Passive Immunization of Pasteurella multocida Infected Rabbits

We raised neutralizing antibodies against Pasteurella multocida (PM) in the serum of rabbits and used these antibodies as immunotherapy in PM-infected rabbits. For this purpose five rabbits were vaccinated three times at 21 days interval, using formalized oil base haemorrhagic septicaemia vaccine (OBHSV). A high titer (256 IHA units) of anti-Pasteurella multocida-antibodies in blood serum was determined on 56 day post boosting using indirect haemagglutination (IHA) test. This antibody titer was further enhanced to 1024 IHA units with three consecutive inoculations of virulent PM suspension at 21 days interval. A virulent PM with mean lethal dose (LD50) of 10 was used for challenging the rabbits. The hyperimmune serum (1 ml, 256 IHA units) injected intravenously and intramuscularly to PM-challenged rabbits showed 100% protection and 66.66% protection, respectively, while antigen control group showed 0% protection. Moreover, it was found suitable to passively immunize the animals before exposure or simultaneously with the exposure of PM. Taken together, our experimental data shows that the hyperimmune serum can therapeutically be used as passive vaccine to prevent infections against PM.