (c ontrol). Blood samples and nasal wash specimens were collected before vacci nation and one week after each vaccination (days 7, 21, 35, and 49). Rabbit s 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 (d ay 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 Fiver and lungs. Conclusion: The PMT/CN microspheres stimulated systemic and mucosal immune responses similar in effectiveness (protection) to those in response to une ncapsulated PMT/CN administration.